Research On Speckle Imaging Techniques Of Space Object

Space object images obtained through large ground-based telescopes are often heavily degraded by atmospheric turbulence,which effects the process of identification, detection and posture estimation of space object. AO system, image postprocessing techniques and hybrid imaging techniques are widely used to reduce the influence of atmospheric turbulence and obtain high-resolution image. Speckle imaging techniques, as an important methods of postprocessing techniques, play a crucial role in the astronomical observation. Since AO system has been extensively equipped on ground-based telescopes, image quality obtained has been improved evidently. But due to limited AO ability, images corrected by AO system must be further restored by post processing techniques. Hence combining conventional speckle imaging techniques and AO is of important practical value. Under the above-mentioned background, the main work in this paper is as follows:1) The relative accurate estimation of magnitude spectrum of the space object with or without AO system is fulfilled. The speckle transfer function(the most important parameter in magnitude spectrum estimation) is calculated theoretically using two methods. The speckle transfer function based on AO is modified. An effective method to remove noise effect in the magnitude spectrum estimation is proposed on the condition that the photon noise and additive noise are present in the imaging system,.2) Two key procedures in the phase spectrum estimation are fulfilled, which are the calculation of the bispectrum and phase spectrum reconstruction from the bispectrum. A coordinate system to calculate the bispectrum is established, which converts the complex quadruple cycling operation to relative simple matrix operation. The estimation of space object phase spectrum by iterative phase reconstruction from the bispectrum is estimated. The effect of optical system noise on phase spectrum estimation is analyzed.The results of speckle imaging restoration of simulated and real images show that speckle imaging techniques can effectively restore space object images with or without AO correction and greatly improve images resolution.