Communications – electrical: acoustic wave systems and devices – Echo systems – Side scanning or contour mapping sonar systems
Reexamination Certificate
2002-09-30
2004-03-30
Lobo, Ian J. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Echo systems
Side scanning or contour mapping sonar systems
C367S100000, C367S131000
Reexamination Certificate
active
06714481
ABSTRACT:
STATEMENT OF THE GOVERNMENT INTEREST
The invention described herein may be manufactured and used by or for the Government of the United States of America for Governmental purposes without the payment of any royalties thereon or therefore.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates generally to systems and methods for active sonar systems and, more particularly to a sonar system which utilizes a Volterra model for improved sonar signal detection and classification.
(2) Description of the Prior Art
Active sonar signal propagation and reflection have intrinsic properties that are notably affected by the channel and/or target characteristics. Often, one knows through measurements, the signal transmitted into the propagation channel and the waveform at the receiver output. The difficulty is to accurately measure, estimate, and characterize what happens between the excitation input and output.
Signal distortion in an active sonar system may arise for many reasons such as, for example, irregular sea bottoms and surface interactions, nonlinear resonant scattering within the propagation channel, reverberation, nonhomogenous responses due to channel and/or target interactions, target scattering profiles, multipath reflections, noise generated by waves, transmission losses, changing distances from the target, and the like.
Active sonar as used herein refers to sonar systems that utilize radiating acoustic sources to probe an area to be searched so as to illuminate the submerged object. One example of this type of sonar system is a conventional sonar device wherein a highly directional beam of sonic energy periodically radiates from a scanning transducer which in turn also operates as a receiver to detect echoes reflected from any object(s) within the propagation channel. Modern active sonar systems commonly provide multibeam capabilities as well. Sonar devices tend to have relatively high transmission losses which increase as a function of the frequency of the propagated energy.
A large number of active sonar data processing techniques rely on linearity in an acoustic signature (e.g., temporal fluctuations, power spectra) for extracting and identifying information about a particular target illuminated by the active transmission. However, if linear techniques are applied to a target-of-interest in which the target and/or channel response is actually nonlinear, then subsequent purely linear processing of these data leads to results that can be incorrect and misleading.
Various inventors have attempted to solve the above and related problems as evidenced by the following patents.
U.S. Pat. No. 4,195,359, issued Mar. 25, 1980, to Miller et al., discloses an automatic echo detection and classification system wherein sonar equipment transmits pulses toward a target in predetermined and equal time intervals and receives background, dopplered and undopplered echoes which are produced as video output and audio output, the improvement which comprises means for establishing a non-directional background reference signal voltage from the video output, means for separating the audio output into dopplered signal voltage outside the reverberation band and undopplered signal voltage within the reverberation band, means for algebraically adding the background reference signal voltage to both the dopplered and undopplered signal voltages, a first amplifier for the resultant dopplered signal voltage, a target indicator alarm, a first energizing circuit therefore operative by the amplified dopplered signal voltage to indicate that a target has been located, means for obtaining from the resultant undopplered signal voltage a selected signal voltage above a predetermined level, a first gate normally in closed position, a first multivibrator therefore and operable by the selected undopplered signal voltage to move to open position for a predetermined interval to pass a first echo of a predetermined duration, a second gate normally in open position for passing the first echo after it has passed the first gate, a second multivibrator for the second gate operative to close the second gate for a predetermined period, an amplifier for the undopplered signal voltage of the first echo after it has passed through both the first and second gates, a second energizing circuit for the target alarm, said second circuit including the second multivibrator, and being operative to energize the second multivibrator by the amplified undopplered signal voltage of the first echo after it has passed through the second gate and after the predetermined period for which the second gate is closed and a second echo appears, which is substantially within the same range as the first echo, the second gate will be open for passing of the second echo to operate the target indicator alarm.
U.S. Pat. No. 4,654,835, issued Mar. 31, 1987, to Paul L. Feintuch, discloses a bistatic sonar employing LMS adaptive spatial prediction which is used to process against surface reverberation from the convergence zone (CZ). Hydrophones spatially separated from the primary array are used as references. The critical behavior exploited by the invention is that since the reverberation may be viewed as an extended source for the reverberation, the correlation drops off with separation between the reference and primary sensors, while it stays constant for the plane wave target return. The reverberation is non-stationary, functionally dependent on the signal (even though the backscatter is statistically uncorrelated with the signal), and spatially extended over the sector of the CZ annulus cut out by the transmitter azimuth beamwidth. The detection of the target is based on the sudden appearance of one strong target point source within a densely packed region of weak point sources that have been constantly present and whose sum is much larger than the target. The use of more than a single reference leads to a minimal improvement in detection performance and may actually degrade performance due to increased algorithm noise. Detection performance tends to increase with increasing separation distance between the primary and the reference hydrophone. For signal, reverberation, and algorithm parameters consistent with modern active sonars operating in the CZ mode, the spatial prediction approach to detection of the plane wave signal will allow detection of targets not possible using conventional active processing, provided the reference hydrophone can be placed to give a normalized correlation of less than 0.05. Such values may be obtained with very reasonable spacing between primary and reference, allowing the reference to be positioned, for example, along the hull aft of the primary array.
U.S. Pat. No. 4,686,532, issued Aug. 11, 1987, to Alastair D. McAulay, discloses a sonar or radar that permits primary distributed scatterers that are close to the sonar or radar, relative to the array dimension, to be rapidly and accurately located and pertinent characteristics to be estimated, such as Doppler and complex scattering strength. The region viewed is partitioned in annuli instead of in angular pie-shaped slices as is normally the case for conventional sonar. This avoids the difficulty with conventional sonar or radar of distinguishing whether a scatterer is in a side lobe or in the main beam in the important case of approaching multiple scatterers, e.g. robotic vehicle sensors or torpedo terminal homing on a target, because near regions may be examined in all directions prior to regions further out. Computational speed is achieved by utilizing precomputation and leaving only part of the computation to be performed in real time.
U.S. Pat. No. 4,969,131, issued Nov. 6, 1990, to William G. Harris, Jr., discloses an echo ranging system of the invention which comprises circuit means to differentiate between shadows cast by objects and the period of time prior to the receipt of the first bottom return, as well as the lack of bottom reverberation for other reasons. Additional circuit means determines if the length of the shadow signa
Katz Richard A.
Nuttal Albert H.
Kasischke James M.
Lobo Ian J.
Nasser Jean-Paul A.
Oglo Michael F.
The United States of America as represented by the Secretary of
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