New gravimetric-only and hybrid geoid models of Taiwan for height modernisation, cross-island datum connection and airbo
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ORIGINAL ARTICLE
New gravimetric‑only and hybrid geoid models of Taiwan for height modernisation, cross‑island datum connection and airborne LiDAR mapping Cheinway Hwang1 · Hung‑Jui Hsu1 · W. E. Featherstone2 · Ching‑Chung Cheng1 · Ming Yang3 · Wenhsuan Huang1 · Chong‑You Wang1 · Jiu‑Fu Huang4 · Kwo‑Hwa Chen5 · Chi‑Hsun Huang1 · Hechin Chen6 · Wen‑Yi Su3 Received: 23 March 2020 / Accepted: 1 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract This paper combines gravity data collected from airborne, shipborne and terrestrial surveys and those derived from satellite altimetry to determine a high-resolution gravimetric and hybrid geoid model (on a 30” × 30″ grid) in and around Taiwan. Some 6000 new land gravity values at a 0.03-mGal precision make a notable contribution to the geoid modeling. Shipborne gravity data in waters 20 km offshore Taiwan were collected to improve the coastal geoid precision. In a circular area of 50 km around each of the five major tide gauges in Taiwan, gravity data were measured to improve vertical datum connections between Taiwan and its four offshore islands. Height anomalies were computed first and then converted to geoid heights. At > 2000 benchmarks, we obtained measured geoid heights to assess the gravimetric-only geoid and to create a hybrid geoid. Our assessments and formal errors from least-squares collocation indicate few cm of standard deviations for both geoid models, but the gravimetric geoid has mean differences of up to 20 cm with the measured geoidal heights. The hybrid geoid is used in RTK-VBS orthometric heighting, achieving a 5-cm precision. The gravimetric geoid is used to determine the relative differences in the ocean’s mean dynamic topography (MDT) between Taiwan and the four offshore islands, which are also compared with those from oceanic and altimetric methods for estimating MDT. Differences in MDT help to identify 41.7 cm and 54.1 cm offsets in the current vertical datums of Penghu and Lanyu islands. In a low-lying, flood-prone region of southern Taiwan, the hybrid geoid improves LiDAR mapping of sub-zero elevation zones by 20 cm, corresponding to 70 years of sea level rise at an assumed rate of 0.286 cm/yr. Keywords Geoid · Height modernization · LiDAR · Oceanic mean dynamic topography · Taiwan · Vertical datum unification
1 Introduction * Cheinway Hwang [email protected]; [email protected] 1
Department of Civil Engineering, National Chiao Tung University, No. 1001, Ta Hsueh Road, Hsinchu, Taiwan
2
School of Earth and Planetary Sciences, Curtin University of Technology, GPO Box U1987, Perth, WA 6845, Australia
3
Department of Geomatics, National Cheng Kung University, No. 1, University Road, Tainan, Taiwan
4
Department of Land Administration, Ministry of the Interior, Taipei, Taiwan
5
Department of Real Estate and Built Environment, National Taipei University, No. 151, University Road, San Shia, New Taipei City, Taiwan
6
National Land Surveying and Mapping Center, Ministry of the Interior, Taichung, Taiwan
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