SMOS, the Earth’s Water Mission
Le Bourget, 13 Juni 2005
SMOS (Soil Moisture and Ocean Salinity), the second Earth Explorer Mission of Opportunity within the European Space Agency (ESA) Living Planet Program, has become a reality. In the month of April, EADS Astrium in Spain being the prime contractor for the satellite’s payload, has delivered the first structural model to ESA. The test campaign has already started at ESTEC to qualify its performance, and so far, with complete success.
The Water Cycle Problem
Oceanographers, geologists and biologists give a great deal of importance to obtaining and quantifying moisture and salinity maps for improving climatologic forecasts, increasing the understanding of the connection between the water cycle and meteorology and providing new approaches to knowledge on the phenomenon of climatic change.
On earth, for example, the water presence in soil, through evaporation or filtration, affects plant growth. Moreover, the retention of water in soil is crucial to weather and climate because soil moisture is a key variable controlling the exchange of water and heat energy between land and atmosphere. This water cycle has a direct impact on the planet’s fresh water reserves.
In the oceans, both temperature and salinity, control the density of seawater. Salinity influences the circulation of water masses in oceans that lead to the formation of climatologic phenomena such as El Niño or La Niña, which cause flooding or droughts. The increase and decrease of salinity due to the water evaporation or rains strongly impact on the water circulation along the oceans that plays a crucial role in regulating the weather and climate.
The missions of opportunity were conceived for advancement in the knowledge of the Earth’s behaviour and in the development of new technologies that permit the elaboration of new observation techniques from space. This mission’s life will last three years and will provide maps of soil moisture and ocean salinity of the whole Earth. SMOS will demonstrate a new measuring technique in the field of remote sensing, to assist in an in-depth study of the structure of the cryosphere. To date, the measurement of these geophysical parameters is localized and not continuous. This is why it is important to have a satellite that provides the measurement of the planet’s two geophysical parameters over the entire surface and with a high rate of repetition (between three and five days).
How To Measure The Moisture And Salinity From Space
All matter emits energy in the form of electromagnetic radiation. The amount of energy radiated will depend on the electrical properties of the material. Moisture and salinity decrease the emissitivity of soil and sea water. SMOS will measure the radiation emitted from Earth’s surface at L-band (1,4 GHz).Traditionally, L-band observations of the Earth were made by making a large rotating antenna to achieve the adequate coverage and spatial resolution. The results was a very expensive and heavy satellite. SMOS, in turn, uses a new technique: Interferometric Radiometer with Synthetic Aperture, which employs a small number of receivers to measure the radiation at the same time. The correlation of the signals of every receiver produces a 50x50 Km image pixel with different incidence angles. Like taking photographs of the same scene from different positions.
To do this, the engineers of EADS Astrium in Madrid, have designed an instrument called MIRAS (Microwave Imaging Radiometer using Aperture Synthesis) which is the result of 10 years of research. A radiometer is an instrument that detects the electromagnetic radiation emitted by a body at a certain temperature within a given frequency band. Since microwaves are sensitive to changes in the dielectric constant of the medium, any change in the water content leads to changes in dielectric properties and affects the emissivity, and therefore the radiant temperature detected by the radiometer. Microwave theorists have encountered a direct relationship between soil moisture and ocean salinity with Earth emissivity at 1.4 GHz.
The Instrument Concept
MIRAS has three arms in “Y” form and a central structure that supports them. Each arm is comprised of three segments that are connected by a hinge. The arms are folded to the sides of the central structure during launch. The payload mechanism consists of a spring-operated motors, a speed regulator and a collection of belts and pulleys that convey engine torque to all arm segments deploying simultaneously, avoiding kinetic moment disturbance to the satellite. Analyses undertaken prove that this configuration, with antennas distributed along the arms, optimises space resolution and Instrument sensitivity. With its arms extended the Instrument has a diameter of 8 meters
There are 69 receivers called LICEF, equally distributed along the arms and in the central structure. Every LICEF is an antenna that measures the radiation emitted from Earth at L-band. All LICEF signals are transmitted through optical fibre to the correlator unit, which performs interferometric cross-correlation of possible combinations or receiver pairs to create the synthetic antenna.
The Mission
The mission is carried out by a the satellite with a total weight of 350 Kg. in a low sun synchronous orbit, with an altitude of 763 Km at an Inclination 98,4º, and a revisit time of 3 days, that passively measures the electromagnetic noise generated by Earth with a radiometric sensitivity of 5K, in addition to a ground operations segment for the control and processing of data. The launch of the satellite with a Rockot vehicle is targeted for March of 2007.
SMOS is the result of cooperation among three European institutions dedicated to the promotion of the space industry and science, which are the ESA (European Space Agency), the French CNES (National Centre for Space Studies) and the Spanish CDTI (Centre for Industrial Technological Development).
The ground segment will consist on two main components. The satellite Operations Ground Segment located in Toulouse (France) to operate the spacecraft and the S-band station in Kiruna (Sweden). And, the Instrument Data Processing Ground Segment located at the ESA facility of Villafranca (Spain) to programme the PLM mission and to received and process the Instrument data.
EADS SPACE and the Earth Explorers
EADS SPACE is also considerably involved in other satellites of the Earth Explorer Missions which are being built. EADS Astrium (UK), for example, is the prime contractor for the ADM-Aeolus wind mission, whereas the Aladin instrument is being developed by Astrium (F). In addition to the lead in the Cryosat ice satellite, EADS Astrium (Friedrichshafen) is also responsible for the platform and the satellite integration of GOCE, the surfer of the gravitational field. Astrium Spain develops and builds the Miras payload of the SMOS mission for the acquisition of data on soil moisture and ocean salinity.
The launch provider Eurockot (Bremen), a unit of EADS SPACE, will carry out the launches of the satellites Cryosat, Goce and Smos on board its Rockot launchers from Plesetzk (800 km north of Moscow).
EADS Astrium is Europe’s leading satellite system specialist. Its activities cover complete civil and military telecommunications and Earth observation systems, science and navigation programmes, and all spacecraft avionics and equipment. EADS Astrium, wholly owned subsidiary of EADS SPACE, which is dedicated to providing civil and defense space systems. In 2004 EADS SPACE had a turnover of €2.6 billion and 11,000 employees in France, Germany, the United Kingdom and Spain.
EADS is a global leader in aerospace, defense and related services. In 2004, EADS generated revenues of € 31.8 billion and employed a workforce of more than 110,000.
Contacts for the Media
| Rémi ROLAND | EADS SPACE (FR) |
Tel.: +33 (0) 1 42 24 27 34 |
| Jeremy CLOSE | EADS SPACE (UK) |
Tel.: +44 (0) 1 438 77 3872 |
| Mathias PIKELJ | EADS SPACE (GER) |
Tel.: +49 (0) 7545 8 91 23 www.space.eads.net |
