相干激光测风雷达高分辨距离门自适应技术研究

Research on high resolution range-gate adaptive technology of coherent wind lidar

脉冲相干激光测风雷达的信号处理通常采用固定长度距离门来划分时域信号,并对每个距离门做频谱计算得到风速度信息。固定距离门的时域信号划分存在中频信号的非整周期截断问题,导致频谱计算时出现频谱泄露而产生误差,使信噪比降低。文中提出一种基于整周期搜索的自适应距离门划分方法,距离门长度与中频信号频率自适应,可实现对信号的整周期分割,避免了频谱处理中的频谱泄漏问题,提高频率估计精度。采用加噪信号对两种处理方法进行仿真分析,结果表明:自适应距离门方法可实现距离门长度与中频信号的自适应,在信噪比小于1 dB时,该方法得到的中频估计误差是固定距离门方法的38%~62%。应用自适应距离门方法处理激光测风雷达系统获取的转盘和风场回波信号,与使用固定距离门方法的激光测风雷达测量结果进行对比。结果表明:自适应距离门划分方法对转盘速度测量的均方根误差为0.19 m/s,大气风速度测量的距离分辨率在7~11 m之间变化,均优于固定距离门方法,实现了激光测风雷达的距离分辨率和测量精度的提升。

The signal processing of pulse coherent wind lidar usually uses fixed range-gate to divide the time domain signal, and perform frequency spectrum calculation for each range-gate to obtain wind speed information.The time domain signal division of the fixed range-gate has the problem of non-periodic truncation of the intermediate frequency signal, which leads to spectrum leakage during spectrum calculation, resulting in errors and reduced signal-to-noise ratio. An adaptive range-gate division method based on full cycle search was proposed. The length of the range-gate was adaptive to the frequency of the intermediate frequency signal, which could realize the full cycle division of the signal, avoide the problem of spectrum leakage and improve frequency estimation accuracy. The two processing methods were simulated and analyzed by adding noise signal. The results show that the adaptive range-gate method can realize the adaptation of the range-gate length and the intermediate frequency signal. When the signal-to-noise ratio was less than 1 dB, the intermediate frequency estimation error obtained by this method was 38%-62% of the fixed range-gate method. The adaptive range-gate division method was used to process the turntable and wind field echo signals obtained by the laser wind measurement radar system, and the results were compared with the wind lidar equipped with the fixed range-gate method. The results show that the root mean square error of the adaptive range-gate method for the speed measurement of the turntable is 0.19 m/s, and the range resolution of atmospheric wind speed measurement varies from 7 to 11 m, which is better than that of fixed range-gate method, and improves the range resolution and measurement accuracy of the wind lidar.