Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
2000-01-26
2002-05-14
Le, Que T. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C250S574000
Reexamination Certificate
active
06388246
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates generally to the field of detection systems, and more particularly, to a system and method for detecting underwater objects.
BACKGROUND OF THE INVENTION
Detection systems are generally used to locate and/or identify objects in a variety of media. For example, underwater detection systems are generally used to detect objects submerged in water. Underwater detection systems generally include a variety of applications, such as commercial, military and recreational. For example, recreational and commercial applications for underwater detection systems may include aquatic animal locating and underwater terrain mapping. Military applications for underwater detection systems may include mine sweeping and/or underwater vessel detection.
One type of underwater detection system is a sonar system. In sonar systems, sound waves are generated and transmitted through the water. The sound waves are reflected by objects submerged in the water. The reflected sound waves are generally analyzed to detect and identify objects submerged in the water. Another type of underwater detection system is a lidar or light detection and ranging system. In a lidar system, a laser transmits pulses of light energy into the water at a predetermined frequency from a generally remote vehicle. Backscattered light energy reflected by the water is generally analyzed to detect the presence of objects submerged in the water.
However, conventional underwater detection systems suffer several disadvantages. For example, sound-based underwater detection systems generally provide inadequate resolution for identifying the underwater object. In lidar systems, optical clutter resulting from generally large amounts of spurious light scattering, such as from water surface reflections, substantially inhibits object detection near the surface of the water. Additionally, because daylight conditions generally produce a large optical background, object contrast is substantially impaired during daylight conditions.
SUMMARY OF THE INVENTION
Accordingly, a need has arisen for an improved underwater detection system and method that provides increased resolution and greater accuracy. The present invention provides a system and method for detecting underwater objects that addresses shortcomings of prior systems and methods.
According to one embodiment of the present invention, a system for detecting an underwater object comprises an optical signal generator operable to generate and transmit an optical signal into the water. The system also includes an absorption cell operable to receive the optical signal reflected from the water and absorb an unshifted frequency component of the reflected optical signal. The system further includes a detector operable to receive a shifted frequency component of the optical signal from the absorption cell to detect the object. Displacement of the water by the object causes an absence of a portion of the shifted frequency component of the optical signal.
According to another embodiment of the present invention, a method for detecting an underwater object comprises generating an optical signal using an optical signal generator and transmitting the optical signal into the water. The method also includes receiving the optical signal reflected from the water at an absorption cell. The method also includes absorbing an unshifted frequency component of the optical signal using the absorption cell and transmitting a shifted frequency component of the optical signal to a detector. The method further includes detecting the object in the water using the shifted frequency component of the optical signal. Displacement of the water by the object causes an absence of a portion of the shifted frequency portion of the optical signal.
The present invention provides several technical advantages. For example, according to one embodiment of the present invention, the system provides detection of submerged objects independent of the composition of the object. For example, the shifted frequency component of the optical signal reflected from the water is received at the detector. Water displacement caused by the object causes an absence of a portion of the shifted frequency component of the optical signal. Thus, detection of the object is independent of the composition of the object.
Another technical advantage of the present invention includes a detection signal that is generally free of background signals. For example, in turbid water, backscattered energy of the optical signal caused by suspended particles, the submerged object and the sea floor is generally unshifted from a predetermined generated frequency and is removed using the absorption cell. Thus, only the shifted frequency component of the optical signal is received at the detector. Therefore, the shifted frequency component of the optical signal provides a generally definitive detection signal.
Other technical advantages will be readily apparent to one skilled in the art from the following figures, descriptions, and claims.
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Fry Edward S.
Kattawar George W.
Pan Xioajiang
Walther Thomas
Baker & Botts L.L.P.
Le Que T.
The Texas A&M University System
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