Study On The Draconitic Year Errors In GPS Station Coordinates

The high precision application of GPS in the study of geoscience must take tiny systematic errors into consideration.However,significant systematic errors(at mm level)with the period of about 351.4 days and its higher harmonics,which are called GPS draconitic year errors,have been found in diverse GPS-derived geodetic products.In this dissertation,the study has been conducted on GPS-derived station coordinate time series obtained from the first operational,the first reprocessing and second reprocessing campains within IGS by means of the Lomb-Scargle periodogram,focusing on the effects of updated data processing methodology on GPS draconitic year errors.The PPP coordinates were calculated using the 24-hour,8-hour,and 4-hour processing intervals,respectively,to analyze changes of the spectra of GPS draconitic year due to aliasing errors of sub-daily signals and ambiguity resolvtion.It's discussed that the latitudinal characteristics of improvement on GPS draconitic year errors within sud-daily solutions,as well as the effects of other factors such as diurnal and semi-diurnal signals in sub-daily solutions,center of mass correction(CMC)of ocean tidal loading,orbits and common mode errors(CME).What's more,we have also analyzed the effect of sub-daily solutions(namely 8 hours and 4 hours)on the seasonal variations in time series,and discussed other anomalous signals.Generally,the main findinds of the dissertation are as follows:(1)Pervasive harmonic signals with a fundamental of 1.04 cpy have been observed in the power spectra of GPS station position residuals for all components,and these anomalous periodic errors in station position residuals derived from the two reprocessing campaings are more remarkable,due to the improved accuracy of error models,while odd draconitic signals of the second reprocessing campaigns are weakened compared to the first reprocessing campaing,which can be attributed to the impact of the Earth radiation pressure.(2)Compared to the standard 24-hour solution,sub-daily solutions can effectively reduce the draconitic year errors in GPS station coordinate time series,indicating that the aliasing of sub-daily signals must contribute to the GPS draconitic year errors.According to the characteristics that the reduction of the draconitic year errors is related to the latitude,we can exclude the multipath errors to a certain extent.In the 8-hour and/or 4-hour solutions,semi-diural signal family with period of 11.73?12.28 hours and diural signal family with period of 22.96?25.14hours were observed,which were centered at 12 hours and 24 hours,respectively.It is concluded that semi-diural and diural signal families can explain some of the GPS draconitic year errors induced by frequency aliasing with standard 24-hour sampling.Ambiguity resolution can reduce GPS draconitic year errors,especially for the East component.However,as the fixing rate decrease with the processing session shorter,the East component get less improvement.(3)The inconsistency between the reference frame of ocean tidal loading used in PPP and that used when satellite orbit and clock products are produced will induce light draconitic singals at low frequencies.The spectrum differences between the two solutions(whether or not the CMC correction is added to the ocean tide)gradually decreased as the data processing session shortened,further illustrating that the aliasing.errors of the sub-daily tidals wave contribute to the GPS draconitic year errors.GPS orbit products contain a large number of GPS draconitic year errors and are transmitted to the station coordinates through PPP solution.PCA spatial filtering results show that the GPS draconitic year errors are highly spatially correlated,indicating that the station-related errors,such as multipath effects,are not the matin sources of the GPS draconitic year errors.(4)The statistical results show that sub-daily solutions help to weaken the annual and semi-annual signals in the station coordinate time series.Compared to the 24-hour solution,the mean and standard deviation of the differences between amplitude and phase of annual and semi-annual signals in 4-hour solution and that of geophysicalmodel are smaller,indicating that the 4-hour solution is more consistent with the geophysical model.(5)The spectral peaks at periods of 14.8 and 14.2 days correspond,respectively,to the aliasing periods of the semi-diurnal M2 tide and diurnal O1 tide with 24-hour processing session.While the 13.6-day periodic signal may on the one hand originate from Mf,and on the other hand may be related to the aliasing of M2 and O1 tides with samlping period at the repeat time of the GPS constellation.At the same time,some signals in semi-diural and diural signal families were consistend with the natural periods or aliasing periods of the ocean tides.So the accuracy of ocean tidal loading still needs to be improved.What's more,the spectral peaks at periods of 15.4,14.8,14.2,13.6,13.1,9.9,9.6 days were observed in GPS orbits,which are close the signals in the station coordinates.The residual anomalous signals in the 4-hour station coordinate time series may originate from the GPS orbit.(6)The distinct peak at period of 7.8 days can be observed in the stations coordinate time series,which are obtained by both GPS and GLONASS data or obtained with GPS orbit and clock products computed in a combined GPS and GLONASS data processing.What's more,there is an anomalous signal in the North direction of the station coordinate time series that is consistent with the Chandler period,which may be related to the incompletely modeled errors of pole tide.