The solar FUV-UV spectrometer flight experiment onboard high-altitude balloon

The solar FUV-UV spectrometer flight experiment onboard high-altitude balloon | 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 The solar FUV-UV spectrometer flight experiment onboard high-altitude balloon Fei WEI, Xuanyi ZHANG This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4439024/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 28 Oct, 2024 Read the published version in Solar Physics → Version 1 posted 7 You are reading this latest preprint version Abstract An experiment measuring the solar far-ultravoilet-ultraviolet (FUV-UV) irradiance with spectral-resolution bettern than 0.1 nm in the wavelength range between 170 to 400 nm, was carried out by the “HongHu-6” high-altitude balloon that flight to the bottom region of the near-space in September 2022. This experiment was based on the fact that solar FUV-UV penetrates through a complex cross-section window of the upper atmosphere, from outer space to the near space. The solar FUV-UV deposits energy in the upper atmosphere, which provides a key to answer scientific questions on the most important energy contributor to overall heating sources of the near space and how the near-space environment responds to solar activities. In the wavelength band between 150 to 210 nm, irradiance maps from active regions of the solar corona, the comparative small cross-section of molecular oxygen allows certain wavelengths of the band to arrive at altitudes between 20 and 30 km above the ground, indicating solar flares could directly impact the bottom region of the near space. The solar UV irradiance in wavelength 170–400 nm is absorbed by the upper atmosphere as a function of wavelength, and deposits energy vertically in the lower regions of the near space. This experiment provides precise experimental data to assess the top-down energy input to the lower regions of the near-space. The solar FUV-UV spectrometer (SUVS) is a compact instrument based on improved Roland circle optics to adapt to the “HongHu-6” balloon payload platform. In this paper, we introduce the scientific goals of the solar FUV-UV spectrum measurement experiment, information on the SUVS instrument, preflight calibration, and the first results from the flight data. the near space SUVS high spectral resolution Far-ultraviolet ultraviolet 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 1 Introduction The near space, about 20 to 100 km above the ground extending from the stratosphere to the lower ionosphere, is a special region that takes significant role for balance between the ecosphere and the outer space, even for the global climate change. The near-space environment has unique characteristic parameters, such as the atmospheric density, composition, temperature, wind speed and photochemical processes, which are impacted by different mechanisms, as driven top-down from the sun and down-top from the lower atmosphere. At present it is unclear that how much the green-house gaseous products and energy due to human activities that had been introduced to the near space, and what is the consequence. In order to further our understanding on variations of the near-space environment, a high-altitude balloon experiment supported by the Chinese Academy of Sciences (CAS) had been carried out to measure the key parameters of the near-space environment, and study their response to the impact of solar storms. There were three instruments carried by the balloon flight to the lower region of the near space, which included a SUVS, an Anemograph, and an Ozone meter. The Anemograph was used to measure the vertical and horizontal speeds of the wind, and the Ozone meter was used to measure the in-situ density of ozone. The SUVS was aimed to measure the solar FUV-UV energy in the broad band wavelength of 170–400 nm, the most important top-down energy contributor to overall heating sources, to assess impact effects to the near-space environment by solar storms. The top-down mechanisms dominated by solar FUV-UV irradiance are wavelength depended for dynamic thermal balance of the upper atmosphere. The UV radiation in wavelength 180–240 nm is important for photochemical ozone production, and that in wavelength 200–350 nm is the main heat source in the stratosphere and mesosphere [Haigh, 1999, 2007; Rozanov et al., 2004, 2006]. In the past decades, information on the solar irradiance from X-ray to UV was collected by a large number of space-borne, air-borne and ground-based instruments. The SOLSPEC spectrometer carried by the SpaceLab 1 in November 1983 measured the solar spectra from 200 nm to 358 nm. The SpaceLab 2 mission in 1985 carrying the SUSIM (Solar Ultraviolet Spectral Irradiance Monitor) measured the solar spectra from 120 nm to 400 nm. The regular measurements with enough accurate to assess the solar UV variations was taken by the Upper Atmosphere Research Satellite (UARS) launched in 1991. However, these observations have been fragmented in time and in wavelength until in 2003 the SORCE spacecraft was