The present invention relates generally to systems and methods for acoustic detection and, more particularly, to systems and methods for rejecting wind noise in acoustic detection systems.
A number of conventional systems detect, classify, and track air and ground bodies or targets. The sensing elements that permit these systems to perform these functions are typically arrays of microphones whose outputs are processed to reject coherent interfering acoustic noise sources (such as nearby machinery). Other sources of system noise include general acoustic background noise (e.g., leaf rustling) and wind noise. Both of these sources are uncorrelated between microphones. They can, however, be of sufficient magnitude to significantly impact system performance.
While uncorrelated noise is addressed by spatial array processing, there are limits to signal-to-noise improvements that can be achieved, usually on the order of 10*log N, where N is the number of microphones. Since ambient acoustic noise is scenario dependent, it can only be minimized by finding the quietest array location. At low wind speeds, system performance will be limited by ambient acoustic noise. However, at some wind speed, wind noise will become the dominant noise source—for typical scenarios, at approximately 5 mph at low frequencies. The primary source of wind noise is the fluctuating, non-acoustic pressure due to the turbulent boundary layer induced by the presence of the sensor in the wind flow field. The impact of an increase in wind noise is a reduction in all aspects of system performance: detection range, probability of correct classification, and bearing estimation. For example, detection range can be reduced by a factor of two for each 3-6 dB increase in wind noise (depending on acoustic propagation conditions).
Therefore, there exists a need for systems and methods that can reduce wind noise so as to improve the performance of acoustic detection systems such as, for example, acoustic detection systems employed in vehicle mounted systems for which the effective wind speed includes the relative velocity of the vehicle when the vehicle is in motion.
Systems and methods consistent with the present invention address this and other needs by providing a multi-sensor windscreen assembly, and associated wind noise rejection circuitry, to enable the detection of a desired acoustic signal while maximizing rejection of wind noise. Multiple sensors, consistent with the present invention, may be distributed across a surface of a three dimensional body, such as a sphere, cylinder, or cone. Adaptive weights may be applied to the signal output from each of the multiple sensors so as to pass low wind noise signals and reject those with high wind noise. Signals from sensors subjected to high levels of unsteady pressures due to wind turbulence may be given low weights and, thus, substantially rejected, while signals from sensors not subjected to these flow disturbances may be given large weights and, thus, substantially passed. The values of the adaptive weights may be continuously, or periodically, updated in order to account for wind direction and speed changes at the multi-sensor windscreen assembly. Systems and methods consistent with the present invention, thus, provide an adaptive windscreen system that can reject wind noise and, thereby, improve the measurement and detection of desired acoustic signals.
In accordance with the purpose of the invention as embodied and broadly described herein, a method of rejecting wind noise includes distributing a plurality of acoustic sensors over a surface of a body; identifying at least one sensor of the plurality of acoustic sensors that is subject to low wind noise; passing signals from the at least one identified sensor as low wind noise signals; and rejecting signals from non-identified sensors of the plurality of acoustic sensors as high wind noise signals.
In another implementation consistent with the present invention, a method of rejecting signal noise includes receiving signals from a plurality of sensors and assigning a weight value to each of the received signals. The method further includes deriving a noise rejected output signal based on a function of the assigned weight values and the received signals.
In a further implementation consistent with the present invention, a windscreen includes a three dimensional body mounted on a first surface, the body configured to rotate with respect to the first surface and comprising at least one second surface. The windscreen further includes a plurality of sensors distributed on the at least one second surface of the body, the sensors configured to sense forces acting upon the body.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, explain the invention. In the drawings,
The following detailed description of the invention refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims.
Systems and methods, consistent with the present invention, provide mechanisms that adaptively reject noise in multiple signals received from a multi-sensor device. A processor of the present invention assigns a weight parameter to each signal of the multiple signals. Each assigned weight parameter may correspond to a noise level of the associated sensor signal. Output circuitry may derive a noise rejected output signal based on a function of the assigned weight parameters and the received signals. In some embodiments, for example, the output circuitry may include multiplier elements and a summer. In this case, the noise rejected output signal may include a summation of the products of each assigned weight parameter with its respective sensor signal.
