Communications: directive radio wave systems and devices (e.g. – Transmission through media other than air or free space
Reexamination Certificate
1999-11-12
2001-07-03
Sotomayor, John B. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Transmission through media other than air or free space
C342S02500R, C342S052000, C342S058000
Reexamination Certificate
active
06255980
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the field of underwater detection of articles. In particular, the present invention is directed to a hybrid radar-acoustic system in which acoustic echoes caused by the presence of a stationary underwater object are identified by a radar detection system coordinated with the acoustic system.
BACKGROUND OF THE INVENTION
Traditional methods for detecting submerged objects include sonars towed through the water and, in recent years, synthetic aperture radar (SAR). The SAR works by imaging the water surface while a current flows such that wind creates capillary waves over regions of shallow water. Since the water moves at speeds that vary according to depth, and the wind-caused by the capillary waves vary according to water speed, and the radar return from a patch of water is higher for a region occupied by capillary waves than for a region of comparatively smooth water, the SAR can reveal bathymerty. Attempts to harness this technique for discovery of smaller objects, such as sea mines, have yielded disappointing performance. Experimental systems that use lasers to read acoustic signals from the water surface have been demonstrated in recent years. They have shown promise, but suffer from the fact that the laser beam is very narrow, and can be deflected from the receiver by small waves on the water surface. A solution to this signal loss has been elusive, and without it, the system development probably will not proceed.
Sometimes conventional technology incorporates a sonar system used to create wave patterns indicative of the presence of the objects. The current search systems use tethered sonar transmitters which are placed in the water to emit acoustic waves that will be modified when striking underwater objects. These are awkward to deploy and control. This is especially true since the system also includes a laser and detector mounted on an airplane for reading wave patterns that are indicative of underwater objects. In the alternative, magnetic detectors can be used rather than laser detectors.
Unfortunately, both types of conventional detection systems have relatively low search rates, and are often defeated by turbid waters. When using a laser system there are often significant degradation caused by surface waves, as well as other environmental conditions.
The use of synthetic aperture radar (SAR) has been considered for the detection of underwater mines. However, this use of SAR has been considered impractical within the limits of the conventional art, which relies upon the use of DC current passing over the underwater targets, while the SAR is used to find the resulting indications of the underwater object. High speed mine detection and other applications requiring both high speeds and precision have proven inappropriate for conventional uses of SAR, along with traditional liquid agitation techniques.
Much underwater detection, such as bottom-mapping, does not require great resolution, so that conventional systems are still quite suitable. However, there are other applications, such as underwater rescue, mine detection and submarine detection that require a systems capable of rapidly scanning and analyzing indicia signals indicative of underwater objects. Speed is especially critical in combat or emergency situations. Therefore, there is a need for an underwater detection system that avoids the relatively slow operation of conventional systems, while still maintaining high degrees of sensitivity and accuracy.
SUMMARY OF THE INVENTION
Accordingly, it is one object of the present invention to overcome the various limitations of the conventional art.
It is another object of the present invention to provide an underwater detection system capable of rapid scanning to accommodate combat conditions, or other emergency situations.
It is another object of the present invention to provide an underwater communication system including underwater acoustic communications links.
It is still a further object of the present invention to provide an underwater detection system capable of accuracy even in turbulent waters.
It is again another object of the present invention to provide an underwater detection system capable of examining large expanses of water without extensive expenditures of time.
It is yet a further object of the present invention to provide an underwater detection system that can utilize existing subsystems such as conventional sonar and SAR units.
It is still an additional object of the present invention to provide an underwater detection system that does not rely upon wind to create capillary patterns for the identification of underwater objects.
These and other goals and objects of the present invention are achieved by a detection system arranged to detect an object under the surface of a liquid medium. The system includes at least one acoustic generator arranged for generating a detectable pattern of waves on the surface of the liquid medium. The acoustic generator operates at a frequency range where the detectable pattern of waves will have reinforcing characteristics at selected observation angles. The system also includes at least one radar device arranged to scan the detectable pattern of waves on the surface of the liquid medium. The radar scanner includes circuitry for coherently adding multiple scans of the detectable pattern of waves. The detection system further includes a linking mechanism for coordinating transmittal of the radar device and the acoustic generator by phase-locking both radar and acoustic transmissions.
Another embodiment of the present invention includes a method of detecting an object under the surface of a liquid medium. The method includes the first step of generating acoustic signals in the liquid medium at a selected frequency range to form wave patterns on the surface of liquid medium. As a result the particular wave patterns will have reinforcing characteristics at predetermined angles of observation. The particular wave patterns will be scanned by radar which is in a phase-locked relationship with the generation of the acoustic signals to detect signals indicative of the particular wave signals at selected observation angles. The detected signals will then be coherently added for at least one selected observation angle to obtain an indication of the object to be detected.
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patent: 4229809 (1980-10-01), Schwalbe
patent: 4891762 (1990-01-01), Chotiros
patent: 5481504 (1996-01-01), Rosenbach et al.
patent: 5579285 (1996-11-01), Hubert
patent: 5729694 (1998-03-01), Holzrichter et al.
patent: 6130641 (2000-10-01), Kraeutner et al.
patent: 6147636 (2000-11-01), Gershenson
patent: 4229809 (1987-12-01), None
patent: 11311671 (1999-11-01), None
Gilbert Harvey A.
Peck Donald G.
Sotomayor John B.
The United States of America as represented by the Secretary of
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