Quick Links
Fourth General Assembly of the International Laser Ranging Service (ILRS)
Nice, France
Thursday, April 27, 2000
Editor's Note: All Attachments are available in hard-copy. Please contact Dr. Michael Pearlman (email Pearlman@cfa.harvard.edu), ILRS Central Bureau Secretary, if you would like a copy of an attachment. The minutes are also available in MS word.
The Fourth General Assembly of the International Laser Ranging Service (ILRS) was held in Nice, France on April 27, 2000, in conjunction with the European Geophysical Society XXV General Assembly. The agenda for the meeting and the list of attendees are included in Attachments 1 and 2.
Governing Board
The Governing Board (GB) Chair, John Degnan, welcomed the participants and reviewed a few of the key developments over the past year. Of note was the progress made by all of the Working Groups in organizing their activities and influencing the direction of the ILRS (see Table 1). The Missions Working Group has formalized the documentation and procedures on new campaigns and missions. The Data Formats and Procedures Working Group has tightened up and standardized many of our procedures and has set up study groups and teams for some of the more complicated issues. The Networks and Engineering Working Groups has developed the new Site Information Log, provided on-line link analysis, and organized the ILRS Calibration Workshop in Florence. The Analysis Working Group has pilot studies well underway toward the development of a standard ILRS solution for station positions and Earth orientation parameters. The SINEX format has been adopted by the analysis groups, and most of the issues with its usage on SLR data have been resolved. The Signal Processing Working Group is computing satellite center-of-mass distributions and developing recommendations for establishing procedures for center-of-mass corrections.
John Degnan also pointed out the expansion of the ILRS network now underway in the Southern Hemisphere (See Figure 1), and the addition of the TIGO and the MLRO.
Central Bureau
Station Performance (Attachment 3)
Van Husson briefly reviewed Network Performance. The Performance Report Card for the last quarter has been issued and is on line. Over the last 12 months, half of the network stations met, or nearly met, the pass criteria in all three categories (LEO, LAGEOS, and high satellites). Twelve stations met or exceeded 20,000 minutes of observations. Twenty-four stations showed improvement in data volume over the previous year, and twenty of the stations met the long term bias stability criteria of 2 cm. Performance is noticeably improving.
Status of the ILRS Website (Attachment 4)
Van Husson also presented some of the web enhancements that have been introduced since the meeting in Florence. A quick reference card has been developed to help users navigate their way around the ILRS site. Interactive queries, mail exploders, campaign statistics, and expanded site information including SOD, DOMES, site coordinates, eccentricities, station status reporting, etc. have been added. The data-flow process and the prediction options for all satellites have been documented. Work is currently underway on the implementation of the Site Information Logs and the SLR Knowledge Base.
Campaigns, Satellite Priorities, and Upcoming Missions (Attachment 5)
Mike Pearlman reviewed the campaigns, satellite priorities, and upcoming missions. The campaigns on GFO-1, Sunsat, and Beacon-C have all been extended through the end of October. The campaign on ERS-1 had been extended through the end of the year, but the satellite failed on March 10 after a long and very successful mission. ERS-1 relied solely on SLR tracking for POD after the on-board PRARE navigation system failed very early in the mission. Three new missions are scheduled for launch during this calendar year. CHAMP has now been delayed until mid-July. JASON-1 and ADEOS II are planned for launch in November and December respectively. Starting with CHAMP, many of the new missions over the next several years are active satellites in low orbits, which will require special effort to ensure adequate orbital coverage and accuracy. The ILRS is in the process of instituting (1) daily and sub-daily prediction services and (2) hourly normal point data updates to the Data Centers to support the rapid prediction turnaround. Stations have been requested to begin submitting their data as rapidly as practicable, and the Data Centers now refresh the available data sets hourly.
Annual Report (Attachment 5)
Progress continues on the ILRS 1999 Annual Report. Several key sections are still missing and the remaining authors were requested to expedite their contributions so that the hard copy report can be issued in a timely manner. Completed sections will be available online via the ILRS web site.
Science Coordinator Report
Peter Dunn reported that scientific results from laser ranging observations were widely presented at the EGS2000 Meeting; half of the twenty-odd talks in the Laser Technology Section of the 'Evolving Geodesy' part of the conference were devoted to science results.
