Communications – electrical: acoustic wave systems and devices – Sonar counter-measures
Reexamination Certificate
1982-08-13
2002-08-27
Pihulic, Daniel T. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Sonar counter-measures
C434S007000
Reexamination Certificate
active
06442104
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to electronic synthesis of sounds, and more particularly, to the digital synthesis of background sounds employed in training simulators which simulate antisubmarine-warfare episodes in real time.
2. Description of the Related Art
Simulators are widely employed today to train personnel in the operation of complex mechanical, electrical and electromechanical systems. A simulator acquaints personnel being trained with problems they will confront in real-life situations without exposing them to the actual risks which they would face in such situations. Such risks would be enhanced greatly by the fact that the personnel confronting them often have little, if any,experience. The use of training simulators is also cost-effective. If untrained or minimally trained personnel were, by necessity, forced to gain experience on actual operating systems, the likelihood of damage to the system or of personnel injury would be much greater precisely because serious consequences could ensue from mistakes or errors in judgment. The use of a simulator, on the other hand, permits inexperienced personnel to learn while they are seemingly performing the tasks for which they are being trained without risk of actual potentially disastrous consequences.
Training on a simulator is most effective if the environment which is created and the problems which are posed are as close to real life as are possible. Among the elements which add to the realism of the simulation are resemblance of the simulator equipment to actual equipment, close approximation of sensory information (including sights and sounds) provided to operating personnel in real-life situations, and the posing of problems which are very similar to those with which the trainees will be confronted after their training programs have been successfully completed.
The above is no less true in the training of antisubmarine-warfare personnel than is the case in any other training situation. Antisubmarine warfare today is characterized by high levels of tactical sophistication and the use of complex equipment.
In a typical antisubmarine-warfare episode, a patrol craft (typically an airplane) drops sonobuoys into the water. These sonobuoys carry hydrophones which pick up acoustic signals propagating through the surrounding water. Each sonobuoy also includes a radio transmitter which relays the acoustic signals picked up back to the patrol craft. Each sonobuoy can be set to transmit on a particular radio-frequency channel. Typically, the receiver on the patrol craft receives 36 such channels, allowing the signals from 36 out of a possible 99 sonobuoys to be monitored.
It is apparent that any simulator which is to provide a realistic simulation of an antisubmarine-warfare episode has a formidable task. The simulator must generate a number of different signals, each with different amplitude and spectral characteristics, many of which are episode related. The simulator must provide a synthesized version of a signal from a sonobuoy which depends on the location of the sonobuoy and of sound sources, relative movement between the two (which causes Doppler effects), and the operating condition of the sonobuoy.
These difficulties have resulted in the use of sophisticated computers to produce such complex simulations. Such a simulation computer is programmed with a vast amount of information and instructions corresponding to a number of antisubmarine-warfare episodes. The simulation computer keeps track of a simulation episode as defined by a training instructor.
The sounds detected by any particular sonobuoy depend on a number of factors, including the location and type of sonobuoy, the presence of noise sources in the water around the sonobuoy, the orientation of these sound sources with respect to the sonobuoy, and the operating condition of the sonobuoy.
A sonobuoy picks up ambient sea sounds, such as those produced by aquatic creatures. These ambient sounds can include, for example, those generated by humpback whales, bottlenose porpoises, and snapping shrimp. Also, sonobuoys and their hydrophone components can generate acoustic noises. For example, one of these sounds is generated when a hydrophone is lowered from a sonobuoy housing to a desired depth. Another sound is that produced by a hydrophone having a faulty lowering mechanism. Such a faulty lowering mechanism results in the hydrophone being “hung”, causing it to bang against the side of the sonobuoy housing. Additional sources of sounds present in antisubmarine warfare are produced by explosions, hulls crumpling, and submarine control devices (such as rudders and ballast tanks).
It is thus clear that ambient sea sounds, including sounds produced by man-made devices, must be produced in antisubmarine-warfare simulators if authentic antisubmarine-warfare episodes are to be simulated.
In previous antisubmarine-warfare simulators, such sounds are generated by analog means such as analog oscillator circuits and analog recorders. The analog approach, however, exhibits many disadvantages. Specifically, analog means and the sound signals they produce are subject to drift and the adverse effects of component aging. Analog tape recorders have maintenance problems and allow very little control over the sounds which they reproduce. Real sounds that are taped, by their very nature, typically contain other sounds which interfere with those which are to be simulated. For example, a tape of transient sounds generated by a submarine's maneuvering system typically also contains submarine-generated sounds such as those from the submarine's power plant as well as background sea sounds. These other signals appear as spurious signal components which interfere with the sounds required for simulation of a particular tactical situation.
The digital synthesis of signals in accordance with the present invention results in much greater control over the synthesized background sound signals and allows the reproduction of sounds that are not contaminated by other, spurious components. The digital signal synthesizer of the present invention can be programmed to introduce such effects as Doppler shift, multipath, and directional characteristics. In most cases, such signal modifications can be accomplished in the present invention without any change in hardware. Rather, they can be effected by changes in the software. Because digital circuits are not subject to drift and other adverse effects which are present in analog circuits, and because digital circuits have no moving parts, initial calibration and subsequent maintenance are greatly simplified in the present invention.
SUMMARY OF THE INVENTION
The present invention is an underwater background acoustic signal synthesizer and method, which generates, on a multiplexed basis, digital signals corresponding to background or ambient antisubmarine-warfare sounds. These digitally synthesized signals are multiplexed onto a bus which conveys them to a multiplier which digitally imparts to them directional characteristics. The digital signals are then applied to a demultiplexer and digital-to-analog converter, which demultiplexes them, converts them to analog form, and assigns them to appropriate channels of an audio system. These channels correspond to the selectable channels of receiving equipment on board the patrol craft. The audio system thus functions as a dummy radio-frequency receiver, and provides audible signals corresponding to those which would be presented to a crew monitoring such a receiver during an actual antisubmarine-warfare episode.
All of the signals which are synthesized by the apparatus and method of the present invention are generated in the digital domain. To reduce the amount of hardware necessary to generate the large number of digital signals required for a realistic simulation, multiplexing is extensively employed.
In general terms, the system of the present invention comprises a first computer, a second computer, a hardware controller, a synthesizer and an o
Friedman Henry Jay
Magnani Timothy Paul
Ridgell, Jr. James Jefferson
Pihulic Daniel T.
Sterne Kessler Goldstein & Fox P.L.L.C.
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