The European Space Agency’s Water Mission, the Soil Moisture and Ocean Salinity
mission (SMOS), was selected in 1999 as the second Earth Explorer opportunity
mission to be implemented and is expected for launch in November 2009. SMOS is an
ESA mission in cooperation with France and Spain that have invested additional funds
and efforts to implement it. SMOS single payload, MIRAS (Microwave Imaging
Radiometer by Aperture Synthesis) a microwave (L-band) interferometer, shall provide
for the first time global observations of soil moisture and ocean salinity to improve our
understanding of the Earth’s hydrological cycle. In spite of the low frequency, 1.4 GHz,
the aperture synthesis method will allow having on ground a spatial resolution down to
30 km.
The SMOS Data Processing Ground Segment (DPGS) is organised to generate
reconstructed images of brightness temperature from the multiple (69 elements) antenna
correlations measured on board and transmitted to the ESA ground stations (primarily
ESAC, near Madrid, Spain). Then these snapshot brightness temperatures are
accumulated along an orbit, and the multi-angular measurements used to retrieve both
soil moisture and ocean salinity, through an iterative adjustment based on modelling the
L-band emissivity of the observed surfaces with the knowledge of auxiliary information
on the environmental characteristics of both soil and ocean. The result will be strips,
approximately 1000 km wide, of the spatial distribution in an Icosahedral Snyder Equal
Area (ISEA) projection, level 4, resolution 9 grid (15.74 km Characteristic Length
Scale) of moisture over the continents and surface salinity over the oceans with an
expected accuracy of 4% and 1 psu respectively. The ESA mandate is to compute and
distribute these level 2 products. However, many users interested in performing large
scale and climate studies are expecting global gridded maps at an improved geophysical
resolution. This can be achieved by temporal and spatial averaging of the SMOS L2
products to reduce noise, and that in the case of ocean salinity we expect can provide
monthly maps at 1º or 2º spatial resolution and accuracy of the order of 0.1 psu.
The Spanish Delegation to ESA and the National Program on Space decided to fund and
implement a specific facility, the SMOS Level 3 and Level 4 Processing Centre (CP34),
to offer these high level products to the international research community, an initiative
similar to the French CATDS (Centre Aval de Traitement de Donées SMOS) set up by
CNES. CP34 (http://www.cp34-smos.icm.csic.es/) has been designed and developed
since 2004 and will be ready for operation at the SMOS launch. It is formed by a
Production and Distribution Centre, located at ESAC close to the SMOS DPGS, and an
Expert Centre in charge of the definition, algorithm development and testing, and
further validation of the CP34 products. The latter is part of the SMOS Barcelona
Expert Centre on Radiometric Calibration and Ocean Salinity (SMOS-BEC,
http://www.smos-bec.icm.csic.es/) installed at the Institute of Marine Sciences in
Barcelona (belonging to CSIC, the Spanish Research Council) in cooperation with the
Universitat Politècnica de Catalunya (UPC).
The CP34 objectives are: 1) Reception of lower level data from the generic SMOS
DPGS; 2) Data driven generation of L3 and L4 SMOS products; 3) Archival of L3 and
L4 products (including LTA), providing a product catalogue to the users; 4)
Dissemination of products to the users; 5) The CP34 is also intended to define and
validate new improved algorithms for the generation of L3 and L4 products. In a first
implementation the L3 ocean salinity products to be generated by CP34 are:

Product 1: Maximum spatial resolution (to locate salinity gradients). Only
temporal averaging of 10 days using a weighted (by measurements uncertainty)
averaging method over the L2 products. Generation frequency once every 3 days.
Output grid: ISEA49.

Product 1B: High spatial resolution. Spatio-temporal averaging of 3 days using
weighted averaging method over the L2 products. Generation frequency once
every 3 days. Output grid: ISEA48 at 31.48 Km

Product 2: GODAE. Spatial averaging of 200 km and temporal averaging of 10
days using optimal interpolation method over the L2 products. Generation
frequency once every 10 days. Output grid: 200 km x 200 km grid.

Product 3: Climatology-like. Spatial averaging of 100 km and temporal averaging
of 30 days using optimal interpolation method over the L2 products. Generation
frequency once every 10 days. Output grid: 100 km x 100 km grid

Product 3a: Seasonal average. Same as product 3 but temporal averaging by
season (JFM, AMJ, JAS and OND) over Product 3. Seasonally generation.

Product 3b: Yearly average. Same as product 3 but temporal averaging by natural
year over Product 3. Yearly generation.
And L3 land products, all with maximum spatial resolution, no spatial averaging over
the L2 products in ISEA49 grid:
o Soil Moisture products:

Product 1a: Temporal averaging of 3 days using simple averaging. Daily
generation.

