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Regional Models

Alaska (GEOID99)


  Authors: D.A. Smith, D.R. Roman     Created: 1999    Resp: D.R. Roman  
      Status: PUBLIC    

Description:
GEOID99 is a gravimetric geoid model for Alaska computed by the National Geodetic Survey (NGS). It is referred to the GRS80 normal ellipsoid in the ITRF96 frame (epoch 1997.0). It has a 1'x1' spatial resolution in latitude and longitude. Unlike the grid for the conterminous United States, this GEOID99 model does not incorporate GPS/levelling data. The gravimetric geoid determination for Alaska is based on the same techniques as G99SSS for the conterminous United States, namely on the use of the one-dimensional spherical Fast Fourier Transform (FFT) to evaluate Stokes' integral. It is performed in the framework of a remove-restore procedure, where long wavelengths come from the EGM96 geopotential model, while the terrain correction is computed by using a digital elevation model with a spatial resolution of 30''x60''. Due to poorer data coverage, error estimates for GEOID99 in this region are larger than the ones of G99SSS in the conterminous United States, especially in the tectonically active areas of southern Alaska.

References:
D.A. Smith, D.R. Roman (2001). GEOID99 and G99SSS: 1-arc-minute geoid models for the United States. Journal of Geodesy, 75(9), pp. 469-490.

Alaska