RIPF-Unet for regional landslides detection: a novel deep learning model boosted by reversed image pyramid features

RIPF-Unet for regional landslides detection: a novel deep learning model boosted by reversed image pyramid features | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article RIPF-Unet for regional landslides detection: a novel deep learning model boosted by reversed image pyramid features Bangjie FU, Yange LI, Zheng Han, Zhenxiong FANG, Ningsheng CHEN, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-1886017/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 28 Aug, 2023 Read the published version in Natural Hazards → Version 1 posted 5 You are reading this latest preprint version Abstract Rapid detection of landslides using remote sensing images benefits hazard assessment and mitigation. Many deep learning-based models have been proposed for this purpose, however, for small-scale landslide detection, excessive convolution and pooling process may cause potential texture information loss, which can lead to misjudgement of landslide target. In this paper, we present a novel UNet model for automatic detection of landslides, wherein the reversed image pyramid features (RIPFs) are adapted to compensate for the information loss caused by a succession of convolution and pooling. The proposed RIPF-Unet model is trained and validated using the open-source landslides dataset of the Bijie area, Guizhou Province, China, wherein the precision of the proposed model is observed to increase by 3.5% and 4.0%, compared to the conventional UNet and UNet + + model, respectively. The proposed RIPF-Unet model is further applied to the case of the Longtoushan region after the 2014 Ms.6.5 Ludian earthquake. Results show that the proposed model achieves a 96.63% accuracy for detecting landslides using remote sensing images. The RIPF-Unet model is also advanced in its compact parameter size, notably, it is 31% lighter compared to the UNet + + model. Landslide detection reversed image pyramid UNet remote sensing image Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 1 Introduction As a ubiquitous and typical geological hazard, landslides significantly endanger human lives, infrastructures, and other property security, and occur frequently worldwide (Cigna et al. 2018 ). A reliable inventory of landslides is therefore of critical importance for timely quantitative hazard assessment, disaster relief, and subsequent risk governance, especially in mountainous regions with complex environments and inconvenient transportation (Galli et al. 2008 ). Traditionally, in-site manual investigation was the most commonly used scheme for landslide detection, which required experts and investigators to reach the landslide area and evaluate the landslides' magnitude, position, and hazard mechanisms (Ji et al. 2020 ). However, it is a time-consuming, laborious task, even sometimes risky (Li et al. 2022 ). With the boom of remote sensing technology, as well as improvements in the capacity of obtaining geospatial information on a regional scale, remote sensing technology has been extensively employed in various fields, such as for the investigation purpose of hydrology (Brinkhoff et al. 2022 ; Rajesh et al. 2021 ), geology (Barak et al. 2021 ), soil (Yu et al. 2022 ; Lourenco et al. 2022 ), environment (Petaja et al. 2022 ; Wang et al. 2021 ; Wiggins et al. 2021 ) and forestry (Eskandari et al. 2020 ; Altamirano et al. 2020 ). These remarkable works inspire the application of remote sensing technology in landslide detection. When high-resolution images are available, visual interpretation is a reliable method that creates appropriate interpretation markers to show the boundaries of landslides by considering the landslides’ colour, texture, shape, position, and other factors hidden in the remote sensing images. These markers are used by experts to further analyse and confirm the landslide area (Tanoli et al. 2017 ). The basic principle of using remote sensing images for landslide interpretation can be summed up as the spectral difference caused by the loss of vegetation and the exposure of fresh soil and rock (Li et al. 2014 ). Although visual interpretation has been proved able to generate good results in landslides identification (Xu et al. 2015 ), it is usually inefficient and may suffer from interpreters' subjectivity (Fan et al. 2019 ). Thus, several computer visual mothods and machine learning based interpretation methods (Li et al. 2022 ; Chen et al. 2020 ; Merghadi et al. 2020 ; Nhu et al. 2020 ; Han et al. 2019 ; Tien Bui et al. 2019 ; Fan et al. 2019 ; Sun et al. 2017 ; Li et al. 2016 ; Behling et al. 2016 ; Li et al. 2014 ), including linear regression (LR), support vector machine (SVM), random forest (RF), k-nearest neighbour (KNN), and thresholding method, have been conducted to address these issues. These remarkable studies laid a solid foundation for landslide research. However, these works generally cost a lot of time in feature analysis, which consists of enumerating and selecting landslide conditioning factors (e.g., NDVI, NDWI, NDBI, TWI). Meanwhile, some of the crucial parameters in these methods (e.g., kernel function in SVM, max tree depth in RF, k value in KNN), require empirical adjusting, somewhat limiting the methods' flexibility. For instance, as we mentioned in our previous studies (Han et al. 2019 ; Li et al. 2014 ), grey-level threshold is crucial for panchromatic image binarization in landslide detection, but the determination of which is still debated. Recently, convolutional neural networks (CNNs) have shown significant learning capacity in a variety of image-based tasks, including image classification (He et al. 2016 ; Simonyan and Zisserman 2014 ), object recognition (Ren et al. 2017 ), and semantic segmentation (Chen et al. 2018 ; Ronneberger et al. 2015 ). Many CNN algorithms have been proposed and implemented during the last two decades (Howard et al. 2017 ; Chollet 2017 ; He et al. 2016 ; Huang et al. 2016 ; Simonyan and Zisserman 2014 ), each based on a different rationale. In terms of landslides, the CNNs were used to extract the hidden features of the landslides in the remote sensing images, which helped to determine the existence of landslides at the location (Ding et al. 2016 ). Subsequently, CNNs have been widely used to retrieve images containing landslides from image datasets. Many studies (Yu et al. 2017 ; Li et al. 2014 ), used specific algorithms, such as automatic thresholding and region growth algorithms, to delineate the region of the landslides. Up to date, various structures of CNN networks, with different convolutional layers, sizes, and input data channels, have been discussed to analyse the impact of network settings against accuracy (Ghorbanzadeh et al. 2019 ). In addition, multi-channel inputs of the combined spectral and topographic features were used to build CNN models (Su et al. 2021 ; Meena et al. 2021 ), which improved the accuracy of landslide detection. The convolution kernel of CNN can automatically obtain the effective features of images, which enables the understanding of semantic information of objects avoiding empirically determination of complex features (Lecun et al. 2015 ). Additionally, via network training, convolution kernel can further emphasise the distinction between landslide and background, which is essential for the purpose of landslide detection. Thus, CNN can be selected as an important method for image segmentation and inspection of landslides. Among the whole CNN methods, the UNet model has been proven to be an efficient method for landslide detection (Meena et al. 2022 ; Yu et al. 2021 ; Prakash et al. 2020 ; Lei et al. 2019 ). With a succession of convolution, pooling, and deconvolution layers, this method tries to extract the required information from remote sensing images (Badrinarayanan et al. 2017 ; Shelhamer et al. 2017 ). However, the scale of landslides is different in remote sensing images. For tiny and slender landslide detection, the excessive convolution and pooling process may cause potential texture information loss (Li et al. 2019 ; Gu et al. 2019 ). For instance, a \(25\times 25\) pixel landslide target tends to be smaller than \(1\) ( \((25÷{2}^{5})<1\) ) after five pooling processes, which makes its texture information disappear on the feature map (Fig. 1 ). The lost texture information may lead to the following misjudgment of the landslide target. As a result, to successfully detect landslides, especially for a remote sensing image covering a large area, the UNet model needs to be revised so that it can detect landslide boundaries precisely. In this paper, to address the issue of potential texture information loss caused by convolution and pooling in conventional CNN models, a reversed image pyramid feature (RIPF) boosted UNet algorithm for landslide detecting is presented. In this method, the original network structure of UNet models is utilised as the major network structure, while the reversed image pyramid features are employed to augment the feature in the network's decoding phase to increase the model's capacity to differentiate the area of landslides under a complicated backdrop. The RIPF-Unet model is supposed to better identify tiny and slender landslides from exposed surfaces. To verify the performance in RGB remote sensing image dataset, the proposed RIPF-Unet model is trained and tested using an open-source dataset, and the adaptability and effectiveness of the method in the actual area are further tested in the case of the Longtoushan region after the 2014 Ms.6.5 Ludian earthquake. 2 Methodology 2.1 Convolutional neural network The CNN-based networks receive images as input and automatically adjust network parameters during iterative training. The trained network, consisting of thousands of weights at the node of neutral network, will predict with the greatest degree of certainty. Convolution layers, activation layers and pooling layers are common components of CNN designs (Su et al. 2021 ). In general, the convolutional layer is usually followed by an activation operation, which is utilized to extract the nonlinear mapping of features \({F}_{i}\left(Y\right)\) according to Eq. (1), and improve the nonlinear representation capability of neural networks. \({F}_{i}\left(Y\right)=\sigma \left({W}_{i}\times Y+{B}_{i}\right)\) (1) where \({F}_{i}\left(Y\right)\) in Eq. (1) represents the feature graph produced by image \(Y\) through the convolution layer and activation layer. \({W}_{i}\) and \({B}_{i}\) are independent representations of the convolution kernel and bias term that are trained through the network, respectively. The convolution layers are designed for image feature extraction. It is the matrix's dot product and sum operation. Convolution kernels of various sizes \((3\times 3, 5\times 5, 7\times 7)\) can be used in the convolution layers, and the typical convolution process is shown in Fig. 2 a. In Eq. (1), \(\sigma\) represents an activation function, which is commonly linked after the convolution layer to increase the neural network's nonlinear representation capacity. The typical activation functions are ReLU which could be represented by \(\left(\text{m}\text{a}\text{x}\right(0,x\left)\right)\) and Sigmoid \((1/(1+{\text{e}}^{-x}\left)\right)\) , where \(x\) refers to an individual element in the image. The activation process using ReLU functions is shown in Fig. 2 b. The pooling layer is used after several convolutions and activation layers to compress the feature graph for efficient computation. Max-pooling and average-pooling are two major pooling types that preserve the maximum and average of the pool window in the input feature map, respectively. The pool window is typically \(2\times 2\) in size, which corresponds to a downsampling process of \(2\times\) . Figure 2 c depicts the max-pooling process. 