JP2012207963A - Active sonar device and signal detection method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely detect even a target whose travel speed is small by separating the target from reverberation or the like in an active sonar device.SOLUTION: An active sonar device receives an acoustic signal as a wave-receiving signal, performs frequency analysis of the wave-receiving signal, finds the incoming direction and intensity of the wave-receiving signal in each cell on the basis of a result of the frequency analysis with areas of unit frequency width and unit time width in detection as a cell, determines whether a difference in an incoming direction in an adjacent cell is within a second threshold when a cell whose intensity exceeds a first threshold is adjacent in a frequency direction or time direction, and connects the adjacent cells as one detection when the difference is within the second threshold.

Description

  The present invention relates to an active sonar device that radiates sound waves and detects a reflected wave signal from a target, and a signal detection method in the active sonar device.

  Active sonar devices used in the water emit sound waves, detect the reflected waves of the emitted sound waves, and calculate the distance to the target (ie, the reflecting object) from the time difference between receiving the reflected waves from the sound wave radiation. To do. When sensors having a plurality of different directivity patterns are combined as a receiver, the arrival direction of the reflected wave can be known, and the direction in which the target is present can also be obtained. When the target moves, the frequency of the reflected wave shifts due to the Doppler effect. Therefore, the moving speed of the target can also be obtained by performing frequency analysis by applying Fourier transform to the reflected wave. The magnitude of the Doppler shift is proportional to the line-of-sight speed of the target viewed from the active sonar device. The active sonar device is used to detect a target moving in water or in the sea.

As a display method for detecting and notifying a moving target in an active sonar apparatus, there is a method of displaying a frequency analysis result by a spectrogram indicating signal intensity for each frequency as shown in FIG. Here, the horizontal axis represents time, and the vertical axis represents frequency. The signal intensity of the received signal is represented by the luminance on the screen. Here, the brighter the signal intensity, the stronger the signal intensity. In FIG. 1, the transmission frequency f ₀ indicates the frequency of the sound wave pulse radiated from the transmitter of the active sonar device into the water or the sea. Since the frequency analysis of the received signal is executed using a digital algorithm such as FFT (Fast Fourier Transform), the frequency and time are expressed as discrete values. In the spectrogram shown in FIG. For each region of time width and predetermined frequency width (illustrated, small rectangular region, hereinafter referred to as a cell), the signal level in that region is indicated.

In the case shown in FIG. 1, a signal is detected over a very long time at the transmission frequency f ₀ , which is due to the reverberation of the transmitted sound wave pulse. Especially in the sea, it is assumed that a sound pulse with a short duration is emitted as a PCW (pulse continuous wave) signal, which is a pulse of a continuous wave of a certain frequency, due to reflections on the sea surface and sea floor, waves and complex bottom topography. However, reverberation continues at the transmission frequency for a fairly long time. Signal reflected by the target object is moving during the period from time t ₈ to t _15, i.e. the echo is observed. The frequency of the echo is a frequency f ₁ different from the transmission frequency. More specifically, echoes are detected in eight consecutive cells having a frequency of f ₁ and corresponding times of t ₈ to t _15, respectively.

  The active sonar apparatus determines that there is a moving target when there is a detection value region (cell) exceeding the threshold in the spectrogram as shown in FIG. If the detected value exceeds the threshold value in cells at different frequencies (that is, different speeds) or at different times, it is determined that there are a plurality of targets. However, there is a case where a large detection value is shown over a long time like the reverberation described above, and an echo from the target also has a duration equivalent to the duration of the transmitted sound wave pulse. Therefore, in order to reduce false detection, cells that are temporally continuous even if the threshold value is exceeded are connected together. This connection process is called a time connection process. In addition, regarding the frequency, if any of the adjacent frequency cells exceeds the threshold value in consideration of an error associated with the discrete handling in the processing by FFT, These cells are also connected to one. This connecting process is called a frequency connecting process.

  FIG. 2 explains the cell connection process. Regarding time and frequency, for example, a cell marked with “◯” in (a) is a cell having a detection value (level) exceeding a threshold value. In the time concatenation process, as shown in (b), the cell “B” that continues in time is first concatenated to the earliest “A” cell among the cells at the level exceeding the threshold. Then, although it is an adjacent frequency, the “C” cell is continuously connected to the “B” cell in time, and the “D” cell is similarly connected. As a result, “ABCD” is treated as one detection. In the frequency concatenation process, as shown in (c), “E” cells having the same time and adjacent frequencies are connected to the “B” cell. By combining time concatenation processing and frequency concatenation processing, five cells are concatenated as one detection like “ABCDE”.