launched to take continuous monitoring of the solar UV spectrum. Measurement based on air-borne platforms was poorer, as a limited flight time for an air-born craft and rarely allowed in-flight calibration. As a consequence, our present knowledge of the solar FUV-UV variability in different parts of the spectrum and how much energy it deposits in the near space is limited. In order to make good understanding on how much energy from the sun deposits vertically in the near space, a continuous solar FUV-UV dataset is crucial for the exploring experiment. The “HongHu-6” balloon carried the SUVS to flight to the maximum altitude over 25 km above the ground in the late September 2022. The SUVS covers a very broad wavelength band of 170–400 nm, with 0.1 nm wavelength resolution. In section 2 , we describe information on the solar FUV-UV spectrometer, which was designed to adapt to the compact dimensions of the balloon platform. In section 3 , we report the instrument calibration before flight and data processing method. In section 4 , we report the solar FUV-UV spectra measured by the flight experiment. 2 Instrument 2.1 Scientific goal and requirements The scientific goal of the solar FUV-UV Spectrum measurement experiment is aimed to assess the energy from the sun deposited in the near-space environment. This requires precise measurement of the solar irradiance in a broad-band spectral range. Based on the study result of Haigh in 1999, the solar X-ray and EUV-FUV in wavelength less than 170 nm is completely absorbed in the upper atmosphere 50 km above the ground, and the atmospheric compositions of O, O 2 , O 3 and N 2 have a complex transmitting window in the wavelength between 170 nm to 210 nm that allows some of the solar FUV spectra in wavelength band to path through the upper atmosphere to arrive in altitude between 20 km to 50 km, which depends on the atmospheric parameters and the level of the solar activity. In the wavelength from 200 nm to 350 nm, the solar FUV goes through the near space as a function of the wavelength, from completely absorbed, partly absorbed to almost completely transmitting. The SUVS provides precise spectral data in the wavelength 170–400 nm to fulfill the scientific requirements, with high sensitivity in the whole wavelength band, and a wide dynamic range of the flux magnitudes. The special characteristic parameters of the SUVS are listed in the Table 1 . Table 1 Performance of the SUVS onboard the “HongHu-6” high altitude balloon Wavelength Band 170 ~ 400 nm Spectral Resolution 0.1 nm Flux Dynamical Range 2.32×10 − 10 ~9.92×10 − 7 Ergs/pixel/s Field of View ± 1° Cadence 1s 2.2 Instrument The SUVS was installed on the payload platform dragged by the balloon. The rope between the downside of the balloon and the payload platform was about 80 meters in length. In the flight site located in about 37º northern latitude, the Solar Zenith Angle (SZA) changes between about 100º and 38º from sunrise to noon in late September, as shown in Fig. 1 . This allows the SUVS FOV to avoid blocking by the balloon body. In order to keep continually monitoring the solar FUV-UV spectra, the SUVS was mounted on a two-dimension Solar Pointing System (SPS) to automatically search and trace the sun. The SPS was guided by a solar sensor, which provided accurate position information of the sun in 20ms cadence. The SPS was locked while the balloon flied lower than 10 km or in the night time. After the balloon arrived in altitudes upper than 10 km and the sun rose up, the SPS was unlocked by telecommand and started to search the sun. Once the sun was caught in sight, it was kept in the center of the SUVS’s FOV, with the pointing accuracy better than 0.1º. Since the solar disk is a surface light-source about 0.5º in FOV, and the payload platform of the balloon always kept in motion during flight experiment., the Roland optics provide an ideal solution for the SUVS to keep the spectra positions stable to achieve high spectral resolution performance. In a simple configuration of Roland optics, distance between the slit and the grating, and that between the grating and the focal plane, should be long enough to achieve high wavelength-resolution, and a large detector is needed to cover the spectra space from 170 nm to 400 nm, which introduce great challenges to develop an instrument in normal dimensions carried by a balloon platform. In order to make a compact instrument to adapt to the flight requirements, an improved Roland-optics was designed, with two planar mirrors to fold the incidence arm and a concave reflecting mirror to fold the diffracting arm and focus the diffracting spectra to a much smaller focal plane, as shown in Fig. 2 . The incidence slit is 60 µm in width and 10 mm along the slit. The concave Roland grating is 498.1 mm in radius, with line density of 2700 lp/mm, provided by Horiba company. The focal plane is in concave shape with the span-length of 170 mm, which is unable to be matched by a single plane detector. In order to cover all the spectra from 170 nm to 400 nm, 2 sets of