Aerosol Optical Depth over the Sichuan Basin: An Intercomparison of CALIPSO and MODIS Observations (2007-2022)

Aerosol Optical Depth over the Sichuan Basin: An Intercomparison of CALIPSO and MODIS Observations (2007-2022) | 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 Aerosol Optical Depth over the Sichuan Basin: An Intercomparison of CALIPSO and MODIS Observations (2007-2022) Chengyu Hu, Hwee San Lim This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6661860/v3 This work is licensed under a CC BY 4.0 License Status: Posted Version 3 posted You are reading this latest preprint version Show more versions Abstract The Sichuan Basin, a topographically enclosed region in southwestern China, experiences severe aerosol pollution due to high anthropogenic emissions, complex terrain, and frequent cloud cover—conditions that challenge satellite-based retrievals. This study presents a 16-year (2007–2022) intercomparison of Level 2 aerosol optical depth (AOD) products from the Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) and the Moderate Resolution Imaging Spectroradiometer (MODIS) over the Sichuan Basin. After harmonizing the datasets to a common 1°×1° grid, we analyze long-term trends, seasonal cycles, spatial patterns, and regional discrepancies. Both sensors capture the overall declining trend in AOD, consistent with regional air quality improvements. However, systematic differences emerge: discrepancies are most pronounced in winter and spring, when MODIS AOD exceeds CALIPSO by up to 0.15, while summer and autumn show better agreement. At monthly grid-cell scales, correlation is weak (R² = 0.12–0.27), reflecting differences in retrieval physics, sampling density, and environmental conditions. MODIS samples a broader dynamic range, with higher frequencies at both low (0.1–0.2) and high (>0.6) AOD extremes, while CALIPSO's distribution is compressed toward intermediate values. Spatially, both sensors depict higher AOD in the basin interior and western urban cluster, and lower values in surrounding mountains. The bias (MODIS minus CALIPSO) exhibits a clear spatial structure: positive in polluted urban areas (up to +0.8 in spring) and negative in clean mountainous regions. These findings provide practical guidance for data users: MODIS is preferable for capturing fine-scale spatial gradients and extreme events, while CALIPSO offers reliable retrievals in clean environments and adds value through vertical profiling. Neither sensor should be treated as absolute truth; synergistic use leveraging their complementary strengths is recommended for comprehensive aerosol characterization in complex basin environments. Atmospheric Sciences Geophysics Aerosol Optical Depth (AOD) CALIPSO MODIS Intercomparison Sichuan Basin Full Text Additional Declarations The authors declare no competing interests. Supplementary Files graphicalabstract.svg Cite Share Download PDF Status: Posted Version 3 posted You are reading this latest preprint version Show more versions 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. 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MODIS samples a broader dynamic range, with higher frequencies at both low (0.1–0.2) and high (\u0026gt;0.6) AOD extremes, while CALIPSO's distribution is compressed toward intermediate values. Spatially, both sensors depict higher AOD in the basin interior and western urban cluster, and lower values in surrounding mountains. The bias (MODIS minus CALIPSO) exhibits a clear spatial structure: positive in polluted urban areas (up to +0.8 in spring) and negative in clean mountainous regions. These findings provide practical guidance for data users: MODIS is preferable for capturing fine-scale spatial gradients and extreme events, while CALIPSO offers reliable retrievals in clean environments and adds value through vertical profiling. 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