Smithsonian - National Museum of American History, Behring Center

Physical Sciences Collection - Surveying and Geodesy

Browse Makers | Browse Instruments | Index


No image available

EDM (Geodolite)

Catalogue number:

"Spectra-Physics GeodoliteTM 3G Laser Distance Measuring Instrument" and "Spectra-Physics SN 96"

telescope unit 21.25 inches high, 34 inches wide, 16 inches deep; control unit 5.25 inches high, 19 inches wide, 19.25 inches deep; display unit 6.5 inches high, 8 inches wide, 9 inches deep.


The Geodolite is a precise laser-based EDM developed and produced by Spectra-Physics in Mountain View, California. Aero Service Corp., a large aerial surveying firm headquartered in Philadelphia, provided substantial funds for its early development. The first feasibility model, the Mark I, was unveiled in 1964, and was designed as an airborne profile recorder. The improved Mark II was mounted in a Douglas A-26 and, from a height of 1,000 feet, produced a profile of the stadium of the George Washington High School showing each tier of seats, the foot space between them, and the cinder path around the field.

The Mark III, called the Geodolite, was funded in large part by the United States Army Engineer Topographic Laboratories (USAETL), and introduced in the spring of 1966. Lavish advertisements termed it "a rugged, ready-to-go instrument, as practical as it is precise." It was "light enough to go aboard any fixed or rotary wing aircraft for ground roughness determination, control point elevation measurement, ice pressure ridge height analysis, sea state determination, beach slope profiling, [and] high resolution terrain profiling," and could also be used for precise horizontal distance measurements.

Thirty some Geodolites were eventually produced. Each sold for about $50,000. Most were purchased by federal agencies or by private firms working on federal contracts. The transmitter of each is a 1-inch telescope mounted coaxially to the receiver, which is an 8-inch aperture Schmidt Cassegrain, the optical components of which made by Celestron Some units were provided with a trunion mount and used for airborne profiling. Others were provided with an alt-azimuth mount and used for geodetic work. The geodetic instruments used an expensive Startracker photomultiplier tube made by ITT; some aspects of this were covered by patent #3,446,971 for "Optical Ranging System using a beat frequency responsive photomultiplier" granted to Kenneth Ruddock on May 27, 1969, and assigned to Spectra-Physics.

The Geodolite at the Smithsonian has a Startracker tube, and both types of mount. It came from Graydon Russsell, an electronics technician who worked for Spectra-Physics for many years. In 1984, when the manufacture of Geodolites ceased, Russell bought the Geodolite business and kept the existing instruments in repair.

Further Information: