The Rock–Water–Ice Topographic Gravity Field Model RWI_TOPO_2015 and Its Comparison to a Conventional Rock-Equivalent Version

Abstract

RWI_TOPO_2015 is a new high-resolution spherical harmonic representation of the Earth's topographic gravitational potential that is based on a refined Rock-Water-Ice (RWI) approach. This method is characterized by a three-layer decomposition of the Earth's topography with respect to its rock, water, and ice masses. To allow a rigorous separate modeling of these masses with variable density values, gravity forward modeling is performed in the space domain using tesseroid mass bodies arranged on an ellipsoidal reference surface. While the predecessor model RWI_TOPO_2012 was based on the 5 0 Â 5 0 global topographic database DTM2006.0 (Digital Topographic Model 2006.0), the new RWI model uses updated height information of the 1 0 Â 1 0 Earth2014 topography suite. Moreover, in the case of RWI_TOPO_2015, the representation in spherical harmonics is extended to degree and order 2190 (formerly 1800). Beside a presentation of the used formalism, the processing for RWI_TOPO_2015 is described in detail, and the characteristics of the resulting spherical harmonic coefficients are analyzed in the space and frequency domain. Furthermore, this paper focuses on a comparison of the RWI approach to the conventionally used rockequivalent method. For this purpose, a consistent rock-equivalent version REQ_TOPO_2015 is generated, in which the heights of water and ice masses are condensed to the constant rock density. When evaluated on the surface of the GRS80 ellipsoid (Geodetic Reference System 1980), the differences of RWI_TOPO_2015 and REQ_TOPO_2015 reach maximum amplitudes of about 1 m, 50 mGal, and 20 mE in terms of height anomaly, gravity disturbance, and the radial-radial gravity gradient, respectively. Although these differences are attenuated with increasing height above the ellipsoid, significant magnitudes can even be detected in the case of the satellite altitudes of current gravity field missions. In order to assess their performance, RWI_TOPO_2015, REQ_TOPO_2015, and RWI_TOPO_2012 are validated against independent gravity information of current global geopotential models, clearly demonstrating the attained improvements in the case of the new RWI model.

Layer-Based Modelling of the Earth’s Gravitational Potential up to 10-km Scale in Spherical Harmonics in Spherical and Ellipsoidal Approximation

“…The discrepancies shown in Fig. 8 are in good agreement with the findings by Grombein et al (2016) and Kuhn and Hirt (2016).…”

“…RET modelling involves a compression of all masses to a layer of constant (rock) density, resulting in approximation errors in the order of several dozens of mGal, see, e.g. Grombein et al (2016) and Kuhn and Hirt (2016). Therefore, it is very useful to have forward modelling approaches that are adapted to rigorous modelling of mass layers.…”

“…2) RWI TOPO 2015: the Rock-Water-Ice topographic model 2015 (Grombein et al, 2016) is a forwardmodel based on layers of solid rock, water and ice derived from the same data set (Earth2014) as used for the layer-based ETP models in this work. Contrary to this work RWI TOPO 2015 has been generated from an integration in the space domain using a tesseroid approach (see Grombein et al (2013)) and…”

Topographic gravity modeling for global Bouguer maps to degree 2160: Validation of spectral and spatial domain forward modeling techniques at the 10 microGal level

“…Gravity computation techniques—commonly known as gravity forward modeling—can be grouped into two categories, namely spatial domain and spectral domain techniques [e.g., Nahavandchi, ; Kuhn and Seitz , ; Hirt and Kuhn , ]. In the first category, Newton's integral is evaluated in the space domain, e.g., through numerical integration using elementary mass bodies [ Kuhn et al, ; Grombein et al, ], fast Fourier transform (FFT) techniques [ Forsberg , ], or quadrature‐based methods [ Hwang et al, ]. Classical [e.g., Hammer , ; Nowell , ] and modern [e.g., Tsoulis et al, ; Cella , ] terrain correction computations fall into this category, too.…”

A geothermal application for GOCE satellite gravity data: modelling the crustal heat production and lithospheric temperature field in Central Europe

“…A globally uniform linear velocity-to-density conversion is a simplified model, which disregards the concurring effects of temperature, pressure and composition. Nevertheless, we deemed it suitable to model a far-field, very long wavelength effect, which would be difficult to estimate otherwise (for a different approach, based on topography and the Airy-Heiskanen isostatic model, see Grombein et al 2016). Small scale variations are expected to be significantly smoothed out, while still obtaining a more refined and observationbased estimate than the one that would result from a high-pass filter on the gravity model (e.g.…”