As shown in
Each of the multiple sensors 115 may include any type of conventional transducer for measuring force of pressure. A piezoelectric transducer (e.g., a microphone) is one example of such a conventional transducer. In some embodiments of the present invention, each of the multiple sensors 115 may measure acoustic and non-acoustic air pressure.
The weighted signals {w1S1, w2S2, . . . , wNSN} from multiplier elements 315 may be summed at summer 320. The summed weighted signals (w1S1+w2S2+ . . . +wNSN) can be output from wind rejection unit 300 as a noise rejected output signal 325. This noise-reduced output signal 325 may be used in a conventional acoustic detection system (not shown) for detecting, classifying, and tracking objects or targets.
w=[W1w2 . . . wN]T=R−1/1R−11 Eqn. (1)
where
The sensor signals {S1, S2, . . . , SN} may then each be multiplied by their corresponding weight {w1, w2, . . . , wN} of weight vector w [act 405]. For example, a corresponding multiplier element 315 can multiply each sensor signal by a respective assigned weight. The weighted sensor signals {w1S1, w2S2, . . . , wNSN} may then be summed to produce a noise rejected output signal 325 (w1S1+w2S2+ . . . +wNSN) [act 410]. Summer 320 of wind rejection unit 300 may, for example, sum each of the weighted sensor signals. The noise-reduced output signal 325 may, for example, be used in a conventional acoustic detection system for detecting, classifying, and/or tracking objects or targets.
Systems and methods, consistent with the present invention, provide mechanisms that enable the detection of a desired acoustic signal incident at a multi-sensor windscreen assembly while maximizing rejection of wind noise. The multi-sensor windscreen assembly may include multiple sensors distributed across a surface of a three dimensional windscreen, such as a sphere, cylinder, or cone. Noise rejection circuitry may apply adaptive weights to the signal output from each of the sensors so as to pass low wind noise signals and reject high wind noise signals. Signals from sensors subjected to high levels of unsteady pressures due to wind turbulence and wake flow will be given low weights and, thus, substantially rejected, while signals from sensors not subjected to these flow disturbances will be given large weights and, thus, substantially passed. The values of the adaptive weights may be continuously, or periodically, updated in order to account for wind direction and speed changes at the multi-sensor windscreen assembly.
The foregoing description of exemplary embodiments of the present invention provides illustration and description, but is not intended to be exhaustive or to limit the invention to the precise form disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. For example, while certain components of the invention have been described as implemented in hardware and others in software, other configurations may be possible. Furthermore, while the use of weights has been described above as one exemplary method for selecting the sensor signals to be used to compose noise rejected output signal, mechanical rotation of windscreen 105 may provide the mechanism for selecting the sensor signals that are to compose the noise rejected output signal. In such an embodiment, windscreen 105 may be rotated and the signals of the sensors facing into the wind may be used for composing the noise rejected output signal, while signals from sensors facing away from the wind would not be used. In some exemplary embodiments, windscreen 105 may include a streamlined body with fins attached at the rear, thus, permitting windscreen 105 to rotate in the manner of a weathervane.
Also, while series of acts have been described with regard to
The instant application claims priority from provisional application No. 60/301,104, filed Jun. 26, 2001, and provisional application No. 60/306,624, filed Jul. 19, 2001, the disclosures of which are incorporated by reference herein in their entirety. The instant application is related to co-pending Application No. 60/306,624, entitled “Systems and Methods for Adaptive Noise Cancellation” and filed on a same date herewith, the disclosure of which is incorporated by reference herein.
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Number | Date | Country | |
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60306624 | Jul 2001 | US | |
60301104 | Jun 2001 | US |