Problem: Surveying Instruments and Procedures: EDM

Concerning a modern EDM that uses coherent laser light, which of the following atmospheric factors will be the least critical to the accuracy of its measurement of distance?

(A) The air temperature
(B) The barometric pressure
(C) The relative humidity
(D) Each is equally significant

Answer is (C)

Solution: Relative humidity has a relatively small effect on the speed of light waves. However, in using a microwave EDM, an error of 3°F in the difference between the temperature of the wet and dry bulbs of a psychrometer can account for an error of nearly 10 ppm.

This is problem 62(6-47) from the new second edition of ”1001 Solved Surveying Fundamentals Problems” by Jan Van Sickle, PLS. Reprinted with permission from ”1001 Solved Surveying Fundamentals Problems” by Jan Van Sickle, PLS, (1997, 728 pp., Professional Publications Inc.). For details on this and other FLS exam-prep books, call 800/426-1178 or visit www.ppi2pass.com .