高分四号静止卫星辐射性能模拟与信噪比分析——以香港近海岸水体为例
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摘要
随着高分四号(GF-4号)地球同步卫星的发射与初步应用,其兼顾高空间与高时间分辨率的优势在同类型卫星中独具特色,中国对地静止卫星影像的研究也越来越受到重视。为了对GF-4号卫星在轨探测能力进行评估,掌握日内可用影像数据时段以合理安排成像时间提高卫星使用效率与延长寿命,有必要对以暗像元为代表的典型地物(如水体)进行辐射能模拟与信噪比研究。基于MODTRAN辐射传输模型,将香港沿岸水体作为暗目标,对GF-4号静止卫星多光谱遥感全色谱段以及蓝、绿、红、近红外4个多光谱谱段进行标准大气条件下入瞳处辐亮度的模拟,并利用在轨影像进行验证。在此基础上去除大气背景辐射干扰计算有效信噪比,并分别选取一年中春分、夏至、秋分、冬至,4个典型日的模拟数据进行质量分析,探讨一天连续观测中卫星能够获取高质量水体影像的有效时段,尤其是对晨昏时段临界微弱信号的敏感性进行分析。结果表明,夏至、冬至日内表观辐亮度峰值依次为59.26 W/(m~2·sr·μm)、56.20 W/(m~2·sr·μm),均出现在蓝光谱段;夏至、冬至最高地表有效辐亮度分别为17.52 W/(m~2·sr·μm)、12.13 W/(m~2·sr·μm),出现在蓝光谱段,但差距有所缩小。这是由于入瞳处辐射主要受到大气背景辐射的影响,以夏至正午为例,各谱段受背景辐射影响程度达到49.7%—75.5%。为规避背景辐射噪声,提出适用于陆表观测的有效辐射百分比的概念,推导出传统信噪比、有效信噪比以及有效辐射百分比之间的转换关系式,揭示了背景辐射对成像信噪比干扰的定量形式,提出有效信噪比计算方法,并以此为依据,以香港海岸带水体为目标,建立了相应有效信噪比对应时刻表。经计算香港海岸带水体一年中卫星全天有效信噪比均低于50 dB,夏至、冬至最高地表有效信噪比分别为41.0 dB、38.2 dB,其中蓝光谱段模拟效果最差,近红外、全色谱段结果较好。为保障影像质量,以香港海岸带水体有效信噪比35 dB为阈值确定影像获取时段,分别为夏至日北京时间7:49—17:01,冬至日北京时间9:28—15:07。
With the launch and preliminary application of the GF-4 geostationary satellite, the advantages of having both high spatial and temporal resolution enable it to have its own feature in the same type of satellites, and China has attached more importance to the research on geostationary satellite images. To evaluate the on-orbit detection capability of GF-4, thorough assessment is essential to grasp the available time of the image data on the same day and reasonably arrange the boot time to improve satellite use efficiency and prolong its life span.This objective can be accomplished by realistic radiation simulation of the imagery data and signal-to-noise ratio(SNR) study with typical objects represented by dark pixels(such as water). Based on the given spectral capabilities, geometrical, and atmospheric parameters, and in combination with land surface properties(Hong Kong coastal water), the GF-4 sensor hyperspectral remote sensing in standard atmospheric conditions, including Pan wave band and blue, green, red, and NIR-four wave bands, are simulated using the radiative transmission model MODTRAN. On this basis, the interference of atmospheric path radiance is removed to calculate the effective SNR. The data of four typical time nodes in spring equinox, summer solstice, autumn equinox, and winter solstice are selected for analysis. In this way, realistically simulated hyperspectral top-of-atmosphere apparent radiance, ground effective radiance, and path radiance are obtained. The information helps identify the effective time for the satellite to obtain high-quality water images in the observation of the same day, especially analyzing the sensitivity of the critical weak signal during the dawn–dusk period. This work fills the gaps in the data quality assessment and has a positive significance to the scientific and rational use of GF-4. Results show that the highest apparent radiance values of summer solstice and winter solstice are successive at 59.26 and 56.20 W/(m~2·sr·μm), respectively, all in the blue band; and the highest ground effective radiance values of summer solstice and winter solstice are 17.52 and 12.13 W/(m~2·sr·μm), respectively, also in the blue band. The highest effective SNR values of the summer solstice and winter solstice are 41.0 and 38.2 dB, respectively. The simulation results of blue band are the worst, but those of NIR, green, and Pan bands are good. To ensure the image quality, the water effective SNR of 35 dB is set as a threshold value to determine the boot time. The time of image acquisition is 7:49–17:01 in summer solstice and 9:28–15:07 in winter solstice.
