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
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,