Evaluating possible enhancement of INSAT-3D Sounder water vapour retrieval in the tropics

Abstract

The present study makes an attempt to use hyperspectral infrared observations to define optimum sounding instrument on board Indian geostationary satellites. In a multichannel sounding instrument such as Indian National Satellite System (INSAT-3D) and Geostationary Operational Environmental Satellite Sounder, there are three channels in 6–8 µm water vapour (WV) absorption band. In this study, humidity profiles are retrieved by adding another eight channels within 6–8 µm WV absorption band. The retrieved humidity profiles are compared with that retrieved from the hyperspectral sounding instrument Infrared Atmospheric Sounding Interferometer (IASI). It has been found that improvement in humidity profile retrieval with additional eight WV channels is merely ~1%, above the mid-troposphere compared to the profiles retrieved with just three WV channels. However, the retrieval accuracy with that obtained from the IASI spectra has improved by 5–10% compared to existing three as well as eight additional WV channels of a multichannel sounder. This study concludes that in order to improve the humidity retrieval accuracy in the tropics, hyperspectral sounding observations are required since mere increasing of WV channels in a multichannel sounder is having only a small positive impact.