Date: Wed, 3 Dec 2003 07:46:03 -0800
From: Pascal Willis
To: Martine Feissel-Vernier
Cc: Ramesh Govind , John Ries ,
Pascal Willis ,
Laurent Soudarin ,
Jean-Michel Lemoine ,
Suryia Tatevian ,
Serguei Kuzin ,
Gilles Tavernier ,
Jean-Jacques Valette ,
Jean-Pierre Granier ,
Carey Noll ,
Edouard Gaulué , feissel@ensg.ign.fr
Subject: Re: Participation in the IDS-GRACE Campaign
Dear Martine,
here are some comments and suggestions to start the discussion
>Dear colleagues
>
>We had a meeting with the IDS Central Bureau to prepare our contributions
>to the 2003 Analysis campaign: products collection, comparisons,
>evaluations. Our discussions led us to clarify the following aspects that
>we ask you to take into account.
>
>- Exact version of gravity fields considered:
> . the version of GRIM5 to be used is GRIM5-C1
> . the version of GGM01 to be used may be either GGM01C or GGM01S.
the order of the gravity field is also important. Some people use
limited model (70*70) to increase the speed of computation,
potentially loosing here some accuracy.
> I modified accordingly the webpage
> http://lareg.ensg.ign.fr/IDS/events/ctrs_camp_2003.html
>
>- SAA effect on the Jason data: Laurent Soudarin transmitted to me the
> following list of stations that are affected and should be deweighted or
> not considered in the analyses. He originally obtained it from Pascal
> Willis. The stations are the following.
>
> KRUB AREB ASDB CACB EASB HBKB HELB
> LIBB SANB GALA PAQB MAHB PDMB TRIB
>
> This list can be further discussed with other analysts if necessary.
The list needs to be finalized, here is my present list :
AREB ASDB CACB DJIB EASB GALA HBKB HBLA HELB
HEMB KOKA KOLB KRUB LIBB MAHB PAQB PDMB RIDA
RIPB SALB SANB SODB TLHA TRIB
You see that some stations that were not in the original list can now
be detected, thanks to the linearity of the effect. In principle, all
stations that see the satellite within the SAA region (not the
station, but the satellite), even for some small period of time will
be affected. That could give us an uper band.
>- Treatment of the diurnal and semi-diurnal variations in polar motion
> that are due to the oceanic tides: the analysts are requested to follow
> the IERS conventional exchange procedure, namely that the provided
> coordinates of the pole do not contain these variations. A correction
> model is available in the IERS Conventions (1996) at
> http://www.iers.org/iers/products/conv/
>
>- Polar motion rates: my proposal is that they are NOT estimated, as a
> first step. I would suggest that the impact of estimating them be part
> of a second step.
This does not seem to be a good idea. This is different from GPS
present regular processing at IGS and also different from the
proposal that Markus Rothacher is preparing for the IERS combination
pilot experiment. If you set up a different standard, that will mean
that DORIS groups will have to make 2 computations: 1 for IERS and 1
for IDS. I am not sure that IDS groups are ready to handle that on an
operational basis.
Estimating a derivative parameter is not a problem as such. People
just need to be careful by estimation the precision/accuracy at the
epoch of minimum variance and not at 12:00. I suggest that you
discuss this issue with Markus Rothacher at the next IERS Directing
Board meeting in SFO.
He is presently trying to have only 1 GPS common processing for IERS
and for IGS. I think we should do the same and have some coordination
there between DORIS and IERS.
NB: The charter of his working group is presently in a preliminary
form (first version was yesterday). I will send it to you in a
different message. It will be discussed at the IERS/DB in SFO.
>- Epoch of the weekly products: it is requested that the epoch be the
> central date of the data involved.
I do not understand this statement. What does it mean for the weekly
sinex product? is there a day, a hour, minute definition? Do we need
to weight if we have 3 satellites the first day, 1 the second and 4
the third? Do you mean the naming of the file?
>- When submitting your results to the IDS Data centers, please provide a
> "ccc.snx.readme" file, to be stored at the upper level of the
> /2003campaign directory. This file is necessary for any user to
> understand what he will find in the center's subdirectory. It comes in
> addition to the analysis description files "ccctuVV.snx.dsc". See
> http://lareg.ensg.ign.fr/IDS/doc/struct_dc.html#p7.
The specification on the Web is not sufficient for me to guess what
you want. People presently go in the product directory, they look for
the dsc files and then know which series they should use. I see no
need for information in an upper directory. Let's try to keep it
simple and easy to change. Or better explain what you wish.
>- I will maintain a webpage for the monitoring of the analysis campaign:
> http://lareg.ensg.ign.fr/IDS/events/update_camp_2003.html
> This page will not be advertised publicly. It will contain details on
> the exchange of information and progress of actions.
>
>- Please send a message to Jean-Jacques Valette and I when you upload a
> solution at one of the IDS Data Centers.
>
>- Don't hesitate to start any discussion on data analysis you feel useful.
> We can use the mailing list of this message for that. Feel free to add
> other names to it.
>
>An IDS meeting is tentatively planned on 3-5 May 2004 in Paris, right
>after the EGU General Assembly in Nice. It would cover general matters
>concerning the evolution of the IDS. One part of it would be devoted to
>the discussion of the analysis campaign.
as expressed in my previous message, I would favor a 2-day meeting
instead of 3.
let's see if other people want to react on this point outside France
Best regards
Pascal
>Thanking you for your participation.
>Martine Feissel-Vernier
>--
> Martine Feissel-Vernier Internet: feissel@ensg.ign.fr
> Observatoire de Paris and
> Institut Geographique National Telephone: 33 (0) 1 64 15 32 83
> ENSG/LAREG Fax: 33 (0) 1 64 15 32 53
> 8 Av. Blaise Pascal, Champs sur Marne
> 77455 Marne la Vallee Cedex 2, France
>--
--
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 : Pascal.R.Willis@jpl.nasa.gov