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GPS Precise Point Positioning Technique: A Case Study in Iranian Permanent GPS Network for Geodynamics Hamid Reza Nankali National Cartographic Center Of Iran(Research-Institute) Dept of Geodesy and Geodynamics Email: h-nankali@ncc.neda.net.ir Abstract Global Positioning System (GPS) , which is a world-wide precise positioning system has become a popular and very useful device for geodetic survey and crystal deformation observation such as velocity filed of tectonic plate and station coordinates and their velocities. For precise measurements, differential positioning technique is used. Two antenna located a part , receive the signals data simultaneously and the collected datasets are processed together in order to obtain relative location between to observation points. To keep the computational burden associated with the such data feasible, one technique is to determine precise ephemerid from a global distributed network(IGS). Then data from local network are analyzed by estimating receiver parameters, satellite parameter are held fix (precise ephemerid). This Precise Point Positioning(PPP) is simple and very efficient method that must be applied with dual frequency receivers and 24h observation and independent of base station and the reference frame cab be free of distortion imposed by erroneous fiducially constraint on any sites. This paper outlines the use of PPP for processing GPS data(advantages-and disadvantages)with Bernese V5 software and compare the results with relative positioning in the same point of Iranian permanent GPS observation network for crusal deformation monitoring that process with Gamit/Globk software in relative mode. Introduction: Since the inception of the Global Positioning System during the late 1970s, relative processing has dominated the filed of GPS data processing. In fact, until quite recently, it would be true to say that relative processing had a monopoly on precision GPS processing. This all changed during the late 1990s when some competition entered the market place in the form of Precise Point Positioning (PPP). This new technique promises precisions comparable to those achievable from relative processing. The question you might be asking at this point is : " How is this possible?" In order to answer this question. I processed the data of IPGN(Iranian Permanent GPS Observation Network) for crustal deformation monitoring and compare the results with those obtained by Gamit/Globk in relative mode. IPGN consist of 107 permanent GPS station that equipped with precise dual frequency receivers and setup in active part of the country since 2005. Fig 1  Fig 1- Iranian Permanent GPS Network Relative Processing The' relative' part of relative processing suggests that more than one receiver is required and indeed this is the case. The minimum configuration for the determination of precise coordinates for one new point is of course two receivers. However, in order to obtain precise coordinates for a point from GPS data, a number of nuisance parameters first need to be removed from the data. These may be classified as satellite' errors' atmospheric 'errors' and receiver'errorss'. Satellite errors include errors in the reported satellite coordinates and satellite clocks, atmospheric errors include signal delays due to the troposphere and ionosphere while receiver errors include receiver clock errors. Let us consider for a moment how each of these errors might be removed or mitigated. Page 1 of 3
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