expansions of the earth's gravitational potential.
Several models to
degree 360 have been developed since 1986 (Rapp and Cruz,
1986),
through the use of 30' x 30' mean anomalies instead of lOx 1
0
mean
anomalies. And the solutions starting from OSU89A/B (Rapp and pavlis
, 1990) have rigorously used ellipsoidal harmonics for the
analysis
of the terrestrial data to avoid the ellipsoidal
correction term
procedures used in the OSU1986 solutions. However, as progress in
the collection and compilation of new gravity field data is slow·,
improved geopotential models are released only at time intervals of
about five years (Basic et aI., 1989). In the case that the available
global models do not approximate the regionally existing gravity field
data very well, large data collection areas have to be used in order to
get good local gravity field solutions.
This certainly
makes
computations much more cumbersome and expensive, especially
the
application of collocation techniques might even be impossible.
Therefore, one convenient way is the improvement of an available
geopotential model by regional gravity field data, that can then be
used for local computations in connection with a small data collection
area. Weber and Zomorrodian (1988) have described the development of
high-degree model (Nmax=360) that are "tailored" to the gravity data in
a defined local area. Kearsley and Forsberg (1990)
suggests that
the geopotential models, fitted to the local gravity field,
may have
important applications in local or regional geoid solutions.
An
improved reference model will result if new data ( i. e. not used in the
evaluation of the potential coefficients of the original geopotential
model) becomes available. We present in this paper a new geopotential
model DQM94 that has been tailored to an updated set of gravity
anomalies for China. The calculation of the tailored model, complete to
degree and order 360, is based on the OSU91A coefficient set, that was
used as a start model. The new tailored model is compared with results
from the China GPS network, and several other tests have been performed.
Because only 1
0
x1° mean gravity anomalies of China have been used
in the evaluation of the OSU91A model (Rapp et al. ,
1991),
the
comparisons of the two models (DQM94 and OSU91A) with GPS/levelling
data in China show an improved accuracy of the DQM94 model.
THE METHOD
The method is summarized below and is based upon the outline given in
Weber and Zomorrodian (1988).
The standard representation of the earth's disturbing potential IS
taken as follows:
GM 00 a
n
T(r, e, /1,)=- I (-) X1IC:n>.YX1n>.( e, /1,)
(1)
r n=2 r m=-n
187
Several models to
degree 360 have been developed since 1986 (Rapp and Cruz,
1986),
through the use of 30' x 30' mean anomalies instead of lOx 1
0
mean
anomalies. And the solutions starting from OSU89A/B (Rapp and pavlis
, 1990) have rigorously used ellipsoidal harmonics for the
analysis
of the terrestrial data to avoid the ellipsoidal
correction term
procedures used in the OSU1986 solutions. However, as progress in
the collection and compilation of new gravity field data is slow·,
improved geopotential models are released only at time intervals of
about five years (Basic et aI., 1989). In the case that the available
global models do not approximate the regionally existing gravity field
data very well, large data collection areas have to be used in order to
get good local gravity field solutions.
This certainly
makes
computations much more cumbersome and expensive, especially
the
application of collocation techniques might even be impossible.
Therefore, one convenient way is the improvement of an available
geopotential model by regional gravity field data, that can then be
used for local computations in connection with a small data collection
area. Weber and Zomorrodian (1988) have described the development of
high-degree model (Nmax=360) that are "tailored" to the gravity data in
a defined local area. Kearsley and Forsberg (1990)
suggests that
the geopotential models, fitted to the local gravity field,
may have
important applications in local or regional geoid solutions.
An
improved reference model will result if new data ( i. e. not used in the
evaluation of the potential coefficients of the original geopotential
model) becomes available. We present in this paper a new geopotential
model DQM94 that has been tailored to an updated set of gravity
anomalies for China. The calculation of the tailored model, complete to
degree and order 360, is based on the OSU91A coefficient set, that was
used as a start model. The new tailored model is compared with results
from the China GPS network, and several other tests have been performed.
Because only 1
0
x1° mean gravity anomalies of China have been used
in the evaluation of the OSU91A model (Rapp et al. ,
1991),
the
comparisons of the two models (DQM94 and OSU91A) with GPS/levelling
data in China show an improved accuracy of the DQM94 model.
THE METHOD
The method is summarized below and is based upon the outline given in
Weber and Zomorrodian (1988).
The standard representation of the earth's disturbing potential IS
taken as follows:
GM 00 a
n
T(r, e, /1,)=- I (-) X1IC:n>.YX1n>.( e, /1,)
(1)
r n=2 r m=-n
187