ILRS Governing Board Report

Nice, France
April 9, 2003

Attendees and Agenda

Ron Noomen, Graham Appleby, Wolfgang Seemueller, David Carter, Pippo Bianco, Peter Shelus, Georg Kirchner, Werner Gurtner, Hermann Drewes, Bob Schutz, and Mike Pearlman

The meeting agenda and the agenda for the General Assembly are included in Attachments 1 and 2.

Review of Tracking Status

Mission Items

Tracking is proceeding well on the new active satellites, GRACE A/B, Jason, and ENVISAT.

The Reflector tracking campaign ended in February 2003. The IPIE is very pleased with the 3,670 passes acquired from December 2001 through March 2003. Analysis of the data is underway. A limited ADEOS-2 tracking campaign was conducted from December 2002 through January 2003 to help define the orbit. A few pre-approved stations are continuing the tracking support, as great care is being taken not to jeopardize the on-board optical sensors. Etalon tracking was officially changed from campaign to "regular" status in October 2002 to support Earth rotation measurements, gravity field modeling, and station quality control. ICESat was launched on January 12, 2003. A few carefully selected SLR stations started tracking in March 2003, as the tracking operations plan is being developed to avoid risk to the on-board optical detectors. HTSI is generating predictions based on both GPS and SLR. STARSHINE-3 re-entered on January 21, 2003. Although not an official ILRS missions, it was being tracked by some of the stations.

Gravity Probe B is scheduled for launch in November.

Station Items

The Maui SLR has finally emerged from upgrading with much improved performance. The now operational MLRO is providing SLR and LLR data. The Mount Stromlo station was destroyed by fire in January 2003; the station will be rebuilt. The refurbished CRL station at Koganei, Japan is now back in operation. The National Astronomical Observatory, Academia Sinica mobile system is currently undergoing system testing in Beijing in preparation for relocation to the San Juan Technical University in Argentina later this year.

The FTLRS completed an occupation in Ajaccio, Corsica in September 2002 and is now being relocated to Chania, Crete. The TIGO is operational at Concepción Chile. The new SLR stations in Potsdam, Germany and Lviv Ukraine are now operational. Work proceeds on the SLR2000 and the new Lunar Ranging station at Apache Point in Washington State.

Local Survey

Site surveys have been a major problem impacting the space geodetic reference frame, especially related to collocation of techniques needed for TRF combination. Problems include inconsistencies in the ground survey techniques used, the survey network geometries, the survey analysis, the documentation, discrepancies between site survey and TRF results, etc. The ISGN committee under John Bosworth made an assessment of the local survey status for each station in the SLR and VLBI networks; an action plan with priorities was developed.

A Joint Service team with IGN (Zuheir Altimimi), IVS (Chopo Ma), ILRS (Mike Pearlman), and NASA/Survey Team (Jim Long) are building on the earlier activity. This team will probably evolve into a working group within the new IAG organization, perhaps under the IERS. Jim Long has developed and circulated draft survey standards documents and he is running tutorial survey sessions at major meetings. A joint IGN/NASA team was making arrangements to visit Shanghai to participate in a site survey and to compare survey techniques with the Chinese survey team (the SARS epidemic has delayed this). Discussions are underway with HartRAO on a planned site survey

The Survey Team plans to hold a survey workshop for practitioners on Thursday and Friday, October 23 and 24, 2003 in Matera, Italy. The workshop will focus on survey techniques, analysis, data bases, and plans for resolving the local survey shortfalls that currently exist with the SLR and VLBI networks.

Additional people with survey experience are needed on the team to help educate others and to participate in the site surveys at critical stations.

There is concern that some stations may not have ground markers for their local survey ties. These should be strongly recommended.

Operational Issues

Full rate date is now flowing routinely into the Data Centers. The ILRS web site has been updated with a new navigation scheme, a new front-page bulletin board, and additional station performance, diagnostic, and operational practices web pages.

Working Group Highlights

Analysis Working Group

Work proceeds on the Pilot Projects. The Benchmarking and Orbits Project is comparing parameter solutions to isolate "blunders" and software inconsistencies. The Harmonization Project continues the development toward a unified means of identifying system biases. The Positioning and Earth orientation Project continues our development toward unified, official ILRS combination position and EOP products
A Call for Participation under the Positioning and Earth orientation activity was issued in November 2002. Groups responded for both individual SLR solutions and combination products.

The Analysis Working Group met on March 31 - April 1 to review progress and plans paced toward an evaluation of results at the next Working Group Meeting on October 26 - 27. Key dates are submission of benchmark solutions by May 31, submission of analysis solutions by October 1, and evaluation of combination solutions by October 21.

