A Method Of Doppler Velocities Conversion In No Echo Areas

EVAD technique developed from VAD as a mature divergence method is applied more and more extensive in routine operation. However, there are always some different sizes no echo areas in large-scale radar echos, which lead great error when divergence extracted. Given actual wind fields linearly deploy, an approach to fill up radial velocities field in no echo zones with iterative method is documented. On basis of approximate real speeds simulation, which shows that this approach can accurately stuff up the Doppler velocity field in no echos which less than 120 degree, and have obvious effect to improve divergences extracted by EVAD. Three aspects are introduced mainly:There are always some different sizes no echo areas in large-scale radar echos, which lead great error at the wind conversion technique based VAD, EVAD when divergence extracted.The positive velocity short of echo will enlarge the divergence. So VAD technique only can measure the average wind velocity and vane. On basis of approximate real speeds simulation, which shows that this approach can accurately stuff up the Doppler velocity field in no echos.Every radial velocity is in VAD azimuth curve because the linear wind field which obtainedby harmonic analysis to V_r(θ)have noradar mechine noise.In order to gain approximate realspeed simulation . Sirmans method of radar simulated precipitation signal is applicable to the linear wind field.On basis of approximate real speeds simulation,analog two specices no echo area : diseret random area or continuous random area. Then approach to fill up radial velocities field in no echo zones with iterative method is documented ,which shows that this approach can accurately stuff up the Doppler velocity field in no echos which less than 120 degree, and have obvious effect to improve divergences extracted by EVAD.