Search

Radiometric technique for absolute temperature measurement of microwave noise sources under field conditions

To provide a general guide in the interpretation of air-borne microwave radiometer data over the ocean, a limited set of measurements of a simulated ocean surface was conducted. The experiment was designed to measure the apparent or brightness temperature, in the microwave region, of an air-water interface under a variety of conditions. We had available a system of radiometers on the frequencies of 9.3, 15.8, 22.2, and 34 GHz. These radiometers were installed in a NASA aircraft, and our experiment was conducted, with the aircraft parked, by erecting a temporary test tank 8 feet in diameter below the radome housing the radiometers (Figure 1).

Results of numerical experiments on model atmospheres obtained from radiosonde observations indicate that the contribution of the troposphere to the electrical path length at zenith is about 200 cm, and that this length can be inferred to an accuracy of 1 or 2 cm from ground-based microwave radiometric measurements.