SMOS mission overview
For optimum results, SMOS will measure microwave radiation emitted from Earth's surface within the L-band (1.4 GHz) using an interferometric radiometer.
Measurement principles
Moisture and salinity decrease the emissivity of soil and seawater respectively, and thereby affect microwave radiation emitted from the surface of the Earth. Interferometry measures the phase difference between electromagnetic waves at two or more receivers, which are a known distance apart – the baseline.
The SMOS radiometer will exploit the interferometry principle, which by way of 69 small receivers will measure the phase difference of incident radiation. The technique is based on cross-correlation of observations from all possible combinations of receiver pairs. A two-dimensional 'measurement image' is taken every 1.2 seconds. As the satellite moves along its orbital path each observed area is seen under various viewing angles.
From an altitude of around 758 km, the antenna will view an area of almost 3000 km in diameter. However, due to the interferometry principle and the Y-shaped antenna, the field of view is limited to a hexagon-like shape about 1000 km across called the 'alias-free zone'. This area corresponds to observations where there is no ambiguity in the phase-difference.
SMOS will achieve global coverage every three days.
Mission approach
| Mission | SMOS |
| Launched | 2 November 2009 |
| Duration | Minimum 3 years |
| Instrument | Microwave Imaging Radiometer using Aperture Synthesis - MIRAS |
| Instrument concept | Passive microwave 2D-interferometer |
| Frequency | L-band (21 cm-1.4 GHz) |
| Number of receivers | 69 |
| Receiver spacing | 0.875 lambda = 18.37 cm |
| Polarisation | H & V (polarimetric mode optional) |
| Spatial resolution | 35 km at centre of field of view |
| Tilt angle | 32.5 degrees |
| Radiometric resolution | 0.8 - 2.2 K |
| Angular range | 0-55 degrees |
| Temporal resolution | 3 days revisit at Equator |
| Instrument data rate | 89 kbps H & V pol. |
| Mass | Total 658 kg launch mass comprising: platform 275 kg, payload 355 kg, fuel 28 kg |
| Orbit | Sun-synchronous, dawn/dusk, quasi-circular orbit at altitude 758 km. 06.00 hrs local solar time at ascending node. |
| Launcher | Rockot, KM-Breeze upper stage |
| Bus | Proteus (1 m cube) |
| Power | Up to 1065 W (511 W available for payload; 78 AH Li-ion battery. |
| Spacecraft Operations Control Centre | CNES,Toulouse, France |
| S-Band TTC link | 4 kbps uplink, 722 kbps downlink |
| Payload Mission and Data Centre | ESAC, Villafranca, Spain |
| X-Band data downlink | 16.8 Mbps |
SMOS mission milestones
June 2004
Start of payload construction Phases C/D
April 2004
First joint SMOS/Aquarius/Hydros Workshop held in Miami, USA
November 2003
Approval for full implemention
October 2003
End of payload Phase B, design completed
April 2003
Fourth SMOS Workshop held in Porto, Portugal
November 2001
End of payload Phase A with scientific and technical review. Recommendation received to proceed with implementation.
December 2001
Third SMOS Workshop held in Oberpfaffenhofen, Germany
November 2000
Second SMOS Workshop held in Toulouse, France
October 2000
Start of payload feasibility studies (Phase A)
September 1999
First SMOS Workshop held in Barcelona, Spain
April 1999
Selection of SMOS
July 1998
Call for proposals
Last update: 2 November 2009
SMOS: ESA's water mission 
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