High Density Rain Gauge network for Validation of the AMSR-E Rainfall Estimation Algorithm

As part of the Aqua AMSR-E (Advanced Microwave Scanning Radiometer-EOS) validation program, in the summer of 2002 we began deploying a 5 \times 5 rain gauge network with ~5 km spacing (covering an area of ~25 km x 25 km) centered on the Iowa City, Iowa Municipal Airport. This spacing corresponds to the interval between adjacent 89 GHz AMSR-E footprints. The AMSR-E was launched on board the Aqua satellite on May 4, 2002, and we have been collecting AMSR-E data since June 1. We are going through many steps to insure good data quality, most importantly installing two gauges within one meter of each other at each location to alert us to possible problems if the rain rates do not correspond between the two. Together with the existing cluster of rain gauges in the Iowa City airport and its vicinity, the network consists of about 40 sites. We will use these data to answer many questions, ranging from whether there is bias in the satellite rainfall estimates to what are the optimal temporal and spatial scales (including offsets) for comparison of satellite-based estimates with surface rainfall. We will determine the spatial and temporal statistics of instantaneous area-averaged rainfall over the 25 km grid necessary to assess the spatial and temporal sampling errors of our space and time averages, so that the bias can be assessed with statistical significance. We will also determine the appropriate spatial and temporal scales for comparison of level 2 (instantaneous) satellite and ground reference (e.g., spatially averaged rain gauges or radar) estimates. The satellite observes a volume of vertical hydrometeors that contribute to the surface rainfall at a later period of time for a surface area assumed to correspond to the nominal satellite footprint area. Only with this high temporal and spatial resolution rain gauge network can we determine the area and times that should be compared with level 2 estimates so that the contribution from collocation errors to the satellite vs. ground reference difference is quantified and minimized. In the presentation we show preliminary results of the rainfall statistics and the satellite product evaluation.