RHI observation of precipitation with boundary layer wind profiler

A boundary layer wind profiler radar (BLR) has been recently developed to measure lower atmospheric vertical wind profile. The BLR is a kind of wind profiler and is operated at UHF. The BLR is useful for observation of vertical wind profile. In addition, the size of the BLR is smaller than that of a VHF wind profiler and enables to transport for field experiments. One of problems of operational wind profiler is the depreciation of reliability in convective precipitation. The operational wind profiler radar employs the Doppler Beam Swinging (DBS) method while needs the assumption that the atmosphere has horizontal uniformity. However this assumption is not satisfied in some conditions, particularly in severe storms.

A Spaced-antenna technique is one of the useful alternatives to the DBS wind profiling technique. Removing the need to cycle of beam pointing directions, Spaced Antenna Drift (SAD) or Full Correlation analysis method make it possible to estimate wind from data within one vertical beam, relaxing the assumption of horizontal uniformity. This technique has been used by the VHF radars and recently by the UHF boundary wind profiler at NCRA. The Post Beam Steering (PBS) is also a kind of SA technique. The PBS technique enables radar to scan the atmosphere but this technique has been used only by the VHF radars. Because a high powered wide-beam transmitting, a lot of receiving antennas and usually a multi-receiver system are necessary for the PBS. These conditions make the system huge and expensive, therefore, another technique is necessary for the transportable BLR to scan the atmosphere. Angler scanning by narrow beam is easy for the BLR to actualize. This method is identical to Range Height Indicator (RHI) observation with the Doppler radar.

The MRI boundary wind profiling radar equips with an active phased array antenna for the angler scan of emitting beam. The system has only one receiver but each antenna element has a small transmitter and the size of this system is enough small to transport. We made BLR observation in severe rain and compared with the Doppler radar. The results of the measurements have shown that this technique is reliable in high elevation area. However the comparison has also revealed a problem in the low elevation areas of the beam. Examples of these problems will be discussed and suggestion for the solution will be given.