THE 1995 GFZ HIGH RESOLUTION GRAVITY MODEL
Thomas Gruber, Michael Anzenhofer, Matthias Rentsch
GeoForschungsZentrum Potsdam (GFZ), Division 1
D-P AF, D-82230 Oberpfaffenhofen, Germany
e-mail: adp@dfd.dlr.de
INTRODUCTION
In sequence of the GFZ93 high resolution gravity models (Gruber Th., et al, 1993) a new
model, named GFZ95A, which is complete to degree and order 360 of a spherical
harmonic series was computed. The model is based on new data sets, which were collected
during the last months. This new data promises a major step towards a more precise high
resolution gravity model. Especially from new available data over CIS (Community of
Independent States) major progress can be expected with respect to the former models,
which were based on predicted data in this area.
The model is computed by a combination of a long wavelength a-priori gravity model,
mean gravity anomalies and a mean sea surface height model. As a-priori information the
most recent GFZ/GRGS combined gravity model from the GRIM4 series (GRIM4-C4B),
which is complete to degree and order 72 is used. As mean gravity anomalies data set,
basically the July 1989 and October 1990 Ohio State University ftles are used. New mean
anomalies in Asia and South America, provided by BGI are incorporated. Over the
oceans a two years ERS-1 mean sea surface is used, which is based on the complete 35
day repeat cycle phase (multidisciplinary phase) and some additional 3 day repeat cycles.
From terrestrial gravity anomalies and sea surface heights separate normal equations are
generated, using the block-diagonal technique with preconditioned data sets. For lower
degree coefficients the a-priori solution coefficients are added as observations. All normal
equations are combined and successively solved by order to the GFZ95A solution. To
overcome the limitations, caused by using the block-diagonal technique, a new strategy is
presented, which will be used for the next model update.
DATA SOURCES
The GFZ95A solution is computed by a combination of a long wavelength a-priori gravity
field solution, mean gravity anomalies and mean sea surface heights. Each data type is
prepared in a special way, before spherical harmonic normal equations are generated. The
combination is done in terms of adding the different normal equation systems. In this
chapter the different data sets, used for the model are described.
As a-priori solution the new GRIM4-C4B model, complete to degree and order 72 is used
(Schwintzer P. et al, 1995). This solution is a combination of a satellite-only model,
completely derived through orbit perturbation analysis technique, surface gravity and sea
surface data. In the satellite-only solution all together optical, laser and microwave tracking
61
Thomas Gruber, Michael Anzenhofer, Matthias Rentsch
GeoForschungsZentrum Potsdam (GFZ), Division 1
D-P AF, D-82230 Oberpfaffenhofen, Germany
e-mail: adp@dfd.dlr.de
INTRODUCTION
In sequence of the GFZ93 high resolution gravity models (Gruber Th., et al, 1993) a new
model, named GFZ95A, which is complete to degree and order 360 of a spherical
harmonic series was computed. The model is based on new data sets, which were collected
during the last months. This new data promises a major step towards a more precise high
resolution gravity model. Especially from new available data over CIS (Community of
Independent States) major progress can be expected with respect to the former models,
which were based on predicted data in this area.
The model is computed by a combination of a long wavelength a-priori gravity model,
mean gravity anomalies and a mean sea surface height model. As a-priori information the
most recent GFZ/GRGS combined gravity model from the GRIM4 series (GRIM4-C4B),
which is complete to degree and order 72 is used. As mean gravity anomalies data set,
basically the July 1989 and October 1990 Ohio State University ftles are used. New mean
anomalies in Asia and South America, provided by BGI are incorporated. Over the
oceans a two years ERS-1 mean sea surface is used, which is based on the complete 35
day repeat cycle phase (multidisciplinary phase) and some additional 3 day repeat cycles.
From terrestrial gravity anomalies and sea surface heights separate normal equations are
generated, using the block-diagonal technique with preconditioned data sets. For lower
degree coefficients the a-priori solution coefficients are added as observations. All normal
equations are combined and successively solved by order to the GFZ95A solution. To
overcome the limitations, caused by using the block-diagonal technique, a new strategy is
presented, which will be used for the next model update.
DATA SOURCES
The GFZ95A solution is computed by a combination of a long wavelength a-priori gravity
field solution, mean gravity anomalies and mean sea surface heights. Each data type is
prepared in a special way, before spherical harmonic normal equations are generated. The
combination is done in terms of adding the different normal equation systems. In this
chapter the different data sets, used for the model are described.
As a-priori solution the new GRIM4-C4B model, complete to degree and order 72 is used
(Schwintzer P. et al, 1995). This solution is a combination of a satellite-only model,
completely derived through orbit perturbation analysis technique, surface gravity and sea
surface data. In the satellite-only solution all together optical, laser and microwave tracking
61