Research On Spatially Modulated Snapshot Computed Tomographic Polarization Imaging Spectrometer

With the increasing demand of optical remote sensing information acquisition,many researchers are deeply studying polarization spectral imaging technology.This technique can enrich the target characteristics and increase the accuracy of target reconstruction by obtaining two-dimensional spatial information,polarization information and spectral information of the target.Therefore,the technology is widely used in natural resources detection,environmental change detection,military target detection and other fields.Spatially Modulated Imaging Polarimeter(SMIP)is a kind of polarization spectral Imaging technology.By inserting a spatial modulation module into a conventional imaging system,SMIP can measure the target's all-Stokes polarization information,and obtain the target's spectral information by frequently changing the filter and half-wave plate in the structure.SMIP has the advantages of no moving parts and real-time acquisition of dynamic targets.SMIP was first proposed by Japanese scholar OKA,and then the structure and data demodulation algorithm were optimized and improved by domestic and foreign scholars on its basis.Although SMIP technology has been developed for so many years,there are still some shortcomings in SMIP technology:(1)Due to the half-wave plate inside the SMIP system,there will be installation Angle error in the process of installation and adjustment,which leads to the introduction of additional phase delay in the system,resulting in the decrease of the accuracy of polarization information demodulation;(2)Because there are half wave plates and filter plates in the SMIP system,in order to obtain the polarization information of different target bands,the two wave plates need to be replaced frequently,which greatly reduces the detection efficiency;(3)Most of the polarization information demodulation of SMIP systems adopts Fourier frequency domain filtering demodulation method,which will bring the problems of channel cross talk,high frequency loss and demodulation noise in the demodulation process,and reduce the accuracy of polarization information demodulation.At present,these deficiencies of SIMP greatly limit the application of SIMP system engineering.Therefore,in view of the above shortcomings of SMIP system,the following main studies are completed in this paper:The structural optimization of spatial modulation polarization imaging system is studied.Due to the existence of half-wave plate in the structure of the current spacemodulated polarization imaging system,the installation Angle error exists in the installation process,which leads to the introduction of additional phase delay and the reduction of polarization detection accuracy.Therefore,the structure of spatially modulated polarization imaging system is optimized and improved,and the structure of spatially modulated polarization imaging system based on two Savart polarizers is proposed.The new system structure removes the half-wave plate in the SMIP system and uses a Savart polarizer that changes the optical axis and a conventional Savart polarizer as the spatial modulation module of the new system.The characteristics of the improved Savart polarizer in the new system structure are analyzed and the theoretical modeling of the new system structure is given.During the demodulation of polarization information of the new system structure,different filtering functions are used for different Stokes channels to improve the demodulation accuracy of the new system structure.Using the proposed polarization imaging system based on two Savart polarizers,the Angle error of half wave plate installation is avoided,the difficulty of installation is effectively reduced,the cost of instrument development is saved,and the peak signal-to-noise ratio of polarization data demodulation is increased by 2 times.The spectral detection ability of spatial modulation polarization imaging system is studied systematically.Firstly,we learn the structure,the principle and the algorithm for restoring spectral image data of computational tomography spectroscopy.Secondly,SMSIPTSP and computed tomography spectroscopy system are combined to obtain a Spatially modulated snapshot computed tomographic polarization imaging spectrometer system.On this basis,theoretical modeling of the new system structure and calculation of the parameters of key components in the system are carried out,and the data demodulation method is introduced in detail.Spatially modulated snapshot computed tomographic polarization imaging spectrometer system can obtain the polarization,spectrum,intensity and two-dimensional spatial information of the target through one measurement,which makes up for the inability of the spatial modulation polarization imaging system to quickly obtain the target spectrum information.It is of great significance to the engineering application of spatial modulation polarization imaging system.The spatial demodulation algorithm of spatial modulated polarization imaging system is studied.the theoretical modeling of SMIP system is re-established,and the demodulation problem of the polarization information is transformed into the problem of solving the underdetermined equations to find the optimal solution.In order to improve the accuracy of solving the underdetermined equations and suppress the influence of the solving algorithm on the noise in the iterative process,twist-TV algorithm was obtained by combining TV regularization algorithm with Tw IST algorithm.Twist-tv algorithm has the advantages of high precision and fast convergence to solve the polarization information of SMIP system.This paper puts forward the solution of underdetermined equations of the airspace demodulation method to make up for the Fourier pressure impulses domain filtering channel crosstalk and high frequency losses flawed,at the same time,the complexity of the airspace demodulation algorithm is not high,the airspace demodulation polarization information of the spatial modulation of polarization imaging system demodulating peak signal-to-noise ratio was improved 3 db,polarization data of spatial modulation of polarization imaging system of high precision is of great significance.This paper is proposed based on two Savart polariscope spatial modulation of polarization imaging system,a spatial modulation type calculation tomographic polarization spectral imaging system and the airspace demodulation method,the spatial modulation of polarization imaging system in the simulation analysis and experimental verification,and push the spatial modulation of polarization imaging system is of great significance to engineering application.