W-band Mobile Doppler Radar

The W-band mobile Doppler radar is a fully polarimetric radar operating at 95 GHz with a peak transmit power of 1 kW.  A 1.2 m diameter Cassegrain antenna provides a 0.18 beamwidth resulting in a super fine azimuth resolution, while range resolution is typically 30 m.  The radar is integrated on an azimuth-over-elevation pedestal on a modified Ford F350 truck chassis. Boresighted video is used to monitor beam pointing and is recorded for post-experiment interpretation.

The W-band radar was adapted in the early 1990s for severe storm research performed in collaboration with the University of  Oklahoma School of Meteorology.  It was rebuilt in 2004 when the extended interaction klystron and modulator were  replaced.  It currently employs a single antenna with a network of latching circulators serving as a transmit/receive and polarization switch.  The transceiver employs two multiplied frequency sources and a double down-conversion receiver with intermediate frequencies at 1.2 GHz and 120 MHz. A digital receiver samples the final IF signal, producing baseband in-phase and quadrature samples.

Due to the 3 mm wavelength of the radar, the unambiguous velocity interval for W-band radars is very narrow. For example, a pulse rate of 5 kHz provides a Nyquist velocity range of only ±3.95 m/s. A dual-PRT scheme is therefore employed with a ratio of 11:10 providing unambiguous velocity measurements up to 40 m/s.

The animation below (courtesy R. Tanamachi) shows a near surface structure of an EF-0 tornado observed near Tribune, KS on May 25, 2010 during Vortex 2 experiment. Due to significant signal attenuation in precipitation, the maximum usable range is limited to 12 km. While the W-band radar can provide very fine detail owing to the very narrow beam, the scan rate is necessarily slower than that obtained with other coarser-resolution radars. Sector scans were updated on average every 18 s. The animation  on the left shows the reflecitivity field, and on the right is the dual-PRT derived velocity field. The hook region can be located around 8 km north of  the UMass W-band  radar at an elavation angle 0.7 deg, or about 100 m above ground level. The maximum inbound and outbound velocities measured in the second funnel were -24 m/s and +28 m/s. 

Available Documents:

 

[1]     R. Tanamachi, H. Bluestein, W. Lee, K. Orzel, and S. J. Frasier, “GBVTD - retrieved vortex structure in the 26 May 2010 Prospect Valley, Colorado tornado - like vortices”, AMS 35th Conference on Radar Meteorology, September 2011

[2]     S. Frasier, V. Venkatesh, K. Orzel, T. Hartley, J. Salazar, R. Medina, E. Knapp, O. Ibe, H. Bluestein, J. Snyder, R. Tanamachi, “An Overview of X- and W-band Mobile Doppler Radar Observations from VORTEX2 and Current Developments at Umass”, IEEE Radar Conference, May 2011

[3]     H. Bluestein, M. French, J. Houser, J. Snyder, R. Tanamachi, I. PopStefanija, C. Baldi, G. Emmitt, V. Venkatesh, K. Orzel, R. Bluth and S. Frasier, “A summary of data collected during VORTEX-2 by MWR-05XP/TWOLF, Umass X-Pol, and the UMass W-band radar”, 25th Conference on Severe Local Storms, October 2010

[4]     P.S. Tsai, S. Frasier, R. Tanamachi, H. Bluestein, “The Umass Mobile W-Band Radar: System Overview and Sample Observations”, 24th Conference on Severe Local Storms, Savannah, Georgia, 2008