Covariances of Spectroscopic Parameter Uncertainties in Microwave Forward Models and Consequences for Remote Sensing

Characterization of forward-model accuracy is a part of retrieval error analysis, as discussed by Rodgers [1]. We estimate correlated uncertainties in the spectroscopic parameters of models for atmospheric microwave absorption by water vapor (Rosenkranz [14] as modified by Turner et al. [2]) and oxygen (Tretyakov et al. [3]). The uncertainties can be correlated either by definition of the parameters (as for the water vapor continuum with line widths) or by the way in which they are measured (as for line mixing in the oxygen band). Spectroscopic parameter correlations affect the resulting uncertainty in calculated opacity and brightness temperature at any given frequency, as well as correlations between different frequencies. Uncertainty-covariance matrices have been calculated for the spectroscopic parameters with significant impact on the 20-to 60-GHz band, and the uncertainties are propagated to downwelling brightness temperatures and ground-based temperature profile and water-vapor profile retrievals.