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Proceedings Paper

SLR2000: eye-safe and autonomous single-photoelectron satellite laser ranging at kilohertz rates
Author(s): John J. Degnan; Jan F. McGarry
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Paper Abstract

SLR2000 is an autonomous and eyesafesatellite laser ranging station with an expected single shot range precision of about one centimeter and a normal point precision better than 3 mm. The system will provide continuous 24 hour tracking coverage. Replication costs are expected to be roughly an order of magnitude less than current operational systems, and the system will be about 75% less expensive to operate and maintain relative to the manned systems. Computer simulations have predicted a daylight tracking capability to GPS and lower satellites with telescope apertures of 40 cm and have demonstrated the ability of our current autotracking algorithm to extract mean signal strengths as small as 0.000 I photoelectrons per pulse from background noise. The dominant cost driver in present SLR systems is the onsite and central infrastructure manpower required to operate the system, to service and maintain the complex subsystems (most notably the laser and high precision timing electronics), and to ensure that the transmitted laser beam is not a hazard to onsite personnel or to overflying aircraft. In designing the SLR2000 system, preference was given to simple hardware over complex, to commercially available hardware over custom, and to passive techniques over active resulting in the prototype design described here. This general approach should allow long intervals between maintenance visits and the "outsourcing" of key central engineering functions on an "as needed" basis. As a result, many of the signal extraction techniques and engineering designs employed here may have application in remotely operated or even spacebome lidar applications. SLR2000 consists of seven major subsystems: (1) Time and Frequency Reference Unit; (2) Optical Subsystem; (3) Tracking Mount; (4) Correlation Range Receiver; (5) Meteorological Station; (6) Environmental Shelter with Azimuth Tracking Dome; and (7) System Controller. The Optical Subsystem in tum consists of a 40 cm aperture telescope and associated transmit/receive optics, a passively Q-switched microlaser operating at 2 KHz with a transmitted single pulse energy of 135 μJ, a start detector, a quadrant stop detector for simultaneous ranging and subarcsecond angle tracking, a CCD camera for automated star calibrations, and spectral and spatial filters to reduce the daylight background noise. The meteorological station includes sensors for surface pressure, temperature, relative humidity, wind speed and direction, precipitation type and accumulation, visibility, and cloud cover. The system operator is replaced by a software package called the "pseudooperator" which, using a variety of sensor inputs, makes all of the critical operational decisions formerly made by onsite personnel. Keywords: laser ranging, microlasers, laser altimetry, lidar, single photon detection, meteorological instrumentation, satellites, autonomous instruments

Paper Details

Date Published: 22 December 1997
PDF: 15 pages
Proc. SPIE 3218, Laser Radar Ranging and Atmospheric Lidar Techniques, (22 December 1997); doi: 10.1117/12.295646
Show Author Affiliations
John J. Degnan, NASA Goddard Space Flight Ctr. (United States)
Jan F. McGarry, NASA Goddard Space Flight Ctr. (United States)


Published in SPIE Proceedings Vol. 3218:
Laser Radar Ranging and Atmospheric Lidar Techniques
Ulrich Schreiber; Christian Werner, Editor(s)

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