Image Degradation And Restoration Of Central Obscuration Optical Remote Sensing System

Nowadays coaxial reflection and off-axis reflection optical systems are most popular optical system in remote optical sensing systems which have long focal length and high-resolution, for the advantages of compact structure, easy fabrication and high stability. But because of the obscuration of input light due to second mirror, MTF of system degrades greatly in middle frequency, affecting the quality of image. This shortcoming became the technical bottleneck of coaxial reflection optical systems. The issue of this article is to study the image recovery of central obscuration optical remote sensing system.Modulation Transfer Function Compensation (MTFC) has been used widely in optical remote sensing system. We study the MTFC technic in modified Cassegrain optical remote sensing system. We design a Cassegrain optical remote sensing system with 2 meter focal length. Using MTFC technique, PSF (Point Spread Function) of image is obtained by slanted-edge method, then a deconvolution method is used to recover image. Final, several assessment functions are used to evaluate recovery results. At the same time, we study the recovery results for different type remote sensing pictures in different noise and different obscuration ratio.Through comparing different restoration algorithm and different assessment functions, we found RL restoration algorithm had satisfied results in pictures without noise and sparse deconvolution algorithm had good results in noise pictures. GRM and HVSWGM are the best assessment functions in reference methods, and GMG is the best no reference assessment function. GRM assessment function indicates that the image quality is improved 10%-20%. Through experiments for different obscuration ratio, we found this method has satisfied result within 60% obscuration ratio. Above result indicated the MTFC technic has great effect in central obscuration optical systems.