2.2 The conventianal UNet model UNet is a Fully Convolutional Neural Network proposed to solve image-to-image mapping tasks (Fernández and Mehrkanoon 2021 ). Different with typical CNN architectures, UNet exploits a contracting and an expansive path during the convolution and pooling process. The former acts as an encoder of input information, and the latter is a decoder that performs classification on each pixel to reconstruct the segmented output. The encoder of UNet is changeable and aims to extract features from the input image (Liu and Wang 2022 ). In this study, the VGG-16 network was adopted as the encoder network for feature extraction. Meanwhile, a technique called skip connection creates a bridge between the encoder and the decoder, which was used to copy feature maps. Both contracting and expansive paths are more or less symmetrical in their operations, forming a U-shape process. According to the structure of UNet in Fig. 3 a, the contracting path (left side) contains five convolution blocks. Each convolution block consists of several \(3\times 3\) convolution operations (followed by a ReLU activation function) and a \(2\times 2\) max-pooling operation of stride \(2\) for downsampling. On the other hand, each convolution block in the expansive path (right side) consists of a \(2\times 2\) up-convolution operation for upsampling, a concatenation with the corresponding feature map from the contracting path, and two 3x3 convolutions, each followed by a ReLU activation function. To alleviate the checkerboard effect (Odena et al. 2016 ), the up-convolution step is replaced with a \(2\times 2\) upsampling step in this work. In the final stage, the extracted feature map convolves with a \(1\times 1\) kernel and is followed by a sigmoid activation function to carry out the pixel-wise classification part. 2.3 The proposed RIPF-Unet model Through a succession of convolution and pooling layers, the UNet model extracts image feature maps and reconstructs segmented outputs. However, multiple stages of spatial pooling and convolutional layers may cause the potential loss of fine image structure information (Wang et al. 2017 ). Therefore, in the UNet model, the skip connection was employed to concatenate feature maps from the contracting path and expansive path for information transfer. In the same way, the UNet + + model adopts several short connections to minimise the information loss after base-level convolution. The possible loss of image information in base-level convolution, especially high-frequency detailed information, is essential for landslide detection. Therefore, in this study, the reversed image pyramid features are employed to further expand the feature map in the expansive path to recover the information loss caused by convolution. Specifically, the initial image pyramid features are further stacked onto the output of the blocks in expansive path. The proposed network architecture is shown in Fig. 3 b. To stack image pyramid features into the feature maps in expansive path, a novel concatenation module (Fig. 4 ) has been proposed, which consists of three parts, i.e., the feature maps extracted by the contracting path, the original image pyramid feature maps, and the feature maps generated by the expansion path. Through average-pooling, the pyramid feature maps of the original image are scaled to the corresponding size that the concatenation operation requires. Notably, we extended the feature maps at each stage of the expansive path. After the output feature maps of the last convolution block in the expansive path, a convolution kernel of \(1\times 1\) is connected to control the number of channels, and the pixel-level binary classification result is obtained after a sigmoid activation function. 2.4 Loss functions and evaluation indicators The proposed method uses a cross-entropy loss function to update the parameters of the network. The equation for calculating the cross-entropy loss is shown in Eq. (2): \(\text{l}\text{o}\text{s}\text{s}=-\frac{1}{n}\sum _{i=1}^{n} {y}_{i}\text{l}\text{g}\left({t}_{i}\right)+\left(1-{y}_{i}\right)\text{l}\text{g}\left(1-{t}_{i}\right)\) (2) where \({t}_{\text{i}}\) represents the predicted distribution, \({y}_{\text{i}}\) represents the true distribution. The error between the predicted results and the ground truth is calculated using the loss function. The backpropagation updates the network parameters to minimize the value of the cross-entropy loss function. To evaluate the model’s performance, many accuracy indexes can be referred to. In our study, we employ four indexes, including Precision, Recall, Accuracy, and F1 score, as shown in Eq. (3–6), to assess the network's recognition ability, \(\text{Precision}=\frac{\text{T}\text{P}}{\text{T}\text{P}+\text{F}\text{P}}\) (3) \(\text{Recall}=\frac{\text{T}\text{P}}{\text{T}\text{P}+\text{F}\text{N}}\) (4) \(\text{Accuracy}=\frac{\text{T}\text{P}+\text{T}\text{N}}{\text{T}\text{P}+\text{F}\text{P}+\text{T}\text{N}+\text{F}\text{N}}\) (5) \(\text{F}1=2\times \frac{\text{ Precision }\times \text{ Recall }}{\text{ Precision }+\text{ Recall }}\) (6) Results of true positives, true negatives, false positives, and false negatives are represented by \(\text{T}\text{P}\) , \(\text{T}\text{N}\) , \(\text{F}\text{P}\) , and \(\text{F}\text{N}\) in the equation. To get a better segmentation result, the precision, recall and accuracy values should be as high as possible. However, when the segmentation target is smaller in the image, it will be a certain conflict between precision and recall. Thus, the comprehensive evaluation index F1 score is given to assess the model’s performance unbiasedly. Besides the abovementioned four indexes, to evaluate the model's predictive performance for an individual landslide in the dataset, the intersection over union (IOU) index in Eq. (7) is used. \(\text{I}\text{O}\text{U}=\frac{\text{T}\text{P}}{\text{T}\text{P}+\text{F}\text{P}+\text{F}\text{N}}\) (7) 3 Model Training And Analysis 3.1 Public data sets To train the proposed RIPF-Unet model, an open-source dataset in the previous study (Ji et al. 2020 ) is used in this paper. The dataset contains both satellite optical images and landslides boundary shapefiles. The image data was obtained from TripleSat satellite imagery of the Bijie region, Guizhou Province, China (as shown in Fig. 5 a), from May to August 2018. The satellite images were all pre-processed with radiometric calibration, atmospheric correction, orthographic correction, and image fusion. As shown in Fig. 5 b, a total of 770 samples of landslides are included and manually delineated in this dataset. The included landslides samples in this dataset vary in size, and the dataset was created using the anchor box of the present landslides example within a 40m×40m extension as a backdrop. The RGB remote sensing images have a ground resolution of 0.8m, and the shape vector of each landslide was produced using ArcGIS software. Some examples of the landslides and their boundaries are shown in Fig. 6 . 3.2 Model parameter setting In our study, 80% of the image data in the dataset is used for training, while the remaining 20% is for testing. To verify the effectiveness of the proposed model, the conventional UNet and UNet + + networks are also well trained for comparison. All networks have the same training setup. In detail, these models are trained for 20 epochs using the Adam optimizer with a batch size of 4. The original learning rate starts at 10 − 4 and decreases exponentially to 10% after 5 epochs. The size of the input image is adjusted to \(256\times 256\) pixels, and the image pixel values are normalized to During the training process, the data is augmented using random rotation and cropping. The network's output is the probability that any pixel in the image belongs to landslides. The model is trained using a Windows Server equipped with a GeForce TITAN V 12G GPU and an Intel Xeon(R) Gold 6133 CPU. All code is implemented in the Tensorflow deep learning environment. 3.3 Analysis of training results Table 1 lists the accuracy statistics of the different landslide detection methods on the training and validation datasets, which are schematically shown in Fig. 6 . It demonstrates that all three models are able to detect landslides. The overall accuracy for the validation set of RIPF-Unet is 0.9725, the precision is 0.8991, the recall is 0.9490, and the F1-score is 0.9234. The statistical results of the validation dataset show that compared to the conventional UNet and UNet++, the proposed RIPF-Unet model obtains a better detection result. The precision index improves by 3.5% and 4.0%, respectively, while the F1 index improved by 2.3% and 2.7%. Table 1 The indexes statistics of the different landslide detection methods in the open-source dataset Model Training data Validation data Precision Recall Accuracy F1 Precision Recall Accuracy F1 UNet 0.8884 0.9621 0.9725 0.9238 0.8682 0.9390 0.9644 0.9023 UNet++ 0.8863 0.9574 0.9713 0.9205 0.8644 0.9369 0.9633 0.8992 The proposed RIPF-Unet 0.9199 0.9763 0.9811 0.9472 0.8991 0.9490 0.9725 0.9234 Furthermore, the IOU statistics also generate a valid distribution of the different models in each sample. Figure 8 a shows the frequency distribution of the resulting IOU index in the training dataset. The IOU index commonly ranges from 0.8 to 0.9 in UNet and UNet++, while it extends upward to around 0.85 to 0.9 in our proposed RIPF-Unet model. The graph highlights the advantages of our proposed RIPF-Unet. A similar relation can be observed in the validation dataset (Fig. 8 b), that the proposed RIPF-Unet shows a better performance on IOU distribution compared to the other models. The above details support that the proposed RIPF-Unet model has a better accuracy index for the training dataset, compared to the conventional UNet and UNet + + models. This improvement can be explained by the fact that the RIPF-Unet model appropriately complements the decoding network’s information, increasing the abundance of features for decoding network extraction. 