Functional Verification And On-orbit Calibration Method For Space-based Multi-angle Polarization Imager

The Multi-angle Polarization Imager(MAI)mounted on the TG-2 Space Laboratory launched on September 15,2016 is the first multi-angle polarization imager operating in China.In order to verify the cloud phase identification function of MAI,monitor the operational status of MAI in orbit and data quality,this paper mainly carried out the following work:(1)Based on the first airborne cloud phase observation experiment of MAI,combined with the simulation results of vector radiation transmission mode under typical conditions,the comparative analysis of the polarization characteristics observation and numerical simulation of liquid water cloud is carried out,and combined with the corresponding foundation and time the space-based observations were verified and the functions and advantages of MAI in cloud phase observation were examined.(2)In-orbit analysis and correction for MAI level 0 data.Firstly,the dark current characteristics of 13 channels are analyzed by using MAI nighttime observation data,and the unevenness of dark current distribution is corrected by image method,polynomial fitting and linear fitting channel by channel.The possible relative error of introducing the first-level product pixels is significantly reduced.Secondly,based on the full-scale multi-segment analysis and correction method,using the total of 104403 frames of observation data from September 2016 to March 2018,The CCD pixel in MAI polarization channel and the non-polarization channel response characteristics inconsistency was analyzed and corrected,and the image quality was significantly improved after the correction.(3)For the problem of MAI non-in-track calibration device,the on-orbit analysis and correction of MAI level 1 data was carried out.Firstly,the on-orbit monitoring and cross-calibration of MAI reflectivity products were carried out by GOME-2 and MODIS which serve as standard instruments.The results show that the MAI reflectivity has a significant linear relationship with the reference reflectance of standard instruments.The correlation coefficient is more than 0.95;In addition,using the method proposed by Toubbe et.combined with the actual observation of MAI,the polarization calibration of MAI in the solar flare scene is represented by the 865 nm band.The results show that the polarization degree obtained by inversion and by MAI are correlative,the correlation coefficient of which reaches 0.9576,and the overall accuracy of the data is high.This paper starts with the flight test before the launch of the MAI,the inconsistency analysis and correction of the MAI CCD dark current and the pixel response characteristics during the orbital operation,and the calibration of the intensity and polarization degree of the first-class product,basically completing the MAI.Basically finish the functional verification and on-orbit data calibration,in order to contribute to the development of multi-angle polarization remote sensing technology in China.