Abstract: A signal processor for obtaining frequency and bearing information of an ustical signal. Responsive to the acoustical signal, a multimode hydrophone generates a plurality of electrical signals which are combined to form a first omnidirectional signal and two spatially orthogonal directional signals. The directional signals are then combined to form a second omnidirectional signal. Additional circuitry is provided to analyze the two omnidirectional signals using the cross-spectral density function of the two omnidirectional signals to obtain said frequency and bearing information.

Abstract: A multimode hydrophone of small diameter and low weight providing dipole ectivity patterns over a decade range of low frequencies by utilizing a pair of orthogonal dipole signals and a nondirectional reference signal to eliminate directional ambiguity. Each multimode hydrophone is a thin wall tube divided electrically into quadrants which permits differencing or opposing halves to produce signals with dipole directivity patterns and the formation of a nondirectional reference signal by summing all four quadrants. The hydrophone tube comprises inert and piezoelectric materials, selected and combined so as to shift the resonant frequency of the tube lower while keeping the over-all tube diameter as small as possible.