Estimation of total atmospheric water vapor content from split-window radiance measurements

Different studies have shown that the estimation of the surface temperature from split-window algorithms can be greatly improved by a rough knowledge of the total atnwspheric water vapor. In this article, we have tested the split-window covariance variance ratio technique to estimate the total columnar water vapor content. This method has been applied over sea surfaces and over land on two databases. The first dataset contains AVHRR/NOAA9 and ATSR-IR/ERSI data coincident with radio soundings over Europe (land areas). The second one includes ATSR-IR images and water vapor content estimations derived from the microwave radiometer ATSR-MW on board ERSI over the Atlantic Ocean and the Mediterranean Sea. The results show the necessity of using two different algorithms: one for land and another for sea pixels because of the effects c f surface cini.ssivity. Then, two algorithms have been calibrated and validated. The conclusion is that the columnar water vapor content may be estinuzted from thermal infrared .split-window channels with an accuracy better than 0.5 g/cm2, which is, in most cases, enough to improve surface temperature retrievals with infrared radiometers.