Assessment of INSAT-3D Retrieved Temperature and Water Vapour With Collocated Radiosonde Measurements Over Indian Region

Abstract

This article evaluates the performance of Indian National Satellite System (INSAT)-3D sounder temperature (T) and water vapor (WV) by comparing with the collocated radiosonde observations obtained at different stations over Indian region. The assessment is carried out in terms of bias in the INSAT-3D measurements by assuming the radiosonde observations as a standard measurement technique. The study is carried out to find the performance of INSAT-3D sounder data on different surface types (land, coast, and ocean), seasons, and latitude zones. The main findings are the large bias in INSAT-3D-derived T and WV profiles over land compared to the coastal and oceanic stations, which may be attributed to the large contrasting surface emissivities over land. The WV measurements of INSAT-3D showed a relative dry bias of 15%–25% in the lower troposphere. Near the surface, a warm bias (~2 K) is observed over the land, and a cold bias (~1 K) is observed over the coastal and oceanic stations. Cold biases of ~1 K (land) and ~0.5 K (coastal and oceanic) are observed in the middle troposphere. The variability of the T bias is relatively large over land, particularly during winter and premonsoon. The variability of T bias is large in the 25°–35°N latitudinal zone mainly in winter followed by premonsoon, postmonsoon, and monsoon. A consistent warm bias of ~2–3 K is observed in the upper troposphere particularly at around 100 hPa on all the surface types in all seasons over all latitude zones. Thus, bias correction is advised in using these data for upper tropospheric and lower stratospheric (UTLS) studies.