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Regional Models

American Samoa Islands (USGG09/GEOID09)


  Authors: D.R. Roman, Y.M. Wang     Created: 2012    Resp: D.R. Roman  
      Status: PUBLIC    
Description:
USGG2009 is a gravimetric geoid model for the American Samoa Islands computed by the National Geodetic Survey (NGS). It is referred to the GRS80 normal ellipsoid in the ITRF00 frame. It has a 1'x1' spatial resolution in latitude and longitude. It is based on terrestrial and ship-borne surface gravity data from the NGS database and DNSC08 altimetry-derived gravity over the oceans. The geoid determination is performed in the framework of a remove-restore procedure, where long wavelengths come from the EGM2008 geopotential model. In particular the USGG2009 model is based on the use of the one-dimensional spherical Fast Fourier Transform (FFT) with a modified Stokes kernel that retained all signal below degree 120 from EGM2008. The digital elevation model used for the terrain correction has a 3"x3" spatial resolution and it is mainly based on SRTM-DTED1. By comparing the USGG2009 model with the available 22 GPS/levelling benchmarks (ITRF00/NAVD88) in American Samoa Islands (actually in Tutuila Island only), a systematic offset is present with an average of 53.8 cm and a standard deviation of 5.3 cm. The GEOID09 hybrid model for the American Samoa Islands is computed by fitting these GPS/levelling data (NAD83/NAVD88) with the USGG2009 gravimetric model, also taking into account the relationships between NAD83 and ITRF00 reference frames. The fitting is performed by multi-matrix least squares collocation after removing a trend to the residuals. Therefore the GEOID09 model directly relates NAD83(PACP00) ellipsoid heights and NAVD88 orthometric heights. The differences between GEOID09 and GPS/levelling (NAD83/NAVD88) benchmarks have an average of -0.1 cm and a standard deviation of 2.0 cm.  


References:
Y.M. Wang, J. Saleh, X. Li, D.R. Roman (2012). The US Gravimetric Geoid of 2009 (USGG2009): model development and evaluation. Journal of Geodesy, 86(3), pp. 165–180.
D.R. Roman, Y.M. Wang, J. Saleh, X. Li. (2010). Geodesy, geoids, and vertical datums: A perspective from the US National Geodetic Survey. Proceedings of the FIG Congress 2010, Facing the Challenges – Building the Capacity Sydney, Australia.
D.R. Roman, Y.M. Wang, J. Saleh, X. Li. (2009). Final National Models for the United States: Development of GEOID09. Technical Report, NOAA/National Geodetic Survey.
D.R. Roman, Y.M. Wang, J. Saleh, X. Li. (2009). A Gravimetric Geoid Model for the United States: The Development and Evaluation of USGG2009. Technical Report, NOAA/National Geodetic Survey.


American Samoa Island