Research On On-board Radiometric Calibration Method And Application Of Space Hyperspectral Remote Sensor

Radiometric calibration is the process of establishing the quantitative conversion relationship between the output and input of remote sensor,and is an important link in the quantitative application of remote sensing data.Due to the influence of vibration and various harsh radiation environment,the radiation response model established in laboratory calibration cannot continue to describe the on-board radiation response state of remote sensor.It is of great significance to carry out periodic on-board radiometric calibration for remote sensing data quantitative application.This paper investigates the current status of radiometric calibration of remote sensors post-launch,the "Sun+diffuser" space radiometric calibration standard is established,and the technical process of space radiometric calibration standard transfer based on hyperspectral remote sensor is constructed,and the onboard verification of absolute radiometric calibration accuracy and reliability of radiometric standard transfer process of hyperspectral remote sensor is completed.The accuracy of "Sun+diffuser" space radiometric calibration standard is mainly related to the determination of BRDF real-time value of diffuser,spectral calibration accuracy of hyperspectral remote sensors and equivalent solar irradiance.In this paper,the calibration model of hyperspectral remote sensor based on wavelength is deduced and established.Through the ratio fitting method,the amplitude difference between the measured spectrum and the reference spectrum is reduced,and the spectral calibration accuracy is improved.The BRDF degradation monitoring model based on band ratio is established,which eliminates the errors caused by the cosine of the solar zenith angle and transmittance,and improves the degradation monitoring accuracy.The "Sun+diffuser" radiation standard transfer is to transfer the radiation calibration standard to other remote sensors by means of cross calibration with hyperspectral remote sensor as the transfer radiometer.The spectral types and BRDF characteristics of ground objects,solar zenith angle are the key factors affecting the standard transmission accuracy.Firstly,the SGP4 model is used to predict the satellite orbit.When the orbits of the two satellites are approximately parallel,the low and middle latitude regions are cross imaged to obtain rich ground object scene images of different spectral types.Then,by setting the threshold of imaging time interval and zenith angle,the cross-calibration image is filtered to reduce the error caused by the difference of surface characteristics and solar illumination.Finally,the cross-calibration is completed by relative radiometric correction,spatial resampling,uniform calibration area search,pixel by pixel matching and hyperspectral remote sensing data processing.Compared with the traditional cross calibration methods,the frequency and accuracy of cross calibration are improved.The on-board verification of the standard radiometric calibration accuracy and standard transfer technical process based on the "Sun+diffuser" space radiometric calibration is completed.Firstly,the on-board spectral calibration results on June 27,2019 are verified by using the oxygen absorption peak on June 7,2019.The results show that the difference of the center wavelength drift obtained by the two methods is 0.11 nm,and the bandwidth difference is 0.07 nm,which shows the reliability of the spectral calibration results.Then,the accuracy of the absolute radiometric calibration of the satellite calibration spectrometer(SCS)is verified by using the high-precision remote sensors Moderate Resolution Imaging Spectroradiometer(MODIS)onboard Terra and Multispectral Instrument(MSI)onboard Sentinel-2B as reference sensors.Finally,taking SCS as the standard transfer radiometer,the cross-calibration coefficient of COCTS can be obtained by combining the SCS and COCTS images on April 4,2019,and the cross-calibration results were verified by the images on March 13,2019 and April 17,2019.The preliminary verification results show that:(1)SCS can achieve absolute radiometric calibration with uncertainty less than 3%based on the space radiometric calibration standard of "Sun+diffuser".The BRDF attenuation monitoring model and radiation calibration model established in this paper have high accuracy.(2)The design of the transfer process of space radiometric calibration standard is reasonable,and SCS can be used as a standard transfer radiometer to realize radiometric calibration and standard transfer with uncertainty better than 4.1%.In this paper,hyperspectral remote sensor is used as transfer radiometer to transfer the "Sun+diffuser" radiation calibration standard to other remote sensors in the form of cross calibration,which can meet the calibration requirements of most visible and near-infrared remote sensors after launch.It is of great significance to improve the frequency and accuracy of on-board radiometric calibration and unify the radiometric quantification standards of different remote sensors.It is also helpful to improve the application level of remote sensing data quantification and the ability of Earth observation for China.