Patent Application
20120075956
The present invention relates to sonar systems, more particularly, to a sonar system for processing and displaying active sonar return signals.
Civilian and military sea vessels use both active and passive sonar systems for numerous purposes including geological studies, marine life exploration, and military operations such as anti-submarine warfare (ASW). These systems are used to detect the presence of submerged objects by either transmitting a sound wave and detecting its reflected return signal as it propagates through the water (active sonar), or by listening for sound waves generated by these objects (passive sonar).
These return signals are received, processed, and analyzed in an effort to detect a target object. Traditional processing methods include converting the received analog signal to a digital form, filtering, and processing the signal in either the time-domain or frequency-domain using, for example, a Fast Fourier Transform (FFT). The magnitude of the processed signal, as well as its bearing and range, is presented to a sonar operator through, for example, a rasterized display, wherein a target may be visually detected by identifying displayed differences in return signal magnitude.
However, the magnitude of the return signal may be distorted by the propagation medium (normally water), as well as the characteristics of the reflecting object, for example a target or the seafloor. Specifically, signal distortion or other interference may be introduced by any number of factors including: irregular seafloors, reverberation, target scattering, multi-path reflections, noise generated by waves, and changing distances from a target. These interferences are transmitted along with the return signal to the operator's display, thus distorting or masking the image of potential targets and hindering an operator's ability to detect their presence. This is especially true in littoral waters, where scattering and reverberation off of the seafloor creates significant amounts distortion, thus allowing a threat to remain undetected, especially when positioned on or near the seafloor.
As a result, current sonar systems may offer effective target detection only when return signal magnitude levels are above background noise or reverberation magnitude levels. However, when the magnitude of a return signal is less than or approximately equal to the background noise magnitude, systems displaying only return signal magnitude data to an operator are ineffective. Current solutions to these shortcomings include using various waveform types (FM, short pulse, wideband) or lowering the emitted power to reduce scattering. These methods are only marginally effective and still result in high false alarm rates and missed contacts. Other methods use multi-static techniques which are complicated and require multiple sensors or sonar platforms in addition to having a limited effectiveness.
Accordingly, a sonar system which improves an operator's ability to detect submerged objects in high-distortion environments is desired.
In one embodiment of the present invention a sonar system is provided having a transmitter for generating a sonar signal, a receiver for receiving a reflected return signal, and a signal processor for extracting both the magnitude and phase of the reflected return signal. The magnitude and phase data is provided to an operator via a visual display to aid detection of a target object. In a more preferred embodiment, the magnitude and phase data are superimposed, creating a single image representing the magnitude and phase of the return signal.
In another embodiment of the present invention a method for detecting a submerged object using a sonar system is provided. The method includes transmitting at least one sonar signal and receiving a reflected return signal. A signal processor is provided for processing the return signal and extracting both magnitude and phase data therefrom. An object or target is detected by analyzing a visual representation of the return signal magnitude and phase.
It is to be understood that the figures and descriptions of the present invention have been simplified to illustrate elements that are relevant for a clear understanding of the present invention, while eliminating, for purposes of clarity, many other elements found in typical active sonar systems. However, because such elements are well known in the art, and because they do not facilitate a better understanding of the present invention, a discussion of such elements is not provided herein. The disclosure herein is directed to all such variations and modifications known to those skilled in the art.
In the following detailed description, reference is made to the accompanying drawings that show, by way of illustration, specific embodiments in which the invention may be practiced. It is to be understood that the various embodiments of the invention, although different, are not necessarily mutually exclusive. Furthermore, a particular feature, structure, or characteristic described herein in connection with one embodiment may be implemented within other embodiments without departing from the scope of the invention. In addition, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims, appropriately interpreted, along with the full range of equivalents to which the claims are entitled. In the drawings, like numerals refer to the same or similar functionality throughout several views.
