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Mexico North-South Deflections (DMEX97)
This 2’ surface deflection of the vertical grid for Mexico, and North-Central is the DMEX97 model. The computation used about one million terrestrial and marine gravity measurements heldin the NGS database as of March 1997. These gravity measurements were augmented by data contributions from NGA (former National Imagery and Mapping Agency), and satellitealtimeter derived gravity anomalies computed by Sandwell and Smith (1997). The deflection values themselves were obtained by numerical differentiation of cubic spline models along the meridians of the MEXICO97 geoid grid, followed by a correction for curvature of the plumb line, yielding surface deflections of the vertical. Since the EGM96 model was used to fill data gaps south of 20 degrees North latitude, the deflections in and around those regions will be less accurate. The gravity values are based on the International Gravity Standardization Net 1971 (IGSN71). The deflections are referred to Geodetic Reference System 1980 (GRS80) ellipsoidal normals oriented in the International Terrestrial Reference Frame 1994 (ITRF94(1996.0)). We are particularly grateful to NGA (former National Imagery and Mapping Agency) for their assistance and their data contributions.