ILRS Networks and Engineering

Working Group Meeting

Nice, France

April 24, 2002

Attendees:

Graham Appleby, John Degnan, Buddy Donovan, Werner Gurtner, Julie Horvath, Van Husson, Toshi Otsubo, Carey Noll, Mike Pearlman, Ivan Prochazka, Randy Ricklefs, Ulli Schreiber, Wolfgang Seemueller, Peter Shelus, Scott Wetzel

EUROLAS Engineering Meeting:

A meeting on Detecting and Eliminating Errors in the EUROLAS Network was held at Herstmonceux on March 11 and 12. The notes from the meeting are on the ILRS web site:

http://ilrs.gsfc.nasa.gov/reports/special_reports/eurolas_workshop.html

Philosophy

        Long term goal should be mm accuracy

        Detect and reduce systematic errors

        Reduce Random errors (to better expose systematic effects)

        Stations have primary responsibility for data quality (good onsite data screening handling techniques)

Detectors

        C-SPADS

                Residual time walk determination with signal strength measurements or return rate

                Need to properly tune the device to accommodate pulse length dependence

                Carefully check alignment

                Request stations to test SPADs at high and low signal strength modes to quantify change in bias

        PMT

                Residual time walk determination with signal strength

                Avoid time walk with single photon operation

                Be aware of gating issues

Counters and Timers

        SR620 counters from several EUROLAS stations compared at Herstmonceux

                Tests conducted over full dynamic range

                        Individual characteristic for each counter determined

                All counters referred to PPET through earlier comparison at Herstmonceux

                        Characteristics available for application to individual counters

        Some stations will perform ranging tests on satellites at both high and low signal strengths

                NERC will analyze the data

        TU Prague will spearhead a proposal to the EU for a PPET standard to calibrate the SLR Network 

Data Reduction

        Carefully check and monitor system noise - key indicator of problems

        Compute and monitor other pass parameter - skew, kurtosis, etc

        Monitor return rates as a means of checking performance and signal strength

        Introduce minimum number of returns per normal point

                Daytime - 6 points

                        Nighttime - 3 points

                Leave provision for low repetition rate systems

        Reintroduce full rate date flow and archiving

                No real time requirement

                Include calibration data

        Introduce provision for withdrawal by the stations of poor data from the Data Centers (DFP W/G)

        Daily short and long arc quality check by NERC

"Near Real-Time" Distribution of Time Bias and Station Status through AIUB

        Expand usage throughout ILRS network

        Speed up time bias updates by expediting data flow

        Include time biases for all prediction sets used

Other Items

        Exchange stations personnel to spread knowledge

        Circulate a reference barometer around the EUROLAS network for calibration

Site Logs

Van Husson reported that site logs from forty-four stations have now been archived. Logs from Maidanak

And Komsomolsk are still missing. The logs are available on an Excel spread sheet data base with auto

filter search capability. (see ftp://cddis.gsfc.nasa.gov/reports/slrlog/). Where possible, manufacturer's

specifications have been included. All stations are requested to review their file in the site log archive and

report any errors to Van. Stations are also requested to keep their file in the site logs up to date.  New fields

can be added as the need arises. Historical station information will remain available in the old

configuration files. Van is also trying to obtain site log information from deactivated stations.

A file of engineering corrections (range, timing, meteorological, etc.) is also being assembled. These

include corrections determined at the stations (instrument, calibration, etc), but not yet applied to the data.

This facility will be available on line for the analysts to use in data processing. It will avoid the need for

stations to update data already submitted the Data Center files whenever such biases are discovered. New

data should of course be properly corrected.

The site logs also contain the site tie information, which the ISGN is trying to organize. We need to

implement a means of recording the site tie chronology and maintaining these files in an updated manner.

Cloud Cover Camera

John Degnan presented some information about the cloud cover monitor which is part of the

comprehensive meteorology package for the SLR 2000. The camera relies on a 120 by 120 pixel uncooled

IR camera that detects clouds by temperature differences (clouds are warmer than clear sky). The monitor

can see down to 10 degrees altitude and a full sky map take only about 15 seconds. The cost is presently

about $75K, but should be reduced to about $30K if a volume purchase can be organized.  Contact John

Degnan for more details and to express interest.

"Near Real Time" Distribution of Prediction Time Biases 

NERC is presently computing time bias functions using the most recently submitted SLR data accessed

through the Data Centers. The time bias functions (including drag functions) are available through a server

at AIUB. Stations with proper client software (EUROSTAT or just TELNET) can access and display the

functions and use them to update their predictions. Although only a one or two prediction sources are

used by stations for each satellite,  time bias functions for all of the commonly used predictions are

provided by this service. It behooves us to speed up the cycle (data submission, processing, etc.) as much as

possible to improve the predictions, primarily on the low orbiting satellites.

Knowledge Base

The ILRS Bibliography has been established and the Site Logs are in place. The text of many of the recent

articles in the ILRS Bibliography are accessible in electronic format. The next step in the development of

the knowledge base is to improve the means of searching both the ILRS and linked sources for specific

topics. As a start, a list of key words should be developed for each of the articles within the ILRS

bibliography.

Action - Van Husson, John Degnan, and Mike Pearlman: Develop a plan to improve the search capability

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Last modified date: Friday, November 12, 2004
Author: Mike Pearlman
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