Research On Error Analysis And Correction Of Intensity Modulation Module Utilized In The Channeled Spectropolarimetric Remote Sensing Instrument

With the rapidly increasing demands in application fields,such as variation of the environment,exploration of the space and detection of the military targets,the requirements of researchers to the remote sensing instruments have been more and more stricted.Therefore,the new type of spectropolarimetric remote sensing technology,Polarimetric Spectral Intensity Modulation(PSIM)technique,has been addicted to the researchers.Compared with the traditional spectral information acquisition techniques,the PSIM technique can provide polarization information of detection targets,which contains more information about targets.Therefore,it has broad application prospects in the fields of cloud and atmospheric aerosol detection,astronomical observation,earth environment monitoring,and geological resource exploration and so on.The PSIM technique is an advanced technique in the field of polarization spectroscopy which was almost simultaneously proposed by Iannarilli et al.and Oka and Kato in 1999.It can be used for detecting the whole polarimetric and spectral contents of targets from ultraviolet(UV)to long wave infrared(LWIR)band in snapshot mode at the same time,which makes it more suitable for application in spectropolarimetric remote sensing.Refer to the high demand for measurement accuracy of the polarization information in practical applications(for instance,in the field of atmospheric remote sensing,the measurement accuracy of degree of linear polarization is required to be 0.5%),the polarization parameter errors of the polarimetric spectral intensity modulation module,which is the core component of PSIM technique,would directly affect the measurement accuracy and stability of channeled spectropolarimetric remote sensing instrument,which limits the engineering application of PSIM technique and the quantitative application of the data obtained by channeled spectropolarimetric remote sensing instrument.However,there is a lack of systematic research on how to analyze and correct the impacts of the key parameter errors of the polarimetric spectral intensity modulation module.The related work needs further development.This dissertation is focused on error analysis and correction of the polarimetric spectral intensity modulation module used in channeled spectropolarimetric remote sensing instrument,the main research work is as follows:Based on in-depth study of the polarimetric spectral intensity modulation principle,two factors affecting the measurement accuracy and stability of the polarimetric spectral intensity modulation module are summarized: the orientation errors and retardation errors of multiple order waveplates utilized in the polarimetric spectral intensity modulation module.The validity of the analyzed conclusions are verified by numerical simulations.In order to improve the measurement accuracy and maintain the measurement stability of the polarimetric spectral intensity modulation module,the sources and characteristics of the multiple order waveplates polarization errors are analyzed and summarized introduced during the whole process of manufacture and assembly of polarization elements and practical application of the polarimetric spectral intensity modulation module.Then,the correction algorithm of the polarization errors are proposed as following:Firstly,during the assemble stage of the instrument in the laboratory,the polarization errors of multiple order waveplates mainly caused by the assembly error and manufacture tolerance of the polarization elements,are the static systematic error.In order to reduce the infleneces of this type errors of the polarimetric spectral intensity modulation mudule,the corresponding laboratory calibration and correction techniques are put forward.Considering the influences of polarization errors of multiple order waveplates,the modified polarimetric spectral intensity modulation model is theoretically derived,based on which,a modified polarization errors calibration technique is proposed.The modified calibration technique makes full use of the calibration results obtained by classical reference beam calibration technique,specifically,the amplitude information which had been always ignored are used for calibrating the orientation errors.Then the orientation error calibration results can be used for correcting the retardation error calibration results.The proposed technique has higher calibration efficiency,which makes it more suitable for calibrating the instrument.Based on the modified model and the polarization error calibration results,a correction technique is proposed for realizing the algorithmic compensation of the polarization errors of multiple order waveplates.By utilizing this correction technique,there is no need to precisely adjust two multiple order waveplates in the polarimetric spectral intensity modulation module.It can effectively decrease the assembly difficulty and save the cost of instrument development while keeping the measurement accuracy of polarimetric spectral intensity modulation module.Secondly,during the long-term working on track process of the channeled spectropolarimetric remote sensing instrument,the orientation errors and retardation errors of multiple order waveplates mainly caused by mechanical vibration and the stress release,respectively,are the slowly varying systematic errors.In order to reduce the infleneces of this type errors,the corresponding in-orbit periodic calibration technique is proposed.Considering the limited accuracy of the calibration conditions provided by the in-orbit instrument,which is the main restriction to the laboratory calibration technique adopting on track,an easily-implemented in-orbit calibration technique is proposed for periodically calibrating the poalrization errors of multiple order waveplates.On the bases of the accurate polarization errors results of multiple order waveplates obtained by the laboratory calibration technique,this technique only needs two linearly polarized lights generated by an auxiliary polarizer relatively rotated by 45° to complete the in-orbit calibration of orientation errors and retardation errors of multiple orer waveplates.The proposed in-orbit calibration technique has the noteworthy advantages of simplicity and easy implementation,which make it suitable for application in-orbit to periodically correct of channeled spectropolarimeric remote sensing instrument.It can effectively guarantee the long-term high-precision and high-stability measurement requirements of remote sensing instruments.Lastly,during the detection process of the in-orbit instrument,owing to that the retardation of multiple order waveplates is susceptible to ambient temperature fluctuations,the retardation errors are relatively small random errors.In order to reduce the infleneces of this type errors,the corresponding in-orbit adaptive correction technique for actual retardations of multiple order waveplates is proposed.Based on the analysis of the polarization errors influence forms to the polarimetric spectral intensity modulation model and the idea of separating real part with imaginary part for utilization,the in-orbit adaptive correction technique is put forward through making full use of the laboratory calibration results(the in-orbit calibration results are also applicable).The proposed technique can realize the adaptive correction for retardations of multiple order waveplates merely using the measured target light,which has important significance for reducing the influences of ambient temperature fluctuation on the measurement accuracy and stability of the polarimetric spectral intensity modulation module.The effectiveness of the proposed technique can immunize the influences of orientation errors of multiple order waveplates.Utilizing this technique can realize the dynamic calibration and adaptive correction of the channeled spectropolarimetric remote sensing instrument while maintaining the advantages of PSIM technique,which can effectively guarantee the measurement accuracy and stability of the instrument and has great significance for accurate acquisition of spectropolarimetric remote sensing data.In this dissertation,the theoretically derived polarization errors analysis model and the proposed polarization errors calibration and correction techniques applicable for the polarimetric spectral intensity modulation module are of great significance for improving the theoretical basis of PSIM technique and establishing the error analysis and compensation system of the channeled spectropolarimetric remote sensing instrument.It will play an important role on promoting the practical engineering application of the relevant instruments and the quantitative application of the spectropolarimetric remote sensing data.