Time Transfer Between the Goddard Optical Research Facility and the U.S. Naval Observatory Using 100 Picosecond Laser Pulses

C.O. Alley, J.D. Rayner, C.A. Steggerda, J.V. Mallendore, L. Small, S. Wagner

Abstract: A horizontal two-way time comparison link in air between the University of Maryland laser ranging and time transfer equipment at the Goddard Optical Research Facility (GORF) 1.2 rn telescope and the Time Services Division of the U.S. Naval Observatory (USNO) has been established. Flat mirrors of 25 cm and 30 m diameter respectively have been placed on top of the Washington Cathedral and on a water tower at the Beltsville Agricultural Research Center since direct line of sight transmission is not possible. The bent path has a oneway distance of 26 km. Two optical corner reflectors at the USNO, identical to those placed on the Moon during the Apollo program, reflect the laser pulses back to the GORF. Light pulses of 100 ps duration and an energy of several hundred microjoules from a neodymium-YAC laser, Frequency doubled to a wavelength of 532 nm (green) are sent at a rate of 10 pulses per second, The detection at the USNO is by means of an RCA C30902E avalanche photodiode and the timing is accomplished by an HP 5370A computing counter and an HP 1000 computer with respect to a 10 pps pulse train from the Master Clock. The reflected light is detected back at the 1.2 m telescope at the single photoelectron level and the epoch of reception is recorded by a University of Maryland designed event timer attached to a NOVA 2/10 minicomputer. About 100 detection events are recorded for 1000 pulses transmitted, The outgoing pulses have their epoch of transmission recorded by the same event timer, which is driven by an HP cesium beam frequency standard.
Published in: Proceedings of the 14th Annual Precise Time and Time Interval Systems and Applications Meeting
November 30 - 3, 1982
NASA Goddard Space Flight Center
Greenbelt, Maryland
Pages: 243 - 267
Cite this article: Alley, C.O., Rayner, J.D., Steggerda, C.A., Mallendore, J.V., Small, L., Wagner, S., "Time Transfer Between the Goddard Optical Research Facility and the U.S. Naval Observatory Using 100 Picosecond Laser Pulses," Proceedings of the 14th Annual Precise Time and Time Interval Systems and Applications Meeting, Greenbelt, Maryland, November 1982, pp. 243-267.
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