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| Titel |
High-resolution global forward modelling: a degree-5480 global ellipsoidal topographic potential model |
| VerfasserIn |
Moritz Rexer, Christian Hirt, Roland Pail |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250143953
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| Publikation (Nr.) |
 EGU/EGU2017-7725.pdf |
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| Zusammenfassung |
| The development of parallel computing and arithmetically extended integration algorithms
make forward modelling of the gravitational potential of Earth possible on a global scale with
very high resolution. We make use of an efficient spectral integration method and a composite
global source-mass model developed at Technische Universität München over the past two
years. The integration method allows the rigorous definition of an arbitrary number of
volumetric mass layers of laterally varying mass-density that are referenced to an oblate
ellipsoid of revolution. Often used simplifications such as spherical approximations and the
rock-equivalent-topography concept are avoided in our modelling technique. Starting
from band-limited degree-5400 layer-boundaries we demonstrate the creation of a
(non-compensated) degree-5480 ellipsoidal topographic potential model that resolves the
gravity field of Earth down to scales of ∼ 4 km. This involves multiple spherical harmonic
analysis of the height-density functions and their first 25 integer powers to degree
5400. Stark oversampling is required in order to ban aliasing that otherwise would
distort the short-scale gravitational signal. This results in large grids, dimensioned
64801 x 129601 (67 GB), initiating a parallelization of the analysis procedure.
The ellipsoidal topographic potential model shows significant signal amplitudes
in the spectral window ranging from degree 2161 to 5480 and we successfully
demonstrate their importance in combined high-resolution gravity field modelling over
various regions on Earth. As an aside the model reveals interesting insights into
spherical harmonics at short scales: the signal degree variances actually are rising
towards short scales since they refer to the spherical harmonic reference sphere,
where short-scale signals are dramatically amplified due to the attenuation factors
found in the spherical harmonic series expansion. The signal strengths at Earth’s
surface, in contrast, are of monotonously decreasing character towards short scales. |
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