Design And Calibration Method Of Reflectance Transfer Spectrometer

On-orbit radiation measurement accuracy and traceability consistency are key performance indicators for remote sensing instruments.Due to resource constraints,most on-board calibration systems for remote sensing instruments cannot meet the high-precision on-orbit calibration requirements.In order to improve the accuracy of on-orbit calibration in solar reflection spectrum and solve the problem of differences in non-homologous remote sensing data,a reflectance transfer spectrometer based on direct measurement and comparison of solar irradiance and ground radiance is proposed in this paper.Through high-precision cross calibration with different remote sensing instruments,the long-term stable radiation reference transfer is realized.The reflectance transfer spectrometer uses the short-term stability of the response of the instrument to measure the solar spectral irradiance and the spectral irradiance of the ground target in a short time,calculate the spectral reflectance of the ground target,and use it for cross-calibration between remote sensing instruments.This process uses a large-scale attenuation system to attenuate the brightness of the sunlight to the same level as that of the ground target,and achieve direct scanning and imaging of the solar disk.The research contents of this paper include:1.Design of the refletance transfer spectrometer.According to the requirement of spectral refletance measurement and radiation reference transfer,the parameters of refletance transfer spectrometer are determined.The spectrometer uses an offner convex grating.The polarization sensitivity and stray light of the system are simulated and analyzed.Through depolarizer and stray light suppression measures,the influence of polarization and stray light on the measurement and transfer accuracy of spectral reflectance is reduced.2.Research on ground calibration and on-orbit calibration methods of reflectance transfer spectrometer.The ground calibration adopts the standard radiance detector scheme,using a tunable laser as the calibration light source,effectively shortening the transfer link,improving the calibration accuracy,and the calibration results can be traced to international standard units.The on-orbit calibration uses the solar as the calibration light source,and achieves high-precision on-orbit calibration through on-orbit calibration of attenuation coefficient,multi-level calibration and lunar observation.3.Research on calibration method of attenuation coefficient of pinhole aperture.Based on the calibration of the response nonlinearity of the detector,a wide dynamic standard light source and a back-end spectrometer are used to measure the attenuation coefficient of the front-end pinhole aperture.The calibration results show that the attenuation coefficient of pinhole aperture has obvious non-uniformity in both spatial and spectral dimensions.The relative difference of spectral reflectance is reduced from 20% to less than 2% after correction.In terms of design,manufacture and calibration,this paper makes a research on reflectance transfer spectrometer.Compared with the traditional method based on obstruction ratio,the method fully considers the influence of small hole diffraction and non full aperture imaging.In fact,this is more in line with the actual working condition of the instrument.