速度方位显示(Velocity-Azimuth Display, VAD)方法作为一种基于单部激光雷达和同一高度风场均匀的假设前提来反演风场的通用方法已经在业界得到广泛应用, 但其对激光雷达扫描方位角的范围和径向个数的严格要求在一定程度上影响了激光雷达的测量效率。基于此, 提出了一种基于梯度下降算法的VAD风场反演方法。使用梯度下降算法代替目前VAD中的傅里叶级数展开求解的方法。在分析了算法收敛性影响因素的基础上, 确定了算法迭代步长和迭代次数, 从而改善了算法的收敛性, 提高了运算速度。与标准风杯风速计(IEC 61400-12-1)的同步对比实验结果显示: 该方法在激光雷达扫描范围降低到60°和扫描径向个数降低到7个的情况下, 10 min平均的风速、风向相关系数达到0.99, 风速标准偏差、偏差分别为0.52 m/s和0.02 m/s, 风向的标准偏差和偏差分别为5.1°和3.6°。结果证明了该方法在提高激光雷达测量效率的同时仍能保证其准确性, 具有更强的适用性, 可有效提升系统对于动态大气风场监测能力。

The VAD (Velocity-Azimuth Display) method, which is used to retrieve wind field based on one wind lidar system and the assumption of uniform wind in the same level, has been widely used in the industry. To guarantee the accuracy, the azimuthal range of lidar and number of scanning should meet some requirements, which affects measurement efficiency. Based on this, a new wind retrieval method of VAD used for Doppler lidar based on gradient descent algorithm was developed. The gradient descent algorithm was used to replace present Fourier series expansion for the solution of VAD. The convergence and calculation speed were improved by analyzing the factors that affect algorithm convergence and determining the iteration step length and the number of iterations, respectively. In order to demonstrate this modified VAD method, the wind data of coherent Doppler lidar was compared with standard wind cup anemometer (IEC 61400-12-1). The correlation coefficients of the 10 min- averaged wind speed and direction were up to 0.99 in the case that the azimuth range and the number of radial velocity were 60° and 7, with wind speed standard deviation and bias of 0.52 m/s and 0.02 m/s, and with wind direction standard deviation and bias of 5.1° and 3.6°. The results prove that this modified VAD method could improve Doppler measurement efficiency and applicability, and guarantee its accuracy at the same time, which improves the system capability for the monitoring of dynamic complex wind field.