  Cell concatenation processing is effective to prevent false detection, but when the moving speed of the target is low, the Doppler shift amount is also small, so the reverberation frequency and the echo frequency are adjacent and separate the echo from the reverberation. I can't do that. Assuming that the spectrogram as shown in FIG. 1 is obtained, the result of performing the concatenation process on this is shown in FIG. Detections with continued levels (intensities) are regarded as the same signal and are combined into one detection information. As a result, even echoes close to reverberation are integrated into one piece of detection information.

  As a technique for enabling the operator (operator) of the active sonar apparatus to easily determine whether or not there is an echo from the target object separately from the reverberation, on the premise that the above-described connection processing is not performed. There is a spectrogram in which the level (intensity) is expressed in luminance, in which azimuth information is expressed in color. A spectrogram in which azimuth information is expressed in color is also called a colorgram. FIG. 4 shows an example of correspondence between azimuth and color. For example, a signal having an azimuth angle of 0 ° to 45 ° is represented in red, and the luminance in red display is changed according to the signal level. An example in which the echo is displayed separately from the reverberation is shown in FIG. For the sake of explanation, in FIG. 5, the difference in color in each cell depends on the difference in marking shape (for example, an oblique double line or “x” mark) due to a black thin solid line attached to each cell. It is represented.

  However, depending on the display color, it is difficult to see, and the number of colors that can be distinguished by humans is not so large considering the change in brightness at the time of display. It may be difficult to distinguish and visually recognize from.

  As a technique for discriminating and discriminating echoes from a target moving at a low speed from reverberation and the like, Patent Document 1 discloses a method using fixed linearity requirements and exclusion requirements. However, since the method described in Patent Document 1 uses a shaped frequency sweep signal as an acoustic signal radiated in water or in the sea, it is difficult to apply to an existing active sonar apparatus using, for example, a PCW pulse, and transmits the signal. There is a problem that generation of sound wave pulses and processing of received signals are complicated.

JP 2009-150662 A

  As described above, when the moving speed of the target is low, it is not possible to easily identify the echo from the target separately from the reverberation while preventing erroneous detection.

  An object of the present invention is to provide a signal detection method in an active sonar apparatus that can detect a target with a low moving speed separately from reverberation or the like and reliably detect it.

  Another object of the present invention is to provide an active sonar apparatus capable of reliably detecting a target having a low moving speed by separating it from reverberation and the like.

  The signal detection method of the present invention is a signal detection method in an active sonar device, which receives an acoustic signal as a received signal, performs frequency analysis on the received signal, and unit frequency width in detection. And the unit time width region as a cell, the arrival direction and strength of the received signal are obtained for each cell based on the result of frequency analysis, and the cell whose strength exceeds the first threshold is in the frequency direction or When adjacent in the time direction, it is determined whether the difference of arrival directions in the adjacent cells is within the second threshold, and if it is within the second threshold, the adjacent cells are Coupling as detection.

  The active sonar device of the present invention includes a receiver that receives an acoustic signal, a frequency analysis unit that performs frequency analysis on the signal received by the receiver, and a region of unit frequency width and unit time width in detection. As a cell, an azimuth calculation processing unit for obtaining the arrival direction of the acoustic signal for each cell based on the result of frequency analysis, a level detection processing unit for obtaining the intensity of the acoustic signal for each cell based on the result of frequency analysis, When a cell exceeding the threshold value of 1 is adjacent in the frequency direction or the time direction, it is determined whether or not the difference in arrival direction in the adjacent cell is within the second threshold value, and the second threshold value is determined. And a detection connection processing unit that connects adjacent cells as one detection when the value is within the value.

  When cells are connected, connection is not performed between cells with greatly different azimuth differences in arrival directions, so even echoes from targets moving at low speed have different arrival directions from reverberation. It becomes possible to detect reliably based on this.

It is a figure which shows the example of a display of the detection result in an active sonar apparatus. (A)-(c) is a figure explaining a connection process. It is a figure explaining the connection in a detection result. It is a figure which shows the example of a display which displayed the azimuth | direction information in the color and was able to discriminate | determine an arrival azimuth | direction. It is a figure which shows an example of selection of the color according to an azimuth | direction. It is a figure explaining the connection in the active sonar apparatus of one Embodiment. It is a block diagram which shows the structure of the active sonar apparatus of one Embodiment. It is a figure which shows the example of a display based on the position designated by the operator. It is a block diagram which shows the structure of another active sonar apparatus based on one Embodiment.

  In the active sonar apparatus according to the embodiment, cell concatenation processing is performed in order to prevent erroneous detection of an echo from a target. When cells whose signal strength (level) exceeds a threshold value continue, the cells are connected to form one detection. At that time, the arrival direction of the received acoustic signal is taken into account. Those that have a large difference in orientation should not be interconnected. In other words, a threshold value for orientation difference is set as a reference when cells are connected, and the orientation difference between two cells to be connected when performing the time connection processing or frequency connection processing described above is within this threshold value. Connect if there is, otherwise do not connect.