the Roland optics and 6 silicon detectors were used. 3 one-dimension silicon detectors, 1 piece of back-thinned CCD sensor and 2 pieces of back-thinned CMOS sensors, work as a group for each set of the optics. The two groups of detectors are alternatively placed along the concave focal plane to avoid structural intervention, respectively covering the spectra of 170–210 nm, 210–250 nm, 250–290 nm, 290–330 nm, 330–370 nm, 370–405 nm, as shown in Fig. 3 . The CCD sensors are more sensitive in shorter wavelength of 170–250 nm. Both the CCD and CMOS sensors, producted by Hamamatsu company, have quartz glass windows to allow FUV-UV irradiance in wavelength longer than 160 nm incidence. Each of the CCD sensors has 2048×1 effective pixels, 14µm × 500µm each pixel. And the back-thinned CMOS sensor has 2048×1 effective pixels and 14µm × 200µm each pixel. In the total energy of solar electromagnetic irradiance, the FUV-UV spactra are small in ratio comparing to the white light and the infrared compositions. The zero order of the diffraction grating is trapped inside the SUVS, to supress the zero order energy. On the other hand, since the second order of diffracting spectra in 170-200nm are overlapped to the first order of 340-400nm, as shown in Fig. 5 , we used a type of band-passing filter, FGS900-A provided by the Thorlabs company, to suppress the higher diffracting contamination for the CMOS-1B and CMOS-2B sensors. The transmission efficiency of band-pass wavelength filters used for CMOS-1B and CMOS-2B are shown in Fig. 6 . 3 Instrument calibration and data processing 3.1 Instrument calibration For the wavelength range shorter than 200nm, the quantum efficiency of the CCD sensors was calibrated by the synchrotron EUV-FUV facility in the National Synchrotron Radiation Laboratory (NSRL) located in Hefei city, as the result shown in Fig. 7 . For the wavelength range longer than 200nm, the quantum efficiency of the CCD/CMOS sensors is provided by Hamamatsu company. The absolute efficiency of the SUVS was calibrated using a low-pressure mercury lamp as a standard light source in the Chinese National Institute of Metrology (CNIM). The mercury lamp emits spectral lines of 253.6 nm, 296.7 nm, 302.1 nm, 313.2 nm and 365 nm, as shown in Fig. 8 . The solar UV spectrum measured on the ground before flight also gives information about the health of the SUVS and can be used as supplementary calibration, as shown in Fig. 9 . 3.2 Data processing Though multilayer heat-isolation materials had been used for thermal control to shield the solar irradiance directly shining the body of the SUVS, the temperature of the instrument changed in a large range while it flight from the morning to the noon. This makes it challenging for precisely processing the spectra data. Particular attention should be paid to the temperature-relative effects on the performance of the spectrometer. Spectrum shifted as the temperature changed. Deformation of the metal frame supporting the optics and sensors is unignorable when the temperature changes over 2 degrees Celsius. Prolongation or shrinkage of the length between the optics and the sensors made the spectrum to be shifted about 0.1 nm/ºC. The temperature of the mechanical frame was measured in every second, as the same cadence of the spectrum data. The data products of the SUVS had been calibrated according the real-time temperature recorded Dark current with temperature. The dark current is fitted to an increasing function of the detector temperature. It was measured in the laboratory conditions, with the temperature set to -20ºC, -10ºC and 0ºC. The calibrated data for dark current of the CCD/CMOS sensors will be used to correct the flight data. 4 The flight experiment and results The “HongHu-6” balloon experiment was carried out at the Qaidam Basin, located 37.73º north in latitude. The SUVS onboard a “HongHu” balloon was set flight in the date September 28, 2022, from 02: 05am to 02: 00pm Beijing time (same in this chapter). The SUVS was set to sleep and the SPS was locked in night. The SUVS was woken up and the SPS was unlocked by tele-command after the sun rose up. The first time the SPS captured the sun was at 8: 33am, and the SUVS began to record detecting data. Refer to the solar X-ray flux measured by GOES satellites, as shown in Fig. 10 , the solar activity during the experiment kept quiet, which meant that the spectrum data of the SUVS is mainly determined by the SZA and the absorbing effects of the upper atmosphere. The spectral data measure by the SUVS show that in the upper atmosphere the solar FUV-UV spectral flux is much stronger than that on the ground, obvious changes were observed in the solar FUV-UV spectra from morning till noon, as shown in Fig. 11 . Temporal variation of the solar FUV-UV flux as the SZA and altitude changed are shown in Fig. 12 . Since the balloon kept flight in altitude height between 25km to 28.34km, the solar FUV-UV flux was mainly modulated by the SZA, which is relative to the propagating path of the solar irradiance. The solar FUV-UV flux data can tell how much energy is absorbed and deposits in the upper atmosphere. 