Author: Rémi Ferland 

(Remi.Ferland _at_ NRCan-RNCan.gc.ca)
Extracted from IGS-ACS Mail Message Number 352


The IGS contribution spans the period 1997.0 - 2009.5 (563 weeks)
	(GPS weeks 0886-1536)   (1996/12/29 - 2009/07/04)
The pre-2008 solutions are based on the reprocessed products, while
the more recent solutions are based on the IGS official products.
Minor improvements were made to the official products before resubmission.
All weekly solution include weekly station coordinates and apparent
geocenter position estimates as well as daily (at the middle
of the day) pole position, pole rate, and LOD estimates. The weekly
solutions also include full variance-covariance estimate. All weekly
solutions are provided aligned to the IGS05 realization of ITRF2005.
The ACs LOD parameters are calibrated w.r.t. Bulletin A.

For detailed information on the reprocessing see:
http://acc.igs.org/reprocess.html

1) Analysis strategy:
=====================

	The sequential procedures used to generate the official products
and the reprocessed products are almost identical. They differ in:
	1) The official sequential analysis runs forward in time, while
the reprocessed runs backward.
	2) The rejection criterion for the official products was set
at 5 sigmas, while the reprocessed rejection was set an 8 sigmas.

General strategy steps:
	- Rescale covariance information (from previous iteration)
	- Unconstrain
	- Consistency check / Outlier rejection between AC (& GNAAC) and:
		- Reference frame,
		- AC,
		- Previous week (weekly & cumulative) combined solutions,
	- Combine weekly solution,
	- Update cumulative solution.

2) ACs & GNAACs Contribution:
=============================

11 ACs and 2 GNAACs have contributed:

AC         data span       Comments
co[d1]  1997.0 - 2009.5   Excluded ERPs
em[r1]  1997.0 - 2009.5
es[a1]  1997.0 - 2009.5
gf[z1]  1997.0 - 2009.5   Excluded apparent geocenter
gt1     1998.2 - 2002.0   Excluded apparent geocenter
jpl     2008.0 - 2009.5
mi[t1]  1998.0 - 2009.5
ng[s1]  1997.0 - 2009.5
pdr     1997.0 - 2008.0   Excluded ERPs
si[o1]  1997.0 - 2009.5   Excluded pole rate
ul1     1997.0 - 2007.0   Excluded apparent geocenter (no ERPs)

GNAACs     data span       Comments
MIT     2008.0 - 2009.5   Comparison only
ncl     2008.0 - 2009.5   Comparison only

3) Combined Products:
=====================

560 stations with the following # of weekly solutions:
  Weeks
From  To # Stations
101 - 150   64
151 - 200   46
201 - 250   45
251 - 300   30
301 - 350   45
351 - 400   48
401 - 450   42
451 - 500   44
501 - 550   55
551 - 600   37
601 - 653  104
          ----
Total      560

There is a total of 222261 positions estimates resulting in
An average close to 395 stations estimates per weeks.
        Weekly *snx, *res, *sum, *res files are available at CDDIS.

As per the original submisson in Feb 2009, the
remarks concerning the statistics evolution:

- The North weekly weighted average residuals w.r.t. the
reference frame realization and the cumulative solution
have an annual signal with amplitude of 1-2mm.

- A similar annual signal can be seen in the estimated
scale offset w.r.t. the reference frame.

- The number of stations going back to 1997, is holding
at above 175 every week. By comparison, when the original
analysis was done for early 1997, there were ~95 stations
in the weekly combinations.

- The statistics of the residuals w.r.t. the reference
frame are generally best in the weeks 1200-1400 (2003-2006)
period.  The increase after 1400 is most likely due
to extrapolation of the reference frame and a decrease
number of available stations; and before 1200 it is
mostly due to a decrease of the number of available stations

The AC horizontal/vertical consistency is still about
(in mm) w.r.t.:

        IGS05           Combined        Combined
                        Weekly          Cumulative
        2-3 / 7-9       1-2 / 3-4       2-3 / 5-7

The overall ERP consistency of the ACs w.r.t. weekly combination is
still about:
LOD     15 us
XPO     0.05 mas
YPO     0.04 mas
XPOR    0.14 mas/d
YPOR    0.14 mas/d