The IERS plans to move to more stringent data products. They want to move to rigorous combination solutions of networks on a weekly basis with daily EOP resolution. The ILRS is expected to participate with a single or a combination product, which should be available with no more than a 4 - 6 weeks delay. The IERS is planning to undertake a Pilot Project to test this concept. A Combination Working Group will be established on May 1, 2003, a Call for Proposals to do the technique solution combinations will be issued at the end of June, proposals are due on September 15, proposals will be evaluated by early October, and the pilot project will start on January 1, 2004. It is anticipated that this new combination product will replace the current product and that the old SLR, VLBI, and GPS data will be reprocessed in this manner. A time-series of weekly solutions should eventually evolve into multi-year solutions. With this in mind, The Analysis Working Group is updating its solutions to be compatible with this new one week/one day requirements.

A revised plan for station qualification was presented and discussed. With a few modifications, it was recommended that the plan be brought before the Governing Board for approval. (See Station Qualification below).

The Analysis Working Group plans to hold its next meeting at Koetzing/Wettzell, on Sunday and Monday, October 27 and 28, just prior to the ILRS fall meeting.

Networks and Engineering Working Group

The response to the Minimum Number of Returns per Normal Point Criteria that was approved by the Governing Board last year was reviewed. (See Minimum Normal Point Criteria below.)

Some stations are benefiting from the Global Use of Real-Time Time Bias Exchange and Time Bias Prediction File. Another notice will be sent out to encourage implementation

Work is underway by Van Husson on "MyStationPerformance.Com", a means for the stations to get an assessment of their performance. Van is also working on new powerful bias-detection capabilities using a combination of data analysis and ancillary data tools.

As we approach mm range performance, on-station engineering data checks and tests are even more essential to reveal, understand, and correct system biases. It is unrealistic to rely on the after-the-fact analysis only. The working group is initiating a comprehensive Engineering Data File (EDF) that should be maintained at each station, which can be queried in intelligent ways to expose problems. The file would contain station parameters, settings, calibration and ranging information, meteorological data, etc. The working group is developing a flexible format to allow stations to begin by participating at their own level. With the file, each station should be able to check for consistency, linearity, jumps etc., and the analysis groups could easily cross-correlate residual signatures.

Several stations (Matera, RGO, Graz, NASA) have agreed to check the possibilities using their systems, and to implement the data file as soon as a first test format is defined. First results will be reviewed at the Koetzting/Wettzell meeting in October.

Data Formats and Procedures

New data format and integrity checks are now operational at both Data Centers. The barometeric checks still need to be installed at EDC. Full rate data is now being routinely delivered to the Data Centers. A backup to Urgent mail is in process at EDC. There is some feeling that we should rely on the SIC satellite numbers rather than the COSPAR number since the COSPAR numbers are not properly designated at the time of launch.

Prediction Format Study Group

The latest version of the new proposed extended format includes some updates in response to the most recent suggestions. Werner Gurtner has been investigating the accuracy of normal points using the new format and a sample integrator, used LaGrange polynomials of order 6 with the time of interpolation always being in the central interval of the polynomial. On LAGEOS, Starlette and Stella (1) the interpolation in geocentric space (x, y, z) produces orders of magnitude better results than interpolating in topocentric space (az, el, range), and the (2) the interpolation of predictions over a pass gives deviations from the reference orbit of about 1 mm for LAGEOS and worse for other satellites. However, breaking the pass into segments the length of a normal point and fitting these segments gives much smaller deviations. Further improvement can be achieved with a higher order of the interpolation.

Work continues on the format with SLR, LLR, and Mars spacecraft predictions. The next steps for this study group are to revise the formats, work on sample code, document the algorithms, and start field tests.

Refraction Study Group

Several reports were given on refraction. Attempts to update the Marini and Murray model offer some promise, especially at low elevations. Early two wavelength data from Matera looks interesting. Analyses of residual patterns at low elevations also look interesting. There was a general request for the stations to take more low elevation data, down to 0 degrees if possible, on a selected set of satellites to provide a more robust data set for investigation. The CB will query the stations on their constraints to tracking below 20 degrees altitude and request that they lower their tracking horizons as low as possible on selected satellites

Missions Working Group

The Missions Study Group focussed mainly in the issue of Dynamic Priorities. Bart Clark reported on a comprehensive scheduler that is being developed by Honeywell. The system will have sufficient flexibility to interleave passes, adjust priorities by satellite and by station, and make use of historic information and decision algorithms formulated by the ILRS or by subnetworks. Honeywell will implement and manage the program and the service for any stations that are interested. The software is an outgrowth of the schedulers now used by the NASA network and will evolve in steps that are digestible for the field stations.

Mike Pearlman presented some thoughts on less ambitious concepts that had been discussed by several Governing Board members. See Dynamic Priorities below.

