A SIMPLE ALGORITHM FOR DEALIASING VELOCITY AMBIGUITY

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 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 awayspeed 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 minimum 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 the southeastern 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 ones the low signal to noise ratio data have been thresholded.