The scientific contributions of laser data were also demonstrated in papers in the sections on Gravity, Earth Orientation, and Reference Systems. Upcoming events in which new scientific results are anticipated to include the American Geophysical Union Meeting, the WEGENER Meeting and the Laser Workshop in Matera. The ILRS web site includes a description of the applications of laser measurements, which can be downloaded from the Science/Analysis page, to further encourage the scientific application of the systems.
Key Challenges for the ILRS
Key challenges for the ILRS over the next year were identified:
1. strengthen the science liaison activity;
2. maintain the momentum of the Working Groups in developing and addressing their action plans;
3. improve the tracking response to "very" low earth orbiting satellites through improved coordination and predictions in preparation for missions such as CHAMP and GRACE;
4. encourage and help tracking stations and analysis centers to meet their minimum performance criteria;
5. develop an ILRS "standard global solution" for submission to the IERS and for maintenance of the (laser ranging component of the) International Terrestrial Reference Frame (ITRF);
6. continue the process of implementing the modified SINEX format to SLR and LLR solutions to further encourage the use of different data types in combined solutions;
7. continue the development of the ILRS website and data bases, in the areas of technology, science and applications, and operations, and formalize the process by which updates are approved; and
8. continue the process of documenting station configuration and standardizing of processes/procedures.
Subnetwork Reports
EUROLAS (Attachment 6)
Werner Gurtner reported that backup procedures are being sought to cover predictions and data uploading during outages at CDDIS and/or EDC. This is a common problem and needs to be solved for the entire global network. Activities are underway to provide some additional hardware to the Riga station. BKG has chosen the site at Conception, Chile for the first deployment of the Totally Integrated Geophysical Observatory (TIGO) later this year. The MLRO has been installed in the new building in Matera and is presently undergoing tests. A collocation between the SAO system and the MLRO was strongly encouraged prior to the closeout of the SAO system. Work also continues on the FTLRS in preparation for the upcoming launch of the JASON oceanographic mission (TOPEX/Poseidon Follow-on).
WPLTN (Attachment 7 and 8)
John Luck reported on the WPLTN activities. Mt. Stromlo and Yarragadee continue to place among the top performers in the global network. A number of technological developments including autonomous ranging capability have been implemented at the Mt. Stromlo station. The Orroral building is now sealed, and much of the reservation has been returned to nature. The five-week Etalon Campaign in late 1999 was successful, with a considerable increase in data over the campaign period. A follow-on campaign will be scheduled again in late 2000.
Performance of the four KeyStone systems has improved considerably over the past year, however administrative and funding problems are closing in. The systems were built on the premise that an operational agency would assume responsibility for operations. This has not happened and Tateyama and Miura will close at the beginning of June 2000. The long-term fate of Koganei and Kashima is also very uncertain beyond September 2000. The Simosato station is productive again.
Yang Fu Min reported that the performance of the Chinese stations continues to improve (see Attachment 8). The four fixed sites at Beijing, Shanghai, Kunming, and Changchun continue to operate. The move of the Wuhan system is now complete and operations should commence shortly. The past few years have seen upgrades at several of the stations. The Xian Institute of Surveying and Mapping now operates a mobile system. A second mobile system is being built for the Institute of Seismology in Wuhan. The SLR systems have been taking part in a national project, the "Crustal Movements Observation Network of China". Under this program, the mobile systems will occupy fourteen sites around the country over the next several years. Under a cooperative program with the San Juan Observatory, a Chinese SLR system, similar to the Beijing system, is planned for deployment in Argentina at the end of 2001.
There was no report given on the Russian network.
NASA
David Carter reported that MOBLAS-6 is ready for transfer to the Hartebeesthoek Radio Astronomical Observatory in South Africa under a joint NASA and South African National Research Foundation (NRF) program. The system will be shipped in early May 2000. South African station personnel underwent training at GSFC over the period November 1999 to March 2000, and operations are scheduled to be underway in the second half of this year. A draft Memorandum of Understanding between NASA, CONAE, and the University of La Plata in Argentina, for the relocation of TLRS-4 to the Radio Observatory in La Plata, is under review. Transfer could take place as early as spring 2001.
