Hydrologic applications of high-resolution geoestationary satellite rainfall estimates corrected for terrain heights, wind and parallax - the LBA study

The current generation of geosynchronous satellites exhibits considerable improved capabilities in the area resolution, gridding accuracy, and sampling frequency as compared to their predecessors. These improvements have made it possible to accurately observe the life cycle of small scale, short-live phenomenon like rapidly developing thunderstorms, at a very high spatial and temporal resolutions. While the gain in the improved resolution is not significant for synoptic scale cloud systems, it plays a major role on the computation of precipitation values for mesoscale and storm scale systems. Two of the important factor on the accurate precision of precipitation from satellite imagery are the position of the cloud tops as viewed by the satellite and the influence of orographic effects on the distribution of precipitation. The first problem has to do with the fact that the accurate estimation of precipitation from data collect by a satellite in geosynchronous orbit requires the knowledge of the exact position of the cloud tops with respect to the ground below. This is not a problem when a cloud is located directly below the satellite; at large viewing angles the geographic coordinates on satellite images are dependent on cloud heights and distance from the sub-satellite point. The latitude and longitude coordinates for high convective cloud tops are displaced away from the sub-satellite point and may be shifted by as much as 20 Km from the sea level coordinates. The second problem has to do with the variations in rainfall distribution with elevation. Ground observations have shown that precipitation amounts tend to increase with height and that the slope of the hill or mountain that is facing the prevailing wind normally receives greater rainfall then do the lee slopes. This is particularly important in the coastal mountain regions found in Chile. The purpose of the study is to show the recent developments in the National Oceanic and Atmospheric Administration (NOAA) and in the National Aeronautics and Space Administration (NASA) to adjust an infrared satellite rainfall estimation technique and account for orographic and parallax corrections. Description and examples of the procedure using the NOAA/NESDIS experimental satellite rainfall estimation technique for flash flood applications (http://orbit-net.nesdis.noaa.gov/arad/ht/ff) will be presented at the conference with focus on the LBA (Large-Scale Biosphere-Atmosphere Experiment in Amazonia) region.