4 Case Study The proposed RIPF-Unet model has shown satisfactory accuracy using the training and validating dataset. In this section, to test the model’s performance for delineating landslides, the Longtoushan region after the 2014 Ms.6.5 Ludian earthquake is selected as a case study. As shown in Fig. 9 , the Longtoushan region (27°05′30″-27°07′43″N, 103°16′37″-103°19′27″E) locates in Ludian County, Zhaotong City, Yunnan Province. The area was impacted by the Ms.6.5 earthquake on August 3, 2014 (Chen et al. 2015 ). We manually delineated the boundary of landslides in the study area with the empirical interpretation of remote sensing images, and the result is as shown in Fig. 9 d. Figure 10 presents the final detection result using the proposed RIPF-Unet model. The components circled in red lines highlight the landslides, and the rest part refers to the background. To enhance the detection result, we highlight the TP, FN, and FP regions using different colours. Figure 10 demonstrates that most landslides can be effectively detected, with a few incorrect detections of the cloud-covered region. In terms of landslide boundaries, most landslide borders can be delineated, although some trivial errors exist compared to the manual delineated boundaries. Figure 11 depicts the comparison detection results of sub-areas using different models. It is shown that all three models are able to detect the majority area of landslides. Compared to the other two models, RIPF-Unet successfully detects small-medium size landslides as shown in Fig. 11 a and Fig. 11 b, owing to the concatenation of reversed image pyramid features. In addition, the detected landslides’ boundary of RIPF-Unet is relatively consistent with the manually delineated boundary as shown in Fig. 11 c and Fig. 11 d. Further, a clear distinction between landslides and roads (Fig. 11 e) is also observed for the prediction result by the proposed RIPF-Unet, which helps improve the detection accuracy. For the detection results of landslides based on the three deep learning models, a statistical quantification analysis of the detection results is carried out compared to the manually visual interpretation results. Table 2 summarizes the quantitative assessment of the different landslide detection models. As shown in Table 2 , the proposed RIPF-Unet model generally outperforms other models, respectively achieving the highest precision, recall, and accuracy of 0.6764, 0.8109, and 0.9663, and yielding F1 of 0.7376. This improved result is attributed to the correct detection of tiny and slender landslides, as well as more precise boundary detection, compared with other models. Compared to UNet, our proposed RIPF-Unet has better assessment indexes with no substantial increase in parameter memory. In contrast with these baseline models, RIPF-Unet's recall metrics improved by 0.4% and 1.9%, respectively. While the F1 metrics improved by 1.6% and 1.6%, demonstrating the RIPF-Unet’s advantages in the landslide detection task. Table 2 the indexes statistics of the different landslides detection models in the case study area Model Parameters Size Assessment Index Precision Recall Accuracy F1 UNet 95.0MB 0.6599 0.8071 0.9644 0.7261 UNet++ 138.0MB 0.6674 0.7951 0.9649 0.7257 RIPF-Unet 95.1MB 0.6764 0.8109 0.9663 0.7376 5 Discussion 5.1 Impact of initial learning rate Although the proposed RIPF-Unet model has a relatively better detection result, and the dynamic learning rate setting has a certain universality for model training, it still needs further discussion on the initial learning rate. Because the initial learning rate often determines whether the model can converge quickly in a short time (Shi et al. 2021 ), and is an essential network parameter set in the study. In this work, we have performed a sensitivity analysis using different initial learning rates, i.e., \(5{\text{E}}^{-5}\) , \(1{\text{E}}^{-5}\) , \(1{\text{E}}^{-4}\) , and \(5{\text{E}}^{-4}\) , against the model’s performance. However, in the actual experiment, the model cannot converge while the learning rate is set to \(5{\text{E}}^{-4}\) , hence the influence of the learning rate of \(5{\text{E}}^{-4}\) is not taken into account here. Using the RIPF-Unet model as an example, we trained the model using the rest three initial learning rates and calculated the loss in the validation dataset. As seen in the graph (Fig. 12 ), the loss under the three learning rates tends to be steady eventually. In general, a lower loss indicates a better performance of the model on the validation dataset. When the learning rate is set to \(1{\text{E}}^{-4}\) , it can be seen that the overall loss of the model is superior. As a result, in the model training process, the initial learning rate was set to \(1{\text{E}}^{-4}\) , and the model with the lowest loss on the validation dataset is chosen as the actual prediction model. 5.2 Impact of image pyramid’s embedding position In the study, an important design of our method is to incorporate the image pyramid features into the UNet model. However, various embedding positions will result in different extraction results of the model, which potentially have an impact on the model's performance. In this experiment, we try to concatenate the reversed image pyramid features in three different embedding patterns in the model, i.e., embedding the image pyramid in the expansive path (RIPF-Unet-R), the contracting path (RIPF-Unet-L), and directly embedding the image pyramid in both the contracting path and the expansion path (RIPF-Unet-LR). Figure 13 represent the loss curves of different models in the validation dataset, it can be found that the loss of RIPF-Unet-R, RIPF-Unet-L, and RIPF-Unet-LR that are embedded with the image pyramid is better than that of conventional UNet and UNet++, indicating that the method of embedding the image pyramid features is effective. Compared to these methods, it can be concluded that RIPF-Unet-R has a relatively lower loss. Therefore, incorporating the reversed image pyramid into the expansive path is a better choice. 5.3 Limitations and Future Work Our proposed RIPF-Unet has achieved satisfactory results on the open-source dataset. Meanwhile, we also carried out landslide detection in the Longtoushan region as a case study. From the detected results of the case study (as shown in Fig. 10 ), it can be seen that the landslides have been effectively detected. However, due to the differences in image spectrum, resolution, and shadow between regions, the detection precision of the case study is not as outstanding as that of the open-source dataset. To improve the generalisation ability of the model, it is crucial to building a large-scale landslide dataset that contains more landslide samples from different regions. In addition, considering that RGB images are the most commonly used and easily accessible remote sensing data when landslide events occur, we only explore the feasibility of the model to identify landslides on RGB images. In future work, additional consideration of some geological or geographical factors is more conducive to landslide detection tasks. 6 Conclusions To address the issue of imprecise boundary detection of landslides owing to the information loss caused by convolution and pooling, this study proposed a novel UNet model (RIPF-Unet) boosted by reversed image pyramid features (RIPFs). Specifically, we designed a novel concatenation module, which incorporates the high-level and low-level pyramid features of the original image into the expansive path to compensate for the information loss. The proposed RIPF-Unet model is trained and validated using the open-source landslide dataset of the Bijie area, Guizhou Province, China, wherein the precision of the proposed model is observed to increase by 3.5% and 4.0%, and the F1 index improved by 2.3% and 2.7%, compared to the conventional UNet and UNet + + models, respectively. This improvement can be explained by the fact that the RIPF-Unet model appropriately complements the decoding network’s information, increasing the abundance of features for decoding network extraction. In addition, the proposed RIPF-Unet model is applied to the case of the Longtoushan region after the 2014 Ms.6.5 Ludian earthquake. Results show that the proposed model achieves a 96.63% accuracy for detecting the landslides using the Gaofen-1 images. Notably, the RIPF-Unet model is advanced in its compact parameter size and is 31% lighter compared to the Unet + + model, which indicates that the RIPF-Unet model is more suitable for mobile and portable platforms. However, the proposed FIPF-Unet is potentially limited for landslide detection in a larger area, due to the differences in image spectrum, resolution, and shadow between regions. To improve the generalisation ability of the model, in future work, it is crucial to building a large-scale landslide dataset. Declarations Competing interests The authors declare that they have no competing interests. Acknowledgements This study was financially supported by the National Key R&D Program of China (Grant No. 2018YFD1100401); the National Natural Science Foundation of China (Grant No. 52078493); the Natural Science Foundation for Excellent Young Scholars of Hunan (Grant No. 2021JJ20057); the Innovation Provincial Program of Hunan Province (Grant No. 2020RC3002). 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Cite Share Download PDF Status: Published Journal Publication published 28 Aug, 2023 Read the published version in Natural Hazards → Version 1 posted Reviewers agreed at journal 21 Sep, 2022 Reviewers invited by journal 12 Aug, 2022 Editor invited by journal 27 Jul, 2022 Editor assigned by journal 24 Jul, 2022 First submitted to journal 22 Jul, 2022 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-1886017","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":128512562,"identity":"5f474411-7b9d-49dc-9211-57d26e76af33","order_by":0,"name":"Bangjie FU","email":"","orcid":"","institution":"Central South University School of Civil Engineering","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Bangjie","middleName":"","lastName":"FU","suffix":""},{"id":128512563,"identity":"66dd5552-ccef-4374-9d87-53b453cb2651","order_by":1,"name":"Yange LI","email":"","orcid":"","institution":"Central South University School of Civil Engineering","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yange","middleName":"","lastName":"LI","suffix":""},{"id":128512564,"identity":"7b662506-daee-4df0-abf8-2fbf5d61fe5c","order_by":2,"name":"Zheng Han","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA40lEQVRIie3QPQrCMBTA8VcCcYn7K1p6BaVQFz+uohTqUnB1FNydFT1EVrdAQJceQNFBKXRyKCjipLYF17RugvkPIcP7hSQAOt0vhvkqACqTfGdMyhMmvibYL0ns5XRzvsHRbplRdGXQtrgg8UlFjNVm6NQhbq6Xvltj4Dtc0FZDRQgGbg1BGvwQUMJADrhgFFWE4uiekR7fhyS92KuYMAyomWSH7xikFxPFBDF9AoD0eOi75qrhOQtJXSWx515sPkB2+FZGyWXctWbbaawkWaT6/GyzryJF82nGo8SQTqfT/XFvR0ZGCy4U1ZkAAAAASUVORK5CYII=","orcid":"","institution":"Central South University School of Civil Engineering","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Zheng","middleName":"","lastName":"Han","suffix":""},{"id":128512565,"identity":"b2a974e9-7a29-49b1-bf44-437ae10edb35","order_by":3,"name":"Zhenxiong FANG","email":"","orcid":"","institution":"Central South University School of Civil Engineering","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Zhenxiong","middleName":"","lastName":"FANG","suffix":""},{"id":128512566,"identity":"7fc7f889-4b1a-483e-9b2f-68893b0c78af","order_by":4,"name":"Ningsheng CHEN","email":"","orcid":"","institution":"Institute of Mountain Hazards and Environment Chinese Academy of Sciences","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Ningsheng","middleName":"","lastName":"CHEN","suffix":""},{"id":128512567,"identity":"8ebb0656-fe80-4d41-beec-d93f15a76019","order_by":5,"name":"Guisheng HU","email":"","orcid":"","institution":"Institute of Mountain Hazards and Environment Chinese Academy of Sciences","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Guisheng","middleName":"","lastName":"HU","suffix":""},{"id":128512568,"identity":"34c64955-f23f-45be-8aef-3569c706ca98","order_by":6,"name":"Weidong WANG","email":"","orcid":"","institution":"Central South University School of Civil Engineering","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Weidong","middleName":"","lastName":"WANG","suffix":""}],"badges":[],"createdAt":"2022-07-22 14:40:02","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-1886017/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-1886017/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11069-023-06145-0","type":"published","date":"2023-08-28T15:09:33+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":25340334,"identity":"d32680d7-fd42-444c-b3ca-128042346970","added_by":"auto","created_at":"2022-08-17 20:42:30","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":261976,"visible":true,"origin":"","legend":"\u003cp\u003eFeature maps of sequential pool process. Yellow boxes: small-scale landslide target. From pool1 to pool3, the landslide’s structure information is retained. After pool3, the small-scale landslide disappears on the feature map.