Facilitating Joint Analysis of Data From
Several Systems Using Geophysical Models
Hans-Peter Plag, William C. Hammond, Geoffrey Blewitt
Nevada Bureau of Mines and Geology and Seismological Laboratory
University of Nevada, Reno
Reno, NV, USA
Motivation
•The 'three pillars of geodesy':
- Earth's Shape (Geokinematics)
- Earth's Gravity Field
- Earth Rotation
(Fourth pillar:
- remote sensing of the atmosphere)
Output:
- Reference Frame
- Observations of the Shape
- Gravitational Field and
- Rotation of the Earth
Many different observational techniques are used to observe Earth's
shape, gravity field, and rotation in situ, airborne, and spaceborne.
Motivation
Motivation
Motivation
Science questions potentially benefiting from geodetic observations:
Convection:
chemical anomalies or temperature anomalies?
whole mantle convection or layered convection?
Plate tectonics: location of and processes at plate boundaries?
extent of deformation zones?
Ice sheets/glaciers and sea level: ice load history?
present-day mass changes?
Ocean circulation; mass and energy balance: variations and changes?
separation of steric and non-steric component?
Hydrological cycle: quantifying the fluxes?
variations in continental water storage?
Atmospheric circulation: past and present air pressure and wind fields?
Tides:
validation of ocean tide models?
Seismic waves and free oscillations: structure and mechanical parameter of
the solid Earth?
e.g., Rummel et al., 2009
Societal challenges potentially benefiting from geodetic observations:
Disasters: knowing the locations, nature, and probability of hazards; particularly
geohazards;
Water: Monitoring the global water cycle and land water storage changes;
Climate change: detecting climate change signals in the dynamics;
Sea level rise: detecting rapid sea level rise in a timely many
Are we as a community exploiting the full
potential of the rich, accurate,
comprehensive, and complementary
geodetic observations in the three pillars?
State-of-the-Art
Current approach to geodetic data interpretation:
- many studies within one pillar:
- surface displacements;
- in situ or spaceborne gravity;
- Earth rotation;
- often only one type of observations, e.g.:
- GNSS
- InSAR
- forward models/studies often focused on one phenomenon (e.g.,
partial loads: atmosphere, land water storage, ocean)
- recent progress towards more integrated models (e.g., Juettner and
Plag, 1998, Thomas et al., 2005)
- recently significant progress with joint inversions for mass loads
(e.g., Gross et al., 2004; Wu et al., 2006, ..., 2011)
- combination of techniques: e.g. InSAR and GPS;
Lui et al., 2011; Hammond et al., 2011
Combination of Techniques
Example: Combination of GPS and InSAR using models
Hammond et al., 2011
Integrated Models
Dynamical Integrate Modular Earth Rotation System (DIMERS)
Modules of DIMERS:
(i) a quasi rigidly rotating core,
(ii) a quasi rigidly rotating mantle including
crust,
(iii) a non-global equilibrium ocean,
(iv) an autonomous atmosphere,
(v) a deformation system which represents
the deformation of core, mantle and crust
disregarded in (i) and (ii)
Emerging system characteristics:
Chandler wobble period and Q
Nearly diurnal free wobble period and Q
...
Coordinate system for all subsystem:
dynamical Tisserand system of the mantle
(DTM) with origin placed in the CoM of the
mantle
Results of joint analyses, joint inversions, and model studies
indicate that there is a considerable potential of geodetic
observations to constrain Earth system models.
Geodesy and Earth System Models
Solid Earth mainly is a rigid, static boundary condition
Model Comparison
Geodetic models:
"Earth System models":
- focused on the solid Earth;
- focused on the climate system;
- forces from atmosphere, ocean,
cryosphere are inputs;
- solid Earth is a rigid boundary;
- no dynamic feedback from the
solid Earth to atmosphere, ocean,
and cryosphere;
- no feedbacks between climate
system and solid Earth;
- geodetic observations are not
assimilated in models
- Earth observations are assimilated
to constrain the past
What about geodetic data assimilation in a Earth system
framework?
Geodetic Data Assimilation
Assimilation of geodetic observations in models:
- tropospheric water contents in numerical weather forecast models
- satellite altimetry-derived sea surface variations in ocean
circulation models
- GRACE-derived water equivalents in models of terrestrial water
storage (e.g. (G)LDAS)
Direct assimilation of geodetic observations in system
models virtually not done.
Community Modeling Frameworks
Should we create a community modeling
framework that would facilitate the joint
analysis and interpretation of geodetic
observations?
Geodetic Data Assimilating System (GDAS)
Analysis of geodetic observations in an Earth system
model concept:
- parameterizing the Earth system:
- surface mass loads (land, ocean, atmosphere)
- modeling of processes:
- solid Earth processes (tectonics, strain, rotation, ...)
- known contributions (tides, tidal loading, …)
Geodetic Data Assimilating System (GDAS)
Analysis of geodetic observations in an Earth system
model concept:
i
+
Point measurements:
Si(x) = ∫σ(x') Gs(x,x') ds
+
Filtered, averaged observations: Local models for:
Sij = F(Si(x))
- tectonics,
- post-seismic strain,
Global models for:
- ...
- earth tides;
- rotational effects;
- tidal loading;
- post-glacial rebound;
- ...
Geodetic Data Assimilating System (GDAS)
Challenge:
Different spatial and
temporal resolution of
geodetic observations
Superconducting
gravimeters
GRACE
GPS/GNSS
Geodetic Data Assimilating System (GDAS)
Analysis of geodetic observations in an Earth system
model concept:
- parameterizing the Earth system:
- surface mass loads (land, ocean, atmosphere)
- modeling of processes:
- solid Earth processes (tectonics, strain, rotation, ...)
- known contributions (tides, tidal loading, …)
Fingerprint approach for loads:
- compute fingerprints for unit mass load on grid elements;
- determine loads for each grid element;
- global grid, 1 degree spatial resolution:
- 64,800 elements;
- ~4*109 fingerprints for each parameter;
- possible to include lateral heterogeneities
- nested approach: high spatial resolution in vicinity, low
resolution in the far-field.
Geodetic Data Assimilating System (GDAS)
Analysis of geodetic observations in an Earth system
model concept:
- parameterizing the Earth system:
- surface mass loads (land, ocean, atmosphere)
- modeling of processes:
- solid Earth processes (tectonics, strain, rotation, ...)
- known contributions (tides, tidal loading, …)
- propagating the system state constrained by all available
geodetic observations:
- surface displacements (> 10,000 points)
- gravity (GRACE, in situ)
- Earth rotation
- altimetry
- ...
- system propagation in time: Kalman filter approach
Facilitating Joint Analysis of Data From
Several Systems Using Geophysical Models
A community-based Geodetic Data Assimilation System (GDAS) with:
- parametrized surface loads,
- local geophyscial models
- global geophyscial models
would:
- allow for assimilation of geodetic observations in an Earth system context;
- facilitate joint analyses of multi-technique observations;
- support local and regional studies with regional and global contributions;
- provide a framework to develop community products for use in other
disciplines;
- have a significant impact on eductation.