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Final report presented by partner UNIPD for the period 01 April2003 - 31 July 2006

Caporali A., Facchinetti C., Bonafede L.

Reports on Geodesy

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2006

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z. 3/78

85-155

EN

Within the Project our group has been responsible of WP6, which addresses the stability of time series of coordinates of GPS stations used in the project. In addition we have supported WP1, WP4, WP7 and WP10.1, as scheduled. The time series we have analysed result from WP1 and WP5. We have combined normal equations from the EUREF network, and selected those stations which are relevant to the CERGOP 2 project. Likewise for Italian and Austrian stations we have stacked normal equations pertaining the national networks, and obtained time series which are useful to the science part of the Project. Finally we have addressed the normai equations of the CEGRN campaigns, up to the CEGRN 03 campaign, constructed time series and checked for their continuity. An in depth analysis of the time series was done for those sites which have been active with continuity for at least three years. We did this analysis for all the stations which met this requisite, including time series of a number of stations computed by the Austrian partner OLG. The analysis consisted in the identification, in the time and frequency domains of specific signatures, typically annual and semi annual, affecting the time series and can be of various origin, such as seasonal water flow or thermal dilatation of the antenna mount. After removal of the periodic signals, the power spectral density has been computed and the white and coloured components in the noise could be characterized. We report in most cases flicker phase noise at low frequencies and white noise at higher frequencies (>2 cycles/year), with a few exceptions in which the noise is white at all frequencies. A few stability problems are reported. In particular our own ASIA station was affected by mount instability in connection to a heavy snow storm in February 2006. This event was promptly noticed from the analysis and the mount problem could be solved. We have checked for local instabilities by looking at deviations of the estimated velocities from the expected pattern. We have verified that the stations contributing to the project have velocities agreeing with theoretical predictions. When this does not happen, then the station in most cases has a marginal tracking his tory, and we suspect that the discrepancies are attributable to a weak data set, more than true instability. The contribution to the Project includes, besides the data analysis part, two new permanent stations which were installed in Asiago and Rovigo as part of the Project, and regularly operated. Two doctoral stipendia have been awarded, and a Web page dedicated to our WP6 has been constructed, regularly maintained and linked to the Project's web page.

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Final report presented by partner UNIPD for the period 01 april 2003 - 31 july 2006

Caporali A., Facchinetti C., Bonafede L.

Reports on Geodesy

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2006

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z. 4/79

399-417

EN

Within the Project our group has been responsible ofWP6, which addresses the stability of time series of coordinates of GPS stations used in the project. In addition we have supported WP1, WP4, WP7 and WP10.1, as scheduled. The time series we have analysed result from WP1 and WP5. We have combined normal equations from the EUREF network, and selected those stations which are relevant to the CERGOP 2 project. Likewise for Italian and Austrian stations we have stacked normal equations pertaining the national networks, and obtained time series which are useful to the science part of the Project. Finally we have addressed the normal equations of the CEGRN campaigns, up to the CEGRN 03 campaign, constructed time series and checked for their continuity. An in depth analysis of the time series was done for those sites which have been active with continuity for at least three years. We did this analysis for all the stations which met this requisite, including time series of a number of stations computed by the Austrian partner OLG. The analysis consisted in the identification, in the time and frequency domains of specific signatures, typically annual and semi annual, affecting the time series and can be of various origin, such as seasonal water flow or thermal dilatation of the antenna mount. After removal of the periodic signals, the power spectral density has been computed and the white and coloured components in tte noise could be characterized. We report in most cases flicker phase noise at low frequencies and white noise at higher frequencies (>2 cycles/year), with a few exceptions in which the noise is white at all frequencies. A few stability problems are reported. In particular our own ASIA station was affected by mount instability in connection to a snow storm in February 2006. This event was promptly noticed from the analysis and the mount problem could be solved. We have checked for local instabilities by at deviations of the estimated velocities from the expected pattern. We have verified that the stations contributing to the project have velocities agreeing with theoretical predictions. When this does not happen, then the station in most cases has a marginal tracking history, and we suspect that the discrepancies are attributable to a weak data set, more than true instability. Tie contribution to the Project includes, besides the data analysis part, two new permanent stations which were installed in Asiago and Rovigo as part of the Project, aad regularly operated. Two doctoral stipendia have been awarded, and a Web page to our WP6 has been constructed, regularly maintained and linked to the Projects web page.

