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)