Abstract: Targeted at integrated sensing and communication for small underwater platforms, a single-hydrophone localization method for orthogonal frequency division multiplexing sources is investigated. Based on the frequency domain input-output relationship of communication systems in multipath channels, a measurement model for target localization is constructed by incorporating pilot information. A matched field localization method based on relative multipath delays is developed. An iterative solution algorithm is proposed, in which the time offset estimation for the first-arrival path and the range-depth localization of the acoustic source are alternately performed. For a typical shallow water three-path channel, the Cramér-Rao bound of the localization error is derived. Numerical simulations verify the statistical efficiency of the proposed algorithm under ideal conditions, and a sensitivity analysis with respect to environmental parameter mismatches is conducted. In water tank experiments, more accurate and reliable localization results are obtained by the proposed method compared with the multipath delay matching approach.