Data Centers (Attachment 9)
Wolfgang Seemueller gave a consolidated EDC/CDDIS report. New charts depicting the ILRS data flow, the Directory Structure, and the new hourly data submission scheme were presented. Although checksums accompanying data submitted by the stations have been considered optional, incorrect checksums have presented some concern, and EDC has been rejecting such passes. It was agreed that stations should either omit the checksum, set it to zero, or calculate it correctly. EDC and CDDIS have been working to reconcile differences in pass counts in their respective data archives. A few lapses in transmission and some differences in data acceptance criteria have led to these discrepancies, but they have now been reduced to below the 1% level and scrutiny continues.
Both EDC and CDDIS have suffered several outages and slowdowns, causing concern about our rapid communications and data/prediction procedures. We have a strong need for implementing improved reliability and redundancy.
Working Group Reports
Missions (Attachment 10)
Scott Wetzel reported on the activities of the Missions Working Group. Misidentification of satellites by NORAD has caused considerable confusion for the network. Most of the problems have now been corrected, but the procedure of allocating COSPAR numbers is still a bit loose. We need to pay very careful attention to the numbering of new satellites; especially those involved in multiple launches. The new Signal Processing Working Group is working its way through the array corrections for the SLR satellite constellation. Additional effort is required to make sure that all of the relevant information is provided by the satellite owners. The Missions Support Request Form is now on the ILRS website, but the form still needs a few updates to add some "intelligence". The Working Group and the Central Bureau need to implement a procedure to review user requirements for all satellites being tracked by the network. Concern was again expressed at the lack of notice prior to GFO-1 maneuvers. The Central Bureau will notify the GFO-1 project that more timely notice is required.
Ten missions are planned for launch over the next three years. CHAMP (July 15), JASON-1 (November), and ADEOS-II (December) are scheduled for launch this year. Mission Support Request documents are still required from the latter two missions.
Networks and Engineering (Attachment 11)
Werner Gurtner discussed the activities of the Networks and Engineering Working Group. The Site Log has been drafted and tested at four sites. The form has been submitted to the Central Bureau with a draft set of guidelines for implementation. Within the Site Log formulation, the Working Group has recommended that we adopt a four character station code (similar to the IGS) for general use, from the naming of station files to highlighting maps and tables. An online link budget calculation program, available via the ILRS Web Site, has been updated by Stefan Riepl to compute expected mean signal strength results normalized to LAGEOS as a function of individual station characteristics. Work on the bibliography continues by the Central Bureau. Provisions for adding key words to each article and keeping the bibliography current needs to be implemented. At the recommendation of the Working Group, the ILRS information distribution system is being reorganized. SLReports will now be used for centralized distribution of routine operational reports and a "Hotmail" facility will be established for urgent messages. A centralized distribution system for predictions is also being examined.
Data Formats and Procedures (Attachment 12 and 13)
John Luck presented the activities of the Data Formats and Procedures Working Group. Many of the Working Group recommendations on website information on predictions, SOD and DOMES designators, and weekly monitoring of station status have been implemented. Daily IRV generation has been established. Data checksums have been eliminated, the maneuver message has been finalized, and some changes to the IRV format have been recommended. A centralized exploder for predictions has also been suggested (see above). A Refraction Study Group has been established under Stefan Riepl (see Attachment 13). The group will assess current models, define new models, and recommend procedures for improved data collection and implementation. A report on its activities will be given at the Matera Meeting.
Analysis (Attachment 14)
Ron Noomen reported on the activities of the Analysis Working Group. At the Florence meeting in September 1999, the working group met to define products, formats and procedures for several pilot projects to generate, compare, and combine analysis solutions from the different groups as a fundamental step toward developing a definitive "ILRS solution" for submission to the IERS. Pilot projects on positioning and Earth orientation were established. The working group held a workshop in Frankfurt in January. Thirteen groups submitted first results on the pilot project. Problems concerning data products and formats, and other procedural issues were resolved. Two additional pilot projects on orbit comparison and software benchmarking were established. The next meeting of the Analysis Working Group is scheduled for Delft on May 22-23, 2000.
