Subject: [IGSLEO-40] IGS LEO report
From: [email-masked]
To: [email-masked]
Date: Fri, 15 Feb 2002 17:11:25 +0100

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IGS LEO Mail      15 Feb 08:11:42 PST 2002      Message Number 40
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Author: Henno Boomkamp

Dear Colleagues,

Please find attached a report on the IGS LEO meeting in Potsdam, January 2002.

Based on the conclusions of the meeting some concrete actions are proposed.
As part of these actions the report contains an invitation for presentations in
a
dedicated IGS LEO session during the Ottawa Workshop. if you would like to
present on that occasion, please reply as soon as possible with a title and
short abstract.

Best regards,

Henno Boomkamp

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IGS LEO meeting - Potsdam 23/01/2002
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The IGS LEO meeting in Potsdam was well attended, which shows that a wide
interest
exists in applications of LEO GPS data. With the release of the CHAMP data in
May last
year and several other operational LEO missions arriving soon, the IGS LEO
centres can
gear up their activities. The technical analysis within the IGS LEO pilot
project has so far
been dominated by CHAMP POD. During the CHAMP Science Meeting separate sessions
were dedicated to that topic, so that the IGS LEO meeting mainly focussed on a
discussion
about its future policy.

Agenda of the meeting
----------------------------------
(I) Status and policy:
* Proposed development of IGS LEO processing (Henno Boomkamp)
* Discussion on proposed development versus current status of IGS LEO analysis
(All)
(II) Technical presentations:
* Presentation on the CHAMP Orbit Comparison campaign (Henno Boomkamp)
* Presentation on TUM fine ambiguity resolution orbits (Markus Rothacher)

Summary of the discussion
----------------------------------------
From the discussions during and after the meeting it became clear that different
centres have
different expectations of the IGS LEO pilot project. The following points of
view on future IGS
LEO activities were brought forward:

(1) The value of LEO GPS data must still be established more clearly. The main
task of the
pilot project would be to do this kind of analysis, which could be done off-line
without needing
much in terms of additional infrastructure or processing capability.

(2) The lack of LEO GPS data - at least until recently - and the lack of
processing capability or
data infrastructure still prevent proper GPS LEO analysis. To enable adequate
study of the
impact of LEO data on IGS products, the IGS LEO pilot project should stimulate
the development
of the processing capability of LEO GPS data at a substantial number of
Associate Analysis Centres.

(3) The IGS LEO pilot project could give more priority to applications of GPS to
the LEO satellites
and not mainly concentrate on benefits of using LEO data for IGS processing.
Some IGS LEO
products could be considered if there is a genuine demand for it.

In general terms these views are not incompatible, but they set different
priorities. What seems to
be lacking is a clear definition of the scope and objectives of the IGS LEO
pilot project. For creating
some clarity on this point, the initial intentions of the IGS LEO working group
can be briefly recalled here.

The call for participation in support of LEO missions (IGS mail 2669) invited
proposals related
to LEO POD, to a high performance IGS ground station network and to the
development of
processing capability for high rate and / or LEO flight receiver data at data
centres and analysis
centres. This same announcement mentions a pilot project as one of the suggested
activities,
with the following objectives:  "Generating scientific POD for the LEO
satellites ...;  AACs will
demonstrate POD for these satellites as data is made available ..;.  AACs will
investigate and
asses potential improvement of the suite of IGS classic products".

The Pilot Project activities have so far focussed on POD for CHAMP, but the
orbit comparison
campaign suggests that CHAMP POD will soon reach a mature status. Logical next
steps for the
pilot project will be to extend the CHAMP campaign over a longer period of time
and/or to involve
other satellites (notably JASON). On the other hand, the availability of more
LEO data and adequate
POD will make it possible to initiate projects related to the second objective
of the pilot project, i.e.
assessing the impact of the LEO data on the classic IGS products, as brought up
under point (1) above.

Other areas of interest that were expressed by the IGS LEO working group in the
call for proposals
have not received much attention so far (i.e. high performance ground network,
developing
processing capability at data centres and analysis centres). The availability of
adequate analysis
capabilities is a necessary condition for assessing the impact of LEO data on
the classic IGS products,
and it would be a natural task for the current pilot project to ensure that this
analysis capability is present.
This is what point (2) of the discussion was about, and it was also the essence
of the initial presentation
on proposed IGS LEO processing.

