Calibration and expected performances of ENVISAT-1 MWR

ENVISAT-1 microwave radiometer (MWR) is an instrument designed and developed for the European Space Agency (ESA) by European Industry as part of ENVISAT-1 scientific payloads developed by ESA. It is a two channels passive Dicke microwave radiometer, operating at 23.8 and 36.5 Ghz. By receiving and analyzing the Earths generated and reflected radiation at these two frequencies, this instrument is able to measure the amount of water content in the atmosphere within a 20 Km diameter field of view immediately beneath the satellites track. The MWR output products are of prime importance for wind/wave products of radar altimeter providing correction of atmospheric propagation data, for direct evaluation of brightness temperature to characterize polar ice and land surface properties and for sea surface temperature accurate measurements. In order to achieve the required accuracy and sensitivity performance, a two points calibration concept is adopted with hot and cold calibration reference points: periodically the measurements of earth scene radiation are interrupted to allow the measurement of an on-board calibration load and of the deep cold space. Given this on- board calibration architecture, a specific pre-flight calibration and characterization activity is necessary in order to develop a ground calibration and characterization philosophy has been developed by Alenia Spazio. In this paper, an overview of radiometric performance prediction is reported, with extensive description of the foreseen calibration and characterization activities. Moreover, a general description of in-flight calibration is provided.