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 20012007[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 subdaily 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 subdaily 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 subdaily 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 subdaily 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 subdaily 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 subdaily 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 CHISQ 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 CHISQ): 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 CHISQ): 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.
Table 1 the processing result of 010424XE.NGS
Table 2 the processing result of 020711XE.NGS
Table 3 the processing result of 031021XE.NGS
Table 4 the processing result of 040601XA.NGS
