A Method Of Estimating White-Light Point Spread Function Based On Wavefront Sensing

There are various factors that cause the remote sensing image blurrig, such as atmospheric turbulence, jitter and a berration of the imaging system. Image restoration is one of the ways to resolve this problem. In remote sensing image restoration,accurately estimating the point spread function(PSF) is the key and difficulty. Algorithms for image restoration, such as wiener filtering restoration, Lucy- Richardson filtering restoration, are often based on the known PSF. Although blind restoration method is widely used and also has got many achievements, the PSF can’t be estimated by blind restoration in low contrast conditions.In practical recovery works, the accuracy of the estimated PSF is usually not high. In remote sensing, the space cam era’s aberration is the key factor of image blurring, so measuring the wave-front error and then estimating the PSF of the space camera is practical and very useful.This paper proposes a method of estimating the PSF of space camera based on in-orbit wave-front sensing. Three wave-front sensors ar e used to measure the wave-front errors of the space camera. The white light PSF is estim ated by weighted integration of the single sub-wavelength PSFs.For monochromatic light, the PSF can be cal culated by Fourier Transformation. For a white light imaging system, the PSF is a wei ghted integration of the monochromatic PSFs. The weighting coefficient is the product of the sun-light spectrum, spectral reflection factor of the object, spectral transmission factor of the optical system, and the spectral response of the image detector. Because different object has a dif ferent spectral reflection factor, to be practical and simple, we use an average spectr al reflection factor of typical ground scenes instead which will induce error in the PSF estimations by using the average reflection factor instead of the real one. This er ror is analyzed in the paper which shows that the error is in order of 10-2, even 10-3.Experiments are made to compare the PSF calculated based on wave-front errors and the PSF measured. In the experim ents, the PSF is calculated using the wave-front information given by the Hartm ann-Shack detector. Meanwhile, the m easured PSF of the optical system is obtained by a CCD ca mera in the focal plane with a point light source as the target. The result shows that the PSF calcu lated and the PSF detected m atch well, the difference between them are smaller than 10%, which strongly proves the feasibility of our method.