5 Conclusion A solar FUV-UV spectrometer with high spectral-resolution 0.1nm in the wavelength band between 170 to 400 nm was designed and set flight onboard the “HongHu-6” high-altitude balloon to assess the solar energy input to the near space. The solar FUV-UV spectra, measured on the ground and that in the flight experiment, show apparent variation of the solar energy vertically deposited in the upper atmosphere. Declarations Author Contribution Dr. Fei Wei wrote the main manuscript and Dr. Xuanyi Zhang prepared figures 10-12. All authors reviewed the manuscript. Acknowledgements This work was supported by the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDA17010203) and the National Key R&D Program of China (Grant No. 2021YFA0718600). References TOBISKA W. 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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-4439024","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":309520159,"identity":"19673ec3-3920-434a-88d0-e082d9d65572","order_by":0,"name":"Fei WEI","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAq0lEQVRIiWNgGAWjYFACxoYPH0jV0jhzBsnWzOYhSb3B8ebGZtsddfb8DcwPPzDU3CFCy5mDjc25Zw4nzjjAZizBcOwZYS1mNxLbH+e2HUgwALKBQXGYCC33HzY2W7bV2RswsH8jUssNxsZmxjZmxg0MPETaYn8msbGxtw3ol8M8xRIJx4jQItl+/GHDT6DD+NvbN374UEOEFgRgBuIEUjSMglEwCkbBKMANAIswOkAs4t5HAAAAAElFTkSuQmCC","orcid":"","institution":"National Space Science Center","correspondingAuthor":true,"prefix":"","firstName":"Fei","middleName":"","lastName":"WEI","suffix":""},{"id":309520160,"identity":"c986d6a3-8fc4-4282-bf43-a93038dab5db","order_by":1,"name":"Xuanyi ZHANG","email":"","orcid":"","institution":"Chongqing Satellite Network System Co. 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9","display":"","copyAsset":false,"role":"figure","size":401076,"visible":true,"origin":"","legend":"\u003cp\u003eThe solar ultraviolet spectra measured on the ground Qaidam Basin by the SUVS on September 17, 2022, at different time from morning to noon (Beijing Time), the altitude of the location is 3.1km.\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-4439024/v1/85b42871eb9ce613551d8d4e.png"},{"id":57595311,"identity":"5e972d99-bfdc-4e97-b2c5-d3b453a0270e","added_by":"auto","created_at":"2024-06-03 06:39:08","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":216288,"visible":true,"origin":"","legend":"\u003cp\u003eX-ray flux measured by GOES on September 28, 2022 indicated quiet solar activity during flight experiment\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-4439024/v1/395935ad637704df903b791c.png"},{"id":57594797,"identity":"292b1a97-6dde-4a31-ba6a-037a896b720a","added_by":"auto","created_at":"2024-06-03 06:31:08","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":682116,"visible":true,"origin":"","legend":"\u003cp\u003eSolar FUV-UV spectrum measured on the near space using SUVS on September 28, 2022\u003c/p\u003e","description":"","filename":"floatimage11.png","url":"https://assets-eu.researchsquare.com/files/rs-4439024/v1/f90adc118b5bd1381b9fdd45.png"},{"id":57594795,"identity":"4d85e95d-433f-49c6-9894-511db79dfe31","added_by":"auto","created_at":"2024-06-03 06:31:08","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":422436,"visible":true,"origin":"","legend":"\u003cp\u003eTemporal variation of the solar FUV-UV irradiance as the SZA and altitude change\u003c/p\u003e","description":"","filename":"floatimage12.png","url":"https://assets-eu.researchsquare.com/files/rs-4439024/v1/ea84cb766730e00f5d7e78f5.png"},{"id":68207335,"identity":"db4f5a09-fe3e-4bcc-a136-329e4d298dfd","added_by":"auto","created_at":"2024-11-04 16:36:50","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3714130,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4439024/v1/2ee852c0-21d7-4039-8786-5a1c1ba46ede.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"The solar FUV-UV spectrometer flight experiment onboard high-altitude balloon","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eThe near space, about 20 to 100 km above the ground extending from the stratosphere to the lower ionosphere, is a special region that takes significant role for balance between the ecosphere and the outer space, even for the global climate change. The near-space environment has unique characteristic parameters, such as the atmospheric density, composition, temperature, wind speed and photochemical processes, which are impacted by different mechanisms, as driven top-down from the sun and down-top from the lower atmosphere. At present it is unclear that how much the green-house gaseous products and energy due to human activities that had been introduced to the near space, and what is the consequence. In order to further our understanding on variations of the near-space environment, a high-altitude balloon experiment supported by the Chinese Academy of Sciences (CAS) had been carried out to measure the key parameters of the near-space environment, and study their response to the impact of solar storms. There were three instruments carried by the balloon flight to the lower region of the near space, which included a SUVS, an Anemograph, and an Ozone meter. The Anemograph was used to measure the vertical and horizontal speeds of the wind, and the Ozone meter was used to measure the in-situ density of ozone. The SUVS was aimed to measure the solar FUV-UV energy in the broad band wavelength of 170\u0026ndash;400 nm, the most important top-down energy contributor to overall heating sources, to assess impact effects to the near-space environment by solar storms.