With the launch and preliminary application of the GF-4 geostationary satellite, the advantages of having both high spatial and temporal resolution enable it to have its own feature in the same type of satellites, and China has attached more importance to the research on geostationary satellite images. To evaluate the on-orbit detection capability of GF-4, thorough assessment is essential to grasp the available time of the image data on the same day and reasonably arrange the boot time to improve satellite use efficiency and prolong its life span.This objective can be accomplished by realistic radiation simulation of the imagery data and signal-to-noise ratio(SNR) study with typical objects represented by dark pixels(such as water). Based on the given spectral capabilities, geometrical, and atmospheric parameters, and in combination with land surface properties(Hong Kong coastal water), the GF-4 sensor hyperspectral remote sensing in standard atmospheric conditions, including Pan wave band and blue, green, red, and NIR-four wave bands, are simulated using the radiative transmission model MODTRAN. On this basis, the interference of atmospheric path radiance is removed to calculate the effective SNR. The data of four typical time nodes in spring equinox, summer solstice, autumn equinox, and winter solstice are selected for analysis. In this way, realistically simulated hyperspectral top-of-atmosphere apparent radiance, ground effective radiance, and path radiance are obtained. The information helps identify the effective time for the satellite to obtain high-quality water images in the observation of the same day, especially analyzing the sensitivity of the critical weak signal during the dawn–dusk period. This work fills the gaps in the data quality assessment and has a positive significance to the scientific and rational use of GF-4. Results show that the highest apparent radiance values of summer solstice and winter solstice are successive at 59.26 and 56.20 W/(m~2·sr·μm), respectively, all in the blue band; and the highest ground effective radiance values of summer solstice and winter solstice are 17.52 and 12.13 W/(m~2·sr·μm), respectively, also in the blue band. The highest effective SNR values of the summer solstice and winter solstice are 41.0 and 38.2 dB, respectively. The simulation results of blue band are the worst, but those of NIR, green, and Pan bands are good. To ensure the image quality, the water effective SNR of 35 dB is set as a threshold value to determine the boot time. The time of image acquisition is 7:49–17:01 in summer solstice and 9:28–15:07 in winter solstice.
引文
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Gordon H R,Brown J W,Brown O B,Evans R H and Smith R C.1988.A semianalytic radiance model of ocean color.Journal of Geophysical Research:Atmospheres,93(D9):10909-10924
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Liu Z Z,Chen B Y,Chan S T,Cao Y C,Gao Y,Zhang K F and Nichol J.2015.Analysis and modelling of water vapour and temperature changes in Hong Kong using a 40‐year radiosonde record:1973-2012.International Journal of Climatology,35(3):462-474[DOI:10.1002/joc.4001]
Lodhi M A and Rundquist D C.2001.A spectral analysis of bottom-induced variation in the colour of Sand Hills lakes,Nebraska,USA.International Journal of Remote Sensing,22(9):1665-1682[DOI:10.1080/01431160117495]
