Observed and theoretical millimeter wave emission in the tropics

Surface measurements of atmospheric emission at 20, 31, and 90 GHz have been compared to theoretical values calculated from simultaneous radiosonde measurements and well-known absorption models. Measurements were made at continental locations in the United States, and islands and ships in the Atlantic and tropical western Pacific oceans. Observations of clear sky emission in the tropics during 1993 showed much poorer agreement with theoretical emission than observed at continental locations. The reason for the larger discrepancy in the tropics may be due to errors in the radiosonde humidity element when operated in the extremely humid environment. In order to obtain additional insight into the cause of the discrepancy, a second set of simultaneous emission and radiosonde measurements in the tropical Pacific region was obtained during a cruise of the NOAA research vessel Discoverer from 15 March to 13 April 1996. Measurements and theoretical emission are compared for both the 1993 and 1996 data sets