Oceanography is the branch of Earth science that studies the
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
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
- 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.