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Refined European sea level estimations by combining altimetry, tide gauges, hydrographic and other data sets

with improved regional GIA modeling and tailored regional GRACE gravity field models

RESEL-GRACE

Jürgen Kusche, Frank Flechtner, Anny Cazenave, Guillaume Ramillien,Bert Vermeersen, Martyn Drury

Kick-off meeting SC, Strasbourg, 25. 8. 2008

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RESEL-GRACE: Aims & Team

J. Kusche, F. Flechtner GFZ Potsdam Satellite Gravity, Mass Transport

A. Cazenave, G. Ramillien LEGOS/CNES Oceanography, Altimetry

B. Vermeersen TU Delft Glacial Isostasy, RheologyM. Drury U Utrecht

overall budget 478,400 €

Aims:Refine ESL estimates by combining• Altimetry, tide gauges, ARGO float data, hydrographic

data• Improved regional GIA modelling• Tailored regional gravity field models from GRACE

Team:

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Contributions to TOPO-EUROPE themes

Monitoring the Earth systemthrough acquisition, processing and interpretation of satellite gravity and

geodetic data, multi-sensor studies and compiling data and securing long term accessibility to the resultant integrated databases,

Imaging and high-performance computing of the deep Earth and lithosphere

through modelling the contributions to contemporary European sea level changes of glacial isostatic adjustment by regionally varying crust, lithosphere and mantle structures, compositions and rheologies derived from geological fieldwork and laboratory experiments,

Dynamic topography reconstructionthrough full 4-D modelling of spatial and temporal variations in

topography by post-glacial rebound in Europe with particular emphasis on NW-Europe

Process modelling and validationthrough integrating 4-D data sets originating from different geoscientific

fields, including space geodesy

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addition of freshwater Total sea level rise

ArgoArgo

JasonJason

GRACEGRACE

addition of heat

Land uplift

TideTidegaugesgauges

RESEL-GRACE

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Objectives

• Derive regional mean and time-variable gravity models directly from GRACE instrument data for dedicated European areas of interest (Med Sea, Fennoscandia)• for full GRACE time period (mid 2002…today)• using same standards and conventions as currently adopted for

standard spherical harmonic EIGEN-GRACE05S models

• Update the average and regional sea level rates in the Med Sea using multi satellite altimetry data (Jason-1, Envisat, Jason-2, and SARAL/Altika (to be launched in 2009)).

• explain the mass contribution to sea level by using new and independent GRACE measurements of gravity due to redistribution of water mass at the surface of the Earth

• improve estimates of GIA in N-Europe. Improve knowledge of shallow earth structure and rheology of the region. A coupled earth-ice model and the method to constrain the process of GIA with satellite gravity data can and will be used for the Mediterranean as well.

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IP-1IP-1

Mean + time-variableMean + time-variableSatellite gravity (GRACE)Satellite gravity (GRACE)

Collaboration

IP-2IP-2

Altimetry, tide gauge, ARGO Altimetry, tide gauge, ARGO floats floats

IP-3IP-3

GIA, Earth modelsGIA, Earth models

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Goals of IP-1 (GFZ)

GFZ Potsdam, as part of the GRACE SDS, generates monthly spherical harmonic models of the Earth‘s gravity field (currently RL04)

RMS variability of 40 GFZ RL04 monthly geoid models (anisotropically filtered)

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Goals of IP-1 (GFZ)

Here: derive regional mean and time-variable gravity models directly from GRACE instrument data for dedicated European areas of interest

By circumventing the estimation of global spherical harmonic coefficients, we will be able to

• tailor the data analysis strategy (e.g. spatial resolution and spatio-temporal constraints) to the area of interest, taking into account the data coverage and the expected mean/time-variable signal,

• modify and extend our data analysis strategy much more flexible

• separate more accurately the marine contribution from the land part of the gravity field representation (“continental leakage”), and

• accelerate the computation time as only regional data sets will have to be processed against a global background model.

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Goals of IP-2 (LEGOS)

Main goal : measurement of mean sea level variations over the Mediterranean basin since 1993, quantification of the two main causes of these variations (thermal expansion and water mass exchanges) for determining their impacts on coastal regions.

• estimate sea level variability and trends of the whole Med Sea, both on average and at regional scale

• estimate steric contribution using in situ temperature and salinity from ARGO

• estimate water mass balance of the Mediterranean Sea region using tailored GRACE data since mid-2002.

• quantify coastal sea level variations of the Mediterranean basin, both on an absolute and relative basis (using tide gauges data for the latter).

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Goals of IP-2 (LEGOS)

• evaluate separately the spatio-temporal variations of the main components of the absolute sea level:

(1) exchange of fresh water from atmosphere and continents to the sea,

(2) change of sea water density due to temperature/salinity variations

(3) vertical movements of sea bottom due to

(i) elastic response to (un)loading of sea water, and

(ii) long-term solid Earth processes (GIA, active tectonic environment)

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Goals of IP-3 (TUD, UU)

Improve estimates of GIA in N-Europe, and improve our knowledge of shallow earth structure and rheology of the region (necessary as input for estimating absolute sea-level variations in IP-2). Derived coupled earth-ice model and method to constrain the process of GIA with satellite gravity data can be used for other regions as the Mediterranean.

• couple a regional (flat) 3D high-resolution finite-element (FE) model to a 3D thermo-mechanical ice-sheet model (ISM)

• parameterization of ice shelves (is important in this particular area)

• incorporation of a self-gravitating sea level in the FE model

• incorporation of global effects of GIA-induced sea level and horizontal motion

Use available data to constrain the properties of the shallow earth and provide a self-consistent earth- and ice-model combination to describe the process of GIA in N-Europe. Serves as input to establish the contribution of GIA to regional sea level variations. Important part of the work is the development of a suitable inversion procedure, and spatio-spectral techniques that can be applied to static, high-resolution gravity data.

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Goals of IP-3 (TUD, UU)

Focus on the region of N-Europe because of availability of high-quality GPS-, relative sea level-data. To use gravity field information, available models of other geophysical and climatologically driven processes must be used to isolate GIA-signal.

It is expected that the time-variable gravity field from GRACE has a specific temporal signature and can thus be used as aconstraint for the modeling of GIA.

For temperatures and water content of the mantle we will rely on estimates from seismic tomography and electrical conductivity.

Make use of available rock samples. To constrain structural and compositional variables (crystal size, water content) need to develop regional rheological models.