Processing aspects related to permanent GPS arrays

Abstract

Preprocessing is an essential aspect for zero-and double-difference GPS software packages. In the first case we have to produce "clean" code and phase observations on the single receiver and single satellite level, in the second case solely double-difference observations have to be checked. The checks usually are performed on the "minimum constellation" level, i.e., the single receiver level for zero-, the single baseline level for double-difference packages. When analyzing the code observations stemming from a permanent array, this step may be performed in a much more efficient and robust way because the known geometry and, if available, the known atmospheric delays may be removed from the original observations. In an array of n receivers observing m satellites this leaves us with n · m observations and n + m − 1 unknowns (the clock parameters relative to a reference clock). The degree of freedom of f = n · m − (n + m − 1) (for, e.g., n = 10 and m = 10, we have f = 81) allows for a very robust detection of outliers and enables generating a satellite clock file based on code measurements (with very much reduced multipath and noise characteristics). A similar step may be performed with the differences of phase observations between subsequent epochs. Using an analogous procedure as in the case of code observations we may generate phase files with all cycle slips flagged or, in the case of "small-area" arrays, even with cycle slips repaired. Both steps, phase and code cleaning, are performed in the same program unit. We discuss this new development and present first results and applications using data from the AGNES (Automated GPS Network Switzerland) and the IGS (International GPS Service) Networks.

Quality assessment of COSMIC/FORMOSAT-3 GPS radio occultation data derived from single- and double-difference atmospheric excess phase processing

“…In order to investigate the spectrum of the GPS satellite clock offsets at higher frequencies, CDAAC software estimated 1 s GPS clock offsets from about a 100 station global ground network that tracked at a 1 s sampling rate. The Bernese program CLKEST was used to estimate the GPS and ground clock offsets at a 1 s rate (Bock et al 2000, Dach et al 2007. Previously estimated GPS orbits, earth orientation information, ground site coordinates, and zenith troposphere delay parameters are held fixed and the clocks are solved relative to a ground-based H-maser to provide a stable time scale for the solution.…”

High-rate GPS clock corrections from CODE: support of 1 Hz applications

“…Main, Germany, and the Institut für Astronomische und Physikalische Geodäsie, Technische Universität München, Germany, started to generate 5-min GPS clock corrections in September 1995 (Springer 2000) and 30-s GPS clock corrections in 1999 (Bock et al 2000). An efficient approach for generating high-rate GPS clock corrections was developed to support the initial activities in the field of POD for LEO satellites (Bock et al 2002;Bock 2004).…”

Ionospheric Effect Mitigation for Real-Time Single-Frequency Precise Point Positioning

“…Horizontal electron density gradients have been described as a common phenomenon in the middlelatitude region [18], but they have also been investigated in other regions. [19][20][21][22] attempted to introduce ionospheric gradient parameters in GPS network processing, and they found out that these parameters might absorb part of the satellite-and epoch-specific biases. Dai et al [23] has also made similar attempts to estimate ionospheric gradient parameters for ambiguity resolution, hoping that the ionospheric gradient parameters could absorb a significant amount of the spatially correlated ionospheric biases.…”