A vector-hydrophone's minimal composition for finite estimation-variance in direction-finding near/without a reflecting boundary

An underwater acoustic vector-hydrophone is composed of two or three spatially collocated but orthogonally oriented velocity-hydrophones, plus an optional collocated pressure-hydrophone. A minimum vector-hydrophone configuration is herein identified for finite-,variance direction-finding by identifying the necessary and sufficient vector-hydrophone configuration nonsingularity in the Fisher Information Matrix. Three collocated velocity hydrophones are recommended for boundaryless direction-finding (one along the x-axis, y-axis, and z-axis), and a pressure hydrophone collocated with a collocated pair of x-axis and y-axis velocity hydrophones are recommended for direction finding near a rigid-boundary or pressure-release boundary.