Navigation General · GPS & GNSS
Selective Availability (SA), the intentional degradation of GPS civilian signals, was:
- AStill in effect for non-military users as of 2024
- BPermanently discontinued in 2000 but can be re-enabled by the U.S. government✓ Correct
- CReplaced by Differential GPS (DGPS) as the only means of obtaining sub-meter accuracy
- DNever implemented on Block III GPS satellites
Explanation
Selective Availability was turned off on May 1, 2000, improving civilian GPS accuracy from ~100 meters (2 drms) to ~10-15 meters without augmentation. However, U.S. policy allows SA to be re-enabled regionally in national security situations. It was not permanently removed from GPS architecture — it can still be activated.
Authority: Bowditch (Pub. 9), Ch. 13
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