Estimation Method of SAR Doppler Frequency Rate Based on FrFT

一种基于FrFT的SAR多普勒调频率估计方法

Chengdu Technological University, Chengdu 611730, China

Received: 18 April 2020

Abstract

Due to the problem that the existing Doppler frequency rate estimation method is limited by the estimation accuracy, a novel estimation method of Doppler frequency rate is proposed. The present method searches the frequency rate according to the characteristic of the chirp signal in the FrFT domain. Firstly, dechirp is performed on several strong scattering points extracted from the data domain after pulse compression, and a frequency domain focused image is obtained after FFT. Then the maximum point of each distance unit is extracted. The energy of the maximum point is selected by using the window processing. After that, IFFT is performed and the dechirp conjugate reference function is multiplied by using the selected points. FrFT is performed according to the preset orders. The entropy is used to evaluate whether the order of FRFT is optimal or not. The Doppler frequency rate is calculated by using the optimal order. The simulation and real data are processed and analyzed. The present method can estimate the Doppler frequency rate accurately. A well-focused SAR image is obtained after azimuth matching filtering.

摘要

针对现有多普勒调频率估计方法估计精度有限的问题，提出一种新的估计方法，该方法根据线性调频信号在FrFT域具有明显聚焦的特性实现对调频率的搜索。对从脉压后的数据域提取的若干强散射单元分别进行dechirp处理，进行FFT得到频域聚焦图像。提取各距离单元最大值点并进行加窗处理，然后经IFFT变换到慢时间域与dechirp共轭参考函数相乘，根据设定的阶数进行FrFT处理。通过评估FrFT变换后信号的熵值确定阶数是否达到最优，利用搜索的最优阶数计算出多普勒调频率。在实验数据分析部分，分别利用仿真数据以及实测数据对所提方法进行验证，最终结果分析表明该方法具有很高的估计精度，经过方位匹配滤波后可以得到聚焦良好的SAR图像。