Vintage South African invention, the Tellurometer, has a long and glorious international history.

Market need

Before electronic distance measuring (EDM) devices like the Tellurometer and its 1947 predecessor, the Geodimeter, surveyors had for centuries used bars, rods, chains and steel tapes for measuring distances. Compasses and angle measuring devices were used for determining directions and triangulation for extending from base lines.

In the 20th century, radar was introduced for measuring both distance and direction, e.g. in the Shoran and Hiran methods, but these were not sufficiently accurate for normal land surveying.

Thus, in 1954, the South African Department of Trigonometrical Survey framed a need for a system whose accuracy was greater than 1 in 100,000 at distance of up to 30 miles. It needed to be easily man-portable, work on line of sight and have a resolution of a few inches.

Technology solution

The requirement fell to the legendary Trevor Wadley of the Council for Scientific and Industrial Research in Johannesburg, who drew up the design for the Tellurometer, put together the components and was out measuring distances within a remarkably short time.

The first commercial Tellurometer, the Micro-Distancer MRA 1, was introduced in 1957 – the first successful use of microwave in EDM. Plessey, the British electronics company, formed a South African subsidiary in the 1960s to manufacture the product. The company was known as Tellurometer Pty Ltd, later became Tellumat, and contributed further development.

The Tellurometer emits an electronic wave between stations at two points: the remote station reradiates the incoming wave in a similar wave of more complex modulation, and the resulting phase shift provides a measure of the distance travelled. The instrument penetrates haze and mist in daylight or darkness and has a normal range of 30 – 50km, but can extend up to 70km.

Benefits

The Tellurometer design yields high-accuracy distance measurements over geodetic distances, but is also useful for second order survey work, especially where the terrain is rough and temperatures extreme.

Subsequent versions had unique applications and improvements. The MRB2 or Hydrodist was a marine version used in coastal surveys and for calibrating ships using other survey navigation systems. They were used in this capacity by the Army of the Republic of Vietnam in the late 1960s.

After the Tellurometer, the next revolution in surveying technology was the use of satellite receivers – firstly, transit system satellites, and after them GPS satellites. The next revolution in surveying was laser rangefinders, commonly using time of flight.

The Tellurometer is another South African innovation whose praises cannot be sung loud enough!

Trevor Lloyd Wadley – Genius of the Tellurometer can be ordered from Mary Wadley von Hirschberg. It sells at R155 (for South African destinations) including postage and packaging. Contact Mary Wadley von Hirschberg, maryvh@iafrica.com