A model for the dependence of MSU brightness temperature on lapse rate

An analytical model is developed for microwave sounding unit (MSU) channel 2 radiance that is both simple and accurate. The basis of the model is a parameterization of the pressure and temperature dependence of the absorption coefficient of oxygen in the 60 GHz band. The parameterization allows a closed expression to be derived for the brightness temperature at the top of an atmosphere consisting of layers within each of which the lapse rate is constant. The model may be inverted to derive the lapse rate of the troposphere in terms of the MSU brightness temperature and surface temperature and, therefore, provides a framework within which the two temperature records may be interpreted.