The GEOID-GUAYAQUIL2021 model for the rural area of the Guayaquil Canton in Ecuador was calculated by the Universidad de las Fuerzas Armadas ESPE, Sangolquí, Ecuador. It is based on a non-conventional technique, such as Cokriging (Goovaerts, 1997), through the combination of GPS data/differential leveling and a densely sampled auxiliary variable. The GPS satellite positioning was performed using the Static Differential method through dual-frequency receivers in each point; regarding the level heights they were obtained by second-level differential leveling.

The geoid undulation from the EGM2008 model with spatial resolutions of 1 arc min was proposed as an auxiliary variable for the interpolation of geodetic undulation in combination with dispersed GPS data (Odera and Fukuda, 2015). Ordinary, Residual and Universal Cokriging and Kriging techniques were used and their results were compared to select the best for achieving accuracy. In particular, a “split-off” validation was performed by excluding a subset of data, repeating the processing, and then comparing the results with the one obtained with the full dataset. This validation yielded that the solution based on Universal Cokriging was the most accurate with an RMSE of 8 cm and RSR of 0.0282, obtained just with 66 samples (20% of the dataset). This model is presented as a practical alternative for obtaining level heights for various geoscience applications.

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).