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Observing the ocean

Scientists and seafarers have been observing the oceans since the late 18th century. Then measurements were conducted only over limited areas and periods of time and therefore were sparse and incomplete. Nowadays the ocean is observed globally, timely and reliably through in-situ measurements and satellite remote sensing. These achievements were made possible through many international scientific experiments and advances in information technology and telecommunication.

Despite these technological advances however, oceanographers still face many difficulties. The vastness of the ocean does not allow for a complete sample of the system. Instrument limitations and observation errors have to be addressed and hence there is need for dynmaic ocean model systems. Through data assimilation techniques, ocean models provide an optimal framework to make the most of the limited observations available.

Jason-1 satelliteCourtesy NASA/JPL-Caltech

Oceanographic parameters that are observed include temperature, salinity, currents, ice parameters, sea surface topography, waves, colour, turbulence and nutrients.

The GODAE requirements for remote data focus on satellite altimetry, sea surface temperature and surface winds. Furthermore there is a continued requirement for direct measurements of ocean temperature and salinity profiles.

In-situ measurements are made through many different platforms. The Argo network is a global array of free-drifting profiling floats measuring temperature and salinity of the upper 2000m of the ocean in real-time.

 

Argo status October 2007 Credit to the Argo Project Office

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Other observation system programmes are the global tropical mooring buoy network, the ship-of-opportunity (SOOP) XBT programme, the global surface drifting buoy network and the OceanSites time series reference station network. Further tools and techniques that are used to observe the ocean inlcude the CTD probe (Conductivity, Temperature and Depth), ocean gliders (move on set trajectories), tide gauges and seal data.

GODAE places great emphasis on global coverage and the complementarity between in situ and remote sensing data.
The observational data needed for GODAE model/assimilation systems can be separated into:
  1. Atmospheric forcing (wind stress, wind speed, air temperature, specific humidity, precipitation)
  2. Data for assimilation (e.g. altimetry, Argo, SST-data)
  3. Validation data (e.g. hydrography)
  4. Ancillary data (climatologies, bathymetry, river inflows)
Note that the separation into data types is neither definitive nor unique, (e.g. forcing data can be used as one of the controls of the assimilation process).

 

→ Read more: Instruments and measurements

(Last Updated: 31-03-2009)