\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-1886017/v1/d47bc493424bee0c4621655f.png"},{"id":25340773,"identity":"2e53016d-d69e-431e-a836-033be43ac86a","added_by":"auto","created_at":"2022-08-17 20:52:30","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":246637,"visible":true,"origin":"","legend":"\u003cp\u003eConvolution operation in CNNs with a kernel size of 3 x 3\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-1886017/v1/6f49cd0f35e6952c681a336a.png"},{"id":25340336,"identity":"055304a1-dee2-47aa-b349-5e670ef67a7d","added_by":"auto","created_at":"2022-08-17 20:42:30","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":409898,"visible":true,"origin":"","legend":"\u003cp\u003eThe UNet (a) architecture with vgg-16 as the backbone. The contracting path (left) encodes information by downsampling the input image five times. The expansive path (right) decodes the information to reconstruct the spatial information. The RIPF-Unet (b) architecture consists of the original UNet architecture and original image pyramid features, which are used to avoid information loss.\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-1886017/v1/7da9a6a60ceb329304faff1a.png"},{"id":25340668,"identity":"cc5c236e-10cf-45c2-b2ba-1cbb103d0082","added_by":"auto","created_at":"2022-08-17 20:47:30","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":83751,"visible":true,"origin":"","legend":"\u003cp\u003eConcatenate structure\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-1886017/v1/8f9f993b6092a9a697a1f8fb.png"},{"id":25340340,"identity":"0b81b991-4af2-4085-b711-66623b2867f5","added_by":"auto","created_at":"2022-08-17 20:42:30","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":530504,"visible":true,"origin":"","legend":"\u003cp\u003eLocation of the landslide samples in the dataset. (a) Bijie area in Guizhou Province, China. (b) Landslides location in Bijie area.\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-1886017/v1/b13b5cd803a7eee402d0be95.png"},{"id":25340669,"identity":"076fb712-ecaf-4f3c-802c-70cc74e4624c","added_by":"auto","created_at":"2022-08-17 20:47:30","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":623618,"visible":true,"origin":"","legend":"\u003cp\u003ePart of examples of landslides in the dataset (Ji et al. 2020). The circled fragments represent the landslide areas\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-1886017/v1/b7aeefad48938c2d813b3e0a.png"},{"id":25340671,"identity":"e28ccff8-2e71-4a32-b93d-dfd66def5f5f","added_by":"auto","created_at":"2022-08-17 20:47:30","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":167340,"visible":true,"origin":"","legend":"\u003cp\u003eComparisons of statistics index of different landslides detection methods. (a) statistics index of the training dataset. (b) statistics index of the validation dataset\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-1886017/v1/a428c7370fdb9b8ab920fda4.png"},{"id":25340343,"identity":"01da5093-6e54-450a-8c73-dcb3ef0fdf71","added_by":"auto","created_at":"2022-08-17 20:42:30","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":148562,"visible":true,"origin":"","legend":"\u003cp\u003eFrequency distribution of individual sample’s IOU statistics based on different models. (a) training dataset’s frequency distribution. (b) validation dataset’s frequency distribution.\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-1886017/v1/7f1e681a9a604419d67c5d1e.png"},{"id":25340342,"identity":"6cbc6ad8-d1a9-4454-874d-97bbc7a725e8","added_by":"auto","created_at":"2022-08-17 20:42:30","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":1181461,"visible":true,"origin":"","legend":"\u003cp\u003eThe study area and the landslides in the images. (a)~(b) location of the study area. (c) pre-seismic image. (d) post-seismic image and the manually delineated landslides.\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-1886017/v1/cd89786ac66f23505fc3f00e.png"},{"id":25340774,"identity":"0107482c-b464-4d5c-97ac-354dc5f2da08","added_by":"auto","created_at":"2022-08-17 20:52:30","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":1243420,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of the detection result between the proposed RIPF-Unet model and manually visual delineation\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-1886017/v1/bec16997bf61d692c871ea42.png"},{"id":25340344,"identity":"4daf6833-c214-43f6-a1cb-5f01f04a3a01","added_by":"auto","created_at":"2022-08-17 20:42:31","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":1105284,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of sub-area detection results using different models\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage11.png","url":"https://assets-eu.researchsquare.com/files/rs-1886017/v1/9ecd5331d7e4c232f3c974de.png"},{"id":25340345,"identity":"d55c83d2-583b-4574-b93a-7fe7af07a878","added_by":"auto","created_at":"2022-08-17 20:42:31","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":158649,"visible":true,"origin":"","legend":"\u003cp\u003eLoss under different learning rates\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage12.png","url":"https://assets-eu.researchsquare.com/files/rs-1886017/v1/4d75ef7fb167f293713a39f8.png"},{"id":25340346,"identity":"474fb9d4-f4bb-4365-90dd-83432b6ba5d8","added_by":"auto","created_at":"2022-08-17 20:42:31","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":163315,"visible":true,"origin":"","legend":"\u003cp\u003eLoss curve of different CNN models in the validation dataset\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage13.png","url":"https://assets-eu.researchsquare.com/files/rs-1886017/v1/5b8bb6ed64dcae4a09125901.png"},{"id":42781956,"identity":"89d42826-be6e-4ec3-9491-bdb958cf2795","added_by":"auto","created_at":"2023-09-07 15:15:16","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5722043,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-1886017/v1/2c7164ce-f16e-4e69-b382-35c3c37fea34.pdf"}],"financialInterests":"","formattedTitle":"RIPF-Unet for regional landslides detection: a novel deep learning model boosted by reversed image pyramid features","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eAs a ubiquitous and typical geological hazard, landslides significantly endanger human lives, infrastructures, and other property security, and occur frequently worldwide (Cigna et al. \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). A reliable inventory of landslides is therefore of critical importance for timely quantitative hazard assessment, disaster relief, and subsequent risk governance, especially in mountainous regions with complex environments and inconvenient transportation (Galli et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2008\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eTraditionally, in-site manual investigation was the most commonly used scheme for landslide detection, which required experts and investigators to reach the landslide area and evaluate the landslides' magnitude, position, and hazard mechanisms (Ji et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). However, it is a time-consuming, laborious task, even sometimes risky (Li et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). With the boom of remote sensing technology, as well as improvements in the capacity of obtaining geospatial information on a regional scale, remote sensing technology has been extensively employed in various fields, such as for the investigation purpose of hydrology (Brinkhoff et al. \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Rajesh et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), geology (Barak et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), soil (Yu et al. \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Lourenco et al. \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e2022\u003c/span\u003e), environment (Petaja et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Wang et al. \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Wiggins et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2021\u003c/span\u003e) and forestry (Eskandari et al. \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Altamirano et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). These remarkable works inspire the application of remote sensing technology in landslide detection. When high-resolution images are available, visual interpretation is a reliable method that creates appropriate interpretation markers to show the boundaries of landslides by considering the landslides\u0026rsquo; colour, texture, shape, position, and other factors hidden in the remote sensing images. These markers are used by experts to further analyse and confirm the landslide area (Tanoli et al. \u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). The basic principle of using remote sensing images for landslide interpretation can be summed up as the spectral difference caused by the loss of vegetation and the exposure of fresh soil and rock (Li et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2014\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAlthough visual interpretation has been proved able to generate good results in landslides identification (Xu et al. \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2015\u003c/span\u003e), it is usually inefficient and may suffer from interpreters' subjectivity (Fan et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Thus, several computer visual mothods and machine learning based interpretation methods (Li et al. \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Chen et al. \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Merghadi et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Nhu et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Han et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Tien Bui et al. \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Fan et al. \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Sun et al. \u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Li et al. \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Behling et al. \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Li et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), including linear regression (LR), support vector machine (SVM), random forest (RF), k-nearest neighbour (KNN), and thresholding method, have been conducted to address these issues. These remarkable studies laid a solid foundation for landslide research. However, these works generally cost a lot of time in feature analysis, which consists of enumerating and selecting landslide conditioning factors (e.g., NDVI, NDWI, NDBI, TWI). Meanwhile, some of the crucial parameters in these methods (e.g., kernel function in SVM, max tree depth in RF, k value in KNN), require empirical adjusting, somewhat limiting the methods' flexibility. For instance, as we mentioned in our previous studies (Han et al. \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Li et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), grey-level threshold is crucial for panchromatic image binarization in landslide detection, but the determination of which is still debated.