SMOS

SMOS mission overview

SMOS measurement principle

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.
 
 

Interferometry principle

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

 
 
 
Last update: 2 November 2009

•	SMOS launch (http://www.esa.int/SPECIALS/smos/index.html)
•	Track SMOS (http://www.esa.int/esaLP/SEMF4965P1G_LPsmos_0.html)
•	Access SMOS data (http://earth.esa.int/SMOS/)
More information
•	SMOS - ESA's water mission (BR-288) (http://esamultimedia.esa.int/multimedia/publications/BR-288/pageflip.html)
•	SMOS - la misión del agua de la ESA (BR-278) (http://esamultimedia.esa.int/docs/SMOS/SMOS(Spanish)_28.9.pdf)
•	SMOS – mission de l'ESA dédiée au cycle de l'eau (BR-278) (http://esamultimedia.esa.int/docs/SMOS/BR-278_French_web.pdf)
•	SMOS factsheet (http://esamultimedia.esa.int/docs/SMOS/SMOS_factsheet_22Jun09.pdf)
Special features
•	SMOS: ESA's water mission (http://download.esa.int/mpeg/smos_web_movie.mpg)
From a technological perspective
•	Technology leaps let SMOS follow Earth’s water (http://www.esa.int/SPECIALS/Technology/SEM7I5XRA0G_0.html)
Related links
•	Thales Alenia Space (http://www.thalesgroup.com/)
•	CNES (http://www.cnes.fr/web/CNES-en/455-cnes-en.php)
•	EADS-CASA (http://www.eads.net/1024/en/casa/casa.html)
•	CESBIO SMOS page (http://www.cesbio.ups-tlse.fr/us/indexsmos.html)
•	Ifremer-Cersat Salinity Center (http://www.salinityremotesensing.ifremer.fr/home)
•	German SMOS Project Office (http://www.smos.zmaw.de)
•	SMOS Barcelona Expert Centre (http://www.smos-bec.icm.csic.es/)
•	SMOS Level 3/4 Processing Centre, Spain (http://www.cp34-smos.icm.csic.es/)
•	International Soil Moisture Network (http://www.ipf.tuwien.ac.at/insitu/)