Consistency of Geoid Models, Radar Altimetry, and Hydrodynamic Modelling in the North Sea

• Published in: Marine geodesy 2016-07, Vol.39 (3-4), p.223-237
• Main Authors: Schall, J., Löcher, A., Kusche, J., Rietbroek, R., Sudau, A.
• Format: Article
• Language: English
• Subjects: Altimeters; Altimetry; Atmospheric models; Brackish; Budgeting; Errors; Geodetics; Geoid models; Geoids; GOCE (experiment); hydrodynamic modelling; Marine; North Sea; Oceans; radar altimetry
• ISSN: 0149-0419; 1521-060X
• DOI: 10.1080/01490419.2016.1152334

Radar altimetry, when corrected for tides, atmospheric forcing of the sea surface, and the effects of density variations and mean and time-variable currents, provides an along-track realization of the marine geoid. In this study we investigate whether and how such an 'altimetric-hydrodynamic' geoid over the North Sea can serve for validating satellite-gravimetric geoids. Our results indicate that, using ERS-2 and ENVISAT along-track altimetry and water levels from the high-resolution operational circulation model BSHcmod, we do find distinct differences in RMS fits for various state-of-the art satellite-only models (beyond degree 145 for GRACE-only, and beyond degree 185 for GOCE models) and for combined geoid models, very similar as seen in GPS-levelling validations over land areas. We find that, at spectral resolution of up to about 200, an RMS fit as low as about 7 cm can be obtained for the most recent GOCE-derived models such as GOCO05S. This is slightly above what we expect from budgeting individual errors. Key to the validation is a proper treatment of the spectral mismatch between satellite-gravimetric and altimetric-hydrodynamic geoids. Comparison of data fits and error budget suggests that geoid truncation errors residual to EGM2008 (i.e. EGM2008 commission and omission error) may amount up to few cm.