Infrared continuum water vapor absorption coefficients derived from satellite data

In a recent paper W. B. Grant ["Water Vapor Absorption Coefficients in the 8-13-microm Spectral Region: a Critical Review," Appl. Opt. 29, 451-462 (1990)] reviewed experimental measurements of the water vapor continuum absorption coefficients in the 8-13-microm spectral region. In comparing three different groundbased techniques he concluded that the absorption coefficients used in the HITRAN and LOWTRAN-7 codes are in reasonable agreement with the measurements. These coefficients are approximately 20% lower than those used in the LOWTRAN-6 code. A fourth method of experimentally determining the water vapor absorption coefficients is described which suggests an opposite result. A comparison between sets of satellite measured infrared radiances and ship measurements of sea surface temperature using a model of infrared transmission through the atmosphere gives coefficients that are 20-40% larger than those used in LOWTRAN-6. Agreement between the four different measurement techniques is only posible if a much stronger negative temperature dependence of the continuum absorption coefficients is adopted. This results in significant increases in the coefficients at temperatures below 270 K.