From jim.ray at noaa.gov Wed Apr 13 10:45:15 2011 From: jim.ray at noaa.gov (Jim.Ray) Date: Wed, 13 Apr 2011 13:45:15 -0400 Subject: [IGSMAIL-6384] REMINDER: switch to IGS08/igs08.atx on 17 April 2011 Message-ID: <4DA5E12B.5060908@noaa.gov> IGS users are reminded of the changes that will be made for product files starting 17 April 2011 = GPS wk 1632_0 = MJD 55668: * reference frame IGS08 will replace IGS05 -- see IGSMAIL #6354 * antenna calibrations igs08.atx will replace igs05.atx -- see IGSMAILs #6355 and #6374 A presentation describing these changes is available at http://acc.igs.org/trf/igs08_egu11.pdf and advice on accounting for station-specific position corrections due to the new antenna calibrations is given in IGSMAIL #6356. The impact on user terrestrial frame results will be mostly a scale/height shift of about 6 mm and a Z origin translation of a few mm, with only minor changes in the other Helmert components. The IGS orbits will be unchanged within a few mm. Associated with these changes, the Analysis Centers have been asked to implement two new IERS Conventions (2010) models: * EGM2008 geopotential model -- including updated values for the time-variations of low-degree coefficients (see Conventions Chapter 6) * mean pole model -- see Conventions section 7.1.4, which is used for both the geopotential and for station displacements due to the pole tide; see eqn (7.25) & Table 7.7 In addition, Ken Senior will implement a new generation time scale ensemble, which will cause a phase discontinuity between IGS Rapid and Final clocks published before and after 2011-04-17T00:00Z. For each station and satellite clock, the new Kalman filter ensemble stochastically models its phase (time), frequency, and drift (frequency rate), rather than just a single frequency state till now. An added phase state is included to model a pure white phase noise process, as well as 12-hr and 6-hr harmonic terms for the satellite clocks. The intrinsic stability of this new time scale ensemble is significantly improved over past performance, mainly for intervals longer than a day, which permits softer steering to UTC. A poster presentation giving further information on the new time scale algorithm is available at http://acc.igs.org/clocks/igst-v2_IGS10_poster.ppt --Jim Ray IGS Analysis Coordinator