\u003c/p\u003e \u003cp\u003eRecently, convolutional neural networks (CNNs) have shown significant learning capacity in a variety of image-based tasks, including image classification (He et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Simonyan and Zisserman \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), object recognition (Ren et al. \u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e2017\u003c/span\u003e), and semantic segmentation (Chen et al. \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e2018\u003c/span\u003e; Ronneberger et al. \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Many CNN algorithms have been proposed and implemented during the last two decades (Howard et al. \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Chollet \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; He et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Huang et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2016\u003c/span\u003e; Simonyan and Zisserman \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), each based on a different rationale. In terms of landslides, the CNNs were used to extract the hidden features of the landslides in the remote sensing images, which helped to determine the existence of landslides at the location (Ding et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2016\u003c/span\u003e). Subsequently, CNNs have been widely used to retrieve images containing landslides from image datasets. Many studies (Yu et al. \u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Li et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), used specific algorithms, such as automatic thresholding and region growth algorithms, to delineate the region of the landslides.\u003c/p\u003e \u003cp\u003eUp to date, various structures of CNN networks, with different convolutional layers, sizes, and input data channels, have been discussed to analyse the impact of network settings against accuracy (Ghorbanzadeh et al. \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). In addition, multi-channel inputs of the combined spectral and topographic features were used to build CNN models (Su et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Meena et al. \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), which improved the accuracy of landslide detection. The convolution kernel of CNN can automatically obtain the effective features of images, which enables the understanding of semantic information of objects avoiding empirically determination of complex features (Lecun et al. \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). Additionally, via network training, convolution kernel can further emphasise the distinction between landslide and background, which is essential for the purpose of landslide detection. Thus, CNN can be selected as an important method for image segmentation and inspection of landslides.\u003c/p\u003e \u003cp\u003eAmong the whole CNN methods, the UNet model has been proven to be an efficient method for landslide detection (Meena et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2022\u003c/span\u003e; Yu et al. \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e2021\u003c/span\u003e; Prakash et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2020\u003c/span\u003e; Lei et al. \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). With a succession of convolution, pooling, and deconvolution layers, this method tries to extract the required information from remote sensing images (Badrinarayanan et al. \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2017\u003c/span\u003e; Shelhamer et al. \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). However, the scale of landslides is different in remote sensing images. For tiny and slender landslide detection, the excessive convolution and pooling process may cause potential texture information loss (Li et al. \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2019\u003c/span\u003e; Gu et al. \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). For instance, a \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(25\\times 25\\)\u003c/span\u003e\u003c/span\u003e pixel landslide target tends to be smaller than \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(1\\)\u003c/span\u003e\u003c/span\u003e (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\((25\u0026divide;{2}^{5})\u0026lt;1\\)\u003c/span\u003e\u003c/span\u003e) after five pooling processes, which makes its texture information disappear on the feature map (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The lost texture information may lead to the following misjudgment of the landslide target. As a result, to successfully detect landslides, especially for a remote sensing image covering a large area, the UNet model needs to be revised so that it can detect landslide boundaries precisely.\u003c/p\u003e \u003cp\u003eIn this paper, to address the issue of potential texture information loss caused by convolution and pooling in conventional CNN models, a reversed image pyramid feature (RIPF) boosted UNet algorithm for landslide detecting is presented. In this method, the original network structure of UNet models is utilised as the major network structure, while the reversed image pyramid features are employed to augment the feature in the network's decoding phase to increase the model's capacity to differentiate the area of landslides under a complicated backdrop. The RIPF-Unet model is supposed to better identify tiny and slender landslides from exposed surfaces. To verify the performance in RGB remote sensing image dataset, the proposed RIPF-Unet model is trained and tested using an open-source dataset, and the adaptability and effectiveness of the method in the actual area are further tested in the case of the Longtoushan region after the 2014 Ms.6.5 Ludian earthquake.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"2 Methodology","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Convolutional neural network\u003c/h2\u003e \u003cp\u003eThe CNN-based networks receive images as input and automatically adjust network parameters during iterative training. The trained network, consisting of thousands of weights at the node of neutral network, will predict with the greatest degree of certainty. Convolution layers, activation layers and pooling layers are common components of CNN designs (Su et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). In general, the convolutional layer is usually followed by an activation operation, which is utilized to extract the nonlinear mapping of features \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({F}_{i}\\left(Y\\right)\\)\u003c/span\u003e\u003c/span\u003e according to Eq.\u0026nbsp;(1), and improve the nonlinear representation capability of neural networks.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({F}_{i}\\left(Y\\right)=\\sigma \\left({W}_{i}\\times Y+{B}_{i}\\right)\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(1)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({F}_{i}\\left(Y\\right)\\)\u003c/span\u003e\u003c/span\u003e in Eq.\u0026nbsp;(1) represents the feature graph produced by image \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(Y\\)\u003c/span\u003e\u003c/span\u003e through the convolution layer and activation layer. \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({W}_{i}\\)\u003c/span\u003e\u003c/span\u003e and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({B}_{i}\\)\u003c/span\u003e\u003c/span\u003e are independent representations of the convolution kernel and bias term that are trained through the network, respectively. The convolution layers are designed for image feature extraction. It is the matrix's dot product and sum operation. Convolution kernels of various sizes \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\((3\\times 3, 5\\times 5, 7\\times 7)\\)\u003c/span\u003e\u003c/span\u003e can be used in the convolution layers, and the typical convolution process is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn Eq.\u0026nbsp;(1), \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\sigma\\)\u003c/span\u003e\u003c/span\u003e represents an activation function, which is commonly linked after the convolution layer to increase the neural network's nonlinear representation capacity. The typical activation functions are ReLU which could be represented by \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\left(\\text{m}\\text{a}\\text{x}\\right(0,x\\left)\\right)\\)\u003c/span\u003e\u003c/span\u003e and Sigmoid \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\((1/(1+{\\text{e}}^{-x}\\left)\\right)\\)\u003c/span\u003e\u003c/span\u003e, where \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(x\\)\u003c/span\u003e\u003c/span\u003e refers to an individual element in the image. The activation process using ReLU functions is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb. The pooling layer is used after several convolutions and activation layers to compress the feature graph for efficient computation. Max-pooling and average-pooling are two major pooling types that preserve the maximum and average of the pool window in the input feature map, respectively. The pool window is typically \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(2\\times 2\\)\u003c/span\u003e\u003c/span\u003e in size, which corresponds to a downsampling process of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(2\\times\\)\u003c/span\u003e\u003c/span\u003e. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ec depicts the max-pooling process.