VLBI geodetic precision
with different models
Erhu WEI, Jingnan LIU, Peijing PAN
This article introduces several common ocean tide models and nutation models, and computes
the global VLBI data during 2001-2007 using the OCCAM 5.0 software platform
Tidal fluctuations in water height and
currents will induce retrograde diurnal
variation of equatorial oceanic angular
momentum (OAM), hence small
perturbation on nutation at the level of
1mas and most important contributions
come from water height variations[9].
Considering the influence of anelasticity
covering effect, the ocean tidal effect,
electromagnetism coupling effect, which
produced from the liquid outer core and
solid core and the nonlinearity item. The
MHB_2000 nutation model improves the
accuracy of IAU 1980 nutation theory.
The method of experiment The data resource
In this experiment, we use the software of
OCCAM 5.0 and the data in 2001-2007[10]
computing the corresponding geodetic
parameters. Based on the needs of
the software, we choose the data of
moderate memory (about 1M) to
facilitate rapid comparative analysis.
The method of model combination
In order to compare the use of
different software models in the results between the levels of accuracy, we
classify these models into 6 items: I In the calculation of the daily
and sub-daily change of Earth
Orientation Parameters (EOP)
from ocean tide term, we choose
EANES model; in the calculation
of the precession and nutation, we
choose IAU1980 nutation model; II In the calculation of the daily
and sub-daily change of Earth
Orientation Parameters (EOP)
from ocean tide term, we choose
EANES model; in the calculation
of the precession and nutation, we
choose HERRING nutation model; III In the calculation of the daily
and sub-daily change of Earth
Orientation Parameters (EOP) from
ocean tide term, we choose EANES
model; in the calculation of the
precession and nutation, we choose
MHB_2000 nutation model; IV In the calculation of the daily
and sub-daily change of Earth
Orientation Parameters (EOP)
from ocean tide term, we choose
RAY model; in the calculation of
the precession and nutation, we
choose IAU1980 nutation model; V In the calculation of the daily
and sub-daily change of Earth
Orientation Parameters (EOP) from
ocean tide term, we choose RAY
model; in the calculation of the
precession and nutation, we choose
HERRING nutation model; VI In the calculation of the daily
and sub-daily change of Earth
Orientation Parameters (EOP) from
ocean tide term, we choose RAY
model; in the calculation of the
precession and nutation, we choose
MHB_2000 nutation model;
The criteria of precision compare
In the work of surveying, the power of
the observation is the relative numerical
indicator which denotes its precision. It
is used in weighing various observation
of different precision for handling
these observations. For one group of
observation, if its sigma is smaller,
then its power is larger; or if its sigma
is larger, its power is smaller. In thispaper, the constant “FACTOR” means
the value of the limitation for editing
the data, the OCCAM software then sets
this “FACTOR” value in the control
files “KVLBI.OPT” and “KVLBI_
IE.OPT”, it can compute the limitation
of the observation delay value subtract
the computation delay value. If the
difference between observation delay
value and computation delay value is
bigger than the “FACTOR” multiplies
the expectation of the sigma, that is
to say the precision obtained from
this observation is not good, in this
case, we will reduce the power of this
observation (explained with * in this
paper). If the number of the observations
being reduced is too much, then the
usability of this observation is small.
The data of CHI-SQ is one indicator
of reflecting the precision with kalman
filter method, if its value is close to 1,
then the precision of this result is good.
The analyze of the
experiment result
Based on the combination of the
above models, we compute the data
following the chronological order:
The compare result by
adopting the data of 2001
In calculating the data of the year 2001,
after the relevant solution, we choose
the better data 010424XE.NGS on April
24 to explain the result. The specific
calculating result please refer to table1
(I- VI represent various combination of
different models, the figures shown in this
table represent the value of CHI-SQ):
Table 1 the processing result
of 010424XE.NGS
In the data processing on April 24
2001, we can see that if we choose
ALGOPARK and FORTLEZA as
the reference station for adjustment,
in addition to the fourth group,
the effects of the others are not
ideal. After removing the results
of these two stations, we average
the other four stations, and then we
get the first group of average.
20 |
The analyze of the
experiment result
Based on the combination of the
above models, we compute the data
following the chronological order:
The compare result by
adopting the data of 2001
In calculating the data of the year 2001,
after the relevant solution, we choose
the better data 010424XE.NGS on April
24 to explain the result. The specific
calculating result please refer to table1
(I- VI represent various combination of
different models, the figures shown in this
table represent the value of CHI-SQ):
Table 1 the processing result
of 010424XE.NGS.
In the data processing on April 24
2001, we can see that if we choose
ALGOPARK and FORTLEZA as
the reference station for adjustment,
in addition to the fourth group,
the effects of the others are not
ideal. After removing the results
of these two stations, we average
the other four stations, and then we
get the first group of average.
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