How does differential GPS improve the accuracy of ordinary GPS receivers?

Differential GPS (DGPS) improves the accuracy of ordinary GPS receivers by utilizing a stationary "base station" located at a precisely known position on the ground.1

Because satellite signals can be distorted by the ionosphere and troposphere, or affected by timing errors, standard receivers often experience positional inaccuracies. A DGPS base station continuously monitors these signals and calculates the difference between its known location and the position derived from the satellite data.1

This base station then broadcasts real-time navigation corrections to nearby roving receivers. By applying these corrections, the roving receiver effectively subtracts the common statistical errors from its own position solution, resulting in significantly higher precision than unaugmented systems. These corrections are often transmitted via radio beacons or encoded within commercial radio broadcasts, enabling high-accuracy applications such as precision farming.1