ILRS Governing Board Meeting

Vienna University of Technology

Gusshausstr. 27-29, Room 124, 3^rd^ Floor

**Tuesday, April 26, 2005**

**18:00 -- 21:00**

Attendees: M. Pearlman D. Carter

P. Bianco G. Appleby

R. Noomen W. Seemueller

P. Shelus C. Noll

U. Schreiber W. Gurtner

H. Kunimori

**Opening Remarks:**

Gurtner welcomed the attendees to the first GB meeting this year; we
will have another meeting during the October workshop. A quorum was not
present at the last meeting in San Francisco.

Gurtner noted that once again, agencies responsible for SLR systems are
having funding problems: Geoscience Australia with Yarragadee and KACST
with Riyadh. The CB has sent information to contacts for both stations.

**ILRS Status/Action Items:**

Please consult the handout prepared by the Central Bureau (Appendix A)
for news about the recent activities within the Central Bureau and the
ILRS in general.

Noll reviewed the action items from the December 2004 GB meeting; open
action items and key discussions are given below.

1\. CB will contact missions such as TOPEX, Envisat, GP-B etc. to remind
them that we need recognition in their publications.

Pearlman has contacted several ILRS missions stressing the importance of
giving appropriate credit to the ILRS. Acknowledgements and/or
references in publications, websites, etc. are crucial for continued
funding of the components. Feedback was obtained from J. Ries that TOPEX
will try to push this point within the project, but the satellite is
nearing the end of its lifetime; operations may discontinue at the end
of this year. Envisat contacts have also provided some useful
suggestions on getting the word out to the project and science
community. Appleby pointed out that an email was issued in April from
GFZ/Massmann celebrating the 10 years of successful ERS-2 operations; he
checked the GFZ website and found no mention on the home page about SLR.
Gurtner did find references to retroreflectors when looking deeper into
the website. The ILRS may need to approach the webmasters of various
missions about placing an acknowledgement of the ILRS directly on their
websites.

**Action**: CB should browse all existing mission websites and search
for references to the service and information about the role of SLR for
the mission; if not found, have webmasters add it.

*2. CB will contact the IAG Outreach to suggest that the IAG make its
participants aware of the issue of service recognition issue in
publications, papers, reports, and presentations.*

As stated above, acknowledgement and reference of the services and their
components in scientific publications continues to be a problem for all
services of the IAG. Papers were given at the EGU clearly using SLR data
without a proper citation or acknowledgement to the service. Reference
frame users acknowledge the IERS but not the services in their papers.
It was suggested that any ILRS representatives present at conferences,
etc. should actually stand up and publicly remind the authors of their
obligation to cite the ILRS. Pearlman is working with representatives
from the central bureaus of the other IAG services to develop a solution
that could be used by all. The service representatives agree that a
joint solution is best. One suggestion is to select a few articles from
the ILRS to use in citations. These references would then be made
available on the ILRS web and ftp sites.

*5. If we do not hear anything by mid-January, the CB will send a note
to Drs. Shargorodsky and Vasiliev.*

See discussions on the Russian agreement below.

*8. Gurtner will look at existing list of data problems (previously
maintained by V. Husson) on the ILRS website and see if the webpage can
be re-activated and updated on a regular basis.*

See discussions on data quality and feedback below.

*11. CB will examine the idea of issuing a call for a volunteer on the
dynamic priorities.*

HTSI personnel are working on an implementation of dynamic priorities
utilizing their scheduler; this activity is probably more elaborate than
what the ILRS hoped to use. The ILRS has discussed turning off tracking
of a satellite if tracking has exceeded requirements, etc. (e.g., ICESat
tracking is only required when GLAS is operating). Dynamic priorities
may be a method to handle that situation. The ILRS may simply review
data yield and determine when additional or less effort is needed.
Appleby indicated that NSGF could volunteer to work on this activity if
an algorithm is available.

**Action**: The CB will work with NSGF in implementing a simplified
dynamic priority system.

*12. CB will bring to closure the recommendation on the Galileo request
for tracking support. (Done)*

Approval was sent to Galileo on February 22. Suggestions on cube design
were forwarded to the Galileo project but they were not used.

*13. CB will send a letter broaching the retroreflector issues with the
GPS project. (Done)*

Pearlman sent a letter to Michael Shaw, GPS Project Manager suggesting
that retroreflectors be included on GPS-III series satellites. Although
a direct response has not been received, discussions between NASA and
the project indicate that there is interest. There appears to be little
science that we can get directly from the tracking of GPS, but Yoaz
Bar-Sever/JPL is writing a white paper supporting the retroreflectors
from the point of view of GPS calibration and resolution of the antenna
phase uncertainty. Dave Arnold is looking at some light weight options
for retroreflectors that might be applicable.

