Explain DGPS and how it improves GPS accuracy.

DGPS (Differential GPS) improves positioning accuracy using correction signals from a reference station at known location. The reference station calculates difference between known position and GPS-calculated position, broadcasting corrections to rover receivers. This eliminates common errors like satellite clock, ephemeris, and atmospheric delays affecting both stations similarly. Real-time DGPS provides sub-meter accuracy (0.5-5m) compared to standalone GPS (5-15m). Post-processed DGPS can achieve centimeter accuracy. Used for mapping, navigation, and GIS data collection.