Validation of microwave scattering radiative transfer models using an aircraft radiometer and a ground-based radar

Many microwave radiative transfer models for precipitation have been described in the literature, Regardless of the approximations used to overcome the problem of scattering, a feature common to all models is the need to properly represent the microphysics of the hydrometeor field responsible for producing the scattering signatures. Many assumptions of phase, density and hydrometeor size distributions are made. In support of the modelling effort, the UK Meteorological Office (UKMO) Remote Sensing Instrumentation (RSI) branch has undertaken a measurement campaign to determine the sensitivity of microwave radiative transfer models to the manner in which the atmospheric microphysics is represented. An airborne microwave radiometer operating at 89 and 157 GHz and viewing both upwards and downwards flew at all levels along radials of a high resolution S-band radar during a frontal precipitation event. The aircraft was equipped with a range of thermodynamic and microphysical measurement equipment and conclusions drawn about the structure of the atmosphere using both these and the radar reflectivity measurements. This permitted a `realistic´ representation of the atmosphere in an Eddington approximation code. Radiometer brightness temperatures at both frequencies were then compared with the model output. The paper outlines the approach used to determine the best representation of the microphysics