Keynote: Polarimetric upgrade of the WSR-88D (NEXRAD) network

The US National Weather Service plans to upgrade its WSR-88D radar network to dual polarization. This decision is made possible by a long history of research, measurements, and analysis. Thus, I briefly reflect on the influence of the early pioneers/proponents of polarimetry on the path which led to this plan. The upgrade should start in late 2009 and would be accomplished about 1.5 years later; NSSL has an advisory role in the process. I explain our recommendation for simultaneous transmission and reception of linear orthogonally polarized waves. This upgrade will involve changes in microwave hardware, signal processing, and algorithms. I discuss each of these in sequential order and emphasis that increases with the order of presentation. I indicate solutions and an evolutionary path for processing dual polarization signals such that existing capabilities of the network are not compromised, and improvements are obtained. Support for this path is given with examples on data obtained with the KOUN polarimetric radar (the NOAA/NSSL's research WSR-88D). I conclude by presenting the likely algorithms which should be available at the time of the upgrade. We propose to automatically separate signals due to meteorological scatterers from the ones caused by anything else. This is followed by classification of hydrometeors and then determination of the amounts. I will show some such examples followed by speculations of what might be forthcoming in the future.