Doppler weather radar is one of the most powerful tools for investigating severe mesoscale and microscale weather systems. But a main limitation of Doppler radar is that it only measures the radial component of the wind vector. So the two-dimensional or three-dimensional velocity must been retrieved by way of wind recover technology in order to study the weather systems. The full 3D wind field is extreme important for diagnostic research studies, hazard warning, as well as numerical forecasting. This paper introduces the wind field retrieval techniques based on the single Doppler radar, multiple-Doppler radar and bistatic  multiple-Doppler radar, analyses their merit and demerit and addresses the future research.
In recent years, many theories of single Doppler radar retrieval were proposed. The VAD technique, VVP method and VAP method use radial velocity data to retrieve horizontal wind field, but they are limited to cases  where the wind field is smooth and linear.
Use of one single moving frame can not properly account for the advection of scalar fields in different regions. A scheme with two or more moving frames of reference might be helpful in retrieval. Methods based on the variation are the direction of the future research. Wind and thermodynamic analyses can potentially be used as high-resolution data source for numerical weather models. Several attempts show that it improves the forecast accuracy in the high resolution numerical models initialized with Doppler radar retrieval data.
For dual-Doppler retrieval, simple formulas were obtained for the horizontal wind components, while the vertical velocity component was found to satisfy the air mass continuity equation. The roots of most modern day dual-Doppler analysis techniques are based upon this pioneering investigation. Dual-Doppler radar wind recover techniques improve the result accuracy obviously as compared to the single radar retrieval. But several factors can lead to errors. These factors include contamination of radial wind data(due to sidelobes and ground clutter), the errors of the empirical relationship between the radar reflectivity and the terminal fallspeed of the precipitating particle, spatial interpolation and filter errors, the non-simultaneous nature of the data acquisition(due to the temporal variation within the volume scan time interval), integrating the air mass continuity equation(problem of the boundary condition).In particular, biased errors in the divergence field can be accumulate in the integration process and lead to severe errors in the vertical velocity field. To overcome these problems in some degree, COPLAN method is proposed which scans the tilted plane passing through the two radar positions. It is also used to reduce the complexity of data process. The variational method for interpolating and smoothing data brings a substantial improvement compared to the other classical filtering.Retrieval in the moving frame can not resolve it completely since the frame velocity is obtained from the correlation of reflectivity. Iterative process in the Cartesian coordination will reduce the retrieval accuracy. 
The advantage in increasing the number of radar is in the extending the retrieval coverage and increasing the accuracy of the 3D wind field. The major differences are in the error propagation and the vorticity or the divergence. The method to retrieve the 3D wind field is similar to that of dual-Doppler radar in some degree. One limitation of these techniques is the non-simultaneity of the measurements collected by the different radar which affects the wind field retrieval in the case of the rapidly evolving convective systems.
The bistatic multiple-Doppler radar includes one traditional transmitting Doppler radar and one or more passive, low-cost, non-transmitting receiver at remotes sites, each bistatic receiver measures the radiation scattered by the particle. It is a very important technique with many unique scientific advantages:①initial investment, operational and maintenance cost are less than that of conventional radar;②all radial velocity measurement from the individual volumes are collected simultaneously since there is only one source of radiation. There are two shortcomings for this radar system:①low-gain receiving sites are more sensitive to contanmination from the transmitter sidelobes and to the secondary  scatting from the weather echoes;②low-gain receiving sites are less sensitive to the weak weather echoes. The first one can be reduced with the use of higher-gain receiving antennas, the later one  can be improved with the use of multiple passive sites. Variational method using radial velocity as weak constraint and mass continuity equation as strong constraint is investigated to retrieve the 3D wind field with encouraging result. One major problem is the relatively large data collection times reaching more than 3-5 minutes in one complete volume scan which is inadequate for the highly evolving convective storms.