Minimize Applications: Oceanography

Oceanography is the branch of Earth science that studies the ocean.
In particular, physical oceanography studies the ocean's physical attributes including temperature-salinity structure, mixing, waves, internal waves, tides and currents.

The primary oceanography variable of interest provided by the toolbox for oceanographic applications is the mean dynamic topography resulting from the difference between mean sea surface height (MSSH) measurements from altimeter and the geoid heights.
Altimetric MSSH fields are an a priori auxiliary input data set fields from which a consistently filtered mean dynamic topography is computed by the toolbox.

This requires that a consistent reference system be chosen for geoid and the MSSH (both surfaces expressed relative to the same reference ellipsoid) as well as a consistent permanent tide system. Ideally the same tidal models or other corrections should have been used in the geoid and the altimetric fields.

Furthermore, as from the mean dynamic topography, the associated geostrophic currents can be derived.

Functionalities related to the oceanographic aspects of the toolbox include:

  • Provision of apriori MSSH, MDT and Geoid data on a grid
  • Computation of a GUT MDT (MSSH-GOCE geoid) at a given spatial resolution and on a given structured or unstructured grid as the difference between the apriori MSSH and the geoid. This MDT product is referred to as a “Satellite-only” MDT or MDTS.
  • Spatial and spectral filtering of MSSH or MDT consistent with a specific harmonic geoid height field resolution. Several filtering types and filter scales are provided to user choice.
  • Interpolation of external high resolution MDT on any regular grid or at given points with internally calculated GUT MDT, i.e. combined MDT (MDTC). The spectral content of the MDTS is limited by the spectral content of the geoid model.
    In the case of GOCE, the corresponding MDTS will thus have a centimetric accuracy at a 100 km resolution.

    In some areas of the world ocean, notably coastal areas, straits, semi-enclosed seas such as the Mediterranean Sea and close to steep bottom topography, the MDT is expected to contain signals at shorter spatial scales. T

    he GOCE User Toolbox hence provides the user with more sophisticated MDT computation techniques, allowing to integrate short-scale information from other MDT sources.
    These techniques will be further referenced to as Remove-Restore techniques. Two variants of a remove-restore “combined” technique are included in GUT.

    The first (method A) utilizes a high-resolution a-priori MDT, e.g. from hydrodynamic modelling or observations, to restore the small-scale structure in the ‘satellite’ MDTS.

    The second variant (method B) takes the a-priori MDT as the basis and restores the large-scale structure by comparing the spectral equivalents of an apriori geoid (based on the filtered difference of MSSH and a-priori MDT) and the GOCE geoid.
    This requires that we use the unfiltered version of MDTS (i.e. direct difference of MSSH – Geoid).

  • Change of reference system for MSSH or MDT
  • Computation of altimetric time-varying absolute dynamic topography as the difference between altimetric sea surface heights and a geoid model.
  • Computation of altimetric absolute geostrophic velocities from the spatial gradients of the geoid field in north and east component and along track.
  • Provision of methods to produce a global description of these gridded fields in term of spherical harmonics.