The Research On Doppler Velocity Dealiasing With Millimeter Wave Radar RHI Data

Millimeter wave radar is the new cloud detection equipment, it can detect the fine horizontal and vertical structure of the cloud, and it can help to research the cloud physical characteristics and the evolution of the cloud and precipitation. However, it is likely to cause the velocity aliasing due to its short wavelength. Velocity dealiasing is an effective means to make use of the wind field information obtained by Doppler radar. Two methods aiming at velocity aliasing with millimeter wave radar Range Height Indicator are put forward. A lot of measured data were used to take tests. The main content of the papers and preliminary results are as follows:(1)This research analyze the detecting characteristics of the millimeter wave radar, it is found that compared to the centimeter wave radar, millimeter wave radar has a lot of the advantages. For example, its wavelength is very short. It is more sensitive to small particles. It can detect the fine structure of the cloud. It is not easy to be affected by the Bragg scattering and the ground clutter. And it is suitable to be placed in the mobile system. But it also has many disadvantages due to its short wavelength, the millimeter wave radar is easy to be affected by the attenuation, and the value of the maximum velocity is very small, so it is easy to cause velocity aliasing, sometimes even cause the second time velocity aliasing and several times velocity aliasing.(2)In order to master the features of the millimeter wave radar velocity image in the RHI scanning mode, the wind field is simulated. The simulation results shows that in a uniform wind field condition, as the center of radar, the contour of the velocity is the radial distribution in the image. No matter the wind how to change with the height, at the higher elevation, the value of vertical velocity is very small, and it is less than horizontal velocity, so it will not occur velocity aliasing, and the vertical velocity can be used to the reference of velocity dealiasing. But with the lower elevation, it will appear velocity aliasing gradually, even to many times velocity aliasing.(3)Before the velocity dealiasing, we use the median filtering to process the data. The traditional median filtering is improved. The correlation of the signal data within the adjacent median filter window is taken into the account by the new method. So the number of operations is reduced, the operation efficiency is improved, especially when a large amount of data need to be processed, the effect is very significant.(4) Two methods aiming at velocity aliasing with millimeter wave radar Range Height Indicator are put forward; they are the human-machine interaction method and the automatic method. The main difference between them is how to determine the velocity aliasing area.(5) A lot of measured data were used to take tests. It is proved that the automatic method is the computer automatically determine the velocity aliasing area and Nyquist number, it has high efficiency, so it is suitable for business applications. It is better for few isolated points. But this method appears misjudgment for some case; the main reason is that it is difficult to determine whether the smaller isolated area belongs to velocity aliasing area. The human-machine interaction method needs experienced researchers to determine velocity area, when dealing with some discontinuous and isolated echoes, they can rely on their experience to determine velocity aliasing area and judge the area occurs how many times the velocity aliasing. But this method has lower efficiency when the data is more. The Innovations of this paper including:(1)Two methods aiming at velocity aliasing with millimeter wave radar Range Height Indicator are put forward. A lot of measured data were used to take tests. The advantages and disadvantages of each method are compared. This is very important for the wind field information of millimeter wave radar.(2)Median filtering can properly keep the signal characteristics and multi-dimensional information. It is suitable for the signal processing of Doppler weather radar. The method is introduced to the signal processing of the millimeter wave Doppler radar in this research. The correlation of the signal data within the adjacent median filter window is taken into the account, the traditional median filtering is improved. So the number of operations is reduced, the operation efficiency is improved.