From D. Thu Sep 28 13:16:38 1995 From: D. (D.) Date: Thu, 28 Sep 1995 13:16:38 PDT Subject: [IGSMAIL-1072] Changes in USNO GPS-only Combination Procedure Message-ID: ****************************************************************************** IGS Electronic Mail Thu Sep 28 13:16:38 PDT 1995 Message Number 1072 ****************************************************************************** Author: D. McCarthy, B. Luzum Subject: Changes in USNO GPS-only Combination Procedure Due to the recent results concerning the high-frequency signal in the GPS polar motion, we have modified the procedure used for combining the GPS series. We have eliminated all smoothing in the USNO combination of GPS-only results and changed the epoch of the output series to match the input series. These changes will provide a better representation of the GPS polar motion and the true Earth orientation signal. The new USNO GPS combination is essentially equivalent to the IGS mean pole series but extends much farther back in time. The differences that will result from this change are the smaller residuals seen in the plots and statistics beginning with our report for week 819. These are due to the closer tracking of GPS at high frequencies as well as adjustments to the systematic corrections that we apply. Our current estimate of the GPS accuracy is around +/- 0.1 msec. of arc. While no changes have been made to the basic multi-technique smoothing algorithm, the reduced smoothing and the resulting improved precision of the GPS data will mean that the IERS Rapid Service will follow the GPS polar motion more closely. If unannounced systematic changes occur in any of the IGS Analysis Center procedures, the Rapid Service results may be adversely impacted since we have reduced the ameliorating effects of the smoothing. This could effect the quality of EOP predictions and a priori estimates for future data analysis. Please be careful about any small changes in operations which might have a systematic effect on your results. As in the past, we would appreciate any advance announcement of all such changes and estimates of the resulting differences. We can make adjustments for known modifications, but for unannounced system changes, there will be little recourse. -- Dennis D. McCarthy dmc at maia.usno.navy.mil Head, Earth Orientation Department phone: (202) 653-0066 U.S. Naval Observatory fax: (202) 653-0587 Washington, DC 20392-5420 [Mailed From: Dennis McCarthy ]