Subject: new solution for week 1306/ SPOT2 January 21, 2004
From: Pascal Willis <[email-masked]>
To: IDS_Analysis_Forum <[email-masked]>
Date: Thu, 17 Mar 2005 14:39:53 -0800

Dear colleague,

following the latest email from Philippe Escudier, stating that this 
week was suffering from the effect of an important geomagnetic 
storms, I reprocessed the DORIS data using a new strategy that we 
specifically developed at JPL for such cases.

Additional information on the method can be found in the following 
manuscript that should be in print soon:

Effects of thermosphere total density on LEO orbits during severe 
geomagnetic conditions (October-November 2003) using DORIS and SLR 
data, P. Willis, F. Deleflie, F. Barlier, Y.E. Bar-Sever, L.J. 
Romans, Adv Space Res., in press

You will see in the updated plot that the DORIS/EOP are now very 
close to the GPS/JPL solution (no bias no drift was previously 
removed). The RMS differences (over 7 days) between DORIS/IGN-JPL and 
GPS/JPL EOP solutions changed as follow:

			X	Y
initial submission	8.50	3.49
resubmission		0.95	0.68

All geodetic products for week 1306 (05016) for IGN/JPL as well as 
the relevant documentation were resubmitted to the CDDIS Data Center.

In the new strategy the orbit is less dynamic and is more fitted to 
the DORIS data themselves (drag estimated more frequently with some 
constrains). This could mean that the IDS Analysis Center could gain 
some precision in the geodetic products (at least the EOP) but 
relaxing more the orbit and giving more weight to the DORIS data 
themselves. The final tuning of this relaxation need to be 
investigated in more details and compared between groups.

Many thanks to Philippe Escudier
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]