Abstract: A method and apparatus are provided for determining transmission line parameters of a length of single-wire transmission line that is deployed in seawater. The seawater is utilized as an electrically grounded return for the transmission line such that a two-port network is formed at either end of the transmission line. An alternating voltage of known amplitude and frequency is generated and applied to a first end of the length of transmission line. Open and short circuit parameters at the first end are then determined as a second end of the length of transmission line is alternately switched between a open and short circuit mode. The alternating voltage of known amplitude and frequency is then applied to the second end as the first end is alternately switched between an open and short circuit mode so that open and short circuit parameters may be similarly determined at the second end.