LüC G,Wang W H,Yang W B,Tian Q J,Lu S and Chen Y.2015.Radiance simulation of BUV hyperspectral sensor on multi angle observation,and improvement to initial total ozone estimating model of TOMS V8 total ozone algorithm.Spectroscopy and Spectral Analysis,35(11):2979-2984(吕春光,王维和,杨文博,田庆久,卢山,陈赟.2015.面向高光谱大气臭氧传感器的多观测几何条件下紫外辐射模拟及对TOMS V8算法臭氧初值估算模型改进与评价.光谱学与光谱分析,35(11):2979-2984)[DOI:10.3964/j.issn.1000-0593(2015)11-2979-06]
Lyu C G,Tian J,Yang W B,Tian Q J,Lin Y H,Liu Z M and Zhang HM.2016.Solar-blind ultraviolet upwelling radiance diurnal variation led by observation geometry factors on geostationary attitude sensor limb viewing.Terrestrial,Atmospheric and Oceanic Sciences Journal,27(6):943-953[DOI:10.3319/TAO.2016.05.11.01(AA)]
McClatchey R A,Bolle H J and Kondratyev K Y 1984.A Preliminary Cloudless Standard Atmosphere for Radiation Computation.WCP-112.Boulder,Colorado,USA:World Climate Program
Otterman J and Fraser R S.1979.Adjacency effects on imaging by surface reflection and atmospheric scattering:cross radiance to zenith.Applied Optics,18(16):2852-2860[DOI:10.1364/AO.18.002852]
Qiu R,Wu J,Yang C P,Wang X D and Liu M.2006.Solar radiation transfer in clear atmosphere at 0.45~0.95μm.Journal of Atmospheric and Environmental Optics,1(1):21-26(邱荣,吴健,杨春平,王小东,刘淼.2006.0.45~0.95μm太阳辐射在大气中的传输计算.大气与环境光学学报,1(1):21-26)[DOI:10.3969/j.issn.1673-6141.2006.01.004]
Song P F,Wang S T and Wang X Y.2009.Impact of atmospheric radiance on efficient imaging signal-to-noise ratio in twilight environment.Spacecraft Recovery and Remote Sensing,30(2):30-36(宋鹏飞,王世涛,王小勇.2009.晨昏时段大气辐射对成像有效信噪比的影响.航天返回与遥感,30(2):30-36)[DOI:10.3969/j.issn.1009-8518.2009.02.005]
Sutherland R A,Montoya J R and Thompson J C.2002.Atmospheric effects on visible and infrared scene clutter characerization.Proceedings of SPIE 4718,Targets and Backgrounds VIII:Characterization and Representation.Bellingham,WA:SPIE:235-245[DOI:10.1117/12.478810]
Verhoef W and Bach H.2003.Simulation of hyperspectral and directional radiance images using coupled biophysical and atmospheric radiative transfer models.Remote Sensing of Environment,87(1):23-41[DOI:10.1016/S0034-4257(03)00143-3]
Wan Z,Ren J W,Li X S,Zhao G J and Ren J Y.2008.Analysis of signal-to-noise ratio for remote sensing TDI CCD camera based on radiative transfer model.Infrared and Laser Engineering,37(3):497-500,555(万志,任建伟,李宪圣,赵贵军,任建岳.2008.基于辐射传输模型的TDI CCD遥感相机信噪比分析.红外与激光工程,37(3):497-500,555)[DOI:10.3969/j.issn.1007-2276.2008.03.029]
Wang J T and Yang J Y.2008.Adaptive object tracking based on SNRmaximizing.Journal of Image and Graphics,13(1):89-94(王江涛,杨静宇.2008.基于信噪比最大化的目标自适应跟踪.中国图象图形学报,13(1):89-94)[DOI:10.11834/jig.20080116]
Wang N,Yang J Z,Chen S B,Zhou G Q,Yu Y F and Xiang T T.2015.Simulation to channel on-board spectra of ASTER based on MODTRAN.Earth Science--Journal of China University of Geosciences,40(8):1427-1431(王楠,杨金中,陈圣波,周公器,于亚凤,项甜甜.2015.基于MODTRAN的ASTER通道星上光谱模拟.地球科学--中国地质大学学报,40(8):1427-1431)[DOI:10.3799/dqkx.2015.129]
Wu B Y,Li W and Chen H B.1998.Practical Algorithm for Atmospheric Radiation Transmission.Beijing:China Meteorological Press.(吴北婴,李卫,陈洪滨.1998.大气辐射传输实用算法.北京:气象出版社)
Xu X Z,Li Z T and Xue L J.2004.Analysis and processing of CCDnoise.Infrared and Laser Engineering,33(4):343-346,357(许秀贞,李自田,薛利军.2004.CCD噪声分析及处理技术.红外与激光工程,33(4):343-346,357)[DOI:10.3969/j.issn.1007-2276.2004.04.003]
