Question 961Navigation General

The correct answer is D) Selective Availability. Selective Availability (SA) was a feature used by the U.S. government to intentionally degrade the accuracy of GPS signals available to the general public. When SA was enabled, it introduced errors into the GPS data, reducing the positioning accuracy of standard GPS receivers. By setting SA to zero, this intentional degradation was removed, allowing GPS units to achieve an accuracy equivalent to the Precise Positioning Service, which was reserved for authorized military and government users. The other options are incorrect because: A) Anti-spoofing is a feature that protects GPS signals from being replaced by false signals, but it does not affect the accuracy of the GPS data. B) Auto-correlation is a signal processing technique used in GPS receivers, but it does not directly impact the accuracy of the GPS data. C) Transit refers to an older satellite navigation system, which is not relevant to the accuracy of modern GPS units.