  FIG. 6 shows cell connection in this embodiment. In FIG. 6, in order to indicate the azimuth, each cell is marked with a black thin solid line. Here, the azimuth represented by the vertical double line marking and the diagonal double line marking are used. The azimuth represented is within the threshold with respect to the azimuth difference, and the difference between these azimuth and the azimuth represented by the “x” marking is outside the threshold range for the azimuth difference. Shall. When the spectrogram shown in FIG. 1 is obtained, as shown in FIG. 6, since the direction of signals from reverberation is within a threshold value, they are connected to each other. On the other hand, since the arrival direction of the echo is not within the threshold range with respect to the arrival direction of the reverberation, cells corresponding to the echo are connected to each other, but not connected to cells corresponding to the reverberation. As a result, in the example shown in FIG. 6, the reverberation and the echo are treated as separate detections, and the echo can be detected separately from the reverberation. By displaying the outline of the whole connected cells as one detection, for example, with a bold line, it becomes possible to easily recognize which cell corresponds to which detection on the display screen.

  FIG. 7 shows a specific configuration example of the active sonar apparatus according to the present embodiment.

  This active sonar device is intended to detect a moving target 30, and as described above, the arrival direction of the signal and its intensity for each of a plurality of cells obtained by subdividing the frequency and time. From the viewpoint of detecting the moving target 30, the result is displayed on the screen in the form of a spectrogram, for example. The active sorter apparatus includes a transmitter 31 that transmits a sound wave pulse in water or in the sea, a transmission processing unit 32 that transmits a transmission signal to the transmitter 31 and drives the transmitter 31, and a target 30. A receiver 11 that receives a reflected acoustic signal such as an echo signal in a plurality of different directivity patterns, and a demodulating process is performed on the acoustic signal in each directivity pattern received by the receiver 11. A demodulation processing unit 34 for making a wave signal, a frequency analysis unit 35 for performing frequency analysis on each received signal by FFT for each cell, and a signal level for the received signal for each frequency after frequency analysis. A normalization processing unit 36 that performs normalization processing, a azimuth calculation processing unit 37 that calculates a azimuth by performing azimuth calculation processing on the received signal for each cell subjected to frequency analysis, and a signal level normalized Received wave Based on the direction calculated by the level detection processing unit 38 that performs level detection for each cell based on the signal number and the direction calculation processing unit 37, it is determined whether or not the orientations of the two cells to be connected are within a threshold relating to the orientation difference. A direction determination processing unit 39 for determination, a frequency connection processing unit 40 for performing frequency connection of cells, a time connection processing unit 41 for performing time connection processing of cells, and a spectrogram in which cells are connected by time connection processing and frequency connection processing And a display unit 43 that displays the spectrogram generated by the display processing unit 42. The sound wave pulse radiated by the transmitter 31 into the water or the sea is, for example, a PCW pulse.

  In the configuration shown in FIG. 7, the preprocessing block 21 is configured by the demodulation processing unit 34, and the signal processing block 22 is configured by the frequency analysis unit 35, the normalization processing unit 36, and the azimuth calculation processing unit 37. In addition, the direction determination processing unit 39, the frequency connection processing unit 40, and the time connection processing unit 41 constitute a detection connection processing block 24 that functions as a detection connection processing unit. The detection connection processing block 24 and the level detection processing unit 38 are configured. Constitutes a signal detection block 23. When the transmitter 31 transmits an unmodulated sound wave pulse, it is not necessary to provide the demodulation processing unit 34.

  The detection connection processing block 24 performs connection processing of cells whose detected values exceed the threshold value. In the present embodiment, the frequency connection processing unit 40 and the time connection processing unit 41 are determined by the azimuth determination processing unit 39 even if cells whose detected values exceed the threshold value are adjacent in the time direction or the frequency direction. Based on the result, if the orientation difference of the cells to be connected is not within the threshold regarding the orientation difference, the cells are not connected. As a result, according to the active sonar device shown in FIG. 7, even if the reverberation and echo frequencies are close to each other as shown in FIG. become.

  In the spectrogram displayed on the display unit 43, when the display color of the cell is changed according to the arrival direction of the signal (when the colorgram is displayed), the direction calculation result in the direction calculation processing unit 37 is displayed on the display processing unit 42. The display processing unit 42 may generate a colorgram and display it on the display unit 43.

