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MWR Instrument Description
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3.3 MWR Instrument Description

The Instrument is a dual channel radiometer, operating at 23.8 GHz and 36.5 GHz, based on the Dicke radiometer principle.

The nadir pointing antenna receives radiation in two microwave frequency bands, in linear (vertical) polarisation.

These frequencies are separately routed into the RF front-end, where the two signals are filtered from external interferences, separately down converted and Low Noise amplified.

IF amplification, filtering quadratic detection and continuous interleaved samplings performed by the CEU, which also provides the function of analogue to digital conversion of the scientific data-sample, by means of a Voltage to Frequency converter.

Digitised measurement data are transferred to the common ICU subsystem for transmission to the ground station via OBDH and LBR interfaces to the PPF.

A 2 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 so that to provide a Cold-Reference signal, while the on-board calibration reference load, kept by the thermal control at the instrument physical temperature, provides a Hot Reference signal.

The calibration data-base and post-processing, will allow the calibration of the measured Earth scene data and the optimisation of the instrument accuracy performance.

The Instrument electrical interfaces, for Power, Command and Control will be accomplished via the common ICU of the MWR/Doris instrument composite, which has the tasks to:

translate Higher Level OBDH macrocommands into serial commands for MWR;

acquire MWR serial telemetry and science data packets;

translate them as Higher Level OBDH telemetry reports or as LBR Measurement Data Interface packets;

provide the Instrument with unregulated Primary Power Busses;

provide the instrument with Blanking and control signals;

include a Redundancy Switching Unit, RSU, to control the instrument interface redundancy.

Some interfaces of MWR are directly connected to the PPF, like Operational and Survival Power Buses, Blanking Pulses, Thermistors, but shall be routed in any case via the common ICU.

When integrated on Envisat-1 PPF, the MWR can only be operated as an Instrument Composite by the common ICU, together with the Doris instrument.

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