**NASA SLR Status:**

Carter gave an update on the status of NASA SLR (see presentation in
Appendix B). He is currently working on contracts with personnel at both
Arequipa and Haleakala for resuming activities at the sites. TLRS-4 is
presently undergoing refurbishment at GSFC in preparation for shipment
to Hawaii in late summer 2005. The system will undergo collocation with
MOBLAS-7 prior to transfer to Hawaii. McGarry, Zagwodski, et. al., are
working on moving SLR2000 to an operational state. Other stations in the
NASA network are operational. Tahiti is in the process of hiring another
crewmember; NASA SLR staff will assist in training that person. Carter
reported that recent meetings with NASA HQ have confirmed that they are
committed to their SLR operations for the next 5-7 years. GSFC staff are
working on plans to obtain funding for the SLR2000 prototype
replication. The NASA SLR budget is \~\$4M for operations and SLR2000.

**Working Group Reports:**

*AWG:*

Noomen's AWG presentation is included in Appendix B. The main activity
in the AWG is driven by our principal customer, the IERS. They are very
pleased with our activities. The generation of the ILRS operational
pos+eop product (7 day intervals and solutions for 7-day network
coordinates and 1-day EOPs) has been in place since 11/2003. Some ACs
use Etalon in addition to LAGEOS. ASI is the primary combination center
and DGFI is the backup, but both have the same obligations and produce
the official ILRS products (since 6/2004).

New contributions to the latest ITRF solution have been generated by the
ILRS ACs from the time of the LAGEOS-2 launch and on. The geocenter and
scale components of the weekly station solutions have been checked by
independent analysts and have been found to be very good. The analysts
have had a lot of communication about these solutions, mainly in
resolving problems in point referencing, editing of poor solutions of
individual stations, and biases in older data. The rules used in our
newer operational products may not work for these older data. The IERS
has given the ILRS additional time (until 5/31/2005) to clean up the
outstanding problems. The MERIT campaign (09/1983) would be a good
starting point for the next ILRS products for later ITRF solutions (the
IERS will have to decide whether the ITRF solution will be issued yearly
or less often). Going earlier than that time frame may be difficult due
to lack of data as well as station quality (no station we have now
existed that long ago). Matching the positions of older stations to new
stations as far back as 1983 may also be difficult. Analysis of older
LAGEOS-1 data for effort will not start until after 10/2005; the ACs
will want to include the new models (CoM corrections, troposphere) in
this analysis of older data. The ACs will also use 28-day intervals and
4-day EOPs for these products.

*DFPWG:*

Seemueller's presentation is included in Appendix B. Tests have been
done using the new prediction format at MLRS; Zimmerwald has not used
the new prediction format on satellites but has incorporated the format
in station software. Two topics for the fall ILRS workshop from the
DFPWG were proposed: refraction issues (particularly dispersion) and the
new prediction format.

*MWG:*

Kunimori's presentation is included in Appendix B. Updates on the ALOS,
ICESat, OICETS, and LRO missions were given at the WG meeting on April
25. ALOS requires restricted tracking and will utilize the new
procedures developed within the group. OICETS is an optical
communication experimental satellite scheduled to launch this fall; a
mission support request has been submitted to the ILRS CB and will be
forwarded to the MWG and GB soon.

*NEWG:*

Schreiber explained that the Networks and Engineering Working Group did
not hold a meeting at EGU because most of the engineering oriented
people did not attend EGU.

Pearlman believes we do know what our future technology in SLR is (see
slide in GGOS presentation). Shelus stated that many of the stations
must work on their existing systems to make sure they operate and do not
have time or resources to develop new systems or capabilities; the
stations are waiting for the next generation systems to be developed and
deployed. Pearlman stated that we do need to write out our vision for
SLR for the next 10 years; the VLBI technologists and scientists have
written such a document. Pearlman believes this effort would force the
community to address what it wants to do and how it wants to do it. He
used an example of the S. Koreans from KASI who plan to build a new SLR
system using technology from 15 years ago. Gurtner suggested a small
group be formed to develop this vision as a position paper, which would
include science inputs. Pearlman stated that the GGOS science board
should be issuing requirements that the services must support. Gurtner
also stated we need to know what wavelengths are best for new systems
given the new missions (e.g., transponders) and what retroreflector
technology is in development now. The NEWG should be prepared to give
recommendations in this area to new/upgraded stations prior to
development.

Pearlman stated that we should have a good look at two-color ranging at
this fall's workshop in the UK, where we are and where we can go. Bianco
said that not enough has been done in two-color experiments at this time
because it is difficult and expensive; the charts on the new troposphere
model showed that it does not handle the low wavelengths well. Appleby
stated that we should know what the science drivers are for two-color.
Pavlis is looking at the Zimmerwald two-color data. Gurtner does not
believe that the Zimmerwald two-color data are accurate enough to yield
dispersion information. Schreiber stated that the TIGO laser type was
specifically installed to do dual-color work; however, the field
operations are quite difficult using this type of laser. A session at
the fall workshop should be held where analysts and technologists can
meet to discuss both the data and future of the two-color technology.

