基于阵列点源的光学遥感卫星像质评价方法

Image Quality Evaluation Method for Optical Remote Sensing Satellite Based on an Array of Point Sources

提出一种基于阵列点源的光学遥感卫星像质评价方法,以轻小型、自动化的反射点源阵列作为检测参照目标,最小二乘法二维高斯模型拟合阵列点源影像获得像点坐标,结合地面点源位置测量获得遥感器地面像元分辨率;以点源影像像点坐标为基准,对阵列点源遥感影像数据进行位置配准与高斯模型拟合获得成像系统点扩散函数与调制传递函数值。试验结果表明:像点坐标的共线误差小于0.002像素,地面像元分辨率的相对偏差优于6.5‰,阵列点源可以综合实现光学遥感卫星的像质评价与辐射定标。

Ground pixel resolution and modulation transfer function are two important parameters for image quality evaluation of high spatial resolution optical remote sensing satellites,which are of great significance in target recognition,image interpretation,and information extraction.We present an image quality evaluation method for remote sensor using an array of point sources,which takes the light,small,and automated reflected point source array as reference.Two image quality evaluation parameters of remote sensor ground pixel resolution and modulation transfer function can be obtained at the same time.The twodimensional Gaussian model is used to describe the point spread characteristic of the optical remote sensing satellite imaging system.Selecting the 5×5 pixel values of each reflective point source remote sensing image into the point spread function model and use the least squares method to fit the two-dimensional Gaussian surface to obtain the image point coordinates.According to the ground pixel resolution detection principle and combined with the ground point source position measurement,the ground pixel resolution of the remote sensor is obtained.Based on the image point coordinates,all point source image data are positionally registered,and the image data after data rearrangement is fitted again with the twodimensional Gaussian surface to obtain oversampled,sub-pixel interpolated optical remote sensing satellite imaging system point spread function,and then obtain the system modulation transfer function.In the image quality evaluation test of ZY-3 satellite based on reflective point sources,a 4×4 reflective point source array with non-integer pixel intervals was concentrated on the calibration test site along the flight direction and the linear array direction.The distance between adjacent point sources is 10.25 pixels,and the distance between two point sources is 20.5 pixels.The point spread function of the optical remote sensing imaging system can be sub-pixel interpolated to 0.25 pixels,which can effectively overcome the sampling effect of the imaging system and suppress the influence of random noise.According to the principle of collinearity test,the sum of the centers of adjacent reflection point sources should be equal to the distance between the centers of phase reflection point sources.The test results show that the error of the collinearity test results between the optical remote sensing satellite detector linear array and the flight direction is less than 0.002 pixels.It shows that the extraction result of array point source image point has high precision and accuracy.The standard deviations of the ground pixel resolution detection results in the linear array direction and flight direction of optical remote sensing satellite detectors are 0.0206 and 0.0215,relative deviations are 6.4‰and 6.1‰,which shows that the point source image pixel extraction accuracy is high and the linear array detection element of the remote sensor has good rigidity and stability in a local area.Comparing the results of the on-orbit modulation transfer function detection of the ZY-3 satellite by the array point sources method and the double-edge method,the difference between the two methods in the flight direction and the linear array direction is 0.0002 and 0.0126.Compared with periodic targets,array point sources have the characteristics of light weight,miniaturization,and automation.In the process of quantitative detection of the ground pixel resolution of optical remote sensing satellites,the array point source method is not affected by the subjective factors of image interpreters and can suppress the influence of atmospheric and random noise.The array point source method is a two-dimensional modulation transfer function direct detection method according to the physical definition of modulation transfer function,which can intuitively describe the point spread characteristic of the photoelectric remote sensing imaging system.The array point sources can also be used as a reference target for the radiometric calibration of optical remote sensing satellites.The on-orbit radiometric calibration of remote sensors can be realized by setting up a multi-level point source array on the ground,combined with the measurement of atmospheric optical characteristic parameters.Therefore,the array point sources can comprehensively realize the image quality evaluation and radiometric calibration of optical remote sensing satellites.