The ColSCA-CASM2019 gravimetric geoid model has been computed by the Chinese Academy of Surveying and Mapping (CASM). 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 109.5°W ≤ longitude ≤ 102.5°W, 35.5°N ≤ latitude ≤ 39.5°N with a grid spacing of 1' in both latitude and in longitude. The height anomaly computation from the satellite gravity model GOCO05S, terrestrial and airborne gravity data is based on the spectral combination approach. Spectral weights of each dataset are determined by using the KTH error degree variance estimation method. A remove-compute-restore procedure, based on the EGM2008 global gravity model, is applied to account for the contribution outside local gravity data coverage. A residual terrain correction is computed from the SRTM model to consider the short wavelength components of gravity field generated by the high frequency part of topography. Height anomalies are converted to geoid undulations by using the refined Bouguer anomalies and the gradient of the gravitational potential (Flury and Rummel, 2009). The accuracy of the geoid model, when compared against GSVS17 GPS/leveling, is equal to 3.5 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).