AIRCRAFT MEASUREMENTS OF WATER-VAPOR CONTINUUM ABSORPTION AT MILLIMETER WAVELENGTHS

In preparation for the future AMSU-B mission, measurements of clear-ai r radiative transfer at 89 and 157 GHz were made using a radiometer op erating on the C-130 aircraft of the UK Meteorological Research Flight . Observations of water vapour and oxygen absorption in arctic, middle latitude and tropical atmospheres were obtained. Four different empir ical models of continuum absorption are compared and tested; three are found to be more representative of the observations in middle-latitud e conditions. In the tropical Atlantic, large model deficits are found for these models. The fourth is more representative of observations i n the tropics but over-estimates absorption at middle and arctic latit udes. The results confirm observations taken during other atmospheric field experiments, and laboratory measurements, that a model absorptio n deficit at high humidity exists in the microwave and millimetre wave length regions.