Electromagnetic distance measurement in the U.S. geological survey

Abstract

About 80 units of electromagnetic distance-measuring equipment in several makes are used by the US Geological Survey for control surveys for topographic mapping, mostly in conventional traverse. For mapping in difficult terrain the Airborne Control (ABC) Survey System has been developed, in which a hovering helicopter with a remote electromagnetic distance-measuring unit serves both as a target and as a survey platform. The unique instrumentation of this system includes a hover sight, to enable the pilot to maintain position above a selected ground point; a height indicator, to measure the vertical distance from the ground to the helicopter; a rotating beacon, for a sighting target; and a retractable antenna. Communications between the helicopter and the ground are maintained by radio. This paper is devoted mostly to application in control surveys in the National Topographic Mapping program.