Subject: [IGSLEO-14] CHAMP orbit test period
From: [email-masked]
To: [email-masked]
Date: Wed, 12 Sep 2001 14:22:24 +0100

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IGS LEO Mail      12 Sep 05:33:21 PDT 2001      Message Number 14
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Author: Henno Boomkamp

Dear Colleagues,

Events in the United States urge me to start with an apologee towards
the American groups for this 'business as usual' mail. I was writing this
yesterday just when the news started to come in, and attention shifted
towards the news channels.  At ESOC as anywhere else in Europe we
feel affected by what is happening, but continuing with normal work is
probably not a bad response. I removed any mention of deadlines
though, because contributions from the USA groups are especially
appreciated even if there may be some delays.

The purpose of this mail is to take concrete steps towards exchanging
CHAMP POD results between the various IGS LEO pilot project groups.
Several Associate Analysis Centres of the pilot project are reaching a
more or less mature level of CHAMP orbit determination, and would like
to have some external orbits for verification purposes.  I therefore propose
that all AACs that are reasonably capable of producing CHAMP orbits
prepare POD solutions for a specific period, namely for the interval

            2001/140 to 2001/150  = May 20 to May 30 of 2001 (11 days)

This period corresponds to some of the earliest days for which the CHAMP
data became available to the IGS LEO PP groups, and as a result they
appear to be quite well analysed by various centres. I expect that several
AACs will already have orbit solutions for these days on file.

Carey Noll has offered to set up a CHAMP orbit repository at CDDIS,
which seems convenient for all of us. The precise format for implementing
this repository is still under preparation, but it will be very similar to what
is
already in place for GPS.

As a first step in the orbit exchange campaign, I would like to ask all
interested AACs to respond to this mail, and indicate if and when your
own orbit solutions for the above test period could be made available.
Even if you are not yet satisfied with the current precision of your orbits
(... this also applies to us at ESOC) it may be useful to take part in this
exchange, simply for having the external references.

Practical instructions for uploading and downloading will follow later.
In principle the SP3 format will be used for exchanging orbits, but a
particular CHAMP standard for the formatting characteristics has not yet
surfaced (arc lengths, vector interval, velocity included, clock bias included,
...)
My recommendation would be the following:

           - 24 hour files, from 00:00 to 24:00 (GPS time)
           - 1 minute intervals between vectors
           - Velocity vectors also included in the files
           - Satellite identifier for CHAMP is L06

A more definitive standard for CHAMP SP3 should be an outcome of this first
orbit exchange campaign. For comparing orbits, I'm preparing a flexible orbit
comparator program that will interpolate in SP3 input files whenever necessary,
and will perform a 7-parameter transform to show reference system differences.
This means that, within reason, deviations from the above format can be
tolerated
at least until a clear CHAMP standard is consolidated. This tool can also be
made available to those AACs who do not yet have a similar comparator, but
would like to do some comparisons themselves.

For the longer term, ESOC plans to work towards a routine CHAMP orbit product
that will typically be 24 hr delayed w.r.t. real-time, due to data availability.
We hope
that a reasonable number of other AACs will also start producing near real-time
CHAMP orbits in the not so distant future, in which case ESOC can offer to take
care of routine comparisons, or a form of combination solution. If any AACs can
already confirm that they will contribute routine CHAMP orbits at some point, I
would be interested to find out, but more about that later.

Please note that taking part in the above CHAMP orbit exchange does not imply
any commitment from your AAC to participate in routine CHAMP orbit computations
at a later stage, so please participate if you can.

Best regards,

Henno Boomkamp
IGS LEO Pilot Project AAC coordinator