Session Summaries

In addition to the workshop summary below, summaries are available for the following sessions:

• Scientific Achievements, Applications, and Future Requirements
• Lunar Laser Ranging
• Improved or Upgraded Systems - Poster Session
• New Applications
• Atmospheric Correction and Multiwavelength Ranging
• System Calibration Techniques
• Engineering and QC Analysis
• Automation and Control
• Targets, Signatures, and Biases
• Advanced Systems and Techniques
• Operational Issues

The Fourteenth International Workshop on Laser Ranging continued in the tradition of providing a venue for technologists and analysts to meet and relate the current status of laser ranging from data acquisition through data analysis and interpretation. The workshop was organized into 11 sessions held during the week of June 7 - 11, 2004.  The Workshop was opened with welcoming addresses and some historical overview. The participants were then treated to a briefing on the history of the Real Instituto y Observatorio de la Armada (ROA) which is celebrating its 250th anniversary.

The first day activities, which focused on scientific achievements, applications and future requirements, included an introduction to the new “Global Geodetic Observing System” project which is being organized under the International Association of Geodesy (IAG) to

integrate space geodetic techniques as well as terrestrial observations into a single coordinated entity to support long-term, precise monitoring of the geodetic observables. The intent is to provide observations of the three fundamental geodetic observables, the Earth's shape, gravity field and rotational motion to maintain a stable, accurate and global reference frame for science and applications.  A number of ILRS Analysis and Combination Centers reported on the state of their SLR and LLR derived output products including weekly solutions with sub-cm station position accuracy, geocenter variations at mm-sensitivity, and temporal variations in the low degree/order terms of the gravitational field. SLR observations of EOP continue to improve and SLR observations continue to play an important role in the development of static and time-varying gravity field models.  Poster sessions included status on several current missions, the upgrade status of several SLR stations, SLR as a calibration tool for other techniques, and seasonal environmental signals at laser ranging sites.

In lunar laser ranging, the LLR systems at OCA is being upgraded with new technologies that will include ranging to low Earth orbiting satellites and strategies for finding Lunakhod 1. Efforts are underway to introduce LLR at Mt. Stromlo and work continues on APOLLO at Apache Point with an eye toward operations in 2005. Several papers were given on lunar data analysis and lunar science and analysis.

Under new applications CNES proposed the T2L2 laser time transfer experiment on the Myriade Microsatellite as a means to achieve psec timing. A plan for global laser communications using a network of modified SLR2000 systems was discussed as a means for gigabyte data collection from space vehicles.   There were also three talks on planetary laser altimetry missions including Bepi-Colombo Mercury Mission and Mars Orbiting Laser Altimeter (MOLA).

In the session on atmospheric correction and multi-wavelength ranging the Shanghai Observatory reported using dual wavelength Raman ranging to LEO satellites. The Yunnan Observatory presented the results of an adaptive optics experiment to improve the LLR link budget with tip-tilt mirror pointing corrections using lunar surface features. The Graz station presented results using its new 2 KHz laser on ground and spaceborne targets for studies on turbulence and its influence on ranging. A poster presentation on atmospheric refraction modeling indicated that it might be helpful to improve both the spatial sampling resolution of atmospheric data and the spectral sampling resolution of refractivity measurements for a better understanding of the group velocity as applied to SLR.

Several groups are working on new calibration techniques. Tests at Mt. Stromlo with five spatially distributed calibration targets give uncertainties of a few mm, indicating that systems that rely on single targets may be doing even worse. We probably should stress a multi-target approach. Short target calibration tests at the Herstmonceux station also indicated that multiple targets should be considered if we want to reach mm accuracies. Stability tests at Matera were reported to give LAGEOS full rate data RMS of 5mm and a long term station ranging stability at the mm level.  Reports were given on PICO EVENT Timer, which can now handle repetition rates up to 2KHz, and the new RigaA031ET Event Timer, which showed that linearity and stability is within a few ps and that this may be an inexpensive alternative to other higher priced units.  A presentation was also given on a small electronic device which uses the time difference between the compensated and uncompensated output of the C-Spad to determine return signal strength.

