AIRBORNE RADIOMETRIC OBSERVATIONS OF CLOUD LIQUID-WATER EMISSION AT 89 AND 157 GHZ - APPLICATION TO RETRIEVAL OF LIQUID-WATER PATH

Measurements of the microwave brightness temperature of stratocumulus cloud at 89 and 157 GHz using the Microwave Airborne Radiometer Scanning System on the UK Meteorological Research Flight's C-130 aircraft have been analysed. Comparisons of observed and calculated brightness temperature using models available in the literature have given good agreement for sea-surface emission and atmospheric attenuation in clear and cloudy skies. A nonlinear retrieval scheme has been applied to the observations to retrieve cloud liquid-water paths for comparison with the in situ measurements. Validation of the retrieved liquid-water paths to within 50 g m(-2) has been achieved. Ambiguities between cloud retrievals and water vapour and surface parameters are discussed. The observed differences between the retrieval and the in situ measurement are not found to correlate strongly with cloud temperature, but a higher than expected correlation is found with the drop-size distribution. It is demonstrated that the scheme is applicable to satellite soundings of cloud, and that a similar level of accuracy should be achieved.