AIRCRAFT MEASUREMENTS OF WATER-VAPOR CONTINUUM ABSORPTION AT MILLIMETER WAVELENGTHS

In preparation for the future AMSU-B mission, measurements of clear-air radiative transfer at 89 and 157 GHz were made using a radiometer operating 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 empirical models of continuum absorption are compared and tested; three are found to be more representative of the observations in middle-latitude conditions. In the tropical Atlantic, large model deficits are found for these models. The fourth is more representative of observations in the tropics but over-estimates absorption at middle and arctic latitudes. The results confirm observations taken during other atmospheric field experiments, and laboratory measurements, that a model absorption deficit at high humidity exists in the microwave and millimetre wavelength regions.