Beam-Filling Correction Variability in Emission Based Passive Microwave Rainfall Retrievals

摘要

With the threat of global warming looming over the world's population, it is of paramount importance that both the cause and effect of this phenomenon be identified correctly. Global Climate Models (GCM's) attempt to predict the future, so validating the physical assumptions in these models becomes critical. However, it has been found that these models disagree with current observations, particularly those related to global precipitation variability. Without a proper prediction of that variability, it's contribution to the energy balance (through the release of latent heat) will not be correctly accounted for. This contribution would then be improperly attributed to some other component of the energy cycle, diminishing our ability to establish cause and effect. An additional problem exists in that validation of the hydrological cycle in GCM's is accomplished using primarily space-borne passive microwave sensor observations. Rainfall retrievals from those sensors suffer from their own inaccuracies, and the question must be posed as to whether the observations are correct and the GCM's wrong, or visa versa. One of the major sources of error in the observations is the so-called beam-filling error, caused by variations in rainfall inhomogeneity within the relatively coarse resolutions of today's sensors. Due to past limitations in information about rainfall inhomogeneity, the correction for this error has been set as a constant in rainfall retrievals. Information from the recently launched Tropical Rainfall Measuring Mission Precipitation Radar makes it possible to map global beam- filling corrections in a more realistic manner. This study shows that this correction is not a constant, as previously assumed, and varies on both a regional and temporal scale.