Mobile Rapid Scanning X-band Polarimetric (RaXpol) Doppler Radar System

Although there is widespread interest in developing electronically scanned radars for meteorological applications, such radars have several drawbacks, the most significant being the high cost for a narrow beam system. Furthermore, current electronically scanned antennas are limited to single polarization operation that cannot take advantage of rain rate extraction algorithms based on polarimetric quantities, such as Zdr and Kdp. On the other hand, conventional high speed tracking pedestals have been used by the military for decades and high quality polarimetric reflector antennas are now available as commercial off the shelf items. To take advantage of these readily available technologies, the National Science Foundation awarded an MRI grant to the University of Oklahoma School of Meteorology to develop a novel Rapid mechanically scanning, volume imaging X-band Polarimetric (RaXpol) mobile Doppler radar system for collecting 3D volume scans of severe storms in approximately 30 seconds. RaXpol employs a fast, 180 deg/sec, elevation over azimuth pedestal and a 1 deg beamwidth dual-polarized parabolic reflector antenna. A frequency agile high power transmitter generates equal power V and H polarized pulses and a wideband dual channel receiver is employed for simultaneous reception of the V and H components of the backscattered field. Beam smearing in rapid scanning mode is practically eliminated by transmitting two stepped frequency FM waveforms. The backscattered signal of each sub-pulse segment is separated through frequency domain filtering. The individual sub-pulses are processed using the pulse pair algorithm, after which data from all frequencies is averaged. The radar also has the standard pulse pair and FFT operating modes available for high sensitivity measurements at more conventional scanning speeds.