LARGE-AREA SOIL-MOISTURE ESTIMATION USING INSAT-VHRR INFRARED DATA

It has been shown by earlier workers that rate of change of land surfa ce temperature (DELTAT) during mid-morning hours as determined from th e thermal infrared sensor onboard geosynchronous satellite can provide a good signature of area-averaged soil moisture. In order to examine the feasibility of this approach, a pilot study was undertaken using l imited data of INSAT-VHRR. Since no concurrent measurements of soil mo isture and other meteorological data were available, the analysis was carried out making a number of simplifying assumptions. The observed D ELTAT during April 1991 showed a reasonably good association with arid and semi-arid regions of Rajasthan and Gujarat, respectively, while D ELTAT during September 1991 was found to be negatively correlated with the area-averaged total rainfall data over Gujarat. Although these re sults are encouraging, they can at best be considered as indicative of physical processes in view of the simplifying assumptions. More rigor ous analysis is essential to establish the validity of the approach.