Differential GPS (DGPS) is now the principal system used in hydrographic surveying to accurately determine the position of seabed features.

The principle of DGPS is that a single DGPS monitor station at a known location can compute a range error correction for each GPS satellites in view (the GPS consists of a network of 24 satellites launched by the USA). These error corrections are then broadcast through a radio link to the ships in the vicinity. By applying the corrections to the signals received, a user can typically improve the accuracy in the order of 5 metres or less depending on the quality of the receivers.