Subject: break estimation / computing discontinuities and formal errors
From: Pascal Willis <[email-masked]>
To: IDS_Analysis_Forum <[email-masked]>
Date: Fri, 10 Jun 2005 11:55:23 -0700

Hi Martine,

Could I suggest that add to your table for all considered breaks 
(either detected by at least 1 center or by you or by another source 
such as GPS) and for all available time series, the estimated 
discontinuity as well as its formal error.

I will take Fairbanks (Nov 3, 2002 Earthquake) as an example to 
better explain my proposal.

For Fairbanks in latitude, when I estimate the discontinuity from the 
STCD files available at CDDIS, I get :

DORIS	monthly	LCA	-36.5 +/- 43.6 mm
DORIS	weekly		IGN	-51.4 +/- 14.7 mm

(using the FAIA data after 1996/1/1 and all the FAIB data)

Here are 2 recent GPS result for the Fairbanks stations (FAIR)

GPS	daily		JPL	-65.3 +/- 6.5 mm (using 2002-2003 data only)

(see http://sideshow.jpl.nasa.gov/mbh/all/FAIR.html)

GPS	daily		SOPAC	-54.76 +/- 3.26 mm

(see http://sopac.ucsd.edu/cgi-bin/sector.cgi)

I guess these numbers explain why the LCA group does not detect the 
discontinuity. But their estimation is also compatible with the break 
of -5 cm (within the formal errors, after reweighting).

By the way, it is not clear to me why the standard deviations are so 
different from the 2 solutions. A careful cross-examination of these 
results is required.

If you just put "yes" or "no" in your table, people can think that 
the 2 DORIS time series disagree. In fact, this is not the case. You 
can see it clearly when looking at the estimated discontinuities and 
the formal error per AC.

I would encourage you to do similar analysis for all stations for 
which a break has been proposed before starting the discussion

Each AC could then react and I am sure that we will converge more 
rapidly and learn some more new things

Thanks in advance
Pascal

NB: It also seems that the velocity of the Fairbanks station could 
different after the Earthquake. This may be difficult to see with 
DORIS alone, but I think we could use extra information as well.
-- 
Pascal Willis
Jet Propulsion Laboratory, MS 238-646     Ph : 1-818-393-4748
4800 Oak Grove Drive                      FAX: 1-818-393-4965
Pasadena CA 91109                         Em : [email-masked]