Research On Signal Detection Technology Of Pulse Heterodyne Lidar Based On Time-frequency Transformation

In recent years,coherent lidar has been widely used in the fields of wind measurement,battlefield reconnaissance,and detection of weak targets by virtue of its high sensitivity detection capability in weak echo signals.Compared with direct detection,its detection sensitivity is about 1-2 orders of magnitude higher which can innately suppress background noise and has been a hot spot in international research.This paper focuses on the detection and extraction of weak echo signal of pulse heterodyne coherent laser imaging radar,and studies the detection ability and application range of echo signal from time domain and frequency domain respectively,which plays a theoretical guiding role in the application of the actual coherent laser radar information processing.Firstly,the overall scheme of the detection and extraction of the pulse heterodyne echo signal based on the time-frequency domain transformation is designed by comparing and analyzing the detection and extraction methods of the pulse heterodyne coherent lidar signal,focusing on the heterodyne echo noise suppression and the Fourier transform method of extracting the difference frequency signal and establishing the signal detection and evaluation index system.Secondly,in order to verify and evaluate the time-frequency signal detection and extraction method,the simulation system model of pulse heterodyne lidar is designed and established which can obtain the simulation echo waveform consistent with the actual pulse heterodyne signal characteristics.On this basis,the time-domain peak method,frequency-domain FFT and small wave noise suppression methods are evaluated.The simulation results show that when the SNR is 6d B,the detection probability of the system in frequency domain is 19% higher than that in time domain,and the target reduction degree is 14.25% higher than that in time domain;when the SNR is 12 d B,the detection probability of the system in frequency domain is 25% higher than that in time domain,and the target reduction degree in frequency domain is 20.37% higher than that in time domain.Finally,the experimental system of the pulse heterodyne lidar is designed and built to obtain the intensity image and range image of the near-field target pulse heterodyne coherent lidar.The method proposed in this paper is verified and evaluated by the real laser echo data and the experimental results show that without denoising the echo signal,the target reduction degree of the windowed FFT algorithm is 14% higher than the time domain peak method and the windowed FFT algorithm is 37% higher than that of the time domain peak method;In the case of denoising the echo signal,the target reduction degree obtained by the windowed zero-fill FFT algorithm is nearly 30% higher than the time domain peak algorithm,and the windowed FFT peak algorithm is nearly 36% higher than the time domain peak algorithm;At the same time,the detection probability of the system obtained by the frequency domain processing method is nearly 20% higher than that obtained by the time domain processing.