Yang B X.2005.Study on the SNR of TDICCD camera.Spacecraft Recovery and Remote Sensing,26(2):22-24(杨秉新.2005.TDICCD相机的信噪比的研究.航天返回与遥感,26(2):22-24)[DOI:10.3969/j.issn.1009-8518.2005.02.004]
Yang G J,Liu Q H,Liu Q,Xiao Q,Gu X F and Huang W J.2009.Midinfrared atmosphere radiation transfer analytic model and remote sensing images simulation.Spectroscopy and Spectral Analysis,29(3):629-633(杨贵军,柳钦火,刘强,肖青,顾行发,黄文江.2009.中红外大气辐射传输解析模型及遥感成像模拟.光谱学与光谱分析,29(3):629-633)[DOI:10.3964/j.issn.1000-0593(2009)03-0629-06]
Yang M H,Zhao Y C,Liu T J,Zhang B,Zhao C J and Tong Q X.2003.Study on a method to repair low-ratio S/N band of imaging spectrometer data based on the trend-face of DN value.Journal of Image and Graphics,8(11):1299-1303(杨敏华,赵永超,刘团结,张兵,赵春江,童庆禧.2003.基于DN值趋势面的成像光谱数据低信噪比波段修复研究.中国图象图形学报,8(11):1299-1303)[DOI:10.11834/jig.2003011474]
Zhang H,Yuan J H and Liu E H.2006.CCD noise effects on position accuracy of star sensor.Infrared and Laser Engineering,35(5):629-633,642(张辉,袁家虎,刘恩海.2006.CCD噪声对星敏感器星点定位精度的影响.红外与激光工程,35(5):629-633,642)[DOI:10.3969/j.issn.1007-2276.2006.05.027]
Chen Y H,Zhou J K,Chen X H,Zhou W and Shen W M.2009.Calculation of SNR of a satellite CCD camera based on MODTRAN.Infrared and Laser Engineering,38(5):910-914(陈宇恒,周建康,陈新华,周望,沈为民.2009.基于MODTRAN模型计算星载CCD相机信噪比.红外与激光工程,38(5):910-914)[DOI:10.3969/j.issn.1007-2276.2009.05.033]
Gordon H R,Brown J W,Brown O B,Evans R H and Smith R C.1988.A semianalytic radiance model of ocean color.Journal of Geophysical Research:Atmospheres,93(D9):10909-10924
Kirk J T O.1994.Light and Photosynthesis in Aquatic Ecosystems.Cambridge:Cambridge University Press
Liu Z Z,Chen B Y,Chan S T,Cao Y C,Gao Y,Zhang K F and Nichol J.2015.Analysis and modelling of water vapour and temperature changes in Hong Kong using a 40‐year radiosonde record:1973-2012.International Journal of Climatology,35(3):462-474[DOI:10.1002/joc.4001]
Lodhi M A and Rundquist D C.2001.A spectral analysis of bottom-induced variation in the colour of Sand Hills lakes,Nebraska,USA.International Journal of Remote Sensing,22(9):1665-1682[DOI:10.1080/01431160117495]
LüC G,Wang W H,Yang W B,Tian Q J,Lu S and Chen Y.2015.Radiance simulation of BUV hyperspectral sensor on multi angle observation,and improvement to initial total ozone estimating model of TOMS V8 total ozone algorithm.Spectroscopy and Spectral Analysis,35(11):2979-2984(吕春光,王维和,杨文博,田庆久,卢山,陈赟.2015.面向高光谱大气臭氧传感器的多观测几何条件下紫外辐射模拟及对TOMS V8算法臭氧初值估算模型改进与评价.光谱学与光谱分析,35(11):2979-2984)[DOI:10.3964/j.issn.1000-0593(2015)11-2979-06]
Lyu C G,Tian J,Yang W B,Tian Q J,Lin Y H,Liu Z M and Zhang HM.2016.Solar-blind ultraviolet upwelling radiance diurnal variation led by observation geometry factors on geostationary attitude sensor limb viewing.Terrestrial,Atmospheric and Oceanic Sciences Journal,27(6):943-953[DOI:10.3319/TAO.2016.05.11.01(AA)]
McClatchey R A,Bolle H J and Kondratyev K Y 1984.A Preliminary Cloudless Standard Atmosphere for Radiation Computation.WCP-112.Boulder,Colorado,USA:World Climate Program
Otterman J and Fraser R S.1979.Adjacency effects on imaging by surface reflection and atmospheric scattering:cross radiance to zenith.Applied Optics,18(16):2852-2860[DOI:10.1364/AO.18.002852]
