On characterizing the error in a remotely sensed liquid water content profile

Abstract

The accuracy of a liquid water content profile retrieval using microwave radiometer brightness temperatures and/or cloud radar reflectivities is investigated for two realistic cloud profiles. The interplay of the errors of the a priori profile, measurements and forward model on the retrieved liquid water content error and on the information content of the measurements is analyzed in detail. It is shown that the inclusion of the microwave radiometer observations in the liquid water content retrieval increases the number of degrees of freedom (independent pieces of information) by about 1 compared to a retrieval using data from the cloud radar alone. Assuming realistic measurement and forward model errors, it is further demonstrated, that the error in the retrieved liquid water content is 60% or larger, if no a priori information is available, and that a priori information is essential for better accuracy. However, there are few observational datasets available to construct accurate a priori profiles of liquid water content, and thus more observational data are needed to improve the knowledge of the a priori profile and consequentially the corresponding error covariance matrix. Accurate liquid water content profiles are essential for cloud-radiation interaction studies. For the two cloud profiles of this study, the impact of a 30% liquid water content error on the shortwave and longwave surface fluxes and on the atmospheric heating rates is illustrated.