Colorado geoid modeling at the US National Geodetic Survey
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ORIGINAL ARTICLE
Colorado geoid modeling at the US National Geodetic Survey Yan Ming Wang1
· Xiaopeng Li1 · Kevin Ahlgren1 · Jordan Krcmaric1
Received: 30 April 2020 / Accepted: 31 August 2020 © This is a U.S. Government work and not under copyright protection in the US; foreign copyright protection may apply 2020
Abstract The geoid computation method currently used at the US National Geodetic Survey is based on the analytical downward continuation solution of the Molodensky geodetic boundary value problem. The quasigeoid is computed first in 1 × 1 grids for the whole area, and then, the geoid is obtained by adding the geoid–quasigeoid separation term based on the simple Bouguer anomalies. A few variations in data combination and topographic/gravity reductions are tested, and three models are selected for the Colorado experiment. Historical GPS/leveling data are used as a guide in the computations. The standard deviation of geoid differences between the historical GPS/leveling data and geoid models is 5.2, 5.0 and 4.9 cm for the models of the initial run, the first and second iteration, respectively. After the models were submitted to the Colorado experiment, they were validated using the GSVS17 (Geoid Slope Validation Survey 2017) GPS/leveling data. The standard deviation of the geoid differences on 223 GSVS17 marks is 3.2, 2.6 and 2.3 cm for the three runs, respectively. In addition to the (quasi)geoid models, the geopotential numbers at 223 GSVS17 marks are also computed and submitted to the Colorado geoid computation experiment and it is evaluated in Sánchez et al. (2020 this issue). Keywords Colorado experiment · Geoid computation · Quasigeoid computation · Geoid–quasigeoid · Separation · GRAV-D · GSVS17 · GPS/leveling
1 Introduction The Colorado geoid computation experiment is a joint effort of the international geodetic community (Wang et al. 2020, this issue). As one of the 14 groups from 13 countries, the U. S. National Geodetic Survey (NGS) participated in this experiment and contributed its geoid and quasigeoid models. The geopotential values are also computed from the height anomalies at the 223 GSVS17 marks. This paper records the methods used for the (quasi)geoid computations and the results for the initial run, the first and second iteration at NGS. Since the 1990s, NGS has been computing gravimetric geoid models (Smith and Milbert 1999; Smith and Roman 2001; Roman et al. 2004; Wang et al. 2012). While the computation methods have been refined for better accuracy, a nationwide airborne gravity collection called the Gravity for the Redefinition of the Vertical Datum (GRAV-D, Smith and Roman 2010) has been conducted to fill in areas where terrestrial gravity data are sparse or have poor quality. To
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Yan Ming Wang [email protected] National Geodetic Survey, NOAA, 1315 East-West Highway, Silver Spring, MD 20910-3282, USA
combine the GRAV-D data with terrestrial gravity data and the latest satellite gravity models, the spectral combination method (Jiang and Wang 2016) is used for the initial
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