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 The conventianal UNet model\u003c/h2\u003e \u003cp\u003eUNet is a Fully Convolutional Neural Network proposed to solve image-to-image mapping tasks (Fern\u0026aacute;ndez and Mehrkanoon \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). Different with typical CNN architectures, UNet exploits a contracting and an expansive path during the convolution and pooling process. The former acts as an encoder of input information, and the latter is a decoder that performs classification on each pixel to reconstruct the segmented output. The encoder of UNet is changeable and aims to extract features from the input image (Liu and Wang \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). In this study, the VGG-16 network was adopted as the encoder network for feature extraction. Meanwhile, a technique called skip connection creates a bridge between the encoder and the decoder, which was used to copy feature maps. Both contracting and expansive paths are more or less symmetrical in their operations, forming a U-shape process.\u003c/p\u003e \u003cp\u003eAccording to the structure of UNet in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, the contracting path (left side) contains five convolution blocks. Each convolution block consists of several \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(3\\times 3\\)\u003c/span\u003e\u003c/span\u003e convolution operations (followed by a ReLU activation function) and a \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(2\\times 2\\)\u003c/span\u003e\u003c/span\u003e max-pooling operation of stride \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(2\\)\u003c/span\u003e\u003c/span\u003e for downsampling. On the other hand, each convolution block in the expansive path (right side) consists of a \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(2\\times 2\\)\u003c/span\u003e\u003c/span\u003e up-convolution operation for upsampling, a concatenation with the corresponding feature map from the contracting path, and two 3x3 convolutions, each followed by a ReLU activation function. To alleviate the checkerboard effect (Odena et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2016\u003c/span\u003e), the up-convolution step is replaced with a \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(2\\times 2\\)\u003c/span\u003e\u003c/span\u003e upsampling step in this work. In the final stage, the extracted feature map convolves with a \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(1\\times 1\\)\u003c/span\u003e\u003c/span\u003e kernel and is followed by a sigmoid activation function to carry out the pixel-wise classification part.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 The proposed RIPF-Unet model\u003c/h2\u003e \u003cp\u003eThrough a succession of convolution and pooling layers, the UNet model extracts image feature maps and reconstructs segmented outputs. However, multiple stages of spatial pooling and convolutional layers may cause the potential loss of fine image structure information (Wang et al. \u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Therefore, in the UNet model, the skip connection was employed to concatenate feature maps from the contracting path and expansive path for information transfer. In the same way, the UNet\u0026thinsp;+\u0026thinsp;+\u0026thinsp;model adopts several short connections to minimise the information loss after base-level convolution.\u003c/p\u003e \u003cp\u003eThe possible loss of image information in base-level convolution, especially high-frequency detailed information, is essential for landslide detection. Therefore, in this study, the reversed image pyramid features are employed to further expand the feature map in the expansive path to recover the information loss caused by convolution. Specifically, the initial image pyramid features are further stacked onto the output of the blocks in expansive path. The proposed network architecture is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb.\u003c/p\u003e \u003cp\u003eTo stack image pyramid features into the feature maps in expansive path, a novel concatenation module (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) has been proposed, which consists of three parts, i.e., the feature maps extracted by the contracting path, the original image pyramid feature maps, and the feature maps generated by the expansion path. Through average-pooling, the pyramid feature maps of the original image are scaled to the corresponding size that the concatenation operation requires. Notably, we extended the feature maps at each stage of the expansive path. After the output feature maps of the last convolution block in the expansive path, a convolution kernel of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(1\\times 1\\)\u003c/span\u003e\u003c/span\u003e is connected to control the number of channels, and the pixel-level binary classification result is obtained after a sigmoid activation function.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Loss functions and evaluation indicators\u003c/h2\u003e \u003cp\u003eThe proposed method uses a cross-entropy loss function to update the parameters of the network. The equation for calculating the cross-entropy loss is shown in Eq.\u0026nbsp;(2):\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Tabb\" border=\"1\"\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\text{l}\\text{o}\\text{s}\\text{s}=-\\frac{1}{n}\\sum _{i=1}^{n} {y}_{i}\\text{l}\\text{g}\\left({t}_{i}\\right)+\\left(1-{y}_{i}\\right)\\text{l}\\text{g}\\left(1-{t}_{i}\\right)\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(2)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003ewhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({t}_{\\text{i}}\\)\u003c/span\u003e\u003c/span\u003e represents the predicted distribution, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\({y}_{\\text{i}}\\)\u003c/span\u003e\u003c/span\u003e represents the true distribution. The error between the predicted results and the ground truth is calculated using the loss function. The backpropagation updates the network parameters to minimize the value of the cross-entropy loss function.\u003c/p\u003e \u003cp\u003eTo evaluate the model\u0026rsquo;s performance, many accuracy indexes can be referred to. In our study, we employ four indexes, including Precision, Recall, Accuracy, and F1 score, as shown in Eq.\u0026nbsp;(3\u0026ndash;6), to assess the network's recognition ability,\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Tabc\" border=\"1\"\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\text{Precision}=\\frac{\\text{T}\\text{P}}{\\text{T}\\text{P}+\\text{F}\\text{P}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(3)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\text{Recall}=\\frac{\\text{T}\\text{P}}{\\text{T}\\text{P}+\\text{F}\\text{N}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(4)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\text{Accuracy}=\\frac{\\text{T}\\text{P}+\\text{T}\\text{N}}{\\text{T}\\text{P}+\\text{F}\\text{P}+\\text{T}\\text{N}+\\text{F}\\text{N}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(5)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\text{F}1=2\\times \\frac{\\text{ Precision }\\times \\text{ Recall }}{\\text{ Precision }+\\text{ Recall }}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(6)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eResults of true positives, true negatives, false positives, and false negatives are represented by \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\text{T}\\text{P}\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\text{T}\\text{N}\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\text{F}\\text{P}\\)\u003c/span\u003e\u003c/span\u003e, and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\text{F}\\text{N}\\)\u003c/span\u003e\u003c/span\u003e in the equation. To get a better segmentation result, the precision, recall and accuracy values should be as high as possible. However, when the segmentation target is smaller in the image, it will be a certain conflict between precision and recall. Thus, the comprehensive evaluation index F1 score is given to assess the model\u0026rsquo;s performance unbiasedly. Besides the abovementioned four indexes, to evaluate the model's predictive performance for an individual landslide in the dataset, the intersection over union (IOU) index in Eq.\u0026nbsp;(7) is used.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Tabd\" border=\"1\"\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\text{I}\\text{O}\\text{U}=\\frac{\\text{T}\\text{P}}{\\text{T}\\text{P}+\\text{F}\\text{P}+\\text{F}\\text{N}}\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e(7)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3 Model Training And Analysis","content":"\u003cdiv class=\"Section2\" id=\"Sec8\"\u003e\n \u003ch2\u003e3.1 Public data sets\u003c/h2\u003e\n \u003cp\u003eTo train the proposed RIPF-Unet model, an open-source dataset in the previous study (Ji et al. \u003cspan class=\"CitationRef\"\u003e2020\u003c/span\u003e) is used in this paper. The dataset contains both satellite optical images and landslides boundary shapefiles. The image data was obtained from TripleSat satellite imagery of the Bijie region, Guizhou Province, China (as shown in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003ea), from May to August 2018. The satellite images were all pre-processed with radiometric calibration, atmospheric correction, orthographic correction, and image fusion. As shown in Fig. \u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003eb, a total of 770 samples of landslides are included and manually delineated in this dataset.\u003c/p\u003e\n \u003cp\u003eThe included landslides samples in this dataset vary in size, and the dataset was created using the anchor box of the present landslides example within a 40m\u0026times;40m extension as a backdrop. The RGB remote sensing images have a ground resolution of 0.8m, and the shape vector of each landslide was produced using ArcGIS software. Some examples of the landslides and their boundaries are shown in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec9\"\u003e\n \u003ch2\u003e3.2 Model parameter setting\u003c/h2\u003e\n \u003cp\u003eIn our study, 80% of the image data in the dataset is used for training, while the remaining 20% is for testing. To verify the effectiveness of the proposed model, the conventional UNet and UNet\u0026thinsp;+\u0026thinsp;+\u0026thinsp;networks are also well trained for comparison. All networks have the same training setup. In detail, these models are trained for 20 epochs using the Adam optimizer with a batch size of 4. The original learning rate starts at 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e and decreases exponentially to 10% after 5 epochs. The size of the input image is adjusted to \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(256\\times 256\\)\u003c/span\u003e\u003c/span\u003e pixels, and the image pixel values are normalized to \u003cimg src=\"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAACoAAAAYCAYAAACMcW/9AAABiElEQVRYhe2WwW3CMBSG//SORBIGQHgAJGRWAG9gVsg1RzJBrghFmQBYIBkAGIAMYCYwM/y9NFFTlLahqSqqfBcrtp/9yU/vKQ5J4gl4+WuB79KLdk0v2jX/Q7QoCiil4DgOPM9DFEWdXJrnOZRS7YLYgLWWrusyCAKS5Ol0IgDGcdwU8iXWWmqtCYDL5bJVbKPofr8nAFprqzmtNYUQD4tqrXm5XBjHcWvRxtQfj0dIKeH7fjU3m81gjKnti6IIjuNgtVrhdrvV1s7nM4qiqL4PhwOm02m7lL/RKHq9XmuSHwXej9ZaeJ4HpVRNdrvdYjAYPCT2bdHPKC/f7XYIwxC+7yNJEszn80o2z3MIITCZTH5XdDgc3qWypEzfeDyuvXqSJFgsFhiNRthsNgjDsBNJAM1Vn6bpXTEFQUAp5cPFVPJIMTWKGmPu2pPrusyy7GeWJNfrdevu0ShKklmWUQhBABRCME3THwtKKQmgOvP9y5Yt0RhzF+uQ/Y9zp/SiXdOLds3TiL4CacQ3YGmTimAAAAAASUVORK5CYII=\"\u003e\u0026nbsp;During the training process, the data is augmented using random rotation and cropping. The network\u0026apos;s output is the probability that any pixel in the image belongs to landslides. The model is trained using a Windows Server equipped with a GeForce TITAN V 12G GPU and an Intel Xeon(R) Gold 6133 CPU. All code is implemented in the Tensorflow deep learning environment.