This invention relates generally to acoustic signal correlation, and more particularly to optical correlation using a light emitting diode (LED) array.
Broadband acoustic processing attempts to detect a target and track its path by the use of the target's wide frequency band energy sources. One important processing technique suited to broadband signal detection is correlation. Cross correlation is done by processing the signals from two spatially separated transducers or sensors, such as from two sonobuoys or from the multihydrophone array of a single buoy. The channels of information from these two transducers contain common broadband signals, which, because of the transducer spacing, are detected apart in time. The time delay depends upon the location of the target with respect to the two transducers. The correlator detects the broadband signals and determines the time delay. Correlation done in this way over time allows the target to be tracked.
Broadband acoustic processing requires the ability to perform intra-/inter-sensor data correlation at high speeds. Currently, this operation is performed digitally with high-speed array processing systems using both time domain and frequency domain methods. These processors make use of the fast Fourier transform and the inverse fast Fourier transform algorithms. Although these digital processors are fast, they are also large, complex, and consume large amounts of power.
The invention disclosed herein is an optical correlator. The signals from the transducers are processed optically, using a light emitting diode (LED) array and a charged coupled device (CCD) imaging array. Currently available optical correlators use acousto-optical cells having a fixed delay range equal to the transit time through the cell. These correlators are too fast to be used in low data rate processing and lack signal delay range flexibility and sensitivity.