Onboard Cross-calibration Research Between Two Polarimetric Sensors

Fine particulate matter PM2.5 in atmospheric aerosols has a significant impact on the atmospheric environment and human life,and is one of the key objects of pollutant monitoring.Currently,the monitoring of PM2.5 mainly relies on ground stations.And how to use satellite remote sensing technology to achieve large-scale,high-precision monitoring is an important challenge in this field.With the development of satellite remote sensing technology in recent years,the passive aerosol detection method combining multi-angle,multi-spectrum and polarization detection capabilities is a technical development trend in the application of aerosol observation technology,and is also a new technical solution in the field of polarization remote sensing.In particular,polarization detection method can provide an independent information dimension for atmospheric remote sensing,and is considered to be the observation method with the greatest potential to improve the detection accuracy of atmospheric aerosol and cloud parameters.Based on the requirements and characteristics of PM2.5 satellite remote sensing,the "Polarization CrossFire"(PCF)aerosol detection scheme has been proposed in China.The PCF suite consists of the particulate observing scanning polarimeter(POSP)and the directional polarimetric camera(DPC).While realizing PM2.5 parameter joint retrieval,it also solves the problem of long term onboard accuracy maintenance ability of large field of view(FoV)polarization imaging remote sensors.The latter is the research topic of this paper.This paper intends to use the high precision onboard radiation and polarization calibration capabilities of POSP to realize transfer of radiation and polarization accuracy from POSP to DPC through the crosscalibration method.With a focus on the traditional on-orbit calibration method of DPC and the transferability of relevant calibration parameters,this paper clarifies the polarization detection principle,instrument characteristics,and laboratory calibration model of DPC and POSP based on the basic theory of polarization measurement.By understanding of retrieval model and application requirements of the PCF cooperative detection scheme,the concept of aims at different application levels are also introduced in this paper,as well as the corresponding principles and methods of spectral,temporal,and spatial collaborative configuration of remote sensing system.Before satellite launch,the FoV matching method that ensures the spatiotemporal consistency of the two sensors during onboard observation is studied in detail through aviation experiments.A spatial response weighting distribution model is established for the POSP integral smear effect during acquisition process.This model is used for data fusion of high resolution SIPC to analyze and evaluate the data resolution consistency processing results of two sensors.Based on the correlation results of data with the same resolution,a registration method for the determination of relative geometric relationship between POSP and SIPC in airborne aviation experiment is proposed,which is further applied in the onborad FoV matching process of POSP and DPC.This method can effectively ensure the FoV consistency of the PCF scheme.And according to the DPC onboard geometric calibration and the onboard geolocation results of the two sensors,the absolute FoV relationship between the two sensors is evaluated.After satellite launch,in order to evaluate the accuracy of onboard polarization cross-calibration,the onboard polarization calibration and authenticity testing research are conducted on the reference remote sensor POSP.The key parameters of onboard polarization calibration are calculated by using the data of unpolarized reference assembly and polarized reference assembly,and the time variation characteristics are also analyzed.According to the polarization characteristics of ice cloud targets at large scattering angles,an onboard polarization detection accuracy authenticating method is proposed,which is applied to the POSP data before and after polarization calibration during onboard operation.The results show that onboard polarization calibration can effectively maintain the polarization detection accuracy of POSP.The ice cloud target at large scattering angle can be used to authenticate the polarization detection accuracy of remote sensors.Finally,based on the characteristics of the data set and the geometric correlation of the calibration parameters,the onboard cross-calibration research of DPC productlevel georeferenced grid projection data and pixel-level raw image plane coordinate data is conducted by using different data processing methods.Onboard absolute radiation parameter calibration,relative radiation response variation analysis,and linear polarization comparison results are obtained based on product-level data,with absolute radiometric coefficient changes are less than 3%in half a year,and over 90%of DoLP measurement deviations between the two sensors are less than 0.02.Based on pixellevel data,the relative radiation variation parameters,linear bidirectional attenuation and relative transmittance of the three channels at DPC original pixels in the cross-track direction overlapping FoV of the two sensors are obtained.The variation of the bidirectional attenuation from the center to the edge of the FoV reached 0.03-0.04,and the relative transmittance changes of each polarization channel in two months are within 2-3 ‰.Compared with the traditional natural target calibration method,the onboard cross-calibration and data verification method of the large field of view polarization remote sensor that carried with the high precision polarization remote sensor on the same platform has significant advantages in terms of calibration accuracy,frequency and reliability.