The VAP (Velocity-Azimuth Processing) method was put forward for retrieving the horizontal wind field from single Doppler radar data by Tao Zuyu(1992). Assume that the wind at two neighboring azimuth of difference 2Dq is equal (namely, the local uniformity of wind field), the formula of wind retrieval based on the Doppler velocity profile with azimuth are as follows:

Wind speed: ,Wind direction:

To prove the validity of the retrieved meso-b-scale wind field by VAP method, we compared and contrasted the retrieved wind field from dual-Doppler radar (at Yichang and Jingzhou cities) in observational field experiment of 973 Project with that from single Doppler radar by VAP method. The result shows the retrieved wind field from single Doppler radar by VAP method is quite consistent with that from dual-Doppler radar, and both of them can reveal that there exists an cyclonic stream field which turns the southerly to the easterly, however, the wind field from single Doppler radar covers the whole single radar detection range. The result from the analyses of the assumption of the local uniformity of wind field reveals that the retrieved wind by the VAP method in the distance of 125 km can be used to identify the meso-a-scale and meso-b-scale systems (the spatial scale of 20~200 km). The reconstructed image of the radial velocities from the retrieved wind field by the VAP method is contrasted with the original one from the Doppler radar at Yichang city. Because the VAP method has no any assumption in physics, the two images of radial velocities are quite similar, and this shows that the retrieved wind field is reasonable. But the reconstructed radial velocities from the retrieved winds are less than the observational ones. This is because the VAP method is sensitive to error sources, the observational radial velocities is smoothed before retrieving the horizontal wind field. Therefore, the retrieved horizontal winds may be less 2~3 m/s than the actual ones.

In conclusion, although the retrieved horizontal wind by the VAP method may be less than the actual, it can be used to identify the meso-b-scale structure and to analyze the characteristics of the meso systems in the wind field.