Description:
The Samoa Island gravimetric geoid extends from 11S to 17S and from 174W to 168W with
a spatial resolution of 1'x1'. It is a pure gravimetric geoid included into the USGG2012
(U.S. Gravimetric Geoid) model. The geoid heights are referred to the
GRS80 ellipsoid in the IGS08 (epoch 2005.0) reference frame. The reference
global Earth gravity model is EGM2008, with the incorporation of GOCE and
GRACE information from the GOCO02S model. Since EGM2008 accounts for the
effects of the terrain through about 5' (10 km), SRTM 3" (90 m) data were
used to produce a Residual Terrain Model between 3" and 5', accounting for
much of the high frequency variability seen in the residual gravity signal.
The remove-restore technique employed for the geoid determination is basically
the same of the one used for the previous release (USGG2009), see Wang et al.
(2012), J Geod 86:165-180. Additional information is available at:
http://www.ngs.noaa.gov/GEOID/. The one line header contains the following
parameters:
- Southernmost North latitude
- Westernmost East longitude
- Distance interval in latitude
- Distance interval in longitude
- Number of rows
- Number of columns
- Always equal to one
While the Hybrid Samoa Island geoid extends from 11N to 17N and from 174W to 168W with a
spatial resolution of 1'x1'. It is a hybrid geoid included into the GEOID12A model,
obtained by fitting the corresponding USGG2012 model to GPS-leveling data.
The geoid heights are referred to the GRS80 ellipsoid in the NAD 83 (epoch 2010.0)
reference frame), which is the official geometric datum of the U.S. National Spatial Reference
System. The reference global Earth gravity model is EGM2008, with the incorporation of GOCE and
GRACE information from the GOCO02S model. SRTM data were used to produce a Residual Terrain Model
between 3" and 5', accounting for much of the high frequency variability seen in the residual
gravity signal.
After detecting some defects in the GPS/levelling used to create GEOID12, GEOID12A was developed as a replacement.
In particular changes impacted regions in the states of Alabama, Mississippi, Louisiana, Texas, Oklahoma, and Wisconsin.
There were also some changes in Canada. However, GEOID12A, as with all previous hybrid geoid models (GEOID09, GEOID03),
should not be used in Canada or Mexico or in ocean areas more than 30 km offshore. The regions outside of the Conterminous
United States were unaffected by these changes, but the name of the model for those regions was changed to GEOID12A for
consistency. GEOID12B is a further replacement of GEOID12A with changes only for the Puerto Rico/U.S. Virgin Islands region
based on a corrected set of GPS/levelling data. In all areas other than the Puerto Rico/U.S. Virgin Islands region, GEOID12B
is identical to GEOID12A.
Additional information is available at: http://www.ngs.noaa.gov/GEOID/.
References:
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
D.R. Roman, Y.M. Wang, W. Henning, J. Hamilton (2004). Assessment of the New
National Geoid Height Model - GEOID03. Surveying and Land Information Science,
64(3), pp. 153-162.
Y.M. Wang, J. Saleh, X. Li, D.R. Roman (2012). The U.S. Gravimetric Geoid of
2009 (USGG2009): Model Development and Evaluation. Journal of Geodesy, 86(3),
pp. 165-180. DOI: 10.1007/s00190-011-0506-7
Web of Science ID:
DRCI:DATA2015229007462431
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