Plotting pseudorange multipath with respect to satellite azimuth and elevation

Abstract

In a 2002 issue of GPS Solutions (vol. 6, no. 3) a new plotting program called CF2PS was described. This program gives users increased flexibility when viewing or printing any of the eight “Compact Format” plot files output by TEQC: a multi-purpose software toolkit used for Translating, Editing, and Quality Checking GPS and GLONASS data. While the time-series plots generated by CF2PS are fine for most TEQC data types, for analyzing pseudorange multipath it is often preferable to plot the data with respect to satellite azimuth and elevation angle. This can help identify the location of reflective objects at a site, and can show how high above the horizon the multipath continues or if certain azimuths are affected more than others. Such plots can also show, on an epoch-by-epoch basis, how the L1 pseudoranges might be affected differently from the L2 pseudoranges, or how P-code pseudoranges might be affected differently from C/A-code pseudoranges. This article describes a new C/C++ program that plots pseudorange multipath at each epoch with respect to the corresponding satellite tracks. The resulting plot is similar in appearance to a polar plot or satellite visibility diagram used to show the geometry of the satellites over a certain location. The program has proven to be a useful tool for analyzing continuously operating reference sites, as well as for assisting in the everyday post-processing of static GPS baselines. The program works together with the Generic Mapping Tools (GMT) software and the Ghostscript software to generate PostScript files, which can then be viewed, printed, or converted to other graphic formats for publishing. The source code for the program and an example data set are available on the GPS Toolbox website at http://www.ngs.noaa.gov/gps-toolbox.