Atmospheric turbulence, optical system aberrations and other factors will cause the wavefront of the incident light wave to be distorted, thereby causing the degradation of the optical system's imaging quality. Phase diversity (PD) is an effective approach to measure these wave-front distortions. It uses two or more degraded images to estimate the wavefront aberration in the pupil plane of the imaging system . The essential of the PD is to develop an appropriate optimization algorithm to minimize the evaluation function. Traditional gradient-based nonlinear optimization algorithms, such as conjugate gradient algorithm, and quasi-Newton algorithm, are easily trapped in local minimums, which greatly limits the dynamic range of the PD method. This paper proposes a Modified Sparrow Search Algorithm (MSSA) to solve this problem. Chaotic sequences, Elite Opposition-Based Learning strategy and mutation operators are introduced to enhance the global search ability. The simulation results show that, this algorithm has a dynamic range of larger than 9λ PV and an accuracy of λ/100 rms, while, compared with other swarm intelligence algorithms, it has the advantages of strong search ability, fast convergence speed, and high solution accuracy. Experiments are made, which shows the effectiveness of the algorithm.
High-resolution space observation is of great importance for scientific and military use. To get higher resolution, a larger imaging aperture is highly required. For example, to obtain one-meter ground sampling distance (GSD) in visible band on geostationary orbit (GEO), the pupil diameter of space telescope is around 25 meters. Trying to fabricate and launch so large monolithic mirror will meet many unconquerable obstacles. A feasible scheme is using sparse aperture imaging technique based on small satellites formation. This paper is focused on a sparse aperture telescope consisting of small sub-telescopes to form a Fizeau imaging interferometer. Each sub-telecope is based on a small satellite. Imaging performance of an annular structure consisting of 25 sub-apertures is evaluated by simulation. The influence of phasing error (including piston and tip/tilt) of subapertures on image quality is evaluated. The co-phasing error budget of sparse aperture telescope dependent on field of view is also analyzed. A co-phasing error detection and correction method based on wavefront sensorless adaptive optics (WSLAO) is proposed at last.
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