快速傅里叶变换对刃边法测量遥感相机MTF的影响

摘要

Modulation transfer function (MTF) is an important parameter for imaging quality of optical remote sensor.Knife-edge method is simple and effective for measuring MTF.Fast Fourier transform has been widely applied in this method because of its less calculation.Fast Fourier transform is only used to deal with finite length of digital signal,however,line spread function is an infinite and continuous signal in the spatial domain.So it is necessary to truncate and sample the line spread function.But truncation causes spectrum leakage and sampling causes spectrum aliasing.All these result in the error of MTF measurement.Based on the theory of sampling,this paper analyses the influence of length truncation and sampling interval on MTF.According to different applications and error requirements,the reasonable length truncation and resampling interval are given,and normalize the applications of fast Fourier transform in knife-edge method,are normalized.%调制传递函数(MTF)是反映航天光学遥感器成像性能的重要参数.刃边法是测试MTF一种简单有效的途径,快速傅里叶变换因计算量小在刃边法中得到了广泛应用.由于线扩展函数在空间域是无限连续的信号,而快速傅里叶变换处理的有限长离散序列,对线扩展函数应用快速傅里叶变换时需先对其截断、采样;截断引起频谱泄露,采样造成频谱混叠,泄露与混叠双重效应将导致最终MTF的测量误差.文章基于采样理论,定量分析了线扩展函数截断区间和采样间隔对奈奎斯特频率处MTF的影响.针对不同应用和误差要求,给出了合理的采样间隔、截断区间要求,规范了快速傅里叶变换在刃边法测量光学遥感相机MTF中的应用.