Iranian Permanent GPS Network: Strategy and Processing


Data Centre:
The Master Data Centre for controlling the network and data analysis is settled in Tehran at National Cartographic Centre of Iran. Also we have 4 data centre in Tabriz-Mashhad-Hamedan-Ahvaz that control the operation of their observation sites, data communications, data management and send them to the Terhan for final processing. Data stored by the receivers are downloaded once per day from data centres and master data centre according to define procedure in midnight. The size of data is about 1.6mb that needs 10minutes with digital line. Down loaded data is archived into the database in RINEX format using TEQC program from unavco and compress for final archive in the FTP site of NCC on the 2 server with 300 Gb capacity.

Data processing:
After archiving data, the data processing unit start network solution process of GPS data include the network and IGS stations.

The data processing unit consist of 6 engineering workstations with linux operating system. The data are processed by precise analysis software Gamit-Globk ver 10.20 which was develop by MIT and SIO, in two steps. In the first step Gamit analyzes these data from user specified. Clusters of stations to create loosely constrained (buty ambiguity resolved) estimates of station coordinates. In the second step Globk combine these Gamit output files to create solution file in the SINEX format, containing loosely-constrained estimates for entire network. Globk is basically akalman filter and uses the covariance matrices obtained by Gamit.

The process is performed twice: once with rapid orbit from IGS outputs and the final orbit(Precise ephemrids)after two weeks. The former is used to obtain rapid solution and the later for final solution of whole network.

Outputs and Results:
Several kinds of results obtained by routine analysis such as, time series group of coordinates sites, time series of relative position of two site (baseline time series) displacement vector and also velocity filed. The summery of results and reports can be seen on NCC web site. (http://www.ncc.org/English/geodynamic. Fig8, Fig9 shows the time series of Tehran station and also the present velocity field which produce by GMT. The new next product strain rate map which will appear soon.


Fig 8-GPS Velocity Filed estimated with respect to Eurasia



Fig 9 – Time Series of Tehran station


Conclusion:
IPGN (Iranian Permanent GPS Network) has been showing a enormous information about crustal deformation (plate motion-activity of active faults), and to serve as an active controlling system for GPS surveying. The usage of this network is not limited on crustal deformation. Actually in Iran GPS metrology project is also start and this is another application of this network. The next phase of this project is real time monitoring that start this year. This system will be expanded to more than 700 permanent observation site in the next years.

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