Sound transmission underwater

Good day! I have a system depicted below. I need to know what is the working equation that governs the transmit and receive power of the transmitter and receiver in the diagram. The transmitted signal is a sound wave and not an RF signal, the transmission is underwater. I would like to know what is the governing equation that models the transmit and receive power that also related to the distance between the tx and rx. Thank You!

I would look up a reference "Ocean Engineering" as a place to start. I expect to spherical spreading of the signal and for added fidelity a loss/linear distance factor. You could get even more fancy and looking at thermoclines and the like. First step is the reference and some real basic reading.

Have a look at this web site: http://www.submarineboat.com/hydrophone.htm