Signal Processing Working Group

Center-of-mass corrections (CoM) for the principal spherical geodetic satellites LAGEOS, ETALON and AJISAI for the three main tracking system types, single-photon, C-SPAD and PMT/MCP have been tabulated. The corrections have been evaluated as functions both of numbers of photoelectrons and of data clipping procedures for the single-photon detectors and as functions of pulse width for the 'leading edge' (PMT/MCP) systems.

In order to take best advantage of this information, some measure of estimated return level should be available in the ILRS normal point data taken by all the tracking systems. This information would supplement the general information on detector characteristics that is available in the site log file. The information would probably only need to be fairly 'course' and averaged over each normal point bin.

The Working group will examine whether there is currently enough information in the site logs to properly characterize each station, pursue whatever is missing, and recommend a means of coding signal strength in rough categories in the normal point file.

The Working Group has also been requested to compute CoM values for STARLETTE and STELLA.

Work is underway on the development of a web page that tabulates all of the CoM information for the users. A format has been proposed by Mark Torrence and links to CoM correction tables, taken from Otsubo & Appleby, 2003, are in place for the spherical satellites. Some details have also been tabulated on satellite-fixed coordinates for LRA phase centers on other satellites. See Center of Mass corrections.

Lunar Working Group (Tentative)

The Lunar Ranging Community is preparing a charter for presentation to the GB for the formation of a Standing Working Group.

ILRS Station Qualification

Previous plans for formal qualification of ILRS stations had met resistance from some members of the Governing. Board. Some did not support designation into three categories (Core, Operational, and Associate stations), and some were sensitive to the precipitous "demotion" of weak stations for fear the they would loose local support. There was also the issue of whether special "mobile" stations could qualify on LEO satellites only.

Mike Pearlman presented a revised plan that had been worked up by several members of the Governing Board and revised by the Analysis Working Group.

All ILRS Stations would be classified as Operational or Associate, with all current stations initially considered as Operational. New stations would be accepted as Associate by the Central Bureau upon submission of ILRS Station Response form. Associate stations would become Operational by:

  • submitting a valid site log,
  • delivering at least 10 passes of normal point data to the CB which then pass CB format and data integrity validation,
  • delivering at least 20 LAGEOS passes over a consecutive 3-month period to an ILRS operations center,
  • passing a data evaluation by the Analysis Working Group (see below),
  • being approved by the Governing Board

The data evaluation criteria would be:

  • normal point RMS of 1 cm (Shanghai Criteria)
  • short term range bias stability of 4 cm (twice Shanghai Criteria)
  • normal point acceptance rate of 80%

As of January 1, 2004 all ILRS stations would be evaluated on a quarterly basis. To be classified as Operational, a station must have submitted (1) at least 50 valid LAGEOS passes (as described above) in any 3-month period during the previous 12 months; and (2) a current site log. Those stations that do not satisfy these requirements will be relegated to "Associate" status. Station status, Operational or Associate, would be denoted on Quarterly Report Cards issued by the CB. Stations must range to LAGEOS to be categorized as Operational.

The Analysis Working Group is welcome to designate a network of higher performing core stations for its users and may list this on their web site.

The Governing Board approved this proposal. The CB will send out a notification on Station Qualification and will augment the current Report Card program to denote categories by January 1, 2004.

Assessment of On-line Prediction Updates

Werner Gurtner reported that Graz, Wettzell, Potsdam, Zimmerwald, Grasse, FTLRS and Herstmonceux are presently feeding the on-line tracking exchange. Thirteen stations are accessing the time bias distribution website, presumably for rapid prediction updates. All stations are encouraged to use the service and to give feedback on how the service may be more helpful.

Dynamic Priorities

Mike Pearlman presented some concepts on dynamic priorities that had been under discussion.

We have two cases to consider:

  • Data is very abundant or very sparse and we want to key stations to adjust their tracking priorities; and
  • We want to decrease (or increase) tracking overlap between stations that are in close spatial proximity.

Case 1

In the first case we have mid-altitude satellites such as Be-C and Ajisai that are being overly tracked, while data should be increased on Etalon, GLONASS, and GPS. Two approaches are being considered:

  • The CB would monitor data yield and issue a priority update key on the AIUB real-time prediction service for each satellite based on a GB approved criteria. The key would be based on recent tracking density and elapsed time since the last pass was acquired. The index might run from +2 (top priority) to -2 (do not track at all). Numbers would be adjusted as we gain experience.
  • Stations would be issued the minimum number of passes that we expect per satellite per day or week. When those minimum numbers are achieved, stations should then focus on conflicting lower priority satellites whose minimum has not yet been achieved.

The Analysis Working Group preferred the second option and recommended that we focus on the stations that would be most effective.

