Matched-field source tracking by ambiguity surface averaging

The method of matched-field source tracking by ambiguity surface averaging is demonstrated using low-frequency shallow-water acoustic data recorded on a vertical array. In this method, source motion is taken into account by averaging values from individual, short time-average matched-field ambiguity functions; each resulting average value corresponds to a trial source track. The result is a new ambiguity function which depends on six parameters: the three-dimensional coordinates of the initial and final source positions. A simplification to four parameters is made by assuming the source remains at a constant depth. Only mild restrictions are made on trial tracks considered, and the resulting ambiguity surfaces can be plotted as a function of final coordinates by holding the initial coordinates fixed at the optimal position. When applied to experimental data, the number of high sidelobes present in individual matched-field ambiguity surfaces is greatly reduced. Also, the technique appears robust to uncertainties in replica computation (due to various mismatch problems) and periods when the signal-to-noise ratio is low.