Under engineering and Q/C analysisa study on numerical noise introduced by data fitting procedures concluded that errors as large as one mm could be introduced in normal point data and three mm in single shot data.  A study on interpolation effects indicated that predictions should be integrated at step sizes much smaller than the normal point bin size and that interpolation should be done in x/y/z rather than azimuth/elevation/range. The first version of the Engineering Data File system is working in Riga. The system is being implemented in Potsdam, Graz and Wettzell.

Several groups reported on their QC analysis of network data. In particular, the prediction time bias detection and monitoring system at Herstmonceux is operational, providing rapid-turnaround information to the community.

Several groups reported the implementing of automation and remote control features at their ranging stations. A remote control demonstration via the internet and cell phone of tracking at the Zimmerwald station was very impressive. The new remote control systems for the operation of the GUTS station through dedicated communications lines from the Tsukuba Space Center was also demonstrated. Presentations were also given on the mathematical analysis required to completely define the effects of the telescope and transceiver optics on the SLR2000 laser transmit and receive pulses and on the new Consolidated Laser Ranging Prediction Format,   which provides a single format for SLR, LLR and transponder predictions.

Several new satellites with retroreflectors have been launched, are planned for launch in the next few years, or are being proposed. Some are trying novel approaches to reducing the spread of the return signal. ETS-8 to be launched in geostationary orbit in 2006 will have a return signal strength equal to approximately 1% of that from LAGEOS. The design for the Shenzhou-4, the first Chinese reflector satellite in space was discussed. A report was given on the experience with three different array concepts: Reflector satellite with a distributed array, LARETS spherical satellites with small recessed corner cubes, and Meteor-3M satellite with a Luneberg sphere.  Several talks were also given on analytic orbit design tools for future missions and non-gravitational force modeling for LAGEOS.  Some impressive tests were reported with the Graz 2 KHz laser that singled out individual cube corners on satellites.

Studies continue on satellite signatures and satellite induced range biases that can corrupt the estimation of geodetic observables.  Tests have been conducted at several stations to quantify center-of-mass offset over the operating range of signal strengths. Tests will be formulated by which stations can characterize these effects over their dynamic range of operation.

In the technology session there was a presentation on the Graz 2 KHz laser ranging system which is now fully operational with 10 ps, 400 microjoule pulses at 532nm. Hundreds of thousands of returns per LAGEOS pass are quite common. Work continues on the SLR2000, with results from early satellite passes looking quite promising. The GUTS station reported that remote-controlled operations began in early 2004 with tracking on LEO to GEO satellites. The Mt. Stromlo station is being rebuilt quickly with enhanced systems, more automated expert software, and projected lunar capability. Two-telescopes with  1 m and 1.8 m apertures and a kW-class laser with adaptive optics are also being built at Mt Stromlo for space debris  tracking, laser ablations, and other research programs. A new two-color KHz SLR system being built in Wettzell should be ready for ranging in 2006.

Under technology for the future, presentations were given on a new concept for a compact, totally passive multipass amplifier for a laser transmitter, and new detectors for the eyesafe region of 1500 nm.

In the session on operational issues, several papers were given on network response to the weekend scheduling and funding reductions, progress on resurrecting and improving the station data report card, and the new data structure being adopted by the data centers. Reports were given on the status of the Real Time Station Status Exchange, which a number of stations have already incorporated into their operations.

In addition to updates on many of the current satellite missions on the ILRS roster, reports were also given on the new Korean Research Center (Satrac) and a new solar research and engineering test bed satellite with retroreflectors that is being considered for launch by the Koreans in the 2005-7 timeframe, and a French drag free microsatellite being considered for launch as a test of the Equivalence Principle in 2006.

ROA hosted a reception and a tour to the SLR station and the Observatorio library and museum on Tuesday evening. The tour also included the FTLRS which was collocated at the site.

The participants of the workshop express their sincere appreciation to the ROA for its hospitality in hosting the Fourteenth International Workshop on Laser Ranging.

The Fifteenth Workshop will be held hosted by Geoscience Australia and EOS in Canberra in October 2006.

Michael Pearlman, Program Committee