Description:
This 2' geoid height grid
for Mexico, and North-Central America,
is the MEXICO97 geoid model. The
computation used about one million
terrestrial and marine gravity
measurements held in the NGS database
as of March 1997. These gravity
measurements were augmented by data
contributions from NIMA, and satellite
altimeter-derived gravity anomalies
computed by Sandwell and Smith (1997).
Large data gaps south of 20 degrees
North latitude were filled with
15'x15' gravity values derived from
the EGM96 global geopotential model.
This helped control interpolation
errors across the data gaps during the
gridding of terrain corrected Bouguer
anomalies. After gridding of the
Bouguer anomalies, the Bouguer plate
was restored, a degree 360 model of
gravity anomalies (from EGM96) was
removed, and the residual free-air
anomalies in the data gaps (south of
20 degrees North Latitude) were
zeroed. (This zeroing was found to be
the best way currently available to
yield a reasonable geoid in the data
gaps). The residual Faye anomalies
were converted to residual co-geoid
undulations through a 1-D FFT
formulation of Stokes' integral, and
finally the EGM96 undulation model was
restored, and the indirect effect
applied. This means that in the data
gaps, long wavelength information is
provided by EGM96, short wavelength
information is provided by the 2'x2'
DTED (during the application of the
indirect effect), but medium
wavelength information (usually
provided by gravity measurements) is
missing altogether. Although the exact
accuracy of the geoid in the data gaps
is difficult to ascertain, the quoted
accuracy for EGM96 (which is the
primary source of geoid information in
the data gaps) is below 50 cm in these
areas. The gravity values are based on
the International Gravity
Standardization Net 1971 (IGSN71). The
geoid heights are referred to the
Geodetic Reference System 1980 (GRS80)
ellipsoid, centered at the origin of
the International Terrestrial
Reference Frame 1994 (ITRF94(1996.0)).
Additional information is available
at:
http://www.ngs.noaa.gov/GEOID/models.shtml
We are particularly grateful to NIMA
for their assistance and their data
contributions.
References:
D.A. Smith (1997). Mexico geoid heights (MEXICO97). NOAA/National Geodetic Survey of the United States of America.
D.A. Smith, D.G. Milbert (1999). The GEOID96 high resolution geoid height model
for the United States. Journal of Geodesy,
73(5), pp. 219-236. DOI: 10.1007/s001900050239
Web of Science ID:
DRCI:DATA2019017015400524
|
