To: igsmail@igscb.jpl.nasa.gov Subject: [IGSMAIL-6107]: ESA/ESOC Ultra-Rapid and Rapid GNSS Solutions Message-ID: From: Tim.Springer@esa.int Date: Wed, 17 Mar 2010 17:28:59 +0100 Content-Type: text/plain; charset="us-ascii" Sender: owner-igsmail Precedence: bulk ****************************************************************************** IGS Electronic Mail 17 Mar 09:29:14 PDT 2010 Message Number 6107 ****************************************************************************** Author: Tim Springer Dear IGS Colleagues, With this e-mail we are proud to announce an other important enhancement in our ESA set of IGS products. Starting with GPS week 1574 day 1 our Rapid and our Ultra-Rapid (from hour 12) products are now true GNSS products containing the positions and clock offsets for all "well behaved" GPS and GLONASS satellites. This enhancement has been made possible thanks to the speed improvements that were made in the latest version of our NAPEOS software. As our products are now based on a truly combined GNSS analysis our orbit and clock products allow for very accurate GNSS precise point positioning simultaneously using GPS and GLONASS observations. Especially for kinematic solutions the usage of both systems is of great benefit thanks to the significant increase in the number of satellites from ~30 to ~50. GLONASS clocks. One important thing to notice is a significant difference between our Final and Ultra-Rapid/Rapid GLONASS clocks. When processing both code and phase observations from the GLONASS system one has to estimate what we call an "intersystem bias" for each receiver-Glonass_satellite pair. This is caused by the fact that internally in the current generation of GNSS receivers/antennas the different frequencies of the GLONASS satellites cause different delays in the order of tens of nanoseconds. The estimation of these biases significantly increases the size of the main matrix and thus increases the CPU time. For our Ultra-Rapid/Rapid solutions we have therefore decided to use the GLONASS code measurements only in preprocessing. This mean that in the main parameters estimation we do not use the code observations and consequently we do not have to estimate the intersystem biases as those are only observable by the code measurements. In this way the estimated GLONASS clocks in our Ultra-Rapid/Rapid remain aligned (more or less) to the GLONASS time system whereas the GLONASS clocks from our final solution are aligned to the GPS time system. The difference between the two time systems is around 330-350 ns. So when comparing our Rapid and Final GLONASS clocks you will see this difference. However, after removal of this bias the difference between the satellite clocks is at the level of 0.04 ns. When using the clocks, e.g. for PPP, you will not notice this difference in the values of the intersystem biases you (have to) estimate. Or you, alternatively, you could ignore the GLONASS code observations like we do in our Ultra-Rapid/Rapid solutions. For those people who want to use our GNSS products you will find them on our anonymous ftp: ftp://dgn6.esoc.esa.int/products We hope the GNSS community can make good use of these products! And if you have any comments and or questions please do not hesitate to contact us! If you use our products please make sure to properly acknowledge our efforts (see, e.g., ftp://dgn6.esoc.esa.int/products/000readme.esoc). Many greetings, The ESOC IGS Team. --------------------- Tim Springer Navigation Support Office, OPS-GN (nng.esoc.esa.de) European Space Operations Centre Robert Bosch Strasse 5 64293 Darmstadt Germany Tel: +49-6151-90-2029 Fax: +49-6151-90-3129