Toward combining space and ground-based radar observations: Challenges and Opportunities

In this presentation we will investigate the idea of combining space and ground-based radar rain rate estimates to improve the accuracy of surface rainfall estimates. Adjusting ground-based radar rain rate estimates to spaceborne radar rain rate estimates might be very useful for ungauged basins and wherever gauge adjustment schemes are not useful. We will address the challenges and opportunities we face with such an approach: Can we assume that the satellite rain rate estimates are better than the ground radar estimates? How should we merge the two? During our discussion we will present comparisons of rain rate pdfs derived from the TRMM precipitation radar (PR) with those derived from co-located ground radar observations for several rainfall events and rainfall types. The ground radar estimates are derived from the new NOAA/NSSL Next Generation QPE products (Q2). These are high-resolution quality controlled products (1 km horizontally, updated every 5-min) of instantaneous rain rate and reflectivity mosaics available over the entire continental U.S. Pdfs based on PR-Q2 data from a single overpass as well as data from combined overpasses are compared. Our comparisons utilize the Q2 instantaneous radar-only products, which are available from NSSL, as well as the Q2 instantaneous gauge-adjusted radar products. The gauge adjustment is based on a new procedure developed by the authors using the Q2 hourly gauge-adjusted and hourly radar-only products. Pixel-by-pixel hourly adjustment factors are calculated and applied to the radar-only instantaneous product to generate the first very high-resolution gauge-adjusted radar mosaic. The gauge adjustment effect on the pdf will be demonstrated.