亚米级光学卫星影像邻近效应校正

Adjacency effect correction of optical satellite image with sub-meter spatial resolution

邻近效应是指卫星成像过程中目标物周围自然环境反射的太阳辐射对卫星入瞳处目标像元辐亮度的贡献.它会导致卫星图像清晰度、对比度和信息熵值降低,并且导致表观反射率卫星影像中目标像元反射率介于其真实反射率和背景像元平均反射率之间,严重影响定量遥感精度.背景各像元对邻近效应的贡献权重值主要取决于大气分子光学厚度和气溶胶光学厚度,以及目标像元与背景像元之间的空间距离、反射率差值.目前计算该权重值的权重函数仅考虑了光学厚度和空间距离对该权重值的影响.亚米级空间分辨率卫星影像中地物组合复杂,相邻地物反射率差值对该权重值的影响要考虑.本文提出的自适应大气校正算法可根据光学厚度、空间距离和反射率差值来调整背景各像元对邻近效应的贡献权重值.利用自适应大气校正算法对GF-2全色波段卫星影像进行邻近效应校正,结果表明自适应大气校正算法可有效去除亚米级空间分辨率光学卫星影像中的邻近效应,提高定量遥感精度,改善卫星影像质量.

The adjacency effect,the contribution of the neighboring pixels to the radiance of the line of sight pixel,is caused by the Rayleigh scattering of atmospheric molecules and Mie scattering of aerosol particles.The adjacency effect will cause the reflectance of each pixel in the apparent reflectance satellite image to be between the real reflectance and the average background reflectance,reducing the accuracy of the surface reflectance inversion.Therefore,it is very important to remove the adjacency effect to improve the accuracy of retrieving the surface reflectance from satellite images.The most critical issue of the adjacency effect is to accurately calculate the weight of the contribution of each background pixel to the adjacency effect.The weight value of the contribution of each background pixel to the adjacency effect mainly depends on the spatial distance between the target pixel and the background pixel,the difference in reflectance between the target pixel and the background pixel,and the optical thickness of atmospheric molecules and the optical thickness of aerosol.At present,the commonly used weight function for calculating the weight value considers only the influence of optical thickness and spatial distance on the weight value.These weight functions are applied to a relatively uniform surface.However,when these weight functions are applied to an inhomogeneous surface,they will greatly reduce the accuracy of the adjacency effect correction.The combination of ground features in satellite images with the sub-meter spatial resolution is complex,so the influence of the difference in reflectance between the target pixel and the background pixel on the adjacency effect must be considered.The adaptive atmospheric correction algorithm proposed in this paper can adjust the weight value of the contribution of background pixels to the adjacency effect according to the spatial distance between the target pixel and the background pixel,the difference in reflectance between the target pixel and the background pixel,and the difference between the atmospheric molecules’optical thickness and aerosol optical thickness.The adaptive atmospheric correction algorithm is used to correct the adjacency effect on GF-2 panchromatic satellite images.The results show that the adaptive atmospheric correction algorithm can effectively remove the adjacency effect in sub-meter spatial resolution optical satellite images,improve both the accuracy of quantitative study and the satellite image quality.