Science & Applications

The temperature at the surface of the ocean (SST) is an important physical property that can be measured quite easily from Earth Observation satellites. It is of primary importance for both coastal oceanography and global ocean circulation understanding, and as such Ifremer has developped within CERSAT a dedicated infrastructure and competencies to collect and archive SST observations, produce synthetic and easy-to-use datasets for users and to develop applications.

The ocean suface salinity is a fundamental parameter to better understand and predict ocean circulation, water cycle, climate and their interactions. Measuring this parameter from space is also a huge technical challenge, and two experimental missions will atempt to achieve this goal in the coming years : SMOS (ESA mission to be launched in September 2009) and AQUARIUS (NASA/Argentina mission to be launched in 2010). CERSAT is highly involved in this challenge, as an expert support laboratory for ESA and also as a processing and archiving center for SMOS mission, through the CATDS (Centre Aval de Traitement des Données SMOS) supported by CNES.

The sea surface parameters retrieved from satellite sensors enable to get a better understanding of the air-sea interactions. The scientists of the CERSAT try to define how satellite measurements could help to retrieve correctly and to understand :

• the space and time scales of wind and wave fields,
• the inter-tropical ocean circulation,
• extreme events (cyclones).

They benefit by the CERSAT database, since a multi-satellite and multi-sensor approach is essential for new insights into this research field.

Multiple parameters of the surface layer can be retrieved from space and the most known are the chlorophyll-a and the suspended matters concentration, the turbidity and the light diffuse attenuation coefficient. Phytoplankton contains chlorophyll pigments which absorb light preferentially in the blue. Suspended matters reflect and absorb light, modifying the optical properties of the water. Coloured dissolved organic matters absorb light in the short wavelength. Ifremer has a particular focus on regional areas around french and west european shelves to retrieve accurate estimations of these parameters.

The on-going studies of sea-ice use satellite data from both passive (SMMR, SSM/I, ATSR/M) and active (scatterometers such as ERS/AMI-Wind of ERS-1 and ERS-2, ADEOS/NSCAT or QuikSCAT/SeaWinds) microwave sensors, which are complementary. The scientists of CERSAT use these sensors to :

• discriminate sea-ice (age, type, concentration, etc...),
• screen the edge of the ice-pack,
• monitor the sea-ice drift.

The validation of the sensor products, as well as a daily quality control, are required to get homogeneous and consistent temporal series (winds, waves and sea-ice). Inter-comparison with other sensors is necessary to fulfill this task. Thanks to the colocation system developped by the CERSAT, multi-sensors colocated datasets were generated to make easier intercomparison between various sensors and detection of possible sensor drifts. This section features :

• long term statistical analyses of the measurements from various sensors,
• comparisons and quality analyses of the data from various sensors,
• ongoing monitoring of various sensors.