\u003c/p\u003e \u003cp\u003eThe top-down mechanisms dominated by solar FUV-UV irradiance are wavelength depended for dynamic thermal balance of the upper atmosphere. The UV radiation in wavelength 180\u0026ndash;240 nm is important for photochemical ozone production, and that in wavelength 200\u0026ndash;350 nm is the main heat source in the stratosphere and mesosphere [Haigh, 1999, 2007; Rozanov et al., 2004, 2006]. In the past decades, information on the solar irradiance from X-ray to UV was collected by a large number of space-borne, air-borne and ground-based instruments. The SOLSPEC spectrometer carried by the SpaceLab 1 in November 1983 measured the solar spectra from 200 nm to 358 nm. The SpaceLab 2 mission in 1985 carrying the SUSIM (Solar Ultraviolet Spectral Irradiance Monitor) measured the solar spectra from 120 nm to 400 nm. The regular measurements with enough accurate to assess the solar UV variations was taken by the Upper Atmosphere Research Satellite (UARS) launched in 1991. However, these observations have been fragmented in time and in wavelength until in 2003 the SORCE spacecraft was launched to take continuous monitoring of the solar UV spectrum. Measurement based on air-borne platforms was poorer, as a limited flight time for an air-born craft and rarely allowed in-flight calibration. As a consequence, our present knowledge of the solar FUV-UV variability in different parts of the spectrum and how much energy it deposits in the near space is limited.\u003c/p\u003e \u003cp\u003eIn order to make good understanding on how much energy from the sun deposits vertically in the near space, a continuous solar FUV-UV dataset is crucial for the exploring experiment. The \u0026ldquo;HongHu-6\u0026rdquo; balloon carried the SUVS to flight to the maximum altitude over 25 km above the ground in the late September 2022. The SUVS covers a very broad wavelength band of 170\u0026ndash;400 nm, with 0.1 nm wavelength resolution. In section \u003cspan refid=\"Sec2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, we describe information on the solar FUV-UV spectrometer, which was designed to adapt to the compact dimensions of the balloon platform. In section \u003cspan refid=\"Sec5\" class=\"InternalRef\"\u003e3\u003c/span\u003e, we report the instrument calibration before flight and data processing method. In section \u003cspan refid=\"Sec8\" class=\"InternalRef\"\u003e4\u003c/span\u003e, we report the solar FUV-UV spectra measured by the flight experiment.\u003c/p\u003e"},{"header":"2 Instrument","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Scientific goal and requirements\u003c/h2\u003e \u003cp\u003eThe scientific goal of the solar FUV-UV Spectrum measurement experiment is aimed to assess the energy from the sun deposited in the near-space environment. This requires precise measurement of the solar irradiance in a broad-band spectral range. Based on the study result of Haigh in 1999, the solar X-ray and EUV-FUV in wavelength less than 170 nm is completely absorbed in the upper atmosphere 50 km above the ground, and the atmospheric compositions of O, O\u003csub\u003e2\u003c/sub\u003e, O\u003csub\u003e3\u003c/sub\u003e and N\u003csub\u003e2\u003c/sub\u003e have a complex transmitting window in the wavelength between 170 nm to 210 nm that allows some of the solar FUV spectra in wavelength band to path through the upper atmosphere to arrive in altitude between 20 km to 50 km, which depends on the atmospheric parameters and the level of the solar activity. In the wavelength from 200 nm to 350 nm, the solar FUV goes through the near space as a function of the wavelength, from completely absorbed, partly absorbed to almost completely transmitting.\u003c/p\u003e \u003cp\u003eThe SUVS provides precise spectral data in the wavelength 170\u0026ndash;400 nm to fulfill the scientific requirements, with high sensitivity in the whole wavelength band, and a wide dynamic range of the flux magnitudes. The special characteristic parameters of the SUVS are listed in the Table \u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePerformance of the SUVS onboard the \u0026ldquo;HongHu-6\u0026rdquo; high altitude balloon\u003c/p\u003e \u003c/div\u003e \u003c/caption\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\u003eWavelength Band\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e170\u0026thinsp;~\u0026thinsp;400 nm\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSpectral Resolution\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e0.1 