Signal Processing (Attachment 15)
Graham Appleby reported that the Signal Processing Ad Hoc Working Group continues to work on the impulse response for the spherical satellites. They are looking at satellites with homogeneous retroreflector distributions convolved with Gaussian system response functions. Comparisons are being made between high and low signal strengths and SPAD and MCP detectors. Coordinates of the retroreflectors on Etalon have now been determined. The positions of the retroreflector array panels on GLONASS have been established, and comparisons of GLONASS range data with the derived model are now underway. Considerable effort is being spent on the resolution of the difference between the SLR and microwave data.
Working Group results to date are available on the NERC web site linked through the ILRS website.
http://mtfiles.nerc-monkswood.ac.uk/nercslr/sig/signature.html
Missions Planning for CHAMP (Attachment 16a and 16b)
Rolf Koenig and Scott Wetzel brought us up to date on the mission planning for CHAMP. Flight acceptance review is underway. A final systems integration test is scheduled for the beginning of May. Launch has been postponed until 15 July (12:00 UTC). Test predictions will be issued by early May for tracking system checkout. Forecast of the initial station acquisition schedule (based on the new launch time) is available in Attachment 16a.
Because of the low 470-km orbit, GFZ will generate and issue predictions twice a day, based on the ILRS SLR data and GPS data collected at the GFZ site in Potsdam. HTSI and NERC will generate predictions as backups. Provisions are being made by the ILRS to expedite the data flow from the stations so that the most recent SLR data will be available for the prediction process. Stations are being asked to submit their data as often as practicable each day, with a goal of once per hour.
The Mission Support Plan has been drafted (see Attachment 16b). CHAMP will be tracked at highest priority during the Early Orbit Phase (2 weeks) and the follow-on Commissioning Phase (9 months). The satellite will also be tracked at highest priority during subsequent orbit change phases that may occur a couple of times during the lifetime of the mission.
Report from the Joint IVS-IGS-ILRS Working Group (Attachment 17)
Wolfgang Schlueter reported on the Joint IVS-IGS-ILRS Working Group that was established to help improve the determination of the phase centers of the GPS antennas using a combination of GPS, VLBI, and SLR measurements. The present uncertainty in the location of the electronic GPS phase center may be nearly one meter on some satellites. The idea of using VLBI was proposed by the IVS at the IUGG Meeting in Birmingham last year and then expanded to include SLR. Working Group members include Brian Corey and Ed Himwich from the IVS, Tom Herring and Tim Springer from the IGS, and Graham Appleby and Richard Biancale from the ILRS. The first meeting was held in Kotzting, Germany in February. The Working Group is currently gathering information about the GPS satellites and contacting other experts in related fields (including radio imaging of coherent sources) who could help.
Election of Governing Board Members (Attachment 18)
The current two-year term for ILRS Governing Board members will end in October. The new Board will be installed at the 5th General Assembly, to be held in conjunction with the 12th International Workshop on Laser Ranging in Matera during the week of October 16, 2000. The three Ex-Officio Members will remain on the Board. The seven Appointed Members may remain or be replaced at the discretion of the organizations they represent (i.e., IERS, EUROLAS, WPLTN, or NASA). The members of the Analysis Centers will elect two representatives. One representative will be elected by the members of the Data Centers and one by the Lunar members. Two members-at-large will be elected by the full ILRS membership after all of the previous positions have been filled. The Central Bureau will begin the nomination and election process in June. Nominations and elections will be carried out via email using official membership directories.
Twelfth International Workshop on Laser Ranging
The Twelfth International Workshop on Laser Ranging will be held in Matera, Italy during the week of October 16, 2000. Pippo Bianco reported that arrangements for the facility are being made and that the Organizing Committee is preparing the agenda.
Next Meeting
The 5th ILRS General Assembly and Governing Board Meeting will be held in conjunction with the Laser Ranging Workshop in Matera. The meeting will include a review of the campaigns in progress.
Editor's Note: If you would like to receive the attachments, please send an email request to Mike Pearlman (mpearlman@cfa.harvard.edu). These minutes are also available in Microsoft-Word.
