Passive localization by use of acoustic propagation models, sometimes called ‘‘matched field processing’’ is usually carried out in three steps. First, some appropriate model is selected. Then, model parameters, usually taken from archival data or from auxiliary measurements, are introduced into the model. Finally, acoustic measurements of the field radiated by the source to be located are made that, in combination with the properly parametrized model, allow a solution for the source coordinates to be carried out. Here, such a model‐based approach is used in conjunction with a normal‐mode model. By coupling the procedure with a parameter estimation/identification scheme and using a horizontal (towed) array instead of the usual vertical array, it is shown that the model parameters need not be known a priori in order to carry out the solution. This is in contrast to the standard approach in which the modal functions must be computed directly from the model (wave equation) in order to solve the problem. It is still necessary to base the calculation on a model, but, surprisingly, the sound velocity profile, the ocean depth, and ocean bottom properties need not be known explicitly, since sufficient information to determine the range of the source can be inferred directly from the measured data themselves. Using a sophisticated acoustic propagation model to generate simulated data, coupled with various array processing techniques, the feasibility of the approach is demonstrated.