- The Macrometer Interferometric Surveyor was the first GPS [Global Positioning System] suitable for geodetic work. Its conceptual foundation is Very Long Baseline Interferometry (VLBI), a radio astronomical technique that allows one to determine distances between two receivers on the ground by measuring the phase difference between signals from a radio source on high.
- The story begins in 1967 when, soon after VLBI was introduced, Irwin Shapiro realized that this technique could be used for geodetic work. By 1969, he and colleagues had used quasars to determine the 845-km baseline between large radio telescopes in Massachusetts and West Virginia. In the 1970s, Robert Preston showed that smaller antennas could receive radio signals from artificial satellites; and Charles Counselman III and Hans Hinteregger devised a much more precise VLBI technique known as differential interferometry, and used it to track Apollo astronauts driving around on the moon. The Air Force Geophysics Laboratory funded much of this work.
- With the first GPS satellites up and running, it seemed time to commercialize the VLBI technology. Macrometrics, Inc. was formed in 1981, and it unveiled the Macrometer V-1000 in 1982. Tests conducted by the Federal Geodetic Control Committee yielded results better than 1:300,000, or three times better than first-order standards. Aero Service, a Division of Western Geophysical Co. of America, bought Macrometrics in 1984, and continued producing Macrometers for a few more years.
- Counselman, a consultant to Macrometrics, submitted a patent application in 1982, and assigned the rights to Macrometrics. This application resulted in several patents that covered practically every subsequent GPS receiver made in the United States. The one patent identified on the Macrometer antenna in the Museum (No. 4,647,942) described a "Circularly Polarized Antenna for Satellite Positioning Systems." Others described methods of determining positions from GPS signals that required no knowledge of the GPS encryption codes, no steerable antenna, and only a small part of a VLBI signal-processing system.
- Ref: Macrometrics, Inc., Macrometer Interferometric Surveyor, 1000 Series Field Manual (Woburn, Mass., 1983).
- Robert W. King, et. al., Surveying with GPS, Monograph No. 9, School of Surveying, University of New South Wales (Nov. 1985).
- Currently not on view
- Object Name
- GPS interferometric surveyor, macrometer
- overall: 70.5 cm x 55 cm x 66 cm; 27 3/4 in x 21 5/8 in x 26 in
- ID Number
- accession number
- catalog number
- Credit Line
- Western Atlas International, Inc.
- Data Source
- National Museum of American History
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