ESTIMATION OF LARGE-SCALE MONTHLY RAINFALL OVER INDIAN REGION USING MINIMAL INSAT-VHRR DATA

In this paper, we have examined the possibility of minimizing the numb er of geostationary Very High Resolution Radiometer (VHRR) images requ ired for the estimation of rainfall on large time and space scales usi ng the Arkin's approach. In the selection of appropriate images we are guided by our knowledge of the pattern of diurnal variability of clou diness/rainfall over the region of interest. For the present work, INS AT-VHRR thermal band images over the Indian region for the month of Ju ne 1986 are utilized. Monthly average brightness temperatures (T-b) ov er 2.5 degrees by 2.5 degrees regions, derived from afternoon (0900 UT C) and post-midnight (2100 UTC) INSAT-VHRR thermal infrared band image s, separately and in conjunction, have been compared with the Arkin et al. monthly average rainfall based on 3-hourly INSAT images, as well as with groundbased measurements. The analysis indicates that even one image taken at 0900 UTC daily is able to locate the regions of high c onvection almost as well as depicted by Arkin's analysis based on 3-ho urly images. Inclusion of 2100 UTC images results in marginal improvem ent in the spatial distribution of rainfall. It is also observed that the present results based on 0900 and 2100 UTC VHRR data are somewhat better correlated with groundbased rainfall measurements than the resu lts from Arkin et al.