nm\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFlux Dynamical Range\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e2.32\u0026times;10\u003c/b\u003e\u003csup\u003e\u003cb\u003e\u0026minus;\u0026thinsp;10\u003c/b\u003e\u003c/sup\u003e \u003cb\u003e~9.92\u0026times;10\u003c/b\u003e\u003csup\u003e\u003cb\u003e\u0026minus;\u0026thinsp;7\u003c/b\u003e\u003c/sup\u003e \u003cb\u003eErgs/pixel/s\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eField of View\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e\u0026plusmn;\u0026thinsp;1\u0026deg;\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eCadence\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cb\u003e1s\u003c/b\u003e\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 \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Instrument\u003c/h2\u003e \u003cp\u003eThe SUVS was installed on the payload platform dragged by the balloon. The rope between the downside of the balloon and the payload platform was about 80 meters in length. In the flight site located in about 37\u0026ordm; northern latitude, the Solar Zenith Angle (SZA) changes between about 100\u0026ordm; and 38\u0026ordm; from sunrise to noon in late September, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. This allows the SUVS FOV to avoid blocking by the balloon body. In order to keep continually monitoring the solar FUV-UV spectra, the SUVS was mounted on a two-dimension Solar Pointing System (SPS) to automatically search and trace the sun. The SPS was guided by a solar sensor, which provided accurate position information of the sun in 20ms cadence. The SPS was locked while the balloon flied lower than 10 km or in the night time. After the balloon arrived in altitudes upper than 10 km and the sun rose up, the SPS was unlocked by telecommand and started to search the sun. Once the sun was caught in sight, it was kept in the center of the SUVS\u0026rsquo;s FOV, with the pointing accuracy better than 0.1\u0026ordm;.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eSince the solar disk is a surface light-source about 0.5\u0026ordm; in FOV, and the payload platform of the balloon always kept in motion during flight experiment., the Roland optics provide an ideal solution for the SUVS to keep the spectra positions stable to achieve high spectral resolution performance. In a simple configuration of Roland optics, distance between the slit and the grating, and that between the grating and the focal plane, should be long enough to achieve high wavelength-resolution, and a large detector is needed to cover the spectra space from 170 nm to 400 nm, which introduce great challenges to develop an instrument in normal dimensions carried by a balloon platform. In order to make a compact instrument to adapt to the flight requirements, an improved Roland-optics was designed, with two planar mirrors to fold the incidence arm and a concave reflecting mirror to fold the diffracting arm and focus the diffracting spectra to a much smaller focal plane, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe incidence slit is 60 \u0026micro;m in width and 10 mm along the slit. The concave Roland grating is 498.1 mm in radius, with line density of 2700 lp/mm, provided by Horiba company. The focal plane is in concave shape with the span-length of 170 mm, which is unable to be matched by a single plane detector. In order to cover all the spectra from 170 nm to 400 nm, 2 sets of the Roland optics and 6 silicon detectors were used. 3 one-dimension silicon detectors, 1 piece of back-thinned CCD sensor and 2 pieces of back-thinned CMOS sensors, work as a group for each set of the optics. The two groups of detectors are alternatively placed along the concave focal plane to avoid structural intervention, respectively covering the spectra of 170\u0026ndash;210 nm, 210\u0026ndash;250 nm, 250\u0026ndash;290 nm, 290\u0026ndash;330 nm, 330\u0026ndash;370 nm, 370\u0026ndash;405 nm, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. The CCD sensors are more sensitive in shorter wavelength of 170\u0026ndash;250 nm. Both the CCD and CMOS sensors, producted by Hamamatsu company, have quartz glass windows to allow FUV-UV irradiance in wavelength longer than 160 nm incidence. Each of the CCD sensors has 2048\u0026times;1 effective pixels, 14\u0026micro;m \u0026times; 500\u0026micro;m each pixel. And the back-thinned CMOS sensor has 2048\u0026times;1 effective pixels and 14\u0026micro;m \u0026times; 200\u0026micro;m each pixel.