X-Pol Mobile Doppler Radar

The UMass X-Pol radar is a dual-polarized X-band mobiel Doppler radar operating at 9.4 GHz.  Peak transmit power is 6.25 kW per polarization channel provided by a modified marine navigation radar transmitter.  Typically, a one-microsecond pulse is transmitted providing range resolution of 150 m.  Often used in tandem with the W-band radar, it is deployed on a nearly identical truck platform.  X-Pol employs  simultaneous transmission and reception of both H- and V-polarizations (commonly referred to as STSR or STAR mode) and typically employs a dual-PRT waveform to obtain unambiguous velocities up to 40 m/s.  A refurbished Army Signal Corps SCR-584 model scanning pedestal common to many mobile weather radars is used.  Similar to the W-band radar, the power system employs an inverter supplied from marine batteries that are recharged by the truck’s alternator.

The figure at right shows several sample data products collected by Umass Xpol radar while observing the Goshen County tornado on 5 June 2009.  The four panels are (clockwise from upper left) Reflectivity, Doppler velocity, co-polar correlation coefficient, and Differential Reflectivity. Reflectivity shows a pronounced hook and bounded weak echo region while Doppler velocity shows a tornado vortex signature. A small hole in the correlation coefficient signature may indicate debris scattering and centrifuging of hydrometeors consistent with observations in. However, it may also be attributable to the reduced SNR in this region.