Subject: Re: [ids.analysis.forum] positioning results with Jason/SAA model
From: Laurent soudarin <[email-masked]>
To: [email-masked]
Date: Wed, 22 Feb 2006 19:33:22 +0100

Dear colleagues,

the corrective model for Jason-1 DORIS Doppler data designed by CNES
is available on the CB ftp site under 
ftp.cls.fr/pub/ids/satellites/CORRECTIVE_MODEL_JASON1

This model was optimized and documented in order to be able to deliver an 
operational
module (software) that will be used by the processing centers of DORIS data.
You can get this model and the technical note which gives the principle of 
the model
and allow its implementation and its use.
Please, read the Readme.txt file before getting the model.

Kind regards,

Laurent Soudarin

on behalf of Jean-Michel Lemoine and Hugues Capdeville

Le 15:53 21/10/2005,Laurent soudarin écrit:

>Dear colleagues,
>
>
>Because of the Cryosat launch failure, the renewal of the DORIS 
>constellation is postponed to at least 2008 (Jason-2).
>By then, there are strong chances that we lose an instrument again (Spot2 
>is going over its 16 years !).
>So it is critical to use the capacity of all the operating instruments for 
>the IDS objectives.
>Until now, Jason was not used for the geodetic products because of the 
>South Atlantic Anomaly (SAA) effect on the on-board Ultra Stable 
>Oscillator (USO).
>A model of frequency evolution of the USO was designed and validated by 
>CNES for the first DORIS receiver (called chain 2). An other one is 
>currently being developed for the chain 1 (back-up receiver switched on on 
>June, 28 2004).
>
>This model was implemented within GINS and I used it to process the 
>DORIS/Jason data, including data of the SAA stations, of course (7 months 
>from the period Dec 03 - May 04). Here are some conclusions of this processing:
>
>-Orbits computations show improvement of the orbits and decreasing of the 
>residuals (~0.025 mm/s).
>
>-Comparisons of the station coordinate solutions for Topex and Jason are 
>similar except for 7 SAA stations:
>HBK, Ascension, St Helen, Punta Delgada, Libreville, Santiago, Kourou. The 
>SAA effect is not completely absorbed, but it has no effect on the orbit 
>and on the other stations.
>
>-When these 7 stations are removed from the Jason matrices, the 
>6-satellite combination leads to a gain of 5 to 10 mm in term of 
>positioning precision wrt the 5-satellite combination (Spot-2,-4,-5, 
>Topex, Envisat).
>
>This is shown on the attached plot where the monthly precision is 
>represented for 3 combinations:
>5-satellites (yellow),
>6-satellites keeping the SAA stations in Jason matrices (blue),
>6-satellites without the SAA stations in Jason matrices (red).
>
>These are rather encouraging results.
>I think it's particularly important to focus on this point during the next 
>IDS workshop.
>
>
>Best regards
>Laurent
>
>
>
>