Assessment of EGM2008 in Europe using accurate astrogeodetic vertical deflections and omission error estimates from SRTM/DTM2006.0 residual terrain model data

Abstract

We assess the new EGM2008 Earth gravitational model using a set of 1056 astrogeodetic vertical deflections over parts of continental Europe. Our astrogeodetic vertical deflection data set originates from zenith camera observations performed during 1983–2008. This set, which is completely independent from EGM2008, covers, e.g., Switzerland, Germany, Portugal and Greece, and samples a variety of topography – level terrain, medium elevated and rugged Alpine areas. We describe how EGM2008 is used to compute vertical deflections according to Helmert's (surface) definition. Particular attention is paid to estimating the EGM2008 signal omission error from residual terrain model (RTM) data. The RTM data is obtained from the Shuttle Radar Topography Mission (SRTM) elevation model and the DTM2006.0 high degree spherical harmonic reference surface. The comparisons between the astrogeodetic and EGM2008 vertical deflections show an agreement of about 3 arc seconds (root mean square, RMS). Adding omission error estimates from RTM to EGM2008 significantly reduces the discrepancies from the complete European set of astrogeodetic deflections to 1 arc second (RMS). Depending on the region, the RMS errors vary between 0.4 and 1.5 arc seconds. These values not only reflect EGM2008 commission errors, but also short‐scale mass‐density anomalies not modelled from the RTM data. Given (1) formally stated EGM2008 commission error estimates of about 0.6–0.8 arc seconds for vertical deflections, and (2) that short‐scale mass‐density anomalies may affect vertical deflections by about 1 arc second, the agreement between EGM2008 and our astrogeodetic deflection data set is very good. Further focus is placed on the investigation of the high‐degree spectral bands of EGM2008. As a general conclusion, EGM2008 – enhanced by RTM data – is capable of predicting Helmert vertical deflections at the 1 arc second accuracy level over Europe.

Efficient and accurate high-degree spherical harmonic synthesis of gravity field functionals at the Earth’s surface using the gradient approach

“…• 34 quasigeoid heights from GPS/levelling (Ihde and Sacher 2002) over Southern Germany, • 31598 terrestrial gravity measurements over Switzerland (Swiss Geodetic Commission, Marti 2004), and • 690 astrogeodetically observed vertical deflections (data from Swiss Geodetic Commission, B. Bürki, author's own observations, see Hirt et al 2010a) over Switzerland and Southern Germany. The quasigeoid height differences from the GPS/levelling data are accurate to few cm (Hirt 2011 , see also Table 5), the accuracy of the gravity observations is at the 0.1 mGal level and better (U.…”

“…(16) and (19)] are not corrected here for the ellipsoidal effect, i.e., the difference between spherical and ellipsoidal approximation (e.g., Claessens 2006, p. 89;Jekeli 1999). The RMS-signal strength of the ellipsoidal effect on g δ is less than 0.1 mGal globally (EGM2008 band 2 to 2190) and the RMS is below 0.1″ for ξ (Hirt et al 2010a), whilst the η -component is unaffected (Jekeli 1999). …”

“…comm. 2010) and the accuracy of the vertical deflections varies between ~0.1″ and ~0.5″ (Hirt et al 2010a). …”

Assessment of EGM2008 using GPS/levelling and free-air gravity anomalies over Nairobi County and its environs

“…Several authors have evaluated EGM2008 in different parts of the world (e.g. Huang and Véronneau, 2009;Claessens et al, 2009;Hirt et al, 2010;Pavlis et al, 2012;Featherstone and Olliver, 2013;Odera and Fukuda, 2013;Abeho et al, 2014). Other assessment studies (25 in number) are presented in Newton's Bulletin (2009).…”

Combining EGM2008 and SRTM/DTM2006.0 residual terrain model data to improve quasigeoid computations in mountainous areas devoid of gravity data

“…Often, a standard rock density is uniformly used for the complete RTM, thus neglecting the impact of any local density variations (cf. Hirt 2010).…”