Colorado geoid computation experiment: overview and summary

Yan Ming Wang*, Laura Sánchez, Jonas Ågren, Jianliang Huang, René Forsberg, Hussein A. Abd-Elmotaal, Kevin Ahlgren, Riccardo Barzaghi, Tomislav Bašić, Daniela Carrion, Sten Claessens, Bihter Erol, Serdar Erol, Mick Filmer, Vassilios N. Grigoriadis, Mustafa Serkan Isik, Tao Jiang, Öykü Koç, Jordan Krcmaric, Xiaopeng LiQing Liu, Koji Matsuo, Dimitris A. Natsiopoulos, Pavel Novák, Roland Pail, Martin Pitoňák, Michael Schmidt, Matej Varga, Georgios S. Vergos, Marc Véronneau, Martin Willberg, Philipp Zingerle

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

50 Citations (Scopus)


The primary objective of the 1-cm geoid experiment in Colorado (USA) is to compare the numerous geoid computation methods used by different groups around the world. This is intended to lay the foundations for tuning computation methods to achieve the sought after 1-cm accuracy, and also evaluate how this accuracy may be robustly assessed. In this experiment, (quasi)geoid models were computed using the same input data provided by the US National Geodetic Survey (NGS), but using different methodologies. The rugged mountainous study area (730 km × 560 km) in Colorado was chosen so as to accentuate any differences between the methodologies, and to take advantage of newly collected GPS/leveling data of the Geoid Slope Validation Survey 2017 (GSVS17) which are now available to be used as an accurate and independent test dataset. Fourteen groups from fourteen countries submitted a gravimetric geoid and a quasigeoid model in a 1′× 1′ grid for the study area, as well as geoid heights, height anomalies, and geopotential values at the 223 GSVS17 marks. This paper concentrates on the quasigeoid model comparison and evaluation, while the geopotential value investigations are presented as a separate paper (Sánchez et al. in J Geodesy 95(3):1., 2021). Three comparisons are performed: the area comparison to show the model precision, the comparison with the GSVS17 data to estimate the relative accuracy of the models, and the differential quasigeoid (slope) comparison with GSVS17 to assess the relative accuracy of the height anomalies at different baseline lengths. The results show that the precision of the 1′ × 1′ models over the complete area is about 2 cm, while the accuracy estimates along the GSVS17 profile range from 1.2 cm to 3.4 cm. Considering that the GSVS17 does not pass the roughest terrain, we estimate that the quasigeoid can be computed with an accuracy of ~ 2 cm in Colorado. The slope comparisons show that RMS values of the differences vary from 2 to 8 cm in all baseline lengths. Although the 2-cm precision and 2-cm relative accuracy have been estimated in such a rugged region, the experiment has not reached the 1-cm accuracy goal. At this point, the different accuracy estimates are not a proof of the superiority of one methodology over another because the model precision and accuracy of the GSVS17-derived height anomalies are at a similar level. It appears that the differences are not primarily caused by differences in theory, but that they originate mostly from numerical computations and/or data processing techniques. Consequently, recommendations to improve the model precision toward the 1-cm accuracy are also given in this paper.

Original languageEnglish
Article number127
JournalJournal of Geodesy
Issue number12
Publication statusPublished - Dec 2021

Bibliographical note

Publisher Copyright:
© 2021, This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply.


This study was possible thanks to a strong international cooperation coordinated within IAG, in particular, the IAG Sub-commission 2.2: Methodology for geoid and physical height systems (Ågren and Ellmann 2019); the joint working group 2.2.2: The 1-cm geoid experiment in Colorado (Wang and Forsberg, 2019); the study group 0.15: Regional geoid/quasigeoid modeling—Theoretical framework for the sub-centimeter accuracy of the IAG Inter-Commission Committee on Theory – ICCT (Huang and Wang 2019); and the working group 0.1.2: Strategy for the realization of the IHRS of the Focus Area Unified Height System of the Global Geodetic Observing System—GGOS (Sánchez, 2019; Sánchez and Barzaghi 2020). The authors are especially indebted to the National Geodetic Survey for providing the gravity, topographic and GPS/leveling data sets for this experiment. The authors thank three anonymous reviewers, the Associate Editor and Editor for their time, constructive suggestions and comments, which helped improving the initial version of this manuscript.

FundersFunder number
Focus Area Unified Height System
Institute of Australian Geographers
National Geodetic Survey


    • 1-cm geoid experiment
    • Colorado experiment
    • Geoid computation
    • Geoid-quasigeoid separation term
    • GPS/leveling
    • GRAV-D
    • GSVS17
    • Quasigeoid computation


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