A New Technique to Estimate Precipitation at Fine Scale Using Multifrequency Satellite Observations Over Indian Land and Oceanic Regions

A new technique has been developed to estimate rainfall at very fine scale (hourly rain rate at 0.05 degrees x 0.05 degrees spatial resolution) over India and associated oceanic regions (20 degrees S-40 degrees N, 40 degrees E-130 degrees E). By using infrared (IR) and 6.7-mu m water vapor (WV) channel observations from Meteosat-7, a new rain index (RI) is computed. The index computation is composed of two steps. First, the IR and WV brightness temperatures are divided by their respective nonrainy thresholds to get the IR and WV rain coefficients. The product of these coefficients is defined as the RI. These RIs are collocated against rainfall from the Precipitation Radar (PR) on board the Tropical Rainfall Measuring Mission to develop a relationship between the index and the rain rate. This relationship was utilized to monitor rainfall by applying it to numerous cases of monsoon and tropical cyclones over India and associated oceanic regions. Detailed validation with rain gauges and independent PR observations and comparisons with Global Satellite Mapping of Precipitation (GSMaP) and a regional rainfall algorithm based on IR observations are performed in this study. The present technique shows a correlation coefficient (CC) of 0.74, a bias of 0.086 mm, and a root-mean-square error (rmse) of 4.78 mm when compared with rain gauge. On the other hand, the regional rainfall technique and GSMaP show CCs of 0.72 and 0.59, bias values of 1.59 and 0.338 mm, and rmses of 5.49 and 7.20 mm, respectively, compared with rain gauge. It is observed that the present technique is able to monitor the rainfall with good accuracy at very fine scale over India.