In shallow water, the ocean bottom plays a significant role in the propagation of acoustic energy. Hence, knowledge of the acoustic properties of the ocean bottom is critical in prediction of acoustic propagation in shallow water environments. The US Navy is developing a Multi-Static Active Coherent (MAC) acoustic search system that combines a newly developed coherent source sonobuoy with a field of receiver sonobuoys. With the availability of GPS (Global Positioning System) navigation in the sonobuoys, the feasibility of using data collected during Navy ASW operations to estimate sediment properties is now being explored. MOMAX (Modal Mapping Experiment) is an experiment in which the acoustic field from a moving coherent source on an array of freely drifting buoys equipped with hydrophones, GPS navigation, and radio telemetry are measured. One of the experiment goals is to estimate sediment properties from this data. This approach uses of modal eigenvalues for estimating the sediment properties and hence requires the acoustic field at the receiver to be a function of range which in the case of MOMAX experiments is achieved by a ship towing a source. However, in the conceptual design of the MOMAX experiments, the source is carried by a sonobuoy. In such a situation, it is unlikely that the sonobuoy with the source will move out in range in relation to the receiver sonobuoys and create a horizontal array of sufficient aperture to extract the modal eigenvalues from the data.
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