High Resolution Passive Sonar Imaging by the Phase Closure Technique. Phase I. Establishment of Feasibility

摘要

This is a summary of the final report for the first year of effort in the project entitled High Resolution Passive Sonar Imaging by the Phase Closure Technique. The long-term objective of this effort is to develop techniques for overcoming propagation anomalies and instrumental errors in the location and characterization of noise sources in the ocean using passive sonar. In the problem of detection, location, and classification of noise sources in the ocean, a number of complicating factors arise. These include refractive index variations due to ocean inhomogeneities in density, temperature, or salinity, drifting of hydrophones in a towed array, and reflection effects from the sea surface, sea floor, or submerged objects. These factors all reduce the spatial coherence of sonar signals. An extreme example is the problem of interpretation of multipath signals in the ocean channel beneath Arctic ice. Even in the open sea, there is still a number of effects which significantly reduce the coherence of received signals. The result is that with conventional beamforming techniques there is a limit to the maximum length of a passive sonar array over which coherence can be maintained at a given frequency.