高分二号全色卫星影像大气校正

Atmospheric Correction of Gaofen-2 Panchromatic Satellite Images

利用大气辐射传输模型和指数衰减点扩展函数,发展了一套适用于亚米级分辨率的全色卫星影像的大气校正方法,该方法充分考虑了大气参数(气溶胶、水汽、臭氧及其他吸收气体等参数)、空间分辨率、背景像元与目标像元的空间距离等对邻近效应的影响。结果表明,本文建立的大气校正方法能够有效去除大气及周围环境对卫星入瞳信号的影响,充分解决全色卫星影像中的邻近效应问题,全面提升了卫星影像的质量(清晰度至少提高了155%,对比度至少提高了115%,边缘能量至少提高了247%,细节能量至少提高了204%,调制传递函数至少增大了169%)。

Objective Due to the sub-meter higher spatial resolution of panchromatic satellite images,the imaging process is easily affected by atmospheric scattering and absorption and adjacency effect under low atmospheric visibility,resulting in blurred edges of image objects and reduced image quality,and seriously affects the accuracy of quantitative remote sensing application.Before the application of panchromatic satellite image,atmospheric correction should be carried out to improve image quality.At present,the conventional atmospheric correction software can not correct the panchromatic satellite image,so the digital image processing method is often used to improve the quality of panchromatic satellite image.However,the digital image processing method often brings the problems of noise and excessive enhancement while improving the image quality.Therefore,it is urgent to develop a set of atmospheric correction methods suitable for panchromatic satellite images,eliminate the influence of atmosphere and surrounding environment on the target pixel satellite entry pupil signal,recover the real surface information,and improve image quality in the panchromatic satellite image quantitative remote sensing application.Methods Taking the panchromatic satellite image of GF-2 as an example,this paper develops a set of atmospheric correction method for panchromatic satellite image by using the atmospheric radiative transfer model and the exponential decay point spread function.This method is simple to calculate,and fully considers the influence of atmospheric parameters(parameters of aerosol,water vapor,ozone,and other absorbing gases),spatial resolution,and adjacency effect between background pixels and target pixels on the entry pupil signal of target pixels,which further improves the image quality on the premise of ensuring the truth of panchromatic satellite image information.As an important evaluation index of an optical satellite imaging system,the modulation transfer function(MTF)can comprehensively and objectively characterize the sharpness of the image edge and the expression degree of spatial details,and its value can directly reflect the quality of imaging.Therefore,in order to comprehensively evaluate the quality of panchromatic satellite images after atmospheric correction,the traditional image quality evaluation indexes(clarity,contrast,edge energy,and detail energy)and MTF are simultaneously adopted in this paper to comprehensively and fully evaluate the atmospheric correction results.Results and Discussions The atmospheric correction method for panchromatic satellite images developed in this paper is used to correct the GF-2 panchromatic satellite images of Baotou calibration site under two atmosphere conditions:clean atmosphere and polluted atmosphere.The results show that whether the atmospheric conditions are polluted or clean,the visual effect of the corrected panchromatic satellite images has been improved,the contours of ground objects become clear,the texture information is more abundant,and the recognition of ground objects has also been significantly improved.For high resolution panchromatic satellite images,the atmospheric correction method ignoring the adjacency effect can only improve the image brightness,but does not improve image clarity much.Especially in the case of air pollution,the edge of ground objects in the corrected image is still relatively fuzzy,which is not conducive to the visual interpretation of the image and the extraction of ground objects contour.This further proves that adjacency effect correction is essential for high resolution panchromatic satellite images.By comparing the quality evaluation parameters of each image before and after correction,it can be seen intuitively that the clarity increases by at least 155%,the contrast increases by at least 115%, the edge energy increases by at least 247%, the detail energy increases by at least 204%, andMTF increases by at least 169%.Conclusions Based on the 6SV radiative transfer model, the atmospheric correction method developed in this papercombines the atmospheric point spread function based on the exponential decay model, and fully considers the influence ofatmospheric parameters (parameters of aerosol, water vapor, ozone and other absorbing gases), spatial resolution, and thespatial distance between background pixels and target pixels on the adjacency effect. It can effectively remove the influenceof atmosphere and surrounding environment on the satellite load entry pupil signal in the process of panchromatic satelliteimage imaging, recover the surface truth information in the imaging area which is covered by atmospheric influence, andfully improve the quality of panchromatic satellite image under low atmospheric visibility. After the evaluation of thecorrected panchromatic satellite image quality, it is found that compared with the traditional image quality evaluationindex, MTF can better reflect the improvement and promotion of the sub-meter panchromatic satellite image quality by theproximity effect correction, which highlights the indispensability of the adjacency effect correction in the atmosphericcorrection of the panchromatic satellite image. At the same time, the trend of MTF curve and the level of the value canreflect the spatial acuity of the image and the advantages and advantages of the image quality more comprehensively andobjectively. Therefore, MTF index is recommended to be included in the image quality evaluation system when sub-metersatellite images (such as panchromatic satellite images) are evaluated.