32 research outputs found
DATA BASE DEVELOPMENT AND EVALUATION OF EARTHQUAKE DAMAGE REPORTS UNDER THE SEISIMPACT-THES SYSTEM
Development of a Synthetic Earth Gravity Model by 3D mass optimisation based on forward modelling
Several previous Synthetic Earth Gravity Model (SEGM) simulations are based on existing information about the Earth’s internal mass distribution. However, currently available information is insufficient to model the Earth’s anomalous gravity field on a global scale. The low-frequency information is missing when modelling only topography, bathymetry and crust (including the Mohorovičić discontinuity), but the inclusion of information on the mantle and core does not seem to significantly improve this situation. This paper presents a method to determine a more realistic SEGM by considering simulated 3D mass distributions within the upper mantle as a proxy for all unmodelled masses within the Earth.The aim is to improve an initial SEGM based on forward gravity modelling of the topography, bathymetry and crust such that the missing low-frequency information is now included. The simulated 3D mass distribution has been derived through an interactive and iterative mass model optimisation algorithm, which minimises geoid height differences with respect to a degree-360 spherical harmonic expansion of the EGM2008 global external gravity field model. We present the developed optimisation algorithm by applying it to the development of a global SEGM that gives a reasonably close fit to EGM2008, and certainly closer than a SEGM based only on the topography, bathymetry and crust
A study on the evaluation of the geoid-quasigeoid separation term over Pakistan with a solution of first and second order height terms
Geoid and High Resolution Sea Surface Topography Modelling in the Mediterranean from Gravimetry, Altimetry and GOCE Data: Evaluation by Simulation
Abstract The determination of local geoid models has
traditionally been carried out on land and at sea using gravity
anomaly and satellite altimetry data, while it will be
aided by the data expected from satellite missions such as
those from the Gravity field and steady-state ocean circulation
explorer (GOCE). To assess the performance of heterogeneous
data combination to local geoid determination,
simulated data for the central Mediterranean Sea are analyzed.
These data include marine and land gravity anomalies,
altimetric sea surface heights, and GOCE observations processed
with the space-wise approach. A spectral analysis of
the aforementioned data shows their complementary character.
GOCE data cover long wavelengths and account for
the lack of such information from gravity anomalies. This is
exploited for the estimation of local covariance function models,
where it is seen that models computed with GOCE data
and gravity anomaly empirical covariance functions perform
better than models computed without GOCE data. The geoid
is estimated by different data combinations and the results
showthatGOCEdata improve the solutions for areas covered
poorly with other data types, while also accounting for any
long wavelength errors of the adopted reference model that
exist even when the ground gravity data are dense. At sea, the
altimetric data provide the dominant geoid information.However,
the geoid accuracy is sensitive to orbit calibration errors
and unmodeled sea surface topography (SST) effects. If such
effects are present, the combination of GOCE and gravity
anomaly data can improve the geoid accuracy. The present
work also presents results from simulations for the recovery
of the stationary SST, which show that the combination
of geoid heights obtained from a spherical harmonic geopotential
model derived from GOCE with satellite altimetry
data can provide SST models with some centimeters of error.
However, combining data from GOCE with gravity anomalies
in a collocation approach can result in the estimation
of a higher resolution geoid, more suitable for high resolution
mean dynamic SST modeling. Such simulations can be
performed toward the development and evaluation of SST
recovery methods