Product 1b: Temporal averaging of 10 days using simple averaging. Generation
frequency of once every 10 days.

Product 1b’: Temporal averaging of monthly decades (1st to 10th of the month,
11th to 20th of the month, 21st to last day of the month) using simple averaging.
Generation frequency of once every decade.

Product 1c: Monthly average. Temporal averaging from L3 decade averages.
Monthly generation.

Product 1d: Seasonal average. Temporal averaging from L3 monthly averages.
Seasonally generation.

Product 1e: Yearly average. Temporal averaging from L3 monthly averages.
Yearly generation.
o Vegetation Water Content products
Same averaging and generation frequencies as for Soil Moisture except product 1a
o Dielectric Constant products
Same as for Soil Moisture
The SMOS-BEC was established in 2007 and gathers all the CSIC and UPC research
staff working in different aspects of the SMOS mission, plus several postdoc
researchers, engineers, technicians and PhD students exclusively involved in SMOS
activities. Its objectives are: 1) To develop and validate algorithms for the SMOS CP34
Data Processing Centre; 2) To contribute improving the instrument calibration and
lower level SMOS algorithms during the commissioning phase and beyond; 3) To carry
out activities within the SMOS Validation and Retrieval Team coordinated by ESA; 4)
To support the coordination of efforts by the different SMOS Spanish teams; 5) To host
postgraduate students and visiting scientists to develop their research on SMOS data
processing and applications. At present the main SMOS-BEC activities, for the different
levels of data processing, are:
Level 1:

Support to SMOS BEC higher level activities.

Assessment on advanced error correction techniques and in-orbit validation
procedures.

Assessment on the PMS linearity correction procedure.

Propose methods for noise reduction in the reconstructed images processing.

Propose methods for the scene-dependent bias correction.
Level 2:

Test new formulations for the cost function in the iterative retrieval approach.

Investigate the best option for a semi-empirical model of the roughness effect on
sea surface emissivity using different descriptor parameters.

Analyze the error estimations for the different formulations.

Propose methods for using the Global Navigation Systems signals reflections to
describe the ocean surface roughness.

Study the spatial errors correlation in SMOS and auxiliary data produced/used at
L2.
Level 3:

Act as Expert Support Laboratory (in collaboration with the University of
Valencia) for the CATDS/CP34 EC-SM.

Analyze optimal procedures for spatio-temporal averaging and objective
mapping of L2 salinity data.

Propose a “quick” L3 OS product to be used in validation activities.

Study the use of re-analyzed meteorological information in the generation of L2
and then L3 products.
Level 4:

Investigate the integration of in situ buoys data and ocean circulation numerical
models for the validation of SMOS salinity products.

Analyze SMOS plus in situ Mediterranean and North Atlantic data in the
framework of the SMOS Cal/Val AO proposals with Spanish participation.

Algorithms to build sea surface density maps from SMOS L3 products and SST.

Possible generation of higher spatial resolution coastal products including
additional information from other sources (monitoring buoys, regular surveys,
...)

Study the possible generation of blended SMOS plus Aquarius salinity products.

Propose assimilation schemes of SMOS L2 and L3 OS products in ocean
circulation models.
Others:

Maintain a web site to distribute SMOS information and analysis tools to
research teams.

Host external visitors that want to temporally participate in the BEC activities.

Coordinate the field activities of Spanish cal/val teams and organize sharing
resources.

Coordinate with ESA and other international teams the organization of
validation campaigns using airborne instruments.

Coordinate validation activities with the Aquarius team and study improvements
for the in situ instrumentation (e.g. drifters).

Coordinate activities with CATDS and CP34-PDC.
Since the SMOS mission pre-phase A started in 2000, the SMOS-BEC science team has
contributed with more than 85 published papers in peer-reviewed journals and near 300
communications
to
international
symposia.
Find
detailed
information
at
http://www.smos-bec.icm.csic.es/. These include, among many others, the results of
dedicated studies and field campaigns like WISE (Wind and Salinity Experiment) in
2000 and 2001 and the outcome of several PhD theses completed within the group. A
compilation of results by early 2008 can be found in A. Camps et al. (2008)
Determination of the sea surface emissivity at L-band and application to SMOS salinity
retrieval algorithms: Review of the contributions of the UPC-ICM, Radio Science, 43,
RS3008, doi:10.1029/2007RS003728.
This additional contribution to Oceanobs’09 has been partially funded by the Spanish
Ministery of Science and Innovation through grant ESP2007-65667-C04.