Research > CGPS

Precise Point Positioning Strategy

Precise Point Positioning (PPP) is performed using RINEX GNSS Observation Data from a number of stationary ground receivers defining the IGS Reference Frame along with the Pole, Precise Orbits and Satellite Clock files from the IGS, as well as from the individual contributing Analysis Centers, in order to obtain a set of station coordinates and velocities.

A PPP solution is acquired on a daily basis for each station. The processing procedure consists of three main parts:

1) Preparation Part Satellite Positions from the Precise Orbit files are adjusted to the Bernese extended orbit model (6 osculating elements and 9 dynamical parameters) using associated Pole files. Satellite Clock files are also converted to Bernese format.  

2) Pre-processing Part Pre-processing of the RINEX Observation Data is accomplished to identify and eliminate cycle slips. Smoothed data are converted into the Bernese format (zero-difference code and phase observation files) and used (code observations only) for the receiver clock synchronization.

3) Processing Part Station specific coordinate files are estimated using code and phase measurements. The procedure involves a station by station data reduction with iterative post-fit cleaning. Modeling of the tropospheric delay is done using the Niell Mapping Function (NMF) and meteorological data from a standard sea-level atmosphere.

A weekly combination of the daily generated PPP files is performed in order to compute the final coordinate and velocity file. Over time, the PPP processing reveals information about the stability of the station coordinate determination and the realization of the reference frame.

   The time Series in ITRF2005 can be found in:

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