Preface
In July 1995 the XXI General Assembly of the International Union of Geodesy and
Geophysics was held in Boulder, Colorado. At this meeting the International Association of
Geodesy (lAG) organized a number of symposia to discuss scientific developments and future
directions in a number of areas. One of these symposia was G3, Global Gravity Field and Its
Temporal Variations. This symposium consisted of four invited and 36 contributed papers. The
contributed papers were given as oral or poster presentations. This proceedings volume represents
the written contributions of the four invited papers (appearing as the first four papers in the
volume) and 19 additional papers. The authors were asked to limit the length of their paper to
approximately ten pages, which, in some cases, did limit what an author wanted to say. The papers
in this volume have been placed in the same order as they were presented at the ruGG meeting.
A key theme of the symposium is given in the paper by Nerem, Klosko, and Pavlis where they
discuss applications of gravity field information in geodesy and oceanography. The significant
achievements in determining the gravity field in the ocean areas from satellite altimeter data is
discussed by Sandwell, Yale, McAdoo, and Smith. A review of time changes of the Earth's
gravity field from terrestrial measurements is given by Lambert et aI., and from satellite
perturbation techniques by Eanes and Bettadpur.
A description of new geopotential models is given in the paper by Tapley et al. with the
emphasis on the role of Topex GPS data; by Gruber et aI., and Motao et al who describe new
degree 360 potential coefficient models. Several papers describe the joint (NASA/DMA) project to
develop a new degree 360 model using previously unreleased terrestrial and altimeter data.
Trimmer and Manning describe the analysis of Geosat geodetic mission data for gravity field
information in the oceans; Kenyon and Pavlis discuss the surface gravity data to be used in the
model while Nerem et al. describe new satellite data with some early results of combination
solutions. Improved terrestrial gravity and elevation files are also discussed by Green and
Fairhead. Andersen, Knudsen, and Tscherning describe the use of ERS-1 geodetic mission data to
recover anomalies in an area west of Norway while the use of ERS-1 data to determine a high
resolution gridded mean sea surface is described in the paper by Anzenhofer, Gruber and Rentsch.
An important part of the geopotential model determination is the estimation and evaluation
process. Pavlis, Chan and Lerch, and Jekeli, describe methods and test results of different
procedures to follow in determining high degree potential coefficient models. Methods to evaluate
the geopotential models, once they have been estimated, are described by Burke et al. and Wnuk
and Wilczynska.
A major component of the symposium was the discussion of the time variations of the gravity
field of the Earth. The previously noted papers of Lambert et al. and Eanes and Bettadpur started
the discussion which was continued in several papers with recent results. Cazenave et al. reported
the use of eleven years of Lageos-1 and two years of Lageos-2 data to estimate the time variations
of the first three zonal harmonics. Nerem and Klosko describe time variations of the first four
zonal harmonics and polar motion linking the variations with implications for geophysical
modeling. Hartman and Rosborough describe simulation studies to aid in the understanding the
capability of satellite laser ranging data to estimate variations in the first four zonal harmonics.
Theoretical aspects of time variations in the gravity field of a deformable body are pointed out by
Grafarend, Engels, and Varga with a reference to a comprehensive paper published elsewhere. The
separability of the gravitational field signal and the indirect ocean tide signal in a satellite gravity
field mapping mission is discussed by Schrama.
v
In July 1995 the XXI General Assembly of the International Union of Geodesy and
Geophysics was held in Boulder, Colorado. At this meeting the International Association of
Geodesy (lAG) organized a number of symposia to discuss scientific developments and future
directions in a number of areas. One of these symposia was G3, Global Gravity Field and Its
Temporal Variations. This symposium consisted of four invited and 36 contributed papers. The
contributed papers were given as oral or poster presentations. This proceedings volume represents
the written contributions of the four invited papers (appearing as the first four papers in the
volume) and 19 additional papers. The authors were asked to limit the length of their paper to
approximately ten pages, which, in some cases, did limit what an author wanted to say. The papers
in this volume have been placed in the same order as they were presented at the ruGG meeting.
A key theme of the symposium is given in the paper by Nerem, Klosko, and Pavlis where they
discuss applications of gravity field information in geodesy and oceanography. The significant
achievements in determining the gravity field in the ocean areas from satellite altimeter data is
discussed by Sandwell, Yale, McAdoo, and Smith. A review of time changes of the Earth's
gravity field from terrestrial measurements is given by Lambert et aI., and from satellite
perturbation techniques by Eanes and Bettadpur.
A description of new geopotential models is given in the paper by Tapley et al. with the
emphasis on the role of Topex GPS data; by Gruber et aI., and Motao et al who describe new
degree 360 potential coefficient models. Several papers describe the joint (NASA/DMA) project to
develop a new degree 360 model using previously unreleased terrestrial and altimeter data.
Trimmer and Manning describe the analysis of Geosat geodetic mission data for gravity field
information in the oceans; Kenyon and Pavlis discuss the surface gravity data to be used in the
model while Nerem et al. describe new satellite data with some early results of combination
solutions. Improved terrestrial gravity and elevation files are also discussed by Green and
Fairhead. Andersen, Knudsen, and Tscherning describe the use of ERS-1 geodetic mission data to
recover anomalies in an area west of Norway while the use of ERS-1 data to determine a high
resolution gridded mean sea surface is described in the paper by Anzenhofer, Gruber and Rentsch.
An important part of the geopotential model determination is the estimation and evaluation
process. Pavlis, Chan and Lerch, and Jekeli, describe methods and test results of different
procedures to follow in determining high degree potential coefficient models. Methods to evaluate
the geopotential models, once they have been estimated, are described by Burke et al. and Wnuk
and Wilczynska.
A major component of the symposium was the discussion of the time variations of the gravity
field of the Earth. The previously noted papers of Lambert et al. and Eanes and Bettadpur started
the discussion which was continued in several papers with recent results. Cazenave et al. reported
the use of eleven years of Lageos-1 and two years of Lageos-2 data to estimate the time variations
of the first three zonal harmonics. Nerem and Klosko describe time variations of the first four
zonal harmonics and polar motion linking the variations with implications for geophysical
modeling. Hartman and Rosborough describe simulation studies to aid in the understanding the
capability of satellite laser ranging data to estimate variations in the first four zonal harmonics.
Theoretical aspects of time variations in the gravity field of a deformable body are pointed out by
Grafarend, Engels, and Varga with a reference to a comprehensive paper published elsewhere. The
separability of the gravitational field signal and the indirect ocean tide signal in a satellite gravity
field mapping mission is discussed by Schrama.
v