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn the total energy of solar electromagnetic irradiance, the FUV-UV spactra are small in ratio comparing to the white light and the infrared compositions. The zero order of the diffraction grating is trapped inside the SUVS, to supress the zero order energy. On the other hand, since the second order of diffracting spectra in 170-200nm are overlapped to the first order of 340-400nm, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e, we used a type of band-passing filter, FGS900-A provided by the Thorlabs company, to suppress the higher diffracting contamination for the CMOS-1B and CMOS-2B sensors. The transmission efficiency of band-pass wavelength filters used for CMOS-1B and CMOS-2B are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"3 Instrument calibration and data processing","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Instrument calibration\u003c/h2\u003e \u003cp\u003eFor the wavelength range shorter than 200nm, the quantum efficiency of the CCD sensors was calibrated by the synchrotron EUV-FUV facility in the National Synchrotron Radiation Laboratory (NSRL) located in Hefei city, as the result shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e. For the wavelength range longer than 200nm, the quantum efficiency of the CCD/CMOS sensors is provided by Hamamatsu company. The absolute efficiency of the SUVS was calibrated using a low-pressure mercury lamp as a standard light source in the Chinese National Institute of Metrology (CNIM). The mercury lamp emits spectral lines of 253.6 nm, 296.7 nm, 302.1 nm, 313.2 nm and 365 nm, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. The solar UV spectrum measured on the ground before flight also gives information about the health of the SUVS and can be used as supplementary calibration, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Data processing\u003c/h2\u003e \u003cp\u003eThough multilayer heat-isolation materials had been used for thermal control to shield the solar irradiance directly shining the body of the SUVS, the temperature of the instrument changed in a large range while it flight from the morning to the noon. This makes it challenging for precisely processing the spectra data. Particular attention should be paid to the temperature-relative effects on the performance of the spectrometer.\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eSpectrum shifted as the temperature changed. Deformation of the metal frame supporting the optics and sensors is unignorable when the temperature changes over 2 degrees Celsius. Prolongation or shrinkage of the length between the optics and the sensors made the spectrum to be shifted about 0.1 nm/\u0026ordm;C. The temperature of the mechanical frame was measured in every second, as the same cadence of the spectrum data. The data products of the SUVS had been calibrated according the real-time temperature recorded\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eDark current with temperature. The dark current is fitted to an increasing function of the detector temperature. It was measured in the laboratory conditions, with the temperature set to -20\u0026ordm;C, -10\u0026ordm;C and 0\u0026ordm;C. The calibrated data for dark current of the CCD/CMOS sensors will be used to correct the flight data.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4 The flight experiment and results","content":"\u003cp\u003eThe \u0026ldquo;HongHu-6\u0026rdquo; balloon experiment was carried out at the Qaidam Basin, located 37.73\u0026ordm; north in latitude. The SUVS onboard a \u0026ldquo;HongHu\u0026rdquo; balloon was set flight in the date September 28, 2022, from 02: 05am to 02: 00pm Beijing time (same in this chapter). The SUVS was set to sleep and the SPS was locked in night. The SUVS was woken up and the SPS was unlocked by tele-command after the sun rose up. The first time the SPS captured the sun was at 8: 33am, and the SUVS began to record detecting data.\u003c/p\u003e \u003cp\u003eRefer to the solar X-ray flux measured by GOES satellites, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e, the solar activity during the experiment kept quiet, which meant that the spectrum data of the SUVS is mainly determined by the SZA and the absorbing effects of the upper atmosphere.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe spectral data measure by the SUVS show that in the upper atmosphere the solar FUV-UV spectral flux is much stronger than that on the ground, obvious changes were observed in the solar FUV-UV spectra from morning till noon, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e. Temporal variation of the solar FUV-UV flux as the SZA and altitude changed are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e. Since the balloon kept flight in altitude height between 25km to 28.34km, the solar FUV-UV flux was mainly modulated by the SZA, which is relative to the propagating path of the solar irradiance. The solar FUV-UV flux data can tell how much energy is absorbed and deposits in the upper atmosphere.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"5 Conclusion","content":"\u003cp\u003eA solar FUV-UV spectrometer with high spectral-resolution 0.1nm in the wavelength band between 170 to 400 nm was designed and set flight onboard the \u0026ldquo;HongHu-6\u0026rdquo; high-altitude balloon to assess the solar energy input to the near space. The solar FUV-UV spectra, measured on the ground and that in the flight experiment, show apparent variation of the solar energy vertically deposited in the upper atmosphere.