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv class=\"Section2\" id=\"Sec10\"\u003e\n \u003ch2\u003e3.3 Analysis of training results\u003c/h2\u003e\n \u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e lists the accuracy statistics of the different landslide detection methods on the training and validation datasets, which are schematically shown in Fig. \u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e. It demonstrates that all three models are able to detect landslides. The overall accuracy for the validation set of RIPF-Unet is 0.9725, the precision is 0.8991, the recall is 0.9490, and the F1-score is 0.9234. The statistical results of the validation dataset show that compared to the conventional UNet and UNet++, the proposed RIPF-Unet model obtains a better detection result. The precision index improves by 3.5% and 4.0%, respectively, while the F1 index improved by 2.3% and 2.7%. \u0026nbsp;\u003c/p\u003e\n \u003ctable border=\"1\" id=\"Tab1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eThe indexes statistics of the different landslide detection methods in the open-source dataset\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\" rowspan=\"2\"\u003e\n \u003cp\u003eModel\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"4\"\u003e\n \u003cp\u003eTraining data\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\" colspan=\"4\"\u003e\n \u003cp\u003eValidation data\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePrecision\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eRecall\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAccuracy\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eF1\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePrecision\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eRecall\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAccuracy\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eF1\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUNet\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.8884\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9621\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9725\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9238\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.8682\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9390\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9644\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9023\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUNet++\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.8863\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9574\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9713\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9205\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.8644\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9369\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9633\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.8992\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eThe proposed RIPF-Unet\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9199\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9763\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9811\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9472\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.8991\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9490\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9725\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.9234\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003eFurthermore, the IOU statistics also generate a valid distribution of the different models in each sample. Figure \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003ea shows the frequency distribution of the resulting IOU index in the training dataset. The IOU index commonly ranges from 0.8 to 0.9 in UNet and UNet++, while it extends upward to around 0.85 to 0.9 in our proposed RIPF-Unet model. The graph highlights the advantages of our proposed RIPF-Unet. A similar relation can be observed in the validation dataset (Fig. \u003cspan class=\"InternalRef\"\u003e8\u003c/span\u003eb), that the proposed RIPF-Unet shows a better performance on IOU distribution compared to the other models.\u003cp\u003eThe above details support that the proposed RIPF-Unet model has a better accuracy index for the training dataset, compared to the conventional UNet and UNet\u0026thinsp;+\u0026thinsp;+\u0026thinsp;models. This improvement can be explained by the fact that the RIPF-Unet model appropriately complements the decoding network\u0026rsquo;s information, increasing the abundance of features for decoding network extraction.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4 Case Study","content":"\u003cp\u003eThe proposed RIPF-Unet model has shown satisfactory accuracy using the training and validating dataset. In this section, to test the model\u0026rsquo;s performance for delineating landslides, the Longtoushan region after the 2014 Ms.6.5 Ludian earthquake is selected as a case study.\u003c/p\u003e \u003cp\u003eAs shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e, the Longtoushan region (27\u0026deg;05\u0026prime;30\u0026Prime;-27\u0026deg;07\u0026prime;43\u0026Prime;N, 103\u0026deg;16\u0026prime;37\u0026Prime;-103\u0026deg;19\u0026prime;27\u0026Prime;E) locates in Ludian County, Zhaotong City, Yunnan Province. The area was impacted by the Ms.6.5 earthquake on August 3, 2014 (Chen et al. \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e2015\u003c/span\u003e). We manually delineated the boundary of landslides in the study area with the empirical interpretation of remote sensing images, and the result is as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003ed.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e presents the final detection result using the proposed RIPF-Unet model. The components circled in red lines highlight the landslides, and the rest part refers to the background. To enhance the detection result, we highlight the TP, FN, and FP regions using different colours. Figure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e demonstrates that most landslides can be effectively detected, with a few incorrect detections of the cloud-covered region. In terms of landslide boundaries, most landslide borders can be delineated, although some trivial errors exist compared to the manual delineated boundaries.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e depicts the comparison detection results of sub-areas using different models. It is shown that all three models are able to detect the majority area of landslides. Compared to the other two models, RIPF-Unet successfully detects small-medium size landslides as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003ea and Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003eb, owing to the concatenation of reversed image pyramid features. In addition, the detected landslides\u0026rsquo; boundary of RIPF-Unet is relatively consistent with the manually delineated boundary as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003ec and Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003ed. Further, a clear distinction between landslides and roads (Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003ee) is also observed for the prediction result by the proposed RIPF-Unet, which helps improve the detection accuracy.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFor the detection results of landslides based on the three deep learning models, a statistical quantification analysis of the detection results is carried out compared to the manually visual interpretation results. Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e summarizes the quantitative assessment of the different landslide detection models. As shown in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the proposed RIPF-Unet model generally outperforms other models, respectively achieving the highest precision, recall, and accuracy of 0.6764, 0.8109, and 0.9663, and yielding F1 of 0.7376. This improved result is attributed to the correct detection of tiny and slender landslides, as well as more precise boundary detection, compared with other models.\u003c/p\u003e \u003cp\u003eCompared to UNet, our proposed RIPF-Unet has better assessment indexes with no substantial increase in parameter memory. In contrast with these baseline models, RIPF-Unet's recall metrics improved by 0.4% and 1.9%, respectively. While the F1 metrics improved by 1.6% and 1.6%, demonstrating the RIPF-Unet\u0026rsquo;s advantages in the landslide detection task.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ethe indexes statistics of the different landslides detection models in the case study area\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eModel\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eParameters\u003c/p\u003e \u003cp\u003eSize\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"4\" nameend=\"c6\" namest=\"c3\"\u003e \u003cp\u003eAssessment Index\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePrecision\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eRecall\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eAccuracy\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eF1\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eUNet\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e95.0MB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.6599\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.8071\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.9644\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.7261\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eUNet++\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e138.0MB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.6674\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.7951\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.9649\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.7257\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRIPF-Unet\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e95.1MB\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.6764\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e0.8109\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.9663\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.7376\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"5 Discussion","content":"\u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e5.1 Impact of initial learning rate\u003c/h2\u003e \u003cp\u003eAlthough the proposed RIPF-Unet model has a relatively better detection result, and the dynamic learning rate setting has a certain universality for model training, it still needs further discussion on the initial learning rate. Because the initial learning rate often determines whether the model can converge quickly in a short time (Shi et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2021\u003c/span\u003e), and is an essential network parameter set in the study. In this work, we have performed a sensitivity analysis using different initial learning rates, i.e., \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(5{\\text{E}}^{-5}\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(1{\\text{E}}^{-5}\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(1{\\text{E}}^{-4}\\)\u003c/span\u003e\u003c/span\u003e, and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(5{\\text{E}}^{-4}\\)\u003c/span\u003e\u003c/span\u003e, against the model\u0026rsquo;s performance. However, in the actual experiment, the model cannot converge while the learning rate is set to \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(5{\\text{E}}^{-4}\\)\u003c/span\u003e\u003c/span\u003e, hence the influence of the learning rate of \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(5{\\text{E}}^{-4}\\)\u003c/span\u003e\u003c/span\u003e is not taken into account here.