The Mexican gravimetric geoid: GGM04

GGM04 is the first gravimetric geoid model for Mexico computed by INEGI on 2004 (GGM stands for Geoide Gravimetrico Mexicano). The main input of terrestrial gravity data included 100,000 points inside Mexico and nearly 400,000 more over neighboring countries, all unfiltered. The source for this dataset was INEGI, PEMEX and US-DMA. Marine gravity was derived from Topex/Poseidon altimetry. The used digital terrain models were Mexico-CEM1, US-NED and SRTM. A reference satellite geoid model was also used up to degree and order 40 from the geopotential model GRIM4-S4. The computation methodology was based on the Stokes-Helmert technique with the software provided by the University of New Brunswick (UNB, Canada). The resulting GGM04 model is referred to the GRS80 reference ellipsoid in the ITRF92 frame (epoch 1988.0). The error RMS of geoidal heights is 58 cm, estimated from 1377 GPS/leveling data. 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.