When divers rescue people who have accidents at sea, they are in danger because of parts of obstacles floating in the sea. If they can confirm their own positions, their activities will become much safer. In this study, assuming we specify the positions of the divers rescuing in the accidents and support their works, we investigate undersea positioning technology using the electromagnetic waves with low frequencies less than midrange waves. In some preceding studies, an ultra-long wave of 10 kHz theoretically attenuates 3.5 dB per meter . In addition, the simulation of the position estimation in the vertical section of the sea has already reported. In this report, we indicated the superiority of using Receiving Signal Strength: RSS to the phase difference between a transmitted signal and the received one. We also showed the result of the position estimation of the transmitting antenna at depth from 2 m to 8 m.