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