Retrieval of Foreign-Broadened Water Vapor Continuum Coefficients from Emitted Spectral Radiance in the H2O Rotational Band from 240 to 590 cm-1

The paper presents a novel methodology to retrieve the foreign-broadened water vapor continuum absorption coefficients in the spectral range 240 to 590 cm −1 and is the first estimation of the continuum coefficient at wave numbers smaller than 400 cm −1 under atmospheric conditions. The derivation has been accomplished by processing a suitable set of atmospheric emitted spectral radiance observations obtained during the March 2007 Alps campaign of the ECOWAR project (Earth COoling by WAter vapor Radiation). It is shown that, in the range 450 to 600 cm−1 , our findings are in good agreement with the widely used Mlawer, Tobin-Clough, Kneizys-Davies (MT CKD) continuum. Below 450 cm −1 however the MT CKD model overestimates the magnitude of the continuum coefficient.