Qiu R,Wu J,Yang C P,Wang X D and Liu M.2006.Solar radiation transfer in clear atmosphere at 0.45~0.95μm.Journal of Atmospheric and Environmental Optics,1(1):21-26(邱荣,吴健,杨春平,王小东,刘淼.2006.0.45~0.95μm太阳辐射在大气中的传输计算.大气与环境光学学报,1(1):21-26)[DOI:10.3969/j.issn.1673-6141.2006.01.004]
Song P F,Wang S T and Wang X Y.2009.Impact of atmospheric radiance on efficient imaging signal-to-noise ratio in twilight environment.Spacecraft Recovery and Remote Sensing,30(2):30-36(宋鹏飞,王世涛,王小勇.2009.晨昏时段大气辐射对成像有效信噪比的影响.航天返回与遥感,30(2):30-36)[DOI:10.3969/j.issn.1009-8518.2009.02.005]
Sutherland R A,Montoya J R and Thompson J C.2002.Atmospheric effects on visible and infrared scene clutter characerization.Proceedings of SPIE 4718,Targets and Backgrounds VIII:Characterization and Representation.Bellingham,WA:SPIE:235-245[DOI:10.1117/12.478810]
Verhoef W and Bach H.2003.Simulation of hyperspectral and directional radiance images using coupled biophysical and atmospheric radiative transfer models.Remote Sensing of Environment,87(1):23-41[DOI:10.1016/S0034-4257(03)00143-3]
Wan Z,Ren J W,Li X S,Zhao G J and Ren J Y.2008.Analysis of signal-to-noise ratio for remote sensing TDI CCD camera based on radiative transfer model.Infrared and Laser Engineering,37(3):497-500,555(万志,任建伟,李宪圣,赵贵军,任建岳.2008.基于辐射传输模型的TDI CCD遥感相机信噪比分析.红外与激光工程,37(3):497-500,555)[DOI:10.3969/j.issn.1007-2276.2008.03.029]
Wang J T and Yang J Y.2008.Adaptive object tracking based on SNRmaximizing.Journal of Image and Graphics,13(1):89-94(王江涛,杨静宇.2008.基于信噪比最大化的目标自适应跟踪.中国图象图形学报,13(1):89-94)[DOI:10.11834/jig.20080116]
Wang N,Yang J Z,Chen S B,Zhou G Q,Yu Y F and Xiang T T.2015.Simulation to channel on-board spectra of ASTER based on MODTRAN.Earth Science--Journal of China University of Geosciences,40(8):1427-1431(王楠,杨金中,陈圣波,周公器,于亚凤,项甜甜.2015.基于MODTRAN的ASTER通道星上光谱模拟.地球科学--中国地质大学学报,40(8):1427-1431)[DOI:10.3799/dqkx.2015.129]
Wu B Y,Li W and Chen H B.1998.Practical Algorithm for Atmospheric Radiation Transmission.Beijing:China Meteorological Press.(吴北婴,李卫,陈洪滨.1998.大气辐射传输实用算法.北京:气象出版社)
Xu X Z,Li Z T and Xue L J.2004.Analysis and processing of CCDnoise.Infrared and Laser Engineering,33(4):343-346,357(许秀贞,李自田,薛利军.2004.CCD噪声分析及处理技术.红外与激光工程,33(4):343-346,357)[DOI:10.3969/j.issn.1007-2276.2004.04.003]
Yang B X.2005.Study on the SNR of TDICCD camera.Spacecraft Recovery and Remote Sensing,26(2):22-24(杨秉新.2005.TDICCD相机的信噪比的研究.航天返回与遥感,26(2):22-24)[DOI:10.3969/j.issn.1009-8518.2005.02.004]
Yang G J,Liu Q H,Liu Q,Xiao Q,Gu X F and Huang W J.2009.Midinfrared atmosphere radiation transfer analytic model and remote sensing images simulation.Spectroscopy and Spectral Analysis,29(3):629-633(杨贵军,柳钦火,刘强,肖青,顾行发,黄文江.2009.中红外大气辐射传输解析模型及遥感成像模拟.光谱学与光谱分析,29(3):629-633)[DOI:10.3964/j.issn.1000-0593(2009)03-0629-06]
Yang M H,Zhao Y C,Liu T J,Zhang B,Zhao C J and Tong Q X.2003.Study on a method to repair low-ratio S/N band of imaging spectrometer data based on the trend-face of DN value.Journal of Image and Graphics,8(11):1299-1303(杨敏华,赵永超,刘团结,张兵,赵春江,童庆禧.2003.基于DN值趋势面的成像光谱数据低信噪比波段修复研究.中国图象图形学报,8(11):1299-1303)[DOI:10.11834/jig.2003011474]
Zhang H,Yuan J H and Liu E H.2006.CCD noise effects on position accuracy of star sensor.Infrared and Laser Engineering,35(5):629-633,642(张辉,袁家虎,刘恩海.2006.CCD噪声对星敏感器星点定位精度的影响.红外与激光工程,35(5):629-633,642)[DOI:10.3969/j.issn.1007-2276.2006.05.027]
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