THE ALTIMETRY DERIVED GRAVITY ANOMALIES TO BE
USED IN COMPUTING THE JOINT DMAINASA EARTH
GRAVITY MODEL
Ronald G. Trimmer and Dennis M. Manning
Defense Mapping Agency, Geodesy & Geophysics Department
3200 South Second St., Mail Stop L-41, St. Louis, MO. 63118-3399 USA
314 260-1007, TrimmerR@dma.gov, ManningD@dma.gov,
ABSTRACT. DMA and NASA are producing an improved 360 degree and order Earth
Gravity Model. The derived gravity data sets are the most accurate and complete ever used
in such model development. One of the major data sets is a satellite altimetry derived 30'
mean gravity anomaly fIle. An altimetry working group including members from DMA,
NASA, and Ohio State University made decisions on sources, data preparation, algorithms,
and evaluation of this altimetry fIle.
The major data source for this altimetry fIle is the GEOSAT Geodetic Mission data. An
important step in the GEOSAT data preparation was the application of the NASA Dynamic
Sea Surface Topography model derived from Topex and ERS-l data. Anomalies computed
by KMS and NOAA from ERS-l and other altimetry data were used in the near-polar
regions and a few near-shore areas. Comparisons with high-quality DMA and BGR shipborne gravity observations illustrate the quality and consistency of the fIle.
INTRODUCTION
The Defense Mapping Agency(DMA) and the National Aeronautics and Space
Administration/Goddard Space Flight Center(NASNGSFC) are producing an improved 360
degree and order Earth Gravity Model(EGM). The goal is a global 30' resolution geoid
with an absolute accuracy of + 0.5 meter. In order to extend a satellite only model to a
combination solution model of this resolution, an accurate worldwide 30'x30' mean gravity
anomaly file is required. A major portion of this 30'x30' file is the satellite altimetry derived
30' mean gravity anomaly file that is the subject of this paper.
The altimetry anomaly file compiled for this project was pieced together from GEOSAT,
ERS-l, and multiple source derived anomalies. Anomalies derived from the European
Space Agency's (ESA) ERS-l data were used mainly to extend the coverage of DMA's
GEOSAT anomalies in the near-polar areas. The ERS-l anomalies were provided by the
Danish National Survey and Cadastre or Kort-og Matrikelstyrelsen(KMS) and by the
National Oceanic and Atmospheric Administration(NOAA).
KMS and NOAA provided values in the summer of 1995. These were incorporated into
the altimetry file that was provided to NASA in October 1995. This file is an altimetry only
file. In most cases, in the water areas, altimetry by itself provides the most accurate mean
gravity anomalies. In some areas around Greenland and north of Alaska and Canada,
airborne anomalies in water areas may be used in the model computation.
Comparisons with high quality marine survey data, indicate that in general the GEOSAT
anomalies are slightly better than the ERS-l anomalies overall and significantly better in
high frequency areas. The ERS-l anomalies made an important contribution by extending
71
USED IN COMPUTING THE JOINT DMAINASA EARTH
GRAVITY MODEL
Ronald G. Trimmer and Dennis M. Manning
Defense Mapping Agency, Geodesy & Geophysics Department
3200 South Second St., Mail Stop L-41, St. Louis, MO. 63118-3399 USA
314 260-1007, TrimmerR@dma.gov, ManningD@dma.gov,
ABSTRACT. DMA and NASA are producing an improved 360 degree and order Earth
Gravity Model. The derived gravity data sets are the most accurate and complete ever used
in such model development. One of the major data sets is a satellite altimetry derived 30'
mean gravity anomaly fIle. An altimetry working group including members from DMA,
NASA, and Ohio State University made decisions on sources, data preparation, algorithms,
and evaluation of this altimetry fIle.
The major data source for this altimetry fIle is the GEOSAT Geodetic Mission data. An
important step in the GEOSAT data preparation was the application of the NASA Dynamic
Sea Surface Topography model derived from Topex and ERS-l data. Anomalies computed
by KMS and NOAA from ERS-l and other altimetry data were used in the near-polar
regions and a few near-shore areas. Comparisons with high-quality DMA and BGR shipborne gravity observations illustrate the quality and consistency of the fIle.
INTRODUCTION
The Defense Mapping Agency(DMA) and the National Aeronautics and Space
Administration/Goddard Space Flight Center(NASNGSFC) are producing an improved 360
degree and order Earth Gravity Model(EGM). The goal is a global 30' resolution geoid
with an absolute accuracy of + 0.5 meter. In order to extend a satellite only model to a
combination solution model of this resolution, an accurate worldwide 30'x30' mean gravity
anomaly file is required. A major portion of this 30'x30' file is the satellite altimetry derived
30' mean gravity anomaly file that is the subject of this paper.
The altimetry anomaly file compiled for this project was pieced together from GEOSAT,
ERS-l, and multiple source derived anomalies. Anomalies derived from the European
Space Agency's (ESA) ERS-l data were used mainly to extend the coverage of DMA's
GEOSAT anomalies in the near-polar areas. The ERS-l anomalies were provided by the
Danish National Survey and Cadastre or Kort-og Matrikelstyrelsen(KMS) and by the
National Oceanic and Atmospheric Administration(NOAA).
KMS and NOAA provided values in the summer of 1995. These were incorporated into
the altimetry file that was provided to NASA in October 1995. This file is an altimetry only
file. In most cases, in the water areas, altimetry by itself provides the most accurate mean
gravity anomalies. In some areas around Greenland and north of Alaska and Canada,
airborne anomalies in water areas may be used in the model computation.
Comparisons with high quality marine survey data, indicate that in general the GEOSAT
anomalies are slightly better than the ERS-l anomalies overall and significantly better in
high frequency areas. The ERS-l anomalies made an important contribution by extending
71