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Positioning Methods
Published in Basudeb Bhatta, Global Navigation Satellite Systems, 2021
In the relative or differential technique, whether it is based on code or carrier, it requires a reference or base receiver. For this receiver, the use of observed carrier phase data is a mandatory operational technique that is employed to obtain accurate results from GNSS measurements. Unfortunately, the role of the reference receiver is simply to mitigate errors affecting the rover. This forces users to purchase reference receivers which are not productive in the sense that they do not occupy marks of interest. Also, the cost of a carrier-based reference receiver is high. To overcome this problem, reference station networks have been established by many countries or states and even commercial companies. Currently there are more than 6500 such stations around the world (https://www.trimble.com/trs/findtrs.asp). Data from these reference stations are available for post-processing applications and/or real-time applications. The reference network data can be obtained in the native receiver format or in RINEX format. For the post-processing, data are generally supplied via the Internet. The RINEX format enables data collected from different brands of receiver to be combined and processed.
Indian Plate Motion Revealed by GPS Observations: Preliminary Results
Published in Rakhee Kulshrestha, Chandra Shekhar, Madhu Jain, Srinivas R. Chakravarthy, Mathematical Modeling and Computation of Real-Time Problems, 2021
Yogendra Sharma, Sumanta Pasari, Neha Pasari
For the present study, we have accrued four years (2015–2019) of GPS data from three IGS stations (IISC, HYDE and LCK4) from the Indian plate and one IGS station (LHAZ) from the Eurasian plate along with four additional IGS stations (CHUM, KIT3, POL2 and URUM) from Scripps Orbit and Permanent Array Center (SOPAC). GPS data is generally stored in RINEX (Receiver Independent Exchange) format. The RINEX files are further used for data processing. For high precision research work in geodesy, standard scientific GPS postprocessing software (GAMIT/GLOBK, BERNESE and GIPSY) is utilized. In the present study, we have used GAMIT/GLOBK postprocessing software to analyze the available GPS data. GAMIT/GLOBK is available on the LINUX environment [Herring et al., 2010]. This software is a GPS data processing software developed by the Massachusetts Institute of Technology (MIT) for the estimation of three-dimensional relative positions of a ground station. GAMIT uses GPS broadcast carrier phase and pseudorange observables (stored in RINEX file), also known as GPS readings, satellite ephemeris (stored in navigation file) and satellite orbit data (stored in orbit file). Through the least-squares estimation, it generates values of positions and other parameters (orbits, Earth orientation, ambiguities and atmospheric delays) [Herring et al., 2010; Leberl, 1978]. We have derived the position of GPS station from Eq. (15.2). The linearized form of the equation allows us to implement the least-squares algorithm. The simplified and linear form of Eq. (15.2) is given below d=Ax+v
Precise measurement of continuously operating reference station (CORS) site deviation due to seismic activities and performance analysis of horizontal time-dependent positioning (HTDP) software
Published in Journal of Spatial Science, 2020
Zeeshan Haider, Umar Iqbal Bhatti, Muhammad Ibbtisam Asim
To update these position coordinates, a precise estimation of CORS site deviation associated with seismic activities is required. For this purpose 60 days post-seismic data are used for the precise estimation of AB21 CORS site deviation due to the Aleutian Islands earthquake (23 June 2014). These GPS observation data files are available on National Geodetic Survey (www.ngs.noaa.gov/UFCORS) and UNAVO (www.unavco.org) websites. These GPS data files are in RINEX format. This RINEX observation data file is post-processed by OPUS to achieve cm-level accuracy. A 24 hour observation data file of dual frequency L1 and L2 for each day is processed using PAGES static software. Position coordinates are averaged from three independent, single-baseline solutions, each computed by double-differenced, carrier-phase measurements from one of three nearby CORS. Figure 9 depicts ALBH, FAIR, HOLB and INVK are the reference stations nearest to the AB21 CORS site. In order to increase the accuracy antenna type and height above mark are also required.