| In order to meet urgent needs of air pollution and climate change monitoring,the first Chinese-made spaceborne Directional Polarization Camera was developed by Anhui Institute of Optics and Fine Mechanics,Chinese Academy of Sciences.Compared with the traditional spectral imager,the DPC can not only achieve radiation measurement in 8 bands,but also 3 of them have polarization measurement function,while DPC has 118.740 wide field of view.While considering the technical elements of the radiation calibration of the traditional spectral imager,the DPC calibration also needs to analyze the technical elements of polarization calibration.These unique accuracy influence factors are mainly the response non-uniformity of the channel in different polarization analytic direction of the same polarization band,the polarization effect introduced by wide field of view imaging system polarizing,as well as the imaging blurring effect of frame transfer CCD etc.So a new calibration method,a calibration experiment process,and the calibration data processing algorithm need to be studied.Aims at improving the accuracy and business operational application level of DPC data products,the research on the programme design of automated measurement and control system for laboratory calibration and data processing software,imaging data preprocessing,data product production method,as well as software implementation are carried out.The research work of this paper will establish a set of theoretical and technical methods covering DPC measurement model,laboratory calibration data acquisition and data processing,as well as data product production which provides systematic theoretical and technical support for the development and data quantitative application for the subsequent star-borne polarization imaging instruments in China.The main research contents of this thesis are as follows:(1)An accurate measurement model is not only helpful to the description and analysis of DPC measurement process and the parametric description of its measurement errors,and is also the basis and premise for the realization of quantitative application of data products.DPC has complex structural characteristics and error sources,at the same time,the transitivity property of errors,it further increases the difficulty of building a measurement model.In order to reduce the difficulty of establishing a measurement model and realize parameterization of measurement errors,all optical elements of the optical system are divided into two structural modules of polarized optical elements and non-polarized optical elements.It analyzes the polarization principle of optical elements and gets the specific form of the transmission Mueller matrix of optical elements,and establishes a Stokes parameter measurement model of DPC polarization channel and a radiation measurement model of DPC non-polarization channel.(2)In order to eliminate system errors producted by characteristics of the DPC itself,it is necessary to calibrate all the parameters of the measurement model.According to the DPC measurement model,it is necessary to complete the measurement of calibration parameters and main performance parameters which involves the polarization effect,polarization analysis azimuth,geometric calibration,absolute responsivity calibration,relative spectral response calibration,nonlinearity,non-stability and signal-to-noise ratio etc.At the same time,the measurement of calibration and performance parameters involves the linkage measurement and control of multiple instruments makes the data acquisition more complicated.In order to improve the efficiency and precision of data acquisition,the data acquisition methods and processes of calibration and performance testing are studied.The distributed measurement and control system based on the real-time data exchange module is designed which realizes the separation of measurement and control logic and equipment control logic,and solves the problem of multi-instrument linkage measurement and control in the process of calibration and performance testing.In order to realize the automatic processing of measurement data,meet the timely and accurate requirements of calibration and performance testing data processing,ensure successful accomplishment of the laboratory calibration,it designs and realizes the calibration and performance testing data processing software.And the software solves the problem that traditional manual processing method is difficult to meet the rapid processing requirements for measurement data.(3)In view of the measurement and correction of response non-uniformity of DPC full field of view,and the challenge of existing integrating sphere reference light source in the laboratory not meeting the measurement requirements of DPC full field of view response,it put forward a sectional field of view measurement scheme based on existing integrating sphere reference light source.In order to solve the imaging data stitching problem caused by the lack of common feature target between the sectional field of view imaging data,a splicing algorithm combining the minimum local standard deviation with the local shrinkage is proposed and it realizes the seamless stitching of the sectional field of view imaging data.The results show that the measurement needs of DPC full field of view response can be met by using the sectional field of view measurement scheme.And the measurement uncertainty of the full field of view response is better than 0.67%.(4)In order to reduce the effect of the frame transfer blurring effect of the array CCD on the measurement accuracy of DPC,the production mechanism of the frame transfer blurring effect is analyzed.The frame transfer blurring effect is decomposed into two types of blurring effects,they are response differential frame transfer blurring effect and smear frame transfer blurring effect.Two types of calibration models are established and the optimal calibration sequence is verified.And the feasibility of the frame transfer blurring effect calibration method was verified by using the integrating sphere reference light source imaging and the in-orbit imaging of glint area.The verification results show that the method proposed in this paper can effectively correct the frame transfer blurring effect in the high-brightness target area,and reduce the effect of frame transfer blurring effect on polarization measurement accuracy from 7.28%to 0.43%.(5)In view of the quantitative and operational application requirements of DPC in-orbit imaging data,the data product production software is developed:zero-level and first-level product data subsystems.For the zero-level product data subsystem,the data packet detection and calibration model is designed to solve the effective detection problem of its data packet.And the stitching problem of sorting and recombining packets of the original data packets is solved by using the segmented memory mapping method.For the first-level product data subsystem,the algorithm process of product data processing is designed to ensure the simplicity and efficiency of the data processing process,and realize business operation of data product production. |
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