Date: Tue, 4 Mar 2003 16:36:30 -0800 From: Pascal Willis To: Daniel Gambis , Richard Gross , Zuheir Altamimi , Meise Barbara Cc: Martine Feissel , Gilles Tavernier , Jean-Paul Berthias , Carey Noll , Jean-Jacques Valette , Laurent Soudarin , Serguei Kuzin , Jean-Francois Cretaux , "John C. Ries" , Yoaz Bar-Sever Subject: DORIS/EOP precision vs epoch of minimum variance dear all, following my recent message, I have slightly modified the method to look separately for 2 different epochs of minimum variance for the EOP (one for XPOLE and another one for YPOLE). I give you below the statistics of the IGN/JPL DORIS/EOP vs the GPS/IGS solution (no mean and no trend removed) by satellite, using directly file ign02wd02.eop posted at CDDIS. The first RMS value compares the EOP series at 12:00 The second RMS value compares the EOP series at 12:00 + delta (epoch of minimum variance) The number of data points is the number of EOP values used to estimate the RMS #satellites #datapoints XPOLE_RMS YPOLE_RMS 1 29 2.66 / 2.57 2.04 / 2.05 2 615 2.54 / 2.36 1.59 / 1.43 3 1521 1.94 / 1.84 1.38 / 1.32 4 52 2.42 / 2.27 1.42 / 1.16 5 106 2.23 / 1.89 1.25 / 1.01 With the comments that I gave before, you can see that the more DORIS satellites we have the best results we get (specially for the Y-component). Secondly, the approach of minimum variance provides better consistency with GPS at the 1.0 mas level with 5 satellites in Y, which I think is an important aspect in the assessment of the DORIS accuracy vs the number of available DORIS satellites. When doing periodogram on these series, it is easy to show a strong 5.2 day signal in the Y component (that can be linked to SPOT mis-modelling) and for the X-component, weaker signals at 5.2 days (SPOT again) and 60.0 days (TOPEX). I have put a file for you (delta_time) if you want to do similar tests or just want to use the correct epoch of minimum variance in your tests. For example, I could not do any test before the start of the IGS/EOP series (1996, June 30). There is far more tests that can be done by selecting which satellites are effectively used that day and look for patterns. I would be very much interested to see other type of accuracy assessments for all the available DORIS EOP series. This could help us improve our DORIS modelling and/or estimation strategy. Best regards Pascal ---------------------------------------------------------------------- How to get the file with the epoch of minimum variance ftp lareg.ensg.ign.fr cd incoming get delta_time The file looks like that : mjd t_X (day) t_Y (day) t_mean (day) 48990.50 0.0941994451 -0.0255479633 0.0343257409 48991.50 0.0848377797 -0.0206493185 0.0320942306 48992.50 0.0647661588 -0.0473589660 0.0087035964 ...... 52632.50 0.1109600842 -0.0382938349 0.0363331247 52633.50 0.1382624568 -0.0450430384 0.0466097092 52634.50 0.1287056298 -0.0526637502 0.0380209398 52635.50 0.1364617025 -0.0534530551 0.0415043237 52636.50 0.0766129503 -0.0248054967 0.0259037268 column 1 = Modified Juilan Day column 2 = delta that you need to add to mjd to get the epoch of minimum variance for X Pole column 3 = delta that you need to add to mjd to get the epoch of minimum variance for Y Pole column 4 = average of column 3 and 4 (not the best for correction)