Problem:The Global Positioning System (GPS): Control Segment

Problem: The Global Positioning System (GPS): Control Segment

What is the meaning of selective availability in GPS?

(A) The deliberate degradation of the GPS signal
(B) The encryption of the P code transmissions
(C) The licensing of all GPS receivers by the federal government
(D) The shutdown of selected satellites by the control segment

This is problem 12(11-7) from the new second edition of 1001 Solved Surveying problems by Jan Van Sickle. Reprinted with permission from 1001 Solved Surveying Problems by Jan Van Sickle (1997, 728 pp., Professional Publications Inc.). For details on this and other FLS exam-prep books, call 800/426-1178 or

Answer: A

The Departments of Defense and Transportation developed the Federal Radionavigation Plan. This plan includes the ability to limit the availability of point positioning services superior to the 100-m level to military and specific nonmilitary use. Selective availability (SA) is one way of degrading GPS accuracy by introducing clock errors into the navigation message transmission, providing the user with a false pseudo-range. However, SA had no adverse effect on positioning accomplished by differential GPS techniques.