Directory Title: Alaska Geoid Heights (GEOID96)
Principal Investigator: Dr. Dennis G. Milbert
Contributing Organization: NOAA, National Geodetic Survey, N/NGS5
                           1315 East-West Highway, Room 9349
                           Silver Spring, MD 20910-3282
                           dennis@ngs.noaa.gov

Summary: This 2' x 4' geoid height grid for Alaska is distributed as 
a GEOID96 model.  The computation used 1.1 million terrestrial and 
marine gravity data held in the National Geodetic Survey gravity 
data base in July 1996    These data were augmented by gravity data 
contributions from NIMA (former Defense Mapping Agency).  By means of 
a Fast Fourier Transform (FFT) technique, high frequency corrections 
were made to an underlying EGM96 geopotential model through a remove, 
compute, and restore process.  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.  Unlike the grid for the conterminous United States, this 
GEOID96 grid does not incorporate GPS on leveled benchmarks.  This 
model is a gravimetric geoid in a geocentric, ITRF94(1996.0) reference 
frame.  It is necessary to subtract 12.0 cm from these values to obtain 
the geoid undulation between the best-fit global geopotential surface 
and the GRS80 ellipsoid (both expressed in a tide free system).  
Additional information is available at:
   http://www.ngs.noaa.gov/GEOID/geoid.html
We are particularly grateful to NIMA for their assistance and their 
data contributions.