Furthermore, in the present embodiment, on the spectrogram or colorgram, only signals from a specific direction designated by the operator can be displayed on the screen so that the signals can be detected. For example, there is a case where it is desired to determine whether or not a target exists at a position designated by an operator in a certain water area or sea area. In that case, wave receivers are arranged at a plurality of positions in the water area or the sea area, and reflected waves are received by the wave receivers. For each receiver, only a signal from a designated position is detected and displayed according to the position of the receiver. In the example shown in FIG. 8, three receivers (receivers # 1 to # 3) are arranged in the sea area. When the operator designates a specific position P in the sea area, when displaying the results from the receivers # 1 to # 3, the narrow azimuth ranges θ ₁ , θ ₂ , θ including the position P, respectively. Only the detection result based on the signal from ₃ is displayed.

  In this case, since the position P designated by the operator is expressed as a value in a plane coordinate system (xy coordinate system), for example, the position P is determined for each receiver based on the position of the receiver. It is necessary to calculate which azimuth exists, and display is limited based on the calculated azimuth.

  FIG. 9 shows a specific example of an active sonar apparatus that includes a plurality of receivers and that can display and detect only results based on signals from a specific direction for each receiver based on a position specified by an operator. A configuration example is shown. The active sonar device shown in FIG. 9 is the same as that shown in FIG. 7 except that a plurality of receivers 33 are provided and the position information conversion processing unit 44 and the display restriction instead of the display processing unit. 7 is different from that shown in FIG. 7 in that a processing unit 45 is provided. The plurality of receivers 33 are arranged at different positions, and the demodulation processing unit 34 switches between these receivers 33 and executes demodulation processing. Alternatively, in the preprocessing block 21, the signal processing block 22, and the signal detection block 23, processing for signals from each of the plurality of receivers 33 may be executed in parallel.

  The position information conversion processing unit 44 converts the position input by the operator into an azimuth angle from the receiver for each receiver. The display restriction processing unit 45 has the same function as that of the display processing unit 42 described above, but further, depending on the azimuth angle of each receiver converted by the position information conversion processing unit 44, It has a function to limit the display of the detected signal. Thereby, only the result based on the signal from the specific direction is displayed on the screen of the display unit 43 for each receiver based on the position input by the operator.

21 Preprocessing Block 22 Signal Processing Block 23 Signal Detection Block 24 Detection Connection Processing Block 30 Target 31 Transmitter 32 Transmission Processing Unit 33 Receiver 34 Demodulation Processing Unit 35 Frequency Analysis Unit 36 Normalization Processing Unit 37 Direction Calculation Processing Unit 38 Level detection processing unit 39 Orientation determination processing unit 40 Frequency connection processing unit 41 Time connection processing unit 42 Display processing unit 43 Display unit 44 Position information conversion processing unit 45 Display restriction processing unit

Claims (8)

A signal detection method in an active sonar device,
Receiving an acoustic signal as a received signal;
Performing frequency analysis on the received signal;
Using the region of unit frequency width and unit time width in detection as a cell, obtaining the arrival direction and intensity of the received signal for each cell based on the result of the frequency analysis,
When a cell whose strength exceeds the first threshold is adjacent in the frequency direction or the time direction, it is determined whether the difference in arrival direction in the adjacent cell is within a second threshold; Concatenating the adjacent cells as one detection if within the second threshold;
A signal detection method.   The signal detection method according to claim 1, further comprising: displaying a detection result as a spectrogram using a luminance corresponding to an intensity of the received signal in the cell for each cell.   The signal detection method according to claim 2, wherein the detection result is displayed for each cell using a color corresponding to an arrival direction of the received signal in the cell.   The signal detection method according to claim 2 or 3, wherein a designated position is converted into an azimuth angle, and only a detection result within an angle range including the converted azimuth angle is displayed. A receiver for receiving an acoustic signal;
A frequency analysis unit that performs frequency analysis on the signal received by the receiver;
An area of a unit frequency width and a unit time width in detection as a cell, and an azimuth calculation processing unit for obtaining an arrival direction of the acoustic signal for each cell based on the result of the frequency analysis;
A level detection processing unit for obtaining the intensity of the acoustic signal for each cell based on the result of the frequency analysis;
When a cell whose strength exceeds the first threshold is adjacent in the frequency direction or the time direction, it is determined whether the difference in arrival direction in the adjacent cell is within a second threshold; A detection concatenation processing unit that concatenates the adjacent cells as one detection when it is within the second threshold;
An active sonar device. A display unit;
A display processing unit that displays a detection result as a spectrogram on the display unit using a luminance corresponding to the intensity of the received signal in the cell for each cell;
The active sonar device according to claim 5, further comprising:   The active sonar apparatus according to claim 6, wherein the display processing unit causes the display unit to display the detection result using a color corresponding to an arrival direction of the received signal in the cell for each cell. A display unit;
A position information conversion processing unit that receives a designation of a position and converts the position into an azimuth angle from the receiver;
A display restriction processing unit that causes the display unit to display only the detection result of the arrival direction corresponding to the converted azimuth angle;
The active sonar device according to claim 5, further comprising:

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