基于分数阶傅里叶变换的电离层回波信号处理浅析

Ionospheric Echo Signal Processing Based on Fractional Fourier Transform

电离层是一种特殊的雷达目标,电离层目标的高度是随频率而变化的。通过电离层回波探测可获得电离层的空间层结构,离子浓度变化,电离层高度随频率变化情况等重要信息。电离层探测的传统方法是采用信号脉冲单频点发射,通过接收回波信号时延差测距。测量过程需手动更换测量频率,测量步骤繁琐,耗时较长;同时发射功率较大,电磁辐射危害显著。本文介绍一种基于LFM信号的电离层垂直探测方法 ,利用分数阶傅里叶变换对LFM信号特殊的聚焦作用对电离层回波信号进行分析,发现较传统的处理方法具有更好的时延和功率谱估计特性,较好的克服了传统探测方法的一些弊端。

The Ionosphere is a special radar target. The height of the ionospheric target varies with frequency. Ionospheric sounding can be used to obtain some important information such as the spatial structure of the ionosphere, the variation of the ion concentration, and the variation of the ionospheric height with the frequency. The traditional method of ionospheric sounding is to emit the single frequency pulse signal, by receiving the echo signal of the ionosphere to calculate altitude. It is so fussy by changing the test frequency to get the data in every diffrent hight measurement process, the measurement frequency should be changed manually, and the measurement steps are complicated and time-consumed. Meanwhile, the transmission power is larger and the electromagnetic radiation is harmful. This paper introduces a method of ionospheric vertical detection based on LFM signal. As known the fractional Fourier transform has a special focus on the role of LFM signal. By using the fractional Fourier transform to echo signals, it is better to get more accurate time delay and power spectrum estimation than the traditional ways. So it overcomes some disadvantages of traditional detection methods.