Which navigation system was developed to improve the SPS signal for 10-meter accuracy?

• A. GPS
• B. DGPS
• C. LORAN-C
• D. GLONASS

Answer: (B)

Differential GPS provides real-time corrections to the GPS SPS signals, using fixed reference stations at known coordinates to measure the errors in satellite ranging. Each reference station calculates the difference between its precise position and the position indicated by the GPS signals, producing correction terms for satellite clock, orbit, and propagation delays. That correction data is then broadcast to nearby receivers, which apply it to their own GPS calculations. The result is a much higher position accuracy—typically a few meters rather than the standard around 10 meters for SPS. Other options aren’t augmentations of GPS in this way: LORAN-C is a separate long-range navigation system, and GLONASS is its own GNSS, not the differential augmentation of GPS.