Correction and transmission system for directional target information

Abstract

An object detection system capable of receiving and processing an omnidirional signal and two directional signals to produce a digitized omnidirectional signal, and digitized directional signals which have been corrected to magnetic north. The directional hydrophones produce sin θ and cos θ signals, where θ is the bearing angle of the sensed target from the directional hydrophones' y-axis. Each of the three signals is picked up by a separate hydrophone and is passed through an associated preamplifier and a shaper amplifier and low pass filter before being simultaneously sampled by separate sample/hold circuits. The three sampled signals are multiplexed to an analog to digital converter. The signal produced by a digital magnetic compass is converted to sin θ and cos θ values by appropriate function generators, where θ is the angle between the y-axis and magnetic north. The digital sin θ, cos θ, sin φ and cos φ signals are the multiplied together in a multiplier and the products placed in separate registers and added or subtracted by an adder to produce directional signals corrected to magnetic north according to the formulas sin θ cos φ - cos θ sin φ = sin (θ - φ) and cos θ cos θ + sin θ sin φ = cos (θ - φ). The corrected directional signals are then multiplexed together with the omnidirectional signal and a synchronization word and passed through an encoder to a transmitter for transmission to a distant receiver for processing and analysis.