The third point of view illustrates that the applications of IGS LEO data and
products may be wider
than originally anticipated. The call for proposals for IGS LEO naturally aimed
at improving the
classic IGS products, which is why it is an IGS initiative in the first place.
However if intermediate
LEO products appear, notably LEO orbits and clocks, IGS could consider the
distribution of such
products among the further IGS outputs. A tentative suggestion of
commercialising this kind of
output was made, but this opens up another discussion entirely.

Conclusions from the meeting
---------------------------------------------
* Different views appeared on the way in which IGS LEO should develop. On the
grounds of the
initial call for proposals, the current pilot project could limit itself to
analysis, reflected under (1)
above. In practice the IGS LEO Pilot Project is the only form in which IGS LEO
activities are being
implemented. This means that it may be inevitable to extend the scope of PP
activities to also
include the development of analysis capabilities and data infrastructure. This
is the view that was
noted under point (2). Then, many of the centres that are currently working on
the CHAMP data
have a primary interest in LEO missions rather than IGS/GPS, which
understandably leads to the
view mentioned under (3).

* Because of these different opinions, it seems useful to define the scope of
the IGS LEO pilot
project more clearly and to consolidate a common set of objectives and
priorities.

* Data availability and LEO POD are improving rapidly, which means that concrete
projects
should be started to analyse the impact of LEO data on IGS products, at least
within those
centres that already have combined LEO+GPS analysis capability.

* It will also be good to capitalise on the success of the CHAMP orbit campaign
in some form
by extending the campaign period and/or by setting up a similar campaign for
other satellites.

Actions
------------
1. For creating clarity on the scope and objectives of the IGS LEO pilot
project, I offer to prepare
a draft version of a more or less formal IGS LEO charter or working plan, along
the lines set out
in ftp://igscb.jpl.nasa.gov/igscb/resource/workgroups.txt. Inputs to this draft
will be the initial call
for proposals, the proposals themselves and the recommendations from the various
LEO meetings
in the past, including the 2002 meeting in Potsdam. After review by interested
parties this draft can be
put forward for approval during the IGS Governing Board meeting in Ottawa.

2. Technical analysis for assessing the impact of LEO data on the classic IGS
products can
gradually gain priority over LEO POD. A primary objective of the Ottawa meeting
will be to define
the areas in which concrete projects can be initiated and coordinated through
IGS LEO. Please
note the suggestions for presentations during the Ottawa workshop further below.

3. A follow-up project for the CHAMP Orbit Comparison campaign will be organised
(...soon).

Invitations for presentations during the Ottawa workshop
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Following up on action 2 above, concrete projects should be started soon to gain
insight
in the impact of LEO GPS data on the IGS products. Some relevant knowledge will
already
be available, other potential benefits of the LEO GPS data may not yet have been
acknowledged to full extent.

I would like to invite technical presentations related to this topic for a
dedicated IGS LEO
session during the IGS workshop in Ottawa (8-11 April). The main goal of this
session will
be to determine the areas in which subsequent IGS LEO projects can be organised,
i.e.
to assess what relevant knowledge is available, what processing capability is
available,
and what areas need to be developed further.

Suggested subjects for presentations:

* As mentioned in Potsdam, the presence of LEO data should improve the
separability of
the Z-component in the rapid as well as in the final products. Using CHAMP data,
this effect
can be quantified by centres that have combined GPS+LEO processing capability.
Perhaps
it is also possible to use simulated data for LEOs at different heights and
inclinations, while
validating the quality of these simulations via CHAMP or other LEO, for which
simulations
can be compared with results from real data.

* Differenced data involving a LEO and a ground station or combinations of LEOs
can
provide advantages over pure ground-based difference combinations  (longer base
lines,
no atmosphere, variable LEO geometry). Using CHAMP or SAC-C these effects can be
quantified with real data.

* Perhaps there has been relevant analysis in the past based on TOPEX GPS data
that can
now be repeated with CHAMP data and/or SAC-C data to provide more precise
results.

* Incorporation of LEO data in IGS processing may improve EOP and station
coordinates
observability via links with other Earth-based tracking data (SLR, DORIS).
Presentations are
invited that demonstrate benefits of reference frame or EOP estimation based on
GPS in
combination with other tracking data types.

* Any other contribution that can illustrate potential benefits of LEO GPS data
on the further
GPS products is welcome, of course.

There is not much time left until the Ottawa workshop, but some of the topics
above can
be investigated with relatively modest effort. Please reply as soon as possible
if you are
interested in presenting something in Ottawa, so that a LEO session agenda can
be produced.

Best regards,

Henno Boomkamp