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MIRAS receives faint radio signals from Earth

The Microwave Imaging Radiometer using Aperture Synthesis (MIRAS) instrument is a passive microwave 2-D interferometric radiometer (L-Band, 1.4 GHz, 21 cm) onboard the SMOS satellite. It picks up faint microwave emissions from Earth's surface to map levels of soil moisture, sea surface salinity, sea ice thickness and others geophysical variable such as wind speed over ocean and freeze / thaw soil state.

MIRAS consists of a central structure and three deployable arms. The 69 antenna elements (LICEF receivers) are equally distributed over the three arms and the central structure. Each LICEF is an antenna-received integrated unit that measures the radiation emitted from the Earth at L-band. The acquired signal is transmitted to a central correlator unit, which performs interferometry cross-correlations of the signals.

Data Description

The following SMOS products are available:

  • SMOS baseline science products - The complete Level 1B/1C brightness temperature and Level 2 soil moisture and sea surface salinity datasets. These are the operational baseline products of the SMOS mission.
  • SMOS Near Real Time products - This includes the Level 1C brightness temperature "Light" product (in BUFR format) and the Level 2 soil moisture product generated using a Neural Network algorithm (in netCDF format), distributed by the SMOS ground segment in near real time i.e. respectively within three and four hours from sensing.
  • SMOS NRT Level 2 swath wind speed - SMOS retrieved surface wind speed gridded maps (with a spatial sampling of 1/4 x 1/4 degrees) are available in NetCDF format.
  • SMOS Level 3 daily wind speed - SMOS L3WS products are daily composite maps of the collected SMOS L2 swath wind products for a specific day, provided with the same grid than the Level 2 wind data (SMOS L2WS NRT) but separated into ascending and descending passes.
  • SMOS Level 3C Sea Ice Thickness - This data set contains daily estimations of SMOS retrieved sea-ice thickness and its uncertainty, at the edge of the Arctic Ocean during the period October-April and for Antarctica over the period April-October.
  • SMOS Soil Freeze and Thaw State - The SMOS Level 3 Freeze and Thaw (F/T) product provides daily information on the soil state in the Northern Hemisphere based on SMOS observations and associated ancillary data.
  • SMOS Tropical Cyclone Wind Radii fixes (WRF) - The SMOS WRF product is available in Near Real Time to support tropical cyclone forecasts.

Further information can be found in the data brochure.

Data Tools

A number of tools are available for visualising, processing and analysing SMOS data.

SMOS Toolbox

The SMOS Toolbox provides visualisation of Level-1C and Level-2 products in the Sentinel Application Platform (SNAP).


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The SMOS Data Viewer (SDV) provides a quick and easy way to view SMOS products and the auxiliary files used for generating Level-1 and Level-2 products.


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The SMOS Global Mapping Tool (GMT) is useful for plotting SMOS data into a single global geographical map. The GMT is also able to visualise additional quantities derived from SMOS data.

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SMOS NetCDF Conversion Tool

The SMOS NetCDF Conversion Tool is a self contained command line executable to be used for batch processing of large amounts of files.

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RWAPI can be used to extract information from Level-1 or Level-2 data files in Matlab, as it reads all products related to the retrieval of soil moisture as well as some auxiliary data used as input for the Level-2 processor.

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The SMOS Comparison Tool (SCoT) can be used to compare Level-1 SMOS products of the same type generated with the same schema version for the Data Blocks.


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The Earth Observation Swath and Orbit Visualisation tool (ESOV) can be used to view and select SMOS orbits, but it does not read any data products.


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Calibration and validation activities support the quality measures for SMOS data, by ensuring that the MIRAS instrument is performing well and to established baselines. Ongoing activities are conducted to support this process and reports are available which cover the status and any anomalies which may have occurred throughout the mission lifetime.

MIRAS Quality Control Reports

SMOS data quality information covering monitoring of science and calibration products, providing monthly overviews of the health of MIRAS instrument and product quality, and any MIRAS instrument anomalies that may affect the quality of data acquired.



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