Thursday, 18 January 2007: 9:15 AM
REFRACTIVITY MEASUREMENTS FROM GROUND CLUTTER USING THE NATIONAL WEATHER RADAR TESTBED PHASED ARRAY RADAR
217A (Henry B. Gonzalez Convention Center)
Characteristics of backscattered radar signals are related to the atmospheric conditions in which the radio waves propagate and the electromagnetic signatures of the targets. For echoes reflected from stationary targets, the phase of the received signal is approximately constant assuming the refractive index of the air mass between the radar and the target remains unchanged. Temporal variations in humidity and temperature can cause subtle, yet measurable, phase changes in the backscattered signal. Pioneering work in the use of this technique for near-surface studies of atmospheric moisture/temperature fields has been conducted by Fabry et al. [J. Atmos. Oceanic Technol., 14, 978-987, Aug 1997] using an S-band scanning radar. Scanning radar typically have update times on the order of several minutes. As a result, measurements of phase change are limited to a temporal resolution on the same order. Here, we will investigate the possible advantages of the use of a phased array radar system, which can produce rapid updates on the order of seconds. The S-band Phased Array Radar (PAR), which is the centerpiece of the National Weather Radar Testbed (NWRT) located in Norman, Oklahoma, will be used for this study. The NWRT is the nation's first research facility dedicated to phased array radar meteorology and became available to the community in May 2004. It operates at 3.2 GHz and utilizes a modified version of the Klystron transmitter used on the WSR-88D radar network and thus shares many of the same characteristics. PAR employs the SPY-1A phased array antenna used on Aegis-class cruisers and destroyers and can perform a sector scan of 90 degrees in both azimuth and elevation through electronic scanning. Its 4,352 elements produce a beamwidth of 1.5 degree at broadside and 2.1 degrees at the maximum off-broadside pointing angle of 45 degree. Possible advantages of the use of phased array technology may be the mitigation of smearing of clutter targets due to antenna motion, adaptive mapping of clutter targets, and rapid update times, for example. Results will be presented from recent experiments and comparisons made with a closely spaced array of surface meteorological stations, which are used to provide in-situ validation measurements of refractivity.