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4.2 MWR Instrument

Question 4.12 : What's the design of the EnviSat MWR?

The Envisat MWR, derived from the ERS radiometer but with improved performances and calibration accuracy, is a dual channel passive microwave Dicke radiometer operating at two frequencies: 23.8 GHz and 36.5 GHz. By receiving and analysing the Earth's generated and reflected radiation at these two frequencies, the instrument is able to measure the amount of water content in the atmosphere within a 20 Km diameter.

Question 4.13 : How has the MWR performance been optimised on EnviSat?

Instrument thermal design has been completely revised on EnviSat and an active thermal control has been included to optimise the performance reducing temperature excursions on the Radio Frequency section. Moreover, feed horn design has been optimised to improve some performance and to optimise the beam efficiency performance, which was not specified on ERS.

Question 4.14 : How is calibration on MWR performed?

A two point calibration scheme is adopted, with Hot and Cold reference calibration points, so that periodically, the measurements of the Earth scene radiation are interrupted to allow the measurement of an on board calibration load and of the deep cold space.

The deep cold space measurement shall be accomplished via the Sky horn feed in order to provide a cold reference signal, while on board calibration reference load, kept by the thermal control at the instrument physical temperature, provides a hot reference signal.

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry