PRELIMINARY RESULTS FROM THE
JOINT GSFC/DMA GRAVITY MODEL PROJECT
R. S. Nerem and F. J. Lerch
NASA/Goddard Space Flight Center, Space Geodesy Branch, Code 926,
Greenbelt, MD, 20771, U.S.A.
R. Salman, R. Trimmer, and S. Kenyon
Defense Mapping Agency, Aerospace Center, 3200 S. 2nd St., St. Louis,
MO, 63118, U.S.A.
R. H. Rapp
Dept. of Geodetic Science and Surveying, The Ohio State University,
Columbus, OH 43210, U.S.A.
N. K. Pavlis, S. M. Klosko, J. C. Chan, M. H. Torrence, Y. M. Wang,
and R. G. Williamson
Hughes STX, Greenbelt, MD, 20770, U.S.A.
E. C. Pavlis
Dept. of Astronomy, Univ. of Maryland, College Park, MD 20742, U.S.A.
INTRODUCTION
The NASA Goddard Space Flight Center (GSFC) and the U.S. Defense Mapping
Agency (DMA) with the aid of other organizations such as The Ohio State University are
cooperating in a joint effort to determine a significantly improved degree 360 spherical
hannonic model representing the Earth's gravitational potential. This m~w model will be of
immediate use in defining an undulation model that will be the basis for an enhanced WGS84 geoid, but the model will be general in use and will provide enhancements for a wide
range of applications. The development of the new model is driven, in part, by the need to
determine an accurate geoid undulation model that will be the vertical reference surface for
WGS-84. In addition, the new geoid model will help satisfy increasingly important studies
in ocean circulation (sea surface topography) and geodetic positioning through GPS.
The new model, for which preliminary versions are discussed, incorporates satellite
tracking data from GSFC's extensive archives, as well as a variety of new data including
GPS tracking of several satellites. The surface gravity data used are based on an updated
30' mean anomaly data base developed by DMA. This data set incorporates a substantial
amount of new data that has, become available in Europe, the former Soviet Union (FSU),
South America, Greenland, Africa, Asia and Antarctica. Anomaly values in areas such as
Canada, the United States and Australia are based on updated data files. These data are
used, after suitable corrections, to form normal equations that are combined with the
satellite-derived normal equations.
In addition, 30'x30' mean anomalies derived from the Geosat Geodeltic Mission satellite
altimeter data are used in the project, supplemented with anomalies computed from ERS-l
altimetry where Geosat does not provide coverage. The file is merged with the flles based
on the surface terrestrial data. In areas where no data exists, anomaly estimates are made
92
JOINT GSFC/DMA GRAVITY MODEL PROJECT
R. S. Nerem and F. J. Lerch
NASA/Goddard Space Flight Center, Space Geodesy Branch, Code 926,
Greenbelt, MD, 20771, U.S.A.
R. Salman, R. Trimmer, and S. Kenyon
Defense Mapping Agency, Aerospace Center, 3200 S. 2nd St., St. Louis,
MO, 63118, U.S.A.
R. H. Rapp
Dept. of Geodetic Science and Surveying, The Ohio State University,
Columbus, OH 43210, U.S.A.
N. K. Pavlis, S. M. Klosko, J. C. Chan, M. H. Torrence, Y. M. Wang,
and R. G. Williamson
Hughes STX, Greenbelt, MD, 20770, U.S.A.
E. C. Pavlis
Dept. of Astronomy, Univ. of Maryland, College Park, MD 20742, U.S.A.
INTRODUCTION
The NASA Goddard Space Flight Center (GSFC) and the U.S. Defense Mapping
Agency (DMA) with the aid of other organizations such as The Ohio State University are
cooperating in a joint effort to determine a significantly improved degree 360 spherical
hannonic model representing the Earth's gravitational potential. This m~w model will be of
immediate use in defining an undulation model that will be the basis for an enhanced WGS84 geoid, but the model will be general in use and will provide enhancements for a wide
range of applications. The development of the new model is driven, in part, by the need to
determine an accurate geoid undulation model that will be the vertical reference surface for
WGS-84. In addition, the new geoid model will help satisfy increasingly important studies
in ocean circulation (sea surface topography) and geodetic positioning through GPS.
The new model, for which preliminary versions are discussed, incorporates satellite
tracking data from GSFC's extensive archives, as well as a variety of new data including
GPS tracking of several satellites. The surface gravity data used are based on an updated
30' mean anomaly data base developed by DMA. This data set incorporates a substantial
amount of new data that has, become available in Europe, the former Soviet Union (FSU),
South America, Greenland, Africa, Asia and Antarctica. Anomaly values in areas such as
Canada, the United States and Australia are based on updated data files. These data are
used, after suitable corrections, to form normal equations that are combined with the
satellite-derived normal equations.
In addition, 30'x30' mean anomalies derived from the Geosat Geodeltic Mission satellite
altimeter data are used in the project, supplemented with anomalies computed from ERS-l
altimetry where Geosat does not provide coverage. The file is merged with the flles based
on the surface terrestrial data. In areas where no data exists, anomaly estimates are made
92