Subject: geocenter comparisons / good correlation but TY offset of 25 mm
From: Pascal Willis <[email-masked]>
To: IDS_Analysis_Forum <[email-masked]>
Cc: Zuheir Altamimi <[email-masked]>, Claude Boucher <[email-masked]>, [email-masked], Remy Ferland <[email-masked]>, Markus Rothacher <[email-masked]>, Claude Boucher <[email-masked]>, Yoaz Bar-Sever <[email-masked]>, DORIS SIMB <[email-masked]>, Herve Fagard <[email-masked]>, Richard Biancale <[email-masked]>, Daniel Gambis <[email-masked]>
Date: Thu, 30 Dec 2004 08:08:56 -0800

Dear colleagues,

following my latest emails to this forum, here are more results 
concerning the geocenter comparisons this time.

(see plots below)

First it can be seen that the LCA and IGN/JPL are extremely 
correlated and track the same signal at the same epoch (good news).

However, for the TY translation, there is a clear offset that needs 
to be investigated (-13.8 mm for LCA and +10.8 mm for IGN). I also 
see this offset for the IGN/JPL solution toward ITRF2000 as a very 
constant bias since 1993. I guess that LCA will see the same but with 
an opposite sign since 1993 too. This will probably have an impact on 
the derived EOP too.

Results from additional DORIS groups even on a limited amount of time 
would be extremely valuable to investigate these issues.

The following tables (without removing any signal) show that the LCA 
geocenter is slightly more stable with time than the IGN/JPL solution 
for TX and TY. This is probably due to longer arcs or to more dynamic 
estimations of the orbits. The TZ component is much noisier as 
expected.

LCA

(mm)		Bias		Std Dev
TX		 -2.0		 6.9
TY		-13.8		 6.8
TZ		 -2.8		34.6

IGN/JPL

(mm)		Bias		Std Dev
TX		 -2.5		 7.6
TY		 10.8		 8.4
TZ		 11.2		34.4

Best regards
Pascal

-- 
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]