Research On Calibration Technology Of Multi-spectral Camera For Mars Exploration

This dissertation is originated from "Mars exploration project",one of the national major engineering project in China.As one of the important payloads,the multi-spectral camera is mainly used to obtain multispectral images of the landing site and the patrol area,and then to analyze the distribution of Martian surface materials.Take into account the requirement of instrument design and the realization of scientific objectives,in this dissertation,work has been done on its spectral calibration,radiometric calibration and color calibration.The calibration camera in this paper is an identification piece of multispectral camera for Mars exploration.Firstly,the multi-spectral implementation technology of the Mars exploration multi-spectral camera was analyzed.And based on the theory of filter wheel and the imaging mechanism of the multi-spectral camera,the information transmission model and calibration model of the multi-spectral camera were established comprehensively and systematically.Secondly,the wavelength scanning method was used to calibrate the multi-spectral camera,and the experimental process and data processing flow were provided.A generalized weighted method was proposed by taking the relative spectral response of the multi-spectral camera as a weighting function.The central wavelength was defined as the weighted average of wavelengths against a relative spectral response,while the spectral bandwidth was defined as the generalized w bandwidth when the area within the bandwidth was w% of the total area.The simulation results showed that the relative output deviation was reduced by a maximum of 1.3% and the relative radiation error by a maximum of 1.83%,when performing radiation inversions by using the central wavelength and spectral bandwidth calculated by the generalized weighted method compared with the Gaussian fitting method.Thirdly,a comprehensive and systematic radiometric calibration method,experimental process and data processing flow of Mars exploration multi-spectral camera were established.In dark current calibration,the dark current calibration matrix was divided into two parts,the average dark current and the non-uniformity correction factor between pixels.In the flat field calibration,the optimal flat field matrix was given.In absolute radiometric calibration,based on the laboratory absolute radiometric calibration,the difference of absolute calibration coefficients between different targets on Mars was simulated and analyzed.Finally,the color calibration method of Mars exploration multi-spectral camera was studied.The camera output RGB values were normalized and converted to chromaticity values,and color calibration was carried out in the chromaticity space independent of luminance to correct the color difference caused by the inconsistency between camera spectral response and human visual function.The experimental results showed that the chromaticity space method reduced the calibration color difference by 0.16 and the corrected color difference by 0.65 on average compared with the traditional RGB method.In addition,based on CIE color formula,the conversion of XYZ color space and RGB color space under different calibration light sources was calculated by using the relative spectral distribution of light sources.The conversion matrix under the laboratory D65 light source obtained by using the conversion relation,compared with the standard conversion matrix,the accuracy on the acquisition of the sample’s true value was improved.