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eDr. Fei Wei wrote the main manuscript and Dr. Xuanyi Zhang prepared figures 10-12. All authors reviewed the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThis work was supported by the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDA17010203) and the National Key R\u0026amp;D Program of China (Grant No. 2021YFA0718600).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eTOBISKA W. K, Second generation space environment forecasting for satellite and ground system operations, 42nd AIAA Aerospace Sciences Meeting, Reno Nevada, January 5-8, 2004. \u003c/li\u003e\n\u003cli\u003eMEIER R. 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Physics, Mechanics \u0026amp; Astronomy, 2004, 34(3): 354~360. \u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"solar-physics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"sola","sideBox":"Learn more about [Solar Physics](http://link.springer.com/journal/11207)","snPcode":"11207","submissionUrl":"https://submission.nature.com/new-submission/11207/3","title":"Solar Physics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"the near space, SUVS, high spectral resolution, Far-ultraviolet, ultraviolet","lastPublishedDoi":"10.21203/rs.3.rs-4439024/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4439024/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAn experiment measuring the solar far-ultravoilet-ultraviolet (FUV-UV) irradiance with spectral-resolution bettern than 0.1 nm in the wavelength range between 170 to 400 nm, was carried out by the \u0026ldquo;HongHu-6\u0026rdquo; high-altitude balloon that flight to the bottom region of the near-space in September 2022. This experiment was based on the fact that solar FUV-UV penetrates through a complex cross-section window of the upper atmosphere, from outer space to the near space. The solar FUV-UV deposits energy in the upper atmosphere, which provides a key to answer scientific questions on the most important energy contributor to overall heating sources of the near space and how the near-space environment responds to solar activities. In the wavelength band between 150 to 210 nm, irradiance maps from active regions of the solar corona, the comparative small cross-section of molecular oxygen allows certain wavelengths of the band to arrive at altitudes between 20 and 30 km above the ground, indicating solar flares could directly impact the bottom region of the near space. The solar UV irradiance in wavelength 170\u0026ndash;400 nm is absorbed by the upper atmosphere as a function of wavelength, and deposits energy vertically in the lower regions of the near space. This experiment provides precise experimental data to assess the top-down energy input to the lower regions of the near-space. The solar FUV-UV spectrometer (SUVS) is a compact instrument based on improved Roland circle optics to adapt to the \u0026ldquo;HongHu-6\u0026rdquo; balloon payload platform. In this paper, we introduce the scientific goals of the solar FUV-UV spectrum measurement experiment, information on the SUVS instrument, preflight calibration, and the first results from the flight data.\u003c/p\u003e","manuscriptTitle":"The solar FUV-UV spectrometer flight experiment onboard high-altitude balloon","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-06-03 06:31:04","doi":"10.21203/rs.3.rs-4439024/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-06-10T07:22:42+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-06-09T14:30:04+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"193179987781287071003108371580693975753","date":"2024-05-22T16:49:51+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-05-22T05:36:31+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-05-22T00:50:09+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-05-22T00:50:09+00:00","index":"","fulltext":""},{"type":"submitted","content":"Solar Physics","date":"2024-05-18T01:44:34+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"solar-physics","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"sola","sideBox":"Learn more about [Solar Physics](http://link.springer.com/journal/11207)","snPcode":"11207","submissionUrl":"https://submission.nature.com/new-submission/11207/3","title":"Solar Physics","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"302f9790-2142-49f3-a966-d493d6435c05","owner":[],"postedDate":"June 3rd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-11-04T16:28:24+00:00","versionOfRecord":{"articleIdentity":"rs-4439024","link":"https://doi.org/10.1007/s11207-024-02396-7","journal":{"identity":"solar-physics","isVorOnly":false,"title":"Solar Physics"},"publishedOn":"2024-10-28 16:20:32","publishedOnDateReadable":"October 28th, 2024"},"versionCreatedAt":"2024-06-03 06:31:04","video":"","vorDoi":"10.1007/s11207-024-02396-7","vorDoiUrl":"https://doi.org/10.1007/s11207-024-02396-7","workflowStages":[]},"version":"v1","identity":"rs-4439024","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4439024","identity":"rs-4439024","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}