Estimation of Upper Tropospheric Humidity from water vapour channel of Very High Resolution Radiometer onboard INSAT-3A and Kalpana Satellites

Present study describes a methodology to establish an empirical expression to estimate the upper tropospheric humidity (UTH) from brightness temperature observations in water vapour channel of Very High Resolution Radiometer (VHRR) onboard Indian geostationary satellites INSAT-3A and Kalpana. Radiative transfer simulations for VHRR water vapour channel were made using SBDART model for tropical atmosphere with different upper tropospheric relative humidity values and varying zenith angles. INSAT-3A and Kalpana VHRR sensor response functions (SRF) for water vapour channel were used to simulate the convolved radiances. Estimated UTH values have been compared with corresponding Meteosat-5 observations. Comparison of retrieved UTH is also made with radiosonde observations of relative humidity weighted by water vapour channel weighting function.