\u003c/p\u003e \u003cp\u003eUsing the RIPF-Unet model as an example, we trained the model using the rest three initial learning rates and calculated the loss in the validation dataset. As seen in the graph (Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e), the loss under the three learning rates tends to be steady eventually. In general, a lower loss indicates a better performance of the model on the validation dataset. When the learning rate is set to \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(1{\\text{E}}^{-4}\\)\u003c/span\u003e\u003c/span\u003e, it can be seen that the overall loss of the model is superior. As a result, in the model training process, the initial learning rate was set to \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(1{\\text{E}}^{-4}\\)\u003c/span\u003e\u003c/span\u003e, and the model with the lowest loss on the validation dataset is chosen as the actual prediction model.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003e5.2 Impact of image pyramid\u0026rsquo;s embedding position\u003c/h2\u003e \u003cp\u003eIn the study, an important design of our method is to incorporate the image pyramid features into the UNet model. However, various embedding positions will result in different extraction results of the model, which potentially have an impact on the model's performance. In this experiment, we try to concatenate the reversed image pyramid features in three different embedding patterns in the model, i.e., embedding the image pyramid in the expansive path (RIPF-Unet-R), the contracting path (RIPF-Unet-L), and directly embedding the image pyramid in both the contracting path and the expansion path (RIPF-Unet-LR).\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig13\" class=\"InternalRef\"\u003e13\u003c/span\u003e represent the loss curves of different models in the validation dataset, it can be found that the loss of RIPF-Unet-R, RIPF-Unet-L, and RIPF-Unet-LR that are embedded with the image pyramid is better than that of conventional UNet and UNet++, indicating that the method of embedding the image pyramid features is effective. Compared to these methods, it can be concluded that RIPF-Unet-R has a relatively lower loss. Therefore, incorporating the reversed image pyramid into the expansive path is a better choice.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003e5.3 Limitations and Future Work\u003c/h2\u003e \u003cp\u003eOur proposed RIPF-Unet has achieved satisfactory results on the open-source dataset. Meanwhile, we also carried out landslide detection in the Longtoushan region as a case study. From the detected results of the case study (as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e), it can be seen that the landslides have been effectively detected. However, due to the differences in image spectrum, resolution, and shadow between regions, the detection precision of the case study is not as outstanding as that of the open-source dataset. To improve the generalisation ability of the model, it is crucial to building a large-scale landslide dataset that contains more landslide samples from different regions.\u003c/p\u003e \u003cp\u003eIn addition, considering that RGB images are the most commonly used and easily accessible remote sensing data when landslide events occur, we only explore the feasibility of the model to identify landslides on RGB images. In future work, additional consideration of some geological or geographical factors is more conducive to landslide detection tasks.\u003c/p\u003e \u003c/div\u003e"},{"header":"6 Conclusions","content":"\u003cp\u003eTo address the issue of imprecise boundary detection of landslides owing to the information loss caused by convolution and pooling, this study proposed a novel UNet model (RIPF-Unet) boosted by reversed image pyramid features (RIPFs). Specifically, we designed a novel concatenation module, which incorporates the high-level and low-level pyramid features of the original image into the expansive path to compensate for the information loss.\u003c/p\u003e \u003cp\u003eThe proposed RIPF-Unet model is trained and validated using the open-source landslide dataset of the Bijie area, Guizhou Province, China, wherein the precision of the proposed model is observed to increase by 3.5% and 4.0%, and the F1 index improved by 2.3% and 2.7%, compared to the conventional UNet and UNet\u0026thinsp;+\u0026thinsp;+\u0026thinsp;models, respectively. This improvement can be explained by the fact that the RIPF-Unet model appropriately complements the decoding network\u0026rsquo;s information, increasing the abundance of features for decoding network extraction.\u003c/p\u003e \u003cp\u003eIn addition, the proposed RIPF-Unet model is applied to the case of the Longtoushan region after the 2014 Ms.6.5 Ludian earthquake. Results show that the proposed model achieves a 96.63% accuracy for detecting the landslides using the Gaofen-1 images. Notably, the RIPF-Unet model is advanced in its compact parameter size and is 31% lighter compared to the Unet\u0026thinsp;+\u0026thinsp;+\u0026thinsp;model, which indicates that the RIPF-Unet model is more suitable for mobile and portable platforms.\u003c/p\u003e \u003cp\u003eHowever, the proposed FIPF-Unet is potentially limited for landslide detection in a larger area, due to the differences in image spectrum, resolution, and shadow between regions. To improve the generalisation ability of the model, in future work, it is crucial to building a large-scale landslide dataset.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch1\u003eCompeting interests\u003c/h1\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e\n\u003ch1\u003eAcknowledgements\u003c/h1\u003e\n\u003cp\u003eThis study was financially supported by the National Key R\u0026amp;D Program of China (Grant No. 2018YFD1100401); the National Natural Science Foundation of China (Grant No. 52078493); the Natural Science Foundation for Excellent Young Scholars of Hunan (Grant No. 2021JJ20057); the Innovation Provincial Program of Hunan Province (Grant No. 2020RC3002). These financial supports are gratefully acknowledged.\u003c/p\u003e\n"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAltamirano A, Miranda A, Aplin P, Carrasco J, Catalan G, Cayuela L, Fuentes-Castillo T, Hernandez A, Mart\u0026iacute;nez-Harms MJ, and Peluso F (2020) Natural forests loss and tree plantations: large-scale tree cover loss differentiation in a threatened biodiversity hotspot. Environmental Research Letters 15:124055. https://doi.org/10.1088/1748-9326/abca64.\u003c/li\u003e\n\u003cli\u003eBadrinarayanan V, Kendall A, and Cipolla R (2017) SegNet: A Deep Convolutional Encoder-Decoder Architecture for Image Segmentation. IEEE Transactions on Pattern Analysis \u0026amp; Machine Intelligence 39:2481-2495. https://doi.org/10.1109/TPAMI.2016.2644615.\u003c/li\u003e\n\u003cli\u003eBarak S, Imamalipour A, Abedi M, Bahroudi A, and Khalifani FM (2021) Comprehensive modeling of mineral potential mapping by integration of multiset geosciences data. 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Many deep learning-based models have been proposed for this purpose, however, for small-scale landslide detection, excessive convolution and pooling process may cause potential texture information loss, which can lead to misjudgement of landslide target. In this paper, we present a novel UNet model for automatic detection of landslides, wherein the reversed image pyramid features (RIPFs) are adapted to compensate for the information loss caused by a succession of convolution and pooling. The proposed RIPF-Unet model is trained and validated using the open-source landslides dataset of the Bijie area, Guizhou Province, China, wherein the precision of the proposed model is observed to increase by 3.5% and 4.0%, compared to the conventional UNet and UNet\u0026thinsp;+\u0026thinsp;+\u0026thinsp;model, respectively. The proposed RIPF-Unet model is further applied to the case of the Longtoushan region after the 2014 Ms.6.5 Ludian earthquake. Results show that the proposed model achieves a 96.63% accuracy for detecting landslides using remote sensing images. The RIPF-Unet model is also advanced in its compact parameter size, notably, it is 31% lighter compared to the UNet\u0026thinsp;+\u0026thinsp;+\u0026thinsp;model.\u003c/p\u003e","manuscriptTitle":"RIPF-Unet for regional landslides detection: a novel deep learning model boosted by reversed image pyramid features","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-08-17 20:42:28","doi":"10.21203/rs.3.rs-1886017/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"reviewerAgreed","content":"","date":"2022-09-21T12:33:05+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2022-08-12T14:02:08+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Natural Hazards","date":"2022-07-27T16:04:35+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2022-07-24T07:47:52+00:00","index":"","fulltext":""},{"type":"submitted","content":"Natural Hazards","date":"2022-07-22T10:38:45+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"natural-hazards","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"nhaz","sideBox":"Learn more about [Natural Hazards](https://www.springer.com/journal/11069)","snPcode":"11069","submissionUrl":"https://submission.nature.com/new-submission/11069/3","title":"Natural Hazards","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"4663ac32-c8c8-471e-a17b-c76d2e2aa6e7","owner":[],"postedDate":"August 17th, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2023-09-07T15:12:29+00:00","versionOfRecord":{"articleIdentity":"rs-1886017","link":"https://doi.org/10.1007/s11069-023-06145-0","journal":{"identity":"natural-hazards","isVorOnly":false,"title":"Natural Hazards"},"publishedOn":"2023-08-28 15:09:33","publishedOnDateReadable":"August 28th, 2023"},"versionCreatedAt":"2022-08-17 20:42:28","video":"","vorDoi":"10.1007/s11069-023-06145-0","vorDoiUrl":"https://doi.org/10.1007/s11069-023-06145-0","workflowStages":[]},"version":"v1","identity":"rs-1886017","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-1886017","identity":"rs-1886017","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}