RTM Gravity Forward-Modeling Using Topography/Bathymetry Data to Improve High-Degree Global Geopotential Models in the Coastal Zone

Abstract

We apply the residual terrain modeling (RTM) technique for gravity forward-modeling to successfully improve high-resolution global gravity fields at short spatial scales in coastal zones. The RTM scheme is combined with the concept of rock-equivalent topography, allowing to use a single uniform constant mass-density in the RTM forward-modeling, both at land and sea. SRTM30_PLUS bathymetry is merged with higher-resolution SRTM V4.1 land topography, and expanded into spherical harmonics to degree 2160, yielding a new and consistent high-degree RTM reference surface. The forward-modeling performance is demonstrated in coastal zones of Greece and Canada using ground-truth vertical deflections, gravity from land and shipborne gravimetry, and geoid heights from GPS/leveling, with improvements originating from bathymetry clearly identified. We demonstrate that the SRTM30_PLUS bathymetry carries information on gravity field structures at spatial scales less than 5 arc minutes, which can be used to augment EGM2008 in (rugged) coastal zones, both over land and marine areas. This may be of value (i) to partially reduce the signal omission error in EGM2008/GOCE-based height transfer in areas devoid of dense gravity data, (ii) to fill the gap between land gravity and shipborne gravity along rugged coastlines, and (iii) for the development of next-generation altimetric gravity fields.

Keywords:

• Residual terrain model
• topography
• bathymetry
• coastal zone
• forward-modeling

Acknowledgements

The Australian Research Council (ARC) is acknowledged for funding this study through Discovery Project grant DP120102441. Christian Hirt is the recipient of an ARC Discovery Outstanding Researcher Award (DORA). Ground-truth data for this study were kindly provided by the following institutions and colleagues: Canadian gravity (Gravity & Geodetic Networks Section, Geodetic Survey Division, Natural Resources Canada), Canadian GPS/leveling (Natural Resources Canada, Marc Véronneau), and Greece vertical deflections (ETH Zurich, Dr. Beat Bürki, Dr. Anna Somieski). Sincerest thanks go to all data providers and to two reviewers for their comments on the manuscript. The spherical harmonic analyses were performed using the freely available software archive SHTOOLS (shtools.ipgp.fr).

This paper is dedicated to my colleague and friend Prof. Dr. Volker Böder, Professor for Geodesy and Hydrography at HafenCity University Hamburg, who died tragically in a ship collision during a hydrographic survey on 1 September 2012.