Can polarisation help NEXRAD to provide better rainfall estimates?
University of Reading
It will be difficult to use the polarisation parameters on Nexrad for rainrates below 10 mm/hr because the signals are small and noisy. However, we have found that by looking at the distribution of the Z and the noisy differential reflectivity (ZDR) signals over a 5 km square area we are able to derive the raindrop concentration, Nw, quite accurately and hence compute the value of "a" which could be used in the empirical Z = aR 1.5 relationship. We find remarkable consistency with the Nw derived from a coincident profiler thus confirming the precision and validity of the Z/ZDR technique. Traditionally rainfall rates from radar are evaluated using gauges or a disdrometer, but the disdrometer yields rather different values of Nw, thus demonstrating that the smaller sampling volume of ground based gauges or disdrometers limits their use for evaluating rainfall algorithms.
Wednesday, July 26, 2006
2:00 PM (Refreshments at 1:50 pm)
PSL-South Conference Room (1D403)