Simulation studies of satellite spectral radiances for 11·1, 8·3, 7·3, 6·7 μm IR bands

Starting with an outline of spectral radiance calculation for infrared bands, a simulation study has been presented for 11.1, 8.3, 7.3 and 6.7 μm. Detailed response of the spectral radiance to the meteorological parameters has been studied by generating simulated atmospheric temperature and moisture profiles for Indian atmospheres. It has been found that the responses of the 8.3, 7.3 and 6.7 μm bands are maximum for lower troposphere, middle troposphere and upper troposphere respectively, and these spectral radiances are linearly related to the water vapour content of the relevant layers. The thermal IR window at 11.1 μm is found to be sensitive to not only surface temperature and total water vapour content but also to the boundary layer values of mean temperature and water vapour content.

     

Horizontal moisture distribution from TIROS-N high resolution infrared sounder (HIRS)

A direct linear relationship between water vapour content of lower, middle and upper-middle troposphere respectively with the radiances for 8.3, 7.3 and 6.7 μm spectral observations has been attempted. From the atmospheric simulations such a relationship is found to exist with a good degree of correlation and is seen to be quite insensitive to temperature changes. Such an approach is used to interpret the water vapour imageries obtained from TIROS-N sounder through construction of detailed water vapour distribution maps.