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Colorado Experiment


The main objective of the 1-cm geoid experiment in Colorado was the estimation and comparison of geoid undulations, height anomalies and potential values using the same input data and different methodologies for the gravity field (geoid and quasi-geoid) modelling. The comparison of the results allowed the identification of the differences caused by disparities in the computation methodologies. To get as similar and compatible results as possible, this experiment also included the definition of a set of basic processing requirements (see Sánchez et al. 2018). The input data were provided by the US National Geodetic Survey (NGS) and comprised terrestrial and airborne gravity data, a digital terrain model, and GNSS/levelling data for an area of about 500 km x 800 km in Colorado, USA. With these data, fourteen groups from fourteen countries computed the mentioned gravity-field estimates using their own methodologies (and software).After one preliminary run and two iterations, each group provided geoid and quasi-geoid models at a resolution of 1′x1′ for the complete area and geoid heights, height anomalies, and geopotential values at 223 benchmarks of the Geoid Slope Validation Survey 2017 (GSVS17). The methodologies applied in this experiment, the comparison of the results, and the main conclusions are presented in detail the Special Issue “Reference Systems in Physical Geodesy” of the Journal of Geodesy.

The 1-cm geoid experiment is a joint effort of the Focus Area Unified Height System of the Global Geodetic Observing System (GGOS) and its working group 0.1.2: Strategy for the realization of the IHRS (Sánchez 2019); 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 (Wang and Forsberg 2019); and the study group 0.15: Regional geoid/quasi-geoid modelling - Theoretical framework for the sub-centimeter accuracy of the IAG Inter-Commission Committee on Theory – ICCT (Huang and Wang 2019).

List of gravimetric geoid and quasi-geoid models


Computation method Authors
Institutions Status
1D FFT with Wong-Gore modification of the Stokes kernel V.N. Grigoriadis, et al.              
AUTh / PoliMi PUBLIC
Windowed LSC R. Barzaghi, et al. PoliMi / AUTh PUBLIC



References

Ågren J and Ellmann A (2019). Report of the Sub-commission 2.2: Methodology for Geoid and Physical Height Systems, Reports 2015-2019 of the International Association of Geodesy (IAG), Travaux de l'AIG Vol. 41, Commission 2, pages 33-38.

Huang J and Wang YM (2019). Report of Joint Study Group 0.15: Regional geoid/quasi-geoid modelling – theoretical framework for the sub-centimetre, Reports 2015-2019 of the International Association of Geodesy (IAG), Travaux de l'AIG Vol. 41, Inter-Commission Committee in Theory, pages 40-45.

Sánchez L (2019). Report of the GGOS Focus Area “Unified Height System” and the Joint Working Group 0.1.2: Strategy for the Realization of the International Height Reference System (IHRS), Reports 2015-2019 of the International Association of Geodesy (IAG), Travaux de l'AIG Vol. 41, Global Geodetic Observing System (GGOS), pages 42-51.

Sánchez L, Ågren J, Huang J, Wang Y M, Forsberg R (2018). Basic agreements for the computation of station potential values as IHRS coordinates, geoid undulations and height anomalies within the Colorado 1 cm geoid experiment. Version 0.5, October 30, 2018.

Wang YM and Forsberg R (2019). Report of the Joint Working Group 2.2.2: The 1 cm geoid experiment, Reports 2015-2019 of the International Association of Geodesy (IAG), Travaux de l'AIG Vol. 41, Commission 2, pages 56-58.