Atmospheric Sounding Near 118 GHz

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Abstract
The thermal emission spectrum of the atmosphere near the 118 GHz oxygen resonance has been measured from the NASA Convair-990 aircraft as it flew over clear air and storms. The instrument viewed the ground 45° from nadir with a 7.5° beamwidth. Brightness temperatures were measured in six bands 200 MHz wide centered at frequencies 821–1891 MHz from the line at 118.7505 GHz. The double-sideband super-heterodyne receiver had ∼1 K sensitivity for 1 s integration. Comparison of observed clear air brightness temperatures (from 238 mb) with those computed for a coincident dropsonde yielded agreement within 1.4 K; the retrieved temperature profile agreed with the dropsonde with an average magnitude error of 1.4 K. Observations over precipitation yielded brightness perturbations as large as 30 K. Abstract The thermal emission spectrum of the atmosphere near the 118 GHz oxygen resonance has been measured from the NASA Convair-990 aircraft as it flew over clear air and storms. The instrument viewed the ground 45° from nadir with a 7.5° beamwidth. Brightness temperatures were measured in six bands 200 MHz wide centered at frequencies 821–1891 MHz from the line at 118.7505 GHz. The double-sideband super-heterodyne receiver had ∼1 K sensitivity for 1 s integration. Comparison of observed clear air brightness temperatures (from 238 mb) with those computed for a coincident dropsonde yielded agreement within 1.4 K; the retrieved temperature profile agreed with the dropsonde with an average magnitude error of 1.4 K. Observations over precipitation yielded brightness perturbations as large as 30 K.

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