- Great Theodolite
- The Bache- Wurdemann Compensating Device
- Eimbeck Duplex Bars
- Iced Bar B 17
- Steel Tape with Tape Stretcher
- Invar Tape
- AGA Geodimeter NASM-2A
- Tellurometer Model M/RA 1
- Laser Signal and Prismatic Mirror Reflecting System
- AGA Geodimeters, Models 4D and 4L
- Big Red
- AGA Geodimeter Model 6
- Hewlett-Packard Model 3800B Distance Meter
- Tellurometer Model MA-100
- Ranger III and Rangemaster III
- Topcon ET-1 Total Station
- Trimble GPS Antenna
Tellurometer Model M/RA 1
This photo shows a Tellurometer, which is an instrument that determines distance by measuring the roundtrip travel time of reflected microwaves. Although not as accurate as Geodimeters, which used light waves to measure distances, the greater portability of Tellurometers made these devices popular.
The Coast and Geodetic Survey (C&GS) obtained its first Tellurometer measuring unit in 1957. Developed by the Telecommunications Research Laboratory of the South African Council for Scientific and Industrial Research, Tellurometers used microwaves rather than light waves to measure distances. The unit was the result of the search for an instrument that was lightweight and portable, required a small amount of power, and was accurate over several miles. The first unit used by the C&GS received its "baptism" along the rugged coast of the Aleutian Islands of Alaska.
Humidity affects microwaves more than light waves. Microwave signals are also more affected by power lines, magnetic ground deposits, geomagnetic storms, and other environmental factors. Consequently, microwave electronic distance measurement instruments (EDMI) were never as accurate as lightwave instruments such as Geodimeters. However, the Tellurometer's portability and usability over difficult terrain made it economical and, in highway surveys, it sped up operations and reduced costs.
Neither Geodimeters nor Tellurometers were easy-to-use, stand-alone, push-button systems. Hardy C&GS surveyors were needed to set up the equipment, center it over the marks, make temperature readings and adjustments, and so forth. In addition, warm-up time was needed, particularly before transistors replaced tubes; switches and frequencies had to be properly set; and course and fine readings taken. Tellurometers operated in "master" and "remote" modes and required use of a built-in phone system to coordinate duties. Still, EDMI were a major improvement over the use of cumbersome tapes to measure distances.
- Distance Measurement Instrument Shown: Tellurometer Model M/RA 1
- Location: Unknown
- Manufacture Date: 1950s
- Dates of Use: 1950s - 1960s
- Photo Date: Unknown
Demuth, H. P. (1958). Tellurometer Traverse Surveys. Washington, D. C.: U. S. Government Printing Office.
Poling, A. C. (1961). Tellurometer Manual. Washington. D. C.: U. S. Government Printing Office.
Poling, A. C. (1960). The Tellurometer for Highway Control. Highway Research Board Bulletin 258: Electronic Surveying, 1960 Developments, p 8-12.
Smithsonian Virtual Surveying Instrument Collection. (2006). EDM (Tellurometer M/RA 1). Retrieved June, 2006, from: http://americanhistory.si.edu/collections/surveying/object.cfm?recordnumber=759173.
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