The ColSHAWG-NGS2019 gravimetric geoid model has been computed by the US National Geodetic Survey (NGS). It has been worked out in the frame of the International Association of Geodesy Joint Working Group 2.2.2 "The 1 cm geoid experiment" and the so called "Colorado experiment". The area covered by the model is 251°E ≤ longitude ≤ 257°E, 36°N ≤ latitude ≤ 39°N with a grid spacing of 1' in both latitude and in longitude. The computation method is based on the spherical harmonic analysis scheme. The airborne gravity data are combined with the reference model xGEOID17RefB to produce an enhanced reference spherical harmonic model. This model is then used in a remove-compute-restore procedure, computing residual height anomalies from terrestrial gravity data by using the Wong-Gore modification of the Stokes kernel (truncation degree equal to 980), also including the g1 term because of rugged mountains. Finally, the geoid undulations are obtained by adding the geoid/quasi-geoid separation term (based on the simple Bouguer anomalies) to the computed height anomalies. The accuracy of the geoid model, when compared against GSVS17 GPS/leveling, is equal to 2.3 cm.

The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.

The International Service for the Geoid (ISG) was founded in 1992 (as International Geoid Service - IGeS) and it is now an official service of the International Association of Geodesy (IAG), under the umbrella of the International Gravity Field Service (IGFS). The main activities of ISG consist in collecting, analysing and redistributing local and regional geoid models, as well as organizing international schools on the geoid determination (Reguzzoni et al., 2021).