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MID term report presented by partner UNIPD for the period 01 April 2004 - 30 September 2004

Caporali A., Facchinetti C., Gallini G.

Reports on Geodesy

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2004

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nr 4/71

219--242

EN

Partner UNIPD is responsible for WP6 Time series analysis and provides support to a number of other related WP's. The output of WP6 is foreseen every third month, beginning month 6. At this stage (month 18) we report on the successful generation of time series for all the permanent stations for which we have the data available, that is the EPN stations plus a number of Austrian and Italian permanent stations which are not part of the EPN. Our analysis includes the statistical and spectral analyses of the time series, whenever it is meaningful, i.e. for time series longer than 3 years. The analysis is based on the processing of normal equation files. Each one of them is obtained from the combination of two normal equations for each week, and the multi year solution embodies constraints on the position and velocity datum which are considered as state of the art. According to this combination scheme, more normal equations can be combined, yielding a unified network. We have also developed the presentation and communication framework for our results, in the form of a web page. As soon as time series for other permanent stations in the study area are available, they can be processed accordingly. A number of activities have been done in the support to other WP's. More precisely we have supported WP1 as follows: o Raw data (RINEX) from the newly established stations ASIA and ROVI are sent regularly to the Project's Data Center in Graz; o Processed (NEQ/SNX) files from a network including permanent stations relevant to the Project have been sent to the Project's Data Center and to the responsible of WP5, to prepare the basis for the time series which will be the input to WP6.

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Annual report presented by partner UNIPD for the period 01 April 2003 - 31 March 2004

Caporali A., Facchinetti C., Gallini G.

Reports on Geodesy

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2004

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nr 2/69

39--49

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Precise orbit determination using a LEO-GPS satellite to satellite tracking approach

Caporali A., Dalla Torre A., Facchinetti C.

Reports on Geodesy

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2003

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z. 2/65

221-233

EN

The tracking requirements for a Low Earth Orbit (LEO) satellite are defined by the overall accuracy of the results each mission is designed for. Examples of satellites asking for Precise Orbit Determination are remote sensing satellite and geodetic satellites. The paper addresses some basic considerations for the design of a GPS data processing technique for the high-precision position determination of a GPS/GLONASS receiver. Once the position of the receiver is known, this information can be used to determine the orbit of Low Earth Orbit (LEO) satellites. The precision requirements to be fulfilled have to be compatible with the definition of Precise Orbit Determination (POD): in most of applications the accuracy for post processed data is required to be meter or even sub decimetre in the radial direction, particularly in those cases where a radar altimeter is on board typically for oceanographic applications, or for Intefferometric SAR. The use of GNSS receiver on board and the support of a ground station network with a set of appropriate postprocessing tools allows to fulfil also the more stringent requirements for the Precise Orbit Determination. Two are the major class of teehniques that have been historically used: the Geometric and the Dynamic approaches. Each of these concepts had advantages and disadvantages. The most important advantage of the geometric approach relies on its simplicity and that it has the potential to work in the presence of forces which were absent from the dynamic model. Now that the IGS products have become fairly standardised, and very precise predictions are going to be available in the next future with a very short delay time, and space 'ali in view receivers' are capable of tracking all the visible satellites, and possibly also the GLONASS satellites, the geometric solution has to be reconsidered. The technique chosen to perform these solutions is then the simple geometric point positioning approaeh using, for every epoch, pseudoranges measurements smoothed using phase data. The navigation satellite orbits are taken from the International GPS Service (IGS) products. To test the GPS POD sensor, the data provided by some in-orbit satellites with on board GPS receivers (es: CHAMP and SAC-C) can be used.