Constraints on a geodetic time transfer network in Iran |
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| Authors: | M Khoshmanesh M Mashhadi Hossainali |
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| Institution: | 1. Faculty of Geodesy and Geomatics Engineering, K.N.Toosi University of Technology, 1346 Valiasr Street, Mirdaamaad intersection, Tehran, Iran
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| Abstract: | Iran is a developing country, and nowadays, a demand to establish a time transfer system can be sensed more than anytime. On the other hand, global positioning system (GPS) is one of the most efficient and accurate systems in precise time estimation and dissemination domain. This study aims to investigate the different accuracy limiting effects of a time transfer system in a geodetic point of view. For this purpose, a simulation study is performed in which pseudo-range and carrier phase observations are simulated for some GPS stations in Iran. The baselines for time transfer have been chosen in a way that the maximum effect of each bias source can be analyzed. Therefore, the results of this study can be used in order to design the absolute and relative locations of the GPS stations equipped with external atomic frequencies in Iran considering a specific application. As a result, the most prominent bias source is the site-specific troposphere parameters which produce a variation of more than 1 ns in the time transfer results. Other bias sources including bias in the coordinate components and orbital information have a considerable impact only for time keeping purposes. Additionally, the influence of noise of the carrier phase and pseudo-range observations is analyzed. Variations of clock estimations between consecutive epochs up to 70 ps and day boundary discontinuities up to 0.6 ns, respectively, are the results of measurement errors. On the other hand, a time transfer between H-masers located at US Naval Observatory and National Resources Canada has been conducted to pursue a standard and efficient algorithm to deal with the problem of day boundary jumps. The method of overlapping batches with 12 h coverage of each of the involved days is applied to overcome this problem. The results of this method show a considerable decrease in the magnitude of the day boundary jumps. |
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