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
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.