**Action**: A subgroup of technology and science representatives should
write a white paper on the future vision for SLR (Who is going to do
this?)

**Action**: Bianco should make sure Pavlis has looked at the MLRO
two-color data.

*SPWG:*

Appleby's presentation is included in Appendix B. Presently we do not
have satellite CoM corrections accurate to 1 mm; therefore, it was
suggested that analysts may still need to solve for a range bias. Noomen
stated that solving for the range biases weakens the network solution,
particularly for the core stations. The AWG had already agreed that
range biases of the core stations would not be solved for; solving for
range biases for the other stations would be left up to the individual
analysis centers. The CoM corrections are signal strength dependent, and
therefore inherently uncertain at the few-mm level. Appleby has
characterized a signal strength regime estimate for the most productive
stations. He will extend the calculations, based on the paper with
Otsubo, for the whole ILRS network, and work with the CB to make the
values available at least on the ILRS website.

**Action**: Appleby will provide station signal strength regimes to the
CB for placement in the site logs with perhaps a separate table
automatically updated/extracted and linked to the CoM pages on the ILRS
website. The information is not in the site log now so the format will
have to be modified.

Galileo is about 3500 km higher than GPS. Two engineering versions of
the Galileo satellite will be launched this fall. GSTB-V2/A will have a
retroreflector array "GAIN" furnished by Galileo Industries (ESA) with a
return signal strength comparable to that of GPS. GSTB-V2/B will have an
array built by Surrey Satellite Technology Ltd (UK) with slightly larger
return signal. The subsequent operational satellites will have arrays,
but the design has not yet been settled. Velocity aberration is small
and not a major issue.

*Transponder WG:*

Schreiber presented (see Appendix B) the need for a new working group to
address laser transponders. Gurtner suggested that one responsibility
for this WG would be to obtain information on what the ILRS needs to
plan for future SLR upgrades. The T2L2 mission has been approved; Y.
Fumin and E. Samain are working on it. Kunimori mentioned that the
Japanese are also considering ideas for transponder/optical
communication missions. The opinion of the board is that the formation
of this new WG was a good idea. Schreiber agreed to chair the WG.

**Action**: Schreiber will prepare a charter and a list of members for
the Transponder Working Group; he will contact the proposed members and
confirm participation.

**Russian Satellites:**

Pearlman gave a presentation (see Appendix B) on the proposed agreement
between Federal Space Agency (FSA) of Russia and the ILRS on the launch
and tracking of "novel" SLR satellites using the Luneberg lens. Under
the agreement the Russian Space Agency would build and launch the
satellites and the ILRS would track them and make the data generally
available. This would be an engineering test, but there may be some
application for gravity field studies depending upon the orbit. From
previous experience the satellite maybe difficult to track and it was
recommended that we proceed on a best effort basis. After some
modifications and concurrence from FSA, Gurtner and Pearlman will sign
the agreement on behalf of the ILRS.

**Action**: The CB will edit the Russian agreement and will reply to the
FSA that the ILRS is interested in tracking these new satellites.

**New ILRS Orbit Product:**

Noomen reported that we have a proposal to generate an official ILRS
orbit product. A committee consisting of J. Ries, J. Mueller, R. Koenig,
C. Luceri, and W. Gurtner will work on the particulars for this product.
We hope to start with a test data set using four one-week periods of
LAGEOS data. We will use a procedure similar to that used for the
current data product. It is anticipated that this could be an official
ILRS product within a year.

**Action**: An ILRS orbit product committee should be formed and develop
a plan for the new product.

**Data Analysis and Feedback:**

Gurtner gave a presentation (see Appendix B) on the need for data
analysis and feedback to the ILRS stations and analysis centers. Since
funding cuts affected the capabilities of the ILRS CB, data quality
checks, problem catalogs, consistent analysis with respect to dealing
with errors and problems in the data, etc. are no longer performed as
before. We had several systems in place for checking the data but
unfortunately, these procedures are no longer maintained. Furthermore,
no process currently exists to collect all the AC/AAC reports into a
central place. The ILRS needs to establish procedures where station/data
related problems are dealt with through the whole ILRS system, from
tracking station to analysis center and finally to the general user.
Detected problems need to be archived in a way that the information can
be used in the future for the reprocessing of historical data. We need a
group/institution that will look at all the levels of problem detection.

**Action**: A committee will be formed to work on the specifications and
needs for a "Call for Proposal" to handle data analysis and feedback
(Gurtner, Pearlman, Noomen).

