Communications – electrical: acoustic wave systems and devices – Receiver circuitry
Reexamination Certificate
1999-04-01
2001-03-27
Pihulic, Daniel T. (Department: 3662)
Communications, electrical: acoustic wave systems and devices
Receiver circuitry
Reexamination Certificate
active
06208589
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to a method for screening acoustic signals transmitted by a moving target, which can be submerged, and which will be designated by the name “target,” by eliminating spurious acoustic signals radiated in particular by marine surface vessels, and which impede detection of acoustic signals radiated by the “target.”
2. Description of Related Art
The signals radiated by the “target” are generally detected by using a set of acoustic pickups located in the same horizontal plane and arranged in a line.
The presence of numerous spurious signals with higher energy than the energy of the “target” and due to intense shipping activity makes detection of signals from the “target” increasingly difficult and complicates the job of the operator in charge of detection.
SUMMARY OF THE INVENTION
The invention relates to significantly reducing the number of unwanted signals interfering with the observation of “useful” signals to be detected, in order to decrease the workload of the operator.
The invention relates to a method of screening an acoustic signal (S) or a spectrum line (F) of maximum energy E transmitted by a “target” that can be submerged at sea, from among a multitude of acoustic signals coming from any noise generators (W) radiating acoustic signals of the same type with higher energy than energy E, employing, for example:
a set of N submersible acoustic pickups identically parameterized in surveillance mode, designed to detect the presence of the signal (S) or a desired spectrum line (F), with the set of N pickups defining any number of surveillance cells with two adjacent pickups, each pickup being associated with one or more target detection regions defined as the geographic areas within which the presence of the “target” is deemed detectable and outside which the “target” is deemed nondetectable;
a system for locating the pickups;
a set of elementary geographic areas determined by the intersection of all the target detection regions of the N pickups, each elementary geographic area being defined as a geographic area within which any noise generator is always detectable by the same acoustic pickups;
a set of “special” areas selected from all the above elementary geographic areas, each “special” area relative to a given surveillance cell being defined as an elementary geographic area within which the “target” may be detectable by at least one of the acoustic pickups of the surveillance cell;
a maximum number Nmax of pickups relating to one or more “special” areas of a given surveillance cell able simultaneously to detect the “target”, wherein the acoustic signal (S) or line (F) is detected by a number Nd of acoustic pickups from the set of N pickups, and analyzed by the following series of three consecutive steps:
1) If the number Nd of pickups detecting signal (S) or line (F) is greater than the number Nmax, the signal (S) or line (F) is eliminated,
otherwise, the signal (S) or line (F) is retained for locating the noise generator (W) radiating signal (S) or line (F);
2) Definition of the conditions under which noise generator (W) is located; if these conditions are present, the noise generator is located by step 3 below; otherwise the signal (S) or line (F) is retained;
3) Locating noise generator (W) and determining relative to the “special” areas:
whether noise generator (W) is geographically inside one of the “special” areas, in which case signal (S) or line (F) is retained; otherwise signal (S) or line (F) is eliminated.
The method applies to all fields using passive listening acoustic buoys, fixed or movable lengthwise lines composed of hydrophones or hydrophone arrays, etc. as well as all types of known acoustic signals (spectrum lines, narrow bands, broad bands, transient signals, etc.).
The method according to the invention requires the following two conditions to be met: prior knowledge of the “target” detection region for each of N acoustic pickups in the set as a function of the type of acoustic signal processed and on-going knowledge of the geographic position of the N acoustic pickups in the set.
The principle of the method, applied to a set of submersible acoustic pickups, consists of determining the geographic areas within which any noise generator radiating an acoustic signal will be declared a possible target.
In the first case, the signal detected is retained as such, and subjected to the observation of the operator in charge of detection. In the second case, the signal is eliminated and not subjected to the observation of the operator.
When it is necessary to locate the noise generator, the first step of the method can be eliminated.
The invention is applied to reducing the number of false alarms generated by high-energy acoustic signals radiated by noise generators at the surface of the sea.
REFERENCES:
patent: 5175710 (1992-12-01), Hustson
patent: 5216640 (1993-06-01), Donald et al.
patent: 5481505 (1996-01-01), Donald et al.
Delegation Generale pour l'armement
Oliff & Berridg,e PLC
Pihulic Daniel T.
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