This document provides a method of determining an absolute position of a diver, comprising: providing a dive leader unit having a GPS receiver and an underwater acoustic modem configured to retransmit GPS coordinates of the dive leader unit under water, providing the diver with a monitoring unit comprising several microphones so that it is possible to detect a direction of the dive leader unit, pairing the monitoring unit to the dive leader unit to form a communication network so as to identify differences between system clocks of the dive leader unit and the monitoring unit and make it possible to calculate a distance from the dive leader unit to the monitoring unit. In the monitoring unit, the following steps are performed: receiving the retransmitted GPS coordinates, detecting the direction of the dive leader unit, calculating the distance to the dive leader unit, and calculating the absolute position of the diver based on the retransmitted GPS coordinates, the direction of the dive leader unit and the distance from the dive leader unit to the monitoring unit.