Update of the precision geoid determination in Korea

Abstract

From the late 1990s, many studies on local geoid construction have been made in South Korea. However, the precision of the previous geoid has remained about 15 cm due to distribution and quality problems of gravity and GPS/levelling data. Since 2007, new land gravity data and GPS/levelling data have been obtained through many projects such as the Korean Land Spatilaization, Unified Control Point and Gravity survey on the Benchmark. The newly obtained data are regularly distributed to a certain degree and show much better improvement in their quality. In addition, an airborne gravity survey was conducted in 2008 to cover the Korean peninsula (South Korea only). Therefore, it is expected that the precision of the geoid could be improved. In this study, the new South Korean gravimetric geoid and hybrid geoid are presented based on land, airborne, ship‐borne, altimeter gravity data, geopotential model and topographic data. As for the methodology, the general remove‐restore approach was applied with the best chosen parameters in order to produce a precise local geoid. The global geopotential model EGM08 was used to remove the low‐frequency components using degree and order up to 360 and the short wavelength part of the gravity signal was dealt with by using the Shuttle Radar Topography Mission data. The parameters determined empirically in this study include for Stokes’ integral 0.5° and for Wong‐Gore kernel 110–120°, respectively and 10 km for both the Bjerhammar sphere depth and attenuation factor. The final gravimetric geoid in South Korea ranges from 20–31 m with a precision of 5.45 cm overall compared to 1096 GPS/levelling data. In addition, the South Korean hybrid geoid produces 3.46 cm and 3.92 cm for degrees of fitness and precision, respectively and a better statistic of 2.37 cm for plain and urban areas was achieved. The gravimetric and hybrid geoids are expected to improve further when the refined land gravity data are included in the near future.

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

“…Several authors studied the feasibility of airborne gravity data in regional geoid modelling. For instance, Yu-Shen and Hwang (2010) improved the geoid in Taiwan from 9.5 to 8.7 cm compared to GNSS/levelling, Bae et al (2012) from 6.6 to 5.5 cm in South Korea, and McCubbine et al (2017) from 4.6 to 3.1 cm in New Zealand. Some authors used the GRAV-D airborne gravity data for geoid modelling in test areas in Texas and Iowa, USA (Smith et al 2013;Li et al 2016;Wang et al 2017;Huang et al 2019).…”

Performance evaluation of the Earth Gravitational Model 2008 (EGM2008) – a case study

“…This is because the global geopotential models (GGMs) prompt the long wavelength components of the Earth's gravity field very well (Daho et al, 2008;Krynski and Lyszkowicz, 2006). They do not only provide a basis for the gravity field when emergent high-precision geoid models, but they are also momentous as reference surfaces for conniving local geoids (Bae et al, 2011;Dawod et al, 2010). Countries that are yet to develop geoid models have been using GGMs for the calculation of geoid heights and gravity anomalies through spherical harmonic analysis (Lee et al, 2008).…”