Description:
The Alaska gravimetric geoid extends
from 49N to 72N and from 172E to 126W
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 Alaska geoid extends
from 49N to 72N and from 172W to 126W
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:DATA2017015010667880
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