Case 2

The station overlap condition is mainly in Europe. Some stations in Europe are already registering their real-time status on-line using the AIUB real-time prediction service. One station can see if another is already tracking a particular satellite and then make a decision based on data criteria. The remaining stations in Europe should be encouraged to join in this process and decision-making criteria need to be established. Whether data overlap should be increased or decreased depends on how much overlap is required for data quality control.

The Central Bureau will make a proposal on case 1. A solution for case 2 should probably be proposed by EUROLAS.

Minimum Normal Point Criteria

Many stations are not adhering to the Minimum Number of Returns per Normal Point Criteria approved by the Governing Board. This is an important means of self-examination by the stations and a way to improve the data for our users. The Central Bureau will notify the delinquent stations and prepare a status review for the fall meeting.

Spacecraft Center of Mass

Topic covered under Signal Processing Working Group Report above.

Fall Meeting

The SPIE will not be able to accommodate our ILRS meetings in Barcelona as originally planned due to space limitations. Two alternative proposals have been graciously offered - Koetzing/Wettzell (BKG) and Canberra (AUSLIG). Because of logistics, and the need to arrange a tandem meeting on Local Surveys, the GB preferred that the meeting be held at Koetzing/Wettzell.

The meetings would be held Tuesday through Friday, October 28 - 31. The plan is to have specialized sessions to address specific topics and either bring them to closure or get them properly formulated so they can be properly acted upon. Each Working Group and/or Study Group will be responsible for organizing at least one topic session. Additional topic sessions may also be organized. Topic examples include refraction model, prediction format, spacecraft center-of-mass correction, dynamic priorities, local survey issues, hardware characterization, data flow, etc.

Sessions would be scheduled in tandem so everyone could participate. No formal General Assembly would be scheduled, but a general meeting and a Governing Board Meeting would be organized to allow some discussion
The CB will work with the local meeting organizers and the Working Groups to get the meetings organized.

The Analysis Working Group will schedule a 2-day meeting at Koetzing/Wettzell, just prior to the fall meeting, probably on Sunday and Monday, October 26 and 27. The Survey Group plans to schedule a Working Group Meeting just prior to the Analysis Working Group Meeting. The Survey Group Meeting will probably be held at Matera on Thursday and Friday, October 23 and 24.

ILRS Annual Report

The Annual Report 2001 is available on the web and in hard copy. The call is out for contributions for the Annual Report 2002. This report, which will be structured around issues and topics rather than ILRS entities, should be considerably shorter that the previous reports. The Table of Contents for AR2002 is included as Attachment 1. Assignments have been made and contributions are due to Carey Noll by May 9.

International Workshop on Laser Ranging

All session summaries from the Thirteenth International Workshop on Laser Ranging held in Washington D.C. are posted on the workshop web site along with the workshop summaries and the resolutions.

So far, 66 presentations, 11 posters, and 87 papers are posted on the web site out of a total of 113 papers. The Proceedings will be issued as a CD with hard copy of the science and applications papers. A concerted effort is presently being made to encourage the last few submissions. In particular, we want to include as many of the science papers as possible.

The Fourteenth Workshop will be held in San Fernando from June 7 to June 11, 2004. Each of the Networks has been requested to name a person for the Organizing Committee.

Action Items

  • All Operational stations should have GPS receivers and be IGS Global Station, following IGS Standards with continuous data delivery (CB will check TOR and submit for GB approval);
  • Secure IERS written support for SLR and LLR (Noomen and Shelus)
  • Check all old SLR stations (back through Merit) for Domes Numbers (CB);
  • Check availability and interpretability of early data at least as far back as Lageos I (CB);
  • Activate stations to track down to 0 degrees on Lageos, Jason, Envisat, CHAMP, and GRACE to support refraction studies (CB);
  • Develop proposal on Dynamic Priorities, considering suggestions from the AWG (CB);
  • Resolve data resupply and storage issue (Data Centers, CB);
  • Develop signal strength and detection reporting scheme by stations (SP W/G);
  • Contact delinquent stations on Minimum Normal Point data content issue (CB);
  • Query stations on available site engineering information (NE W/G);
  • Encourage stations to use real-time Prediction Update System (Gurtner/CB);
  • Expedite data flow from stations, through CB, to NERC for more rapid prediction updates; aim for 5 minute cycle intervals (DF&P W/G);
  • Set up Survey Working Group Meeting in Matera in October (CB, ISGN team and IERS);
  • Develop whole protocol and organization for the Survey Working Group (ISGN and IERS);
  • Include time bias for "yesterday's" prediction orbit on Real Time Prediction Update System (NERC);
  • Organize sessions for Koetzing/Wettzell meeting (Working Groups/CB);
  • Announce Station Qualification Policy as approved by the GB (CB);
  • Examine alternative analysis strategies for improving data products (Analysis Working Group, CB);
  • The stations should be queried if they have a ground marker for the station survey reference; if not, it should be strongly recommended (Survey Team and CB)

Attachment 3