The CIMR instrument
The CIMR instrument is a wide-swath, conically-scanning, total power, multifrequency, microwave radiometer. It uses state-of-the-art technologies to provide a new class of high-resolution low-frequency microwave imaging capability that has not been possible to date.
The instrument provides low-frequency dual polarisation channels at 1.4 GHz (L-band), 6.9 GHz (C-band), 10.65 GHz (X-band), 18.7 GHz (K-band) and 36.5 GHz (Ka-band) measurements with high spatial resolution and radiometric sensitivity.
- L-band (1.4 GHz) which enables measurements of sea-surface salinity, sea-ice thickness, soil moisture, vegetation parameters, and wind vectors over the ocean
- C-band (6.9 GHz) which enables measurements of sea-surface temperature, land- and ice-surface temperature, and supports sea-ice parameters
- X-band (10.65 GHz) which enables measurements of sea-surface temperature, land- and ice-surface temperature, and supports sea ice parameters
- K-band (18.7 GHz) which enables measurements of sea ice and snow parameters
- Ka-band (36.5 GHz) which also enables measurements of sea ice and snow parameters at around 4.5 km spatial resolution.
The antenna has two main subsystems: the large deployable reflector and the focal plane feed-array.
The reflector surface is made from over 900 km of gold-coated molybdenum 25 micrometre wire – wire that is thinner than a human hair. The wire is weaved into a mesh that forms the reflector surface of the antenna. Combined with net bands (front and back) and more than1000 inter-connecting tie points, the reflector surface accuracy will be a few tenths of a millimetre.
During launch and to fit within the Vega-C rocket fairing, the reflector is stowed on the side of the satellite in a configuration that reduces the whole antenna to a diameter of 40 cm. Once CIMR is in orbit, the reflector is unfurled through a motorised double shifted-pantograph system. Fully deployed, the reflector measures 8.5 metres in diameter on an 8-metre-long boom.
The unique CIMR antenna enables the instrument to provide high spatial resolution measurements (15 km at C- and X-band, 5 km at K-band and 4.5 km at Ka-band) in dual polarisation.
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A feed configuration of one L-band feed, four dual polarisation C- and X-band feeds, eight dual polarisation K- and Ka-band feeds is required to ensure full surface imaging capability – so achieving a continuous swath without gaps.
In total, the instrument has 50 individual receiver chains. Each chain makes use of internal two-point calibration sources with an individual hot load and an active cold load for every channel. The compact integrated calibration assemblies are located close to the feed outputs to maintain the low noise performance, while the subsequent receiver front end modules are located further away from the feed output where there is more space available.
Detection of the channels is done via a full digital receiver backend with radio frequency interference mitigation and processing capabilities, including full Stokes.
The processed data are transferred from the rotating instrument part to the fixed part of the satellite through a set of roll rings implemented in a scan mechanism assembly.
The total mass of the instrument is about 700 kg, including a set of instrument units to perform various management and control functions.
The CIMR instrument uses observation zenith angles ranging from 52° for the L-band to 55° for the other bands, which as it rotates at a rate of 7.8rpm, gives a swath width of 1900 km (>1700 km L-band). This ensures that 95% of the globe is covered each day with a single satellite (93% for L-band). global coverage is achieved every 48 hours.
The prime contractor for the CIMR satellite is Thales Alenia Space in Italy. The prime contractor for the CIMR microwave instrument is OHB in Italy. The prime contractor for the reflector system is High Performance Space Structure Systems and Large Space Structures in Germany.
