Modulation Transfer Function Measurement Of High-Resolution Sensors And Its Application In Image Restoration

Modulation Transfer Function(MTF)measurement is one of the most important parts in the optical sensor imaging quality evaluation,which could be called the pixel-level radiometric calibration in a narrow sense.With the development of high-resolution earth observation technology,it is one of the standard technical processes to measure MTF and then implement the subsequent image restoration with different features in remote sensing images.Based on the imaging mechanism of the optical sensor and degradation process,the main work and innovation related to procedure optimization of high-resolution sensors on-orbit MTF measurement and the image restoration technology is as follows:1.Based on the development of high-resolution earth observation technology and the real needs of quantitative remote sensing,the thesis analyzes the significance of MTF measurement of imaging system combining the characteristics of MTF measurement of high resolution sensors and the remote sensing imaging link.The domestic and international research status of MTF measurement and image restoration technology,the research content and structure of the paper are also given.2.The imaging properties and characteristics of the diffraction-limited optical imaging system are summarized.The physical meaning of MTF and PSF as one of the image quality evaluation indicators is given,and the mathematical formulas of each imaging link are discussed.The mathematical model of the imaging system degradation effect is also given,which provides a theoretical foundation to the MTF measurement and image restoration.3.The classification of MTF measurement methods is briefly discussed.The fundamentals,testing flow and experiment procedures of the point light source method,the step edge method,the pulse method and the periodic target method are described in details.Characteristics of those methods that utilize images of ground features are compared and analyzed.Comparison experiments are carried out between slant edge method and pulse method based on HIL simulation system and it is found that the MTF calculated by the slant edge method is closer to the MTF value obtained in laboratory test than that of the pulse method in the simulation scenario.4.The traditional MTF measurement method using the slant edge is improved from two aspects: error theory and data processing flow.A gradient-weighted method in the edge detection and a de-noising strategy based on a mobile window is proposed.Those optimized methods can enhance the ESF sample quality and improve the PSF reconstruction precision.Then robust estimation is introduced in the straight line fitting and ESF fitting model,and the experiment results show that the robust estimation greatly enhances the stability and anti-noise performance of the straight edge fitting and ESF fitting.5.Based on the non-blind deconvolution image restoration method,the improved MTF measurement method proposed in this paper is used to obtain the prior information,and the Wiener filter and the least squares filter with the smooth constraint condition are applied in the restoration experiment.At the same time,a contrast restoration experiment is implemented between the aprior information obtained from the conventional slant edge method and that obtained from the optimized methods and then image quality of the restored image is assessed.The results show that the high frequency part of the degraded image is better restored using the smooth constrained least squares filtering with increasing amount of details,clearer contours and almost no ringing effect.Restored images based on optimized aprior information from the proposed MTF measurement method has shown improvement in image quality assessment results,such as in Gray Mean Grads and Laplacian Sum,which indicates that the improved method is feasible,effective and has practical value.