Geoid Determination in South Korea from a Combination of Terrestrial and Airborne Gravity Anomaly Data

Abstract

The determination of the geoid in South Korea is a national imperative for the modernization of height datums, specifically the orthometric height and the dynamic height, that are used to monitor hydrological systems and environments with accuracy and easy revision, if necessary. The geometric heights above a reference ellipsoid, routinely obtained by GPS, lead immediately to vertical control with respect to the geoid for hydrological purposes if the geoid height above the ellipsoid is known accurately. The geoid height is determined from gravimetric data, traditionally ground data, but in recent times also from airborne data. This paper illustrates the basic concepts for combining these two types of data and gives a preliminary performance assessment of either set or their combination for the determination of the geoid in South Korea. It is shown that the most critical aspect of the combination is the gravitational effect of the topographic masses above the geoid, which, if not properly taken into account, introduces a significant bias of about 8 mgal in the gravity anomalies, and which can lead to geoid height bias errors of up to 10 cm. It is further confirmed and concluded that achieving better than 5 cm precision in geoid heights from gravimetry remains a challenge that can be surmounted only with the proper combination of terrestrial and airborne data, thus realizing higher data resolution over most of South Korea than currently available solely from the airborne data.

The New Zealand gravimetric quasigeoid model 2017 that incorporates nationwide airborne gravimetry

“…Airborne gravimetry provides such data coverage over otherwise inaccessible areas (coastal areas and in rough topography). Airborne gravity has been shown to be suitable for regional geoid computations (e.g., Schwarz and Li 1996, Bastos et al 1997, Kearsley et al 1998, Forsberg et al 2000, Novaìk et al 2003, Olesen 2003, Sjöberg and Eshagh 2009, Hájková 2011 and has been used extensively for this purpose over the past 10 years (e.g., in Mongolia (Forsberg et al 2007), Taiwan (Hwang et al 2007), South Korea (Bae et al 2012, Yang 2013, Jekeli et al 2013, Nepal (Forsberg et al 2014), East Malaysia (Jamil et al 2017), Antarctica (Scheinert et al 2008) and the US GRAV-D project (Smith et al 2013;Li et al 2016;Wang et al 2017)). For these reasons, airborne gravimetry appears well suited to account for the shortcomings of the existing gravity data in NZ to improve the gravimetric quasigeoid model.…”

Contribution of GRAV-D airborne gravity to improvement of regional gravimetric geoid modelling in Colorado, USA

“…Historical tide-gauge/levelling-based HRS may be replaced by gravimetric geoid-based HRS. Airborne gravity data was already used for gravimetric and hybrid (models fitted to a local or regional vertical datum) geoid modelling in many areas worldwide including: North Jutland (Kearsley et al 1998), Taiwan (Hwang et al 2007;Hájková 2015), Italy (Barzaghi et al 2009), United Arab Emirates (Forsberg et al 2012), South Korea (Jekeli et al 2013), New Zealand (McCubbine et al 2017, and East Malaysia (Jamil et al 2017).…”

Gravimetric Geoid Modeling from the Combination of Satellite Gravity Model, Terrestrial and Airborne Gravity Data: A Case Study in the Mountainous Area, Colorado

“…The commonly used approaches for the combination of Earth gravity model, terrestrial and airborne gravity data can be divided into three categories. In the first approach, the airborne gravity data are firstly downward continued from the flight altitude to the ground or geoid to merge with the terrestrial gravity data, then the merged gravity data are used to compute the geoid by Stokes' integral (Novak and Heck 2002;Bayoud and Sideris 2002;Hwang et al 2007;Forsberg et al 2000Forsberg et al , 2012Jekeli et al 2013) or least squares collocation (Hwang et al 2007;Scheinert et al 2008;Shih et al 2015).…”