GEOID90: A high-resolution geoid for the United States


  • D. G. Milbert

    1. National Geodetic Survey, N/CG18, Advanced Geodetic Science Branch, National Geodetic Survey, National Ocean Service, NOAA, Rockville, MD 20852
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Recently, geodesy has witnessed a renaissance in geoid computation. The advances over the past decade have taken place at all wavelengths, and have brought forth major improvements in accuracy. An example of a long-wavelength global gravitation model is the GEM-T2 (Goddard Earth Model) solution of Marsh et al. [1989], which is complete to degree and order 36, and incomplete to degree 50. Rapp and Pavlis [1990] have computed a pair of solutions, 0SU89A and 0SU89B (Ohio State University), which are spherical harmonic models of the Earth's geopotential complete to degree and order 360. Although termed high degree global models, these solutions provide the geoid to what we may now consider a medium length scale–about 50-km resolution. High-resolution geoid height modeling has shown the greatest advances in accuracy. Forsberg [1990] computed a geoid model for the Nordic area on a 5-km grid, and obtained 3–7 cm standard deviations when compared to Global Positioning System (GPS) and leveling in local networks of 50–100 km in extent.