Comparison of simultaneous rain drop size distributions estimated from twosurface disdrometers and a UHF profiles

In support of the NASA Tropical Rainfall Measuring Mission (TRMM) Ground Va lidation Program, a suite of surface instruments and vertical pointing Dopp ler radar profilers were deployed in central Florida to quantify the number and size of the rain drops reaching the surface. Analyzing 276 minutes of simultaneous observations from two surface disdrometers and one profiler re vealed good agreement among the instruments for drop sizes > 1.5 mm diamete r but poor agreement for smaller drop sizes. The magnitude of the differenc e in small drop estimation was proportional to the reflectivity (and rainra te). At reflectivities greater than 40 dBZ, the differences in the estimati on of the number of small drops yielded differences in estimates of mass-we ighted diameter of > 13% and of rainrate > 25%. The combined effect of thes e uncertainties impact the interpretation of the precipitation processes an d the development and validation of space-based precipitation retrieval alg orithms.