Research On Polarimetric And Radiometric Calibration Of Channeled Dispersion Imaging Spectropolarimeter

For the past few years,a new remote sensing information detection technology,spectropolarimetric imaging technology has emerged with the increasing demand of optical remote sensing information in the domains of atmospheric monitoring,ground object information inversion and military target identification and the rapid development of remote sensing information acquisition technology.Compared with the traditional remote sensing information acquisition technology,the spectropolarimetric imaging information obtained by this technology can provide more abundant target characteristics,improve the utilization rate of remote sensing information and the accuracy of target inversion.Polarimetric Spectral Intensity Modulation(PSIM)is an advanced spectropolarimetric imaging technology that integrates polarization,spectrum and imaging technologies.This technology only introduces a polarization detection module into the traditional spectral instrument,which can realize the measurement of the polarization spectral information of the whole Stokes vector,without moving parts,which is of great significance for the real-time acquisition of moving target information.Nonetheless,due to the existence of systematic errors such as the alignment error of fast axis of the polarization detection module,the polarization properties of optical system and the random errors such as the variation of on-orbit environmental factors,the existing methods and effects of the polarimetric calibration and radiometric calibration of the system are interfered,and the polarization detection accuracy of the system is reduced.However,at present,the calibration and compensation methods of the above errors are not perfect enough.It is necessary to further study the polarimetric calibration and radiometric calibration of the system.Therefore,the polarimetric and radiometric calibration methods of channeled dispersion imaging spectropolarimeter are studied in this paper.The main research contents are as follows:The calibration of fast axis alignment error and retardation in the polarization detection module is studied deeply.Because the current calibration method of the alignment error of fast axis is not accurate enough,firstly,the existing system polarization radiometric intensity modulation model is improved,and based on this model,a calibration method of the parameters of polarization detection module is proposed.In this method,the alignment error and retardation of two retarders in polarization detection module could be calibrated simultaneously by single measurement of any beam of linearly polarized reference light with known polarization angle.Then,by using the improved model and calibration results of the polarization detection module parameters,the error compensation of Stokes vector polarization information of the target light is carried out.The proposed calibration method can accurately calibrate and compensate the alignment error of fast axis and retardation in the polarization detection module,improve the calibration accuracy of polarization parameters and simplify the calibration process.The method of polarization radiometric calibration in the ground laboratory of the system is studied systematically.Firstly,the polarization radiative transfer model of the system is established,and polarimetric and radiometric calibration parameters are introduced into the model.On this basis,the influence of the polarization properties of optical system on radiometric calibration is analyzed,and a method of polarization radiometric calibration in the ground is proposed.By using the calibration results of polarization detection module parameters and the established polarization radiative transfer model,the polarimetric and radiometric calibration parameters under different fields of view can be decoupled and calibrated.Then,the polarization information restoration process of the Stokes vector of target light is improved by using the polarization radiative transfer model of system and the results of parameters calibration in the model.The proposed method can decouple and accurately calibrate polarimetric and radiometric calibration parameters of the system and eliminate the influence of polarization properties on the polarization and radiometric calibration.After the improved Stokes vector polarization information recovery process,the polarization detection accuracy of the system can be improved,which is of great significance to the engineering and quantitative application of the system.The method of polarization radiometric calibration for the system on orbit is studied.Firstly,the influence of the on-orbit working environment on the retardations introduced by retarders and the polarization detection of the system is simulated.Then,the on-orbit radiometric calibration and polarimetric calibration methods of system are determined,and based on the polarization radiative transfer model of system,the on-orbit polarization radiometric calibration method of the system is proposed.In this method,the on-orbit radiometric calibration results and the detected target light were used to calibrate the alignment of fast axis and retardation under different fields of view in the polarization detection module in real time,and the calibration results were used to correct the on-orbit real radiometric calibration coefficient and compensate the polarization information recovery results.This paper proposed the method of system polarization radiometric calibration on orbit,this method can accurately calibrate and effectively correct the polarimetric and radiometric calibration parameters which changed due to the change of environmental,avoid the influence of the change of environmental on system polarimetric and radiometric calibration,and improve the accuracy of polarization detection and the stability of system on orbit.In this paper,the calibration method of polarization detection module parameters,the system ground and on-orbit polarization radiometric calibration method of channeled dispersion imaging spectropolarimeter are proposed,which are verified by numerical simulation and experiment.These methods could improve the polarization detection accuracy and on-orbit working stability of the system,are of great significance to the system high-precision quantification and engineering application.