Delivered-To: igsmail@igscb.jpl.nasa.gov From: Jim Ray "(NGS" 301-713-2850 "x112)" Message-Id: <200511101617.LAA20665@ness.ngs.noaa.gov> Subject: [IGSMAIL-5252]: BRD orbit accuracy results To: igsmail@igscb.jpl.nasa.gov Date: Thu, 10 Nov 2005 11:17:18 -0500 (EST) Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-igsmail Precedence: bulk ****************************************************************************** IGS Electronic Mail 10 Nov 08:18:01 PST 2005 Message Number 5252 ****************************************************************************** Author: Jim Ray With respect to IGS Mail #5209 by Jim Slater, and for other reasons, it is perhaps interesting to visualize the recent performance of the GPS broadcast orbits. The following plots (also in ps format) are available at ftp://www.ngs.noaa.gov/dist/jimr/brd/ : brd-wrms.pdf -- RMS orbit residuals (1-D) brd-tz.pdf -- Tz translation of orbit constellation brd-rz.pdf -- Rz rotation of orbit constellation brd-clk.pdf -- RMS clock residuals all with respect to the IGS Rapid products (IGR) and shown since 1 Jan 2002. Plotted values are taken from the daily combination reports generated by the IGS Analysis Coordinator. Note that the IGS normally includes all broadcasting satellites, regardless of official health status. However, if any AC fails to submit a solution for a particular satellite, then that satellite is not included in the statistics. So, some of the poorer orbital results are due to satellites that were set unhealthy but tracked by the IGS anyway. Orbit residuals -- These are the RMS differences after removing a daily 7-parameter Helmert transformation, compared to the IGR orbits. There has been a steady (nearly linear) improvement over the past 4 years, from about 2.5 m RMS to 1.3 m RMS now. Axial translation -- There has been a longstanding annual oscillation of the GPS constellation with respect to the equatorial plane, with an average overall bias. That annual trend continues, but with a decreasing amplitude and the north-south bias has gradually faded. Axial rotation -- Rotations about the Z axis are unavoidably connected with the quality of predictions of UT1 variations. The range of GPS Z-rotations has decreased significantly over the past 4 years, esp in the last year. However, recent rotations, while smaller, are temporally more coherent (except possibly in the very latest results). Clock residuals -- Broadcast clock predictions have also improved over the past 4 years, from about 4.5 ns RMS to around 3 ns RMS now. Most of the improvement seemed to occur around late 2003 and has relatively stable and unchanged since then.