Subject: Comparing DORIS orbits

From: Martine Feissel <[email-masked]>
Date: Tue, 2 Apr 2002 16:45:58 +0200 (Paris, Madrid)

Dear colleagues

As you will see in the appended message from Henno Boomkamp (ESA), we are
offered the possibility to associate DORIS orbit comparisons, at least for
JASON and possibly for T/P, with an IGS ongoing project. Not withstanding
developing our own activities for other satellites (e.g. Spot) or
complementary objectives (e.g. reference systems), this gives an excellent
opportunity to interact with this part of the world. 

I encourage you to take this opportunity and to contact Henno to work out
the content/format issues, keeping me informed. As far as the campaign
dates and duration are concerned, it would certainly be advisable to
coordinate them with the GPS side.

Best regards
Martine
-- 
  Martine Feissel                  	Internet:     [email-masked]
  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
-- 

---------- Forwarded message ----------
Date: Tue, 2 Apr 2002 16:32:00 +0100
From: [email-masked]
To: Martine Feissel <[email-masked]>
Cc: [email-masked], Jean-Jacques Valette <[email-masked]>,
    Jean-Michel Lemoine <[email-masked]>, [email-masked],
    Pascal Willis <[email-masked]>,
    Robert Weber <[email-masked]>
Subject: Re: DORIS LEO orbits

Dear Martine,

The future plans for the IGS LEO pilot project include an orbit campaign
for JASON similar to that of CHAMP. For that purpose, I plan to install
JASON webpages similar to those of CHAMP (... which, by the way,
will be updated soon with the latest results - I'll add a header as well).

It is possible that the objectives of the IDS and IGS LEO are not strictly
the same, but regardless of that I can offer to start a JASON orbit webpage
as soon as possible, and do the comparisons for your campaign. The
system here is almost automatic. It will not be a major effort to adapt it
for JASON, and this was foreseen anyway. If there is sufficient interest in
TOPEX/Poseidon, I can do that as well. Even if some of your solutions
may not include GPS data, or some of our solutions will not have DORIS,
it will be useful to compare all such orbits.

With regard to the contributed orbits, I would prefer the following:

(1)  Earth-fixed orbit files in SP3 format, preferably 1-day arcs but this is
     not critical. If velocity vectors are present in both compared files
     of a pair, the velocity differences will also be generated.

       For CHAMP we have installed an orbit repository at CDDIS, it seems
       practical to do the same for JASON.

(2)  A small READ.ME file to describe the POD method. For TOPEX and JASON
     most orbits will be from dynamic solutions, but what is important in this
     case is to indicate
      (A) all tracking data that has been used  (GPS, DORIS, SLR, altimetry,
          ...).
      (B) the terrestrial reference frame in which the orbit has been estimated

(3)  The aim is to have a longer JASON campaign than for CHAMP. JASON POD
     is already more mature so that we don't expect a lot of re-processing. I
     would suggest a period of at least two repeat cycles, but we might as
     well do a full month. If you have already chosen a campaign duration,
     please let me know.
     It will probably not be a problem to run periods even longer than one
     month.

If possible, SLR data should not be used in the POD so that we can keep
it as an independent check. However, if the SLR is needed to reach the
required precision it would be a nonsense to leave it out. Solutions that
include SLR may come out of our analysis slightly better than they really
are, but in the end the GPS and DORIS data will probably dominate the POD.

Please note that I will be in the IGS workshop next week, and on holidays the
week after.  This week you can still reach me at ESOC, after that I will answer
your mails from day 22/4.

Best regards,

Henno Boomkamp

  >----------------------------------------------------------------------------|
  |                                                                            |
  |       To:     Henno Boomkamp/esoc/ESA@ESA                                  |
  |       cc:     Robert Weber <[email-masked]>, John                |
  |       Dow/esoc/ESA@ESA, Jean-Jacques Valette <[email-masked]>,|
  |       Jean-Michel Lemoine <[email-masked]>, Pascal Willis     |
  |       <[email-masked]>, [email-masked]                  |
  |       Subject:     DORIS LEO orbits                                        |
  >----------------------------------------------------------------------------|

Dear colleague

   I visited your webpage http://nng.esoc.esa.de/gps/campaign.html
which shows comparisons of a number of GPS-derived CHAMP orbits. I found
it quite informative and useful - it would be even nicer if the page had
a Heading, so that it gets a name in the list of users bookmarks.

   The DORIS Pilot Experiment is set up to prepare a future International
DORIS Service (IDS), parallel to the IGS, the IVS (for VLBI) and the ILRS
(for laser ranging). In this framework, several analysis centers produce
precise orbits of DORIS-tracked satellites (Spot-n, Topex/Poseidon, Jason
1, Envisat). We are looking for possibilities of comparing these orbits,
in parallel to what is done in the context of the altimetry missions.

   In preparation for the DORIS-IDS Workshop on June 13-14 (see
http://www.cta-congres.com/BIARRITZ2002/twodori.html), we would like
to be able to show some DORIS orbit comparisons for, e.g.,  Jason 1 or
Topex/Poseidon.

   The standard procedure you apply to the CHAMP orbits could meet this
need. Could you devote some time to perform such comparisons, if orbits
would be provided to you in the SP3 format? The number of analysis centers
would be probably around five.

   Looking forward to your response.

Best regards.
Martine Feissel
Analysis Coordinator,
DORIS Pilot Experiment
--
  Martine Feissel                        Internet:     [email-masked]
  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
--