Referring generally to
The DSP 28 may take inputs from the processing computer 14 to drive a waveform generator 30, such as a synthesizer, for providing a signal to at least one transducer 36 for transmitting a sonar signal 37. In operation, the transmitted sonar signal 37 is reflected of an object or target, and produces a return signal 38. The return signal 38 is received by at least one second transducer 34, for example, an array of piezoelectric-based hydrophones. The second transducer 34 provides an analog version of the reflected return signal to a receiver 32. The receiver 32 may include filters, amplifiers, and/or analog to digital converters for providing a digitized version of the return signal to the DSP 28. The DSP 28 may comprise a beamformer, signal filters, and/or demodulators to process the digitized return signal. Likewise, the DSP 28 may include FFT circuitry for converting the time-domain return signal to the frequency-domain.
The resulting return signal data (typically magnitude data) is transferred over the data bus 26, where it may be stored in memory 20 and/or provided to the operator interface 12, such as a display device. The display device may comprise a CRT, plasma, LCD, or other suitable display type for presenting the received return signal data to an operator in a visual manner, usually in the form of a range vs. bearing output.
An objective of the present invention is to improve the ability of an active sonar system to detect a submerged object by processing not only the magnitude of return signals, but also their phase. The phase of a reflected return signal is influenced by the acoustic impedance of the reflecting object. This acoustic impedance is a function of a number of characteristics of the object, most notably its density and Young's Modulus. Accordingly, the acoustic impedance of the target's background, i.e., the ocean and/or the ocean bottom, is typically distinct from the acoustic impedance of the target itself because of their differing material compositions. It follows that a target may be detected by evaluating the phase of the return signals, and more particularly, by detecting variations in return signal phase.
Referring to
x(t)=A*sin [(2πft)±θ]
wherein A is the magnitude of the return signal, f is its frequency, and θ is the signal phase.
A portion of the return signal 105 is received by at least one second transducer 134, for example an array of hydrophones. The at least one second transducer 134 provides a receiver 132 with an analog return signal representative of the received return signal 105. As described above with respect to
In one embodiment of the present invention, the beam-formed return signal is provided to an FFT module 131. The FFT module 131 is used to convert the received time-domain return signal to its frequency-domain Fourier transform. The resulting Fourier transform may be provided to a processor, for example, a signal demodulator 133 for extracting both magnitude and phase data from the transform, with the phase of the transform being equal to the inverse tangent of the imaginary portion divided by the real portion.
While the above describes signal processing in the frequency-domain using an FFT, it is envisioned that the processing of the return signal and the extracting of magnitude and phase data can be accomplished in the time-domain without departing from the scope of the present invention.
In one embodiment of the present invention, the magnitude data 140 and phase data 141 are processed in parallel and provided to a display control module 115. The display control module 115 is operative to provide both the magnitude and phase data 140,141 to the operator display 112. In a preferred embodiment, the magnitude and phase data 140,141 is combined in the display control module 115 such that representative images of both magnitude and phase data are superimposed over each other on the operator display 112. This arrangement allows the operator to simultaneously observe both the magnitude data and the phase data of the returned signals.
In another embodiment, as will be described in more with respect to
It is to be understood that the above-described sonar system, including the arrangement and function of the receiver, DSP, and processing devices may be substituted with any number of suitable arrangements which result in the output of both magnitude and phase data of the received return signal without departing from the scope of the present invention. Likewise, while the combination of magnitude and phase data has been described with respect to a display control module, these operations may be performed by the display device itself, or other suitable devices without departing from the scope of the present invention.
Representative sonar displays will now be shown and described illustrating the above characteristics. Referring generally to
Improved target detection is provided by displaying the phase of return signal. As discussed herein, a target or other reflector will have a unique acoustic impedance which distinctly alters the phase of a signal reflected therefrom. Referring generally to
In an embodiment of the present invention shown in
In a more preferred embodiment, the operator can also control the weighting, or relative strength of the superimposition based on environmental conditions. For example,
While the above describes superimposing phase and magnitude data onto a single operator screen, it is further envisioned that additional embodiments of the present invention may include separate displays of magnitude and phase data, either on individual operator displays, or by toggling between respecting images on a single display.
While the foregoing describes exemplary embodiments and implementations, it will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit and scope of the invention.
