Underwater position determination is provided by combining sonar-derived ranging data between a sonar receiver and a sonar transmitter with GPS position data to provide geographically-referenced position data accurately representing the position of a sonar receiver carried or worn by a diver or submersible vehicle. Function and accuracy enhancements are provided to compensate for diver and sonar transmitter and depth difference and differences of sonar signal propagation speed as well as several techniques of compensation for change of position of the GPS receiver and for logging diver and/or vehicle path.