Abstract
Abstract. Recently available satellite observations from the water vapor channel (6.5–7.1 μm) of the Imager on-board India's geostationary satellite, INSAT-3D have been used to estimate Upper Tropospheric Humidity (UTH). In this study, operationally retrieved UTH product has been compared and validated for the period of Jan–Jun, 2014, using in-situ and satellite measurements. In-situ measurements of UTH have been indirectly derived using humidity profiles obtained from a network of radiosonde stations from NOAA/ESRL database. Meteosat-7 UTH products have been used as satellite measurements. The validation of INSAT-3D UTH against UTH derived from radiosonde profiles shows reasonable agreement, with linear correlation coefficients ranging from 0.78 to 0.87 and the slope of the regression line ranging from 0.52 to 0.77. The UTH tends to overestimate observed humidity by ~4 % with RMS difference of ~12 %. Comparison of INSAT-3D UTH product with Meteosat-7 UTH product suggests a good match with RMS difference of 7.61% and a mean bias of −0.43 %, linear correlation coefficients varying from 0.88 to 0.93 and slope of the regression line varying from 0.64 to 1.08. The UTH products from INSAT-3D and Meteosat-7 have also been inter-compared by validating the two against the UTH derived from a set of collocated radiosonde observations. INSAT-3D UTH shows a RMSD of 10.65 % and bias of 0.78 % which matches very well with Meteosat-7 UTH with a RMSD of 10.31 % and bias of −0.53 %.
Highlights
Water vapor in the atmosphere plays an important role in the Earth’s climate system because of its strong absorption of longwave radiation and through its coupling with other components of the hydrological cycle
The INSAT-3D Upper Tropospheric Humidity (UTH) product computed for pixels free from middle and upper level clouds has been compared and validated with UTH computed from radiosonde profiles, collocated in time and space
The INSAT-3D UTH products were compared with the Meteosat‐7 products that use a look‐up table based algorithm for UTH estimation and validated with the UTH computed from the radiosonde observations of relative humidity for the period of January-June 2014
Summary
Water vapor in the atmosphere plays an important role in the Earth’s climate system because of its strong absorption of longwave radiation and through its coupling with other components of the hydrological cycle. Thapliyal et al [2006] presented a simple methodology to estimate the UTH from Kalpana observations that was based on SB93 using the value of po as 1.0, an assumption that is valid only for narrow tropical region This was followed up by an improved algorithm based on SB96 where po was computed using an empirical functions of latitude and month [Thapliyal et al, 2011].The improved algorithm for the UTH estimation [Thapliyal et al, 2011] from INSAT-3D observations has been developed at the Space Applications Center (SAC).
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