**Tracking Restrictions:**

Gurtner gave an update on satellite tracking restrictions (see Appendix
B). Gurtner, Rickleffs, and HTSI have developed a tracking restrictions
plan and are now at a point where the proposal is acceptable to JAXA for
ALOS tracking. Some final changes are being made to include additional
satellites identification information on the pass segment form. It was
agreed to forego the formal agreement between the satellite owner and
the stations, and rather have the owner qualify stations through
specified tests. JAXA will submit its test plans to the CB for review,
prior to approaching the stations.

**Action**: The CB will inform the stations that JAXA will be contacting
them with the ILRS-approved/evaluated request to track ALOS.

**Action:** JAXA will prepare a station test plan for review by the CB

**Galileo Geodesy Service Provider: Link to the ILRS:**

Gurtner gave a presentation on the Galileo Geodesy Service Provider
(GGSP) CfP (see Appendix B). At least two groups answered the proposal;
the group consisting of GFZ, AIUB, ESOC, IGN, BKG, Wuhan, and NRCan were
awarded this project by the European Commission. The project, which
started this winter, will provide the Galileo terrestrial reference
frame and links from the Galileo ground segment to the IAG services
(IGS, ILRS, IERS). The Galileo project does not want to/cannot deal with
the individual services (including the ILRS) so the GGSP will be the
intermediary. The GGSP will also generate products for the advanced user
community, including predictions and updates to the ILRS.

The group must set up a prototype GGSP over the next few years with the
test bed satellites; a second call for the operational GGSP will be
generated later. A meeting in Darmstadt of the IGS GNSS WG discussed the
role of SLR in Galileo. It was thought that Galileo will probably use
the SLR data in a campaign mode, rather than continuous tracking, at
least for test bed, but this decision is not final. Thus far, the ILRS
has agreed to support the test bed satellites; a request has not yet
been made on the operational configuration. The test bed satellites are
being launched this year for systems tests and to occupy the reserved
frequencies; otherwise they could be in jeopardy. The project wants to
check POD with the microwave pseudo-range signals and timing system
using SLR.

A full constellation of Galileo satellites with retroreflectors could
pose a challenge for the ILRS network. The tracking strategy is not yet
determined; a subset of stations may be adequate. Continuous tracking
may require some dedicated or nearly dedicated stations which would need
funding support from Galileo, perhaps on a regional basis.

Gurtner is considering entering negotiations with the Galileo project
for financial support for the European ILRS sub network. This policy
could then be expanded to other mission sponsors. For example, if ESA
requests ILRS track on a satellite, the agency should financially
support the EUROLAS network. The ILRS needs to develop a future vision.
Space missions with a commercial aspect, or scientific missions with a
large budget (e.g., GP-B), should be asked to assign a small part of
their budget for laser tracking. Tracking a constellation of thirty
Galileo satellites could mean that we have to rethink how we do
business. Any mission approached in such a fashion would continue to go
through ILRS, not directly to station. The ILRS must get involved early
in these missions to make sure the ILRS network is incorporated into the
budget. However, if we start to push this new position, we could weaken
our current financial support from our funding institutions. We may also
find ourselves with erratic year-to-year funding profiles. The stations
could use the additional funding to buy other equipment. No decision was
recommended at the meeting, but the ILRS does need to consider its
financial options. Missions must recognize that the tracking service
cost money.

# GGOS/Pearlman

Pearlman gave an update on the Global Geodetic Observing System (GGOS)
(see Appendix B). GGOS is the current project under development in the
IAG. One of the main focus areas now is to promote GGOS interaction with
several international science and political activities (IGOS, GEO,
etc.). A session on GGOS is planned for the IAG meeting in Cairns
Australia in August 2005. The new structure, including working groups,
of the project was shown; Pearlman is chair of the Ground Networks and
Communication Working Group. A primary focus of this group will be to
integrate and maintain the networks supporting the IAG services (e.g.,
IGS, ILRS, IVS, IDS). GGOS will probably not optimize all networks
together but rather optimize by technique, focusing on what each
technique can provide. A poster from the WG is planned for the Cairns
meeting.

**Fall ILRS Workshop:**

Appleby discussed plans for the fall ILRS workshop, to be held in
Eastbourne, UK. He has reserved the workshop venue for October 3-7. The
ILRS should allocate three days for workshop sessions, one day for WG
and GB meetings, and a half-day (Friday) for the ILRS general assembly.
A draft of the workshop program should be available by June for
iteration. A website has been implemented at
*http://nercslr.nmt.ac.uk/workshop2005/workshop2005.html*.

**Action**: WG chairs should provide topics for the fall workshop to
Appleby. Chairs should also provide the local organizing committee with
an indication of how much time is required for each splinter meeting.

The meeting ended at 21:00. We would like to thank Harald Schuh from the
Technical University of Vienna for providing the facilities and
refreshments for this meeting.