一种简易的多普勒雷达速度模糊纠正技术

A SIMPLE ALGORITHM FOR DEALIASING VELOCITY AMBIGUITY

多普勒天气雷达是监测强对流天气中尺度风场的重要手段。纠正速度模糊是多普勒雷达探测风场信息有效应用的前提。速度模糊纠正技术大多需要首先对模糊点集或非模糊点集进行识别 ,如果无法识别或识别错误 ,将造成纠正过程的失败或需要人工识别。文章提出了一种不需先对模糊点集或非模糊点集进行识别的纠正速度折叠的简便方法。它只需首先将存在折叠的速度场恢复为连续的速度场 ;然后对其速度数值是否存在整体偏移做出判断和调整。给出的存在严重模糊的台风个例的速度模糊纠正实例表明 。

Doppler velocity aliasing will appear when the radial component of the target's velocity is greater than the Nyquist velocity of the radar. A simple and effective algorithm for Doppler velocity dealiasing is put forward based on the characteristics that the wind field is continuous along a ring centered at the radar and an unfolding Doppler velocity-azimuth profile always has a maximal away-speed and a maximal toward-speed. This new algorithm does not require the knowledge of an auxiliary wind field and manual judgement about aliased area. So, the assumptions for finding aliasing points are avoided. It does not need the help of auxiliary wind information and manmade judgment about aliasing velocities. It can be carried out easily and automatically by the computer and has potential to be implemented in operational environment. The dealiasing algorithm has two steps for each PPI scan. The first step is to make the piecewise folded velocity-azimuth curve to be a continuous curve. The second step is to determine whether the continuous velocity-azimuth curve is on the correct level based on the character that an unfolded velocity-azimuth curve always has a maximal away-speed and a maximal toward-speed approximately equal value. If not, the velocity-azimuth curve should be adjusted to the correct level according to the number n, which n=INT((V rmax-V rmin)/V rmax). Where V rmax is the maximum value and V rmin is the minimun value in the velocity-azimuth curve. After the second step, the velocity-azimuth curve will be adjusted to the reasonable velocity interval. For get better result of dealiasing, the above steps can be repeated one or two times. The Doppler velocity data with multi-aliasing collected from Typhoon OTTO observed by Ludao Doppler Radar at thesoutheastern Taiwan on 4th August in 1998 is used to test this dealiasing algorithm. The result shows that this algorithm can effectively dealias multiple folds of Doppler velocities once the low signal to noise ratio data have been thresholded.