JP2014035235A - Pulse detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pulse detection device which accurately detects pulses by reducing a probability of an error alarm in detecting pulses by an echo sounder receiver mounted on a ship.SOLUTION: A pulse detection device which detects burst pulses corresponding to conditions preset by digital signal processing, comprises: means which calculates spectrum by performing frequency analysis of input signal strings; means which calculates a threshold on the basis of background noise; means which compares the calculated spectrum with the calculated threshold and detects an azimuth when the detected spectrum exceeds the threshold; means which determines whether a pulse exists in a section in which the detected spectrum exceeds the threshold; and means which compares calculated pulse duration with preset pulse duration and performs second threshold determination when the calculated pulse duration is shorter than the preset pulse duration.

Description

  The present invention relates to a pulse detection device, and more particularly to a pulse detection device that detects a pulse that matches a preset condition from a signal sequence of a burst signal received by a device that receives a pulse sound emitted from a sound source.

2. Description of the Related Art Conventionally, there is known a pulse detection device that detects a pulse that matches a preset condition from a signal sequence received by a receiver mounted on a ship.
Regarding the pulse detection method, a method corresponding to a rapid change in background noise is disclosed in Patent Document 1. In Patent Document 1, the narrowband analysis result exceeding the threshold is pulsed only when there is a narrowband analysis result exceeding the threshold and a rapid change in the broadband level is not detected by the comparison processing in the wideband. Disclosed is a pulse sound detection device for determining a sound.

Japanese Patent Laid-Open No. 10-268020

  However, the pulse sound detection device according to Patent Document 1 is premised on that the noise does not exceed the threshold because of the relationship between the background noise and the threshold. However, noise having a large directivity width, such as clutter noise, is erroneously detected as a signal due to changes in the surrounding environment. To solve this problem, it is necessary to increase the number of beams and discriminate between noise and signal using a beam having a narrow directivity width. Since the pulse detection device detects the direction of arrival, increasing the number of beams increases the processing load, thereby increasing the hardware scale. Further, in order to form a beam having a narrow directivity width, the scale of the receiver increases.

  The above-described problem is that in the pulse detection device that detects a burst pulse that matches a preset condition by digital signal processing from a signal sequence received by a device that receives a pulse sound emitted from a sound source, the signal that is input If the spectrum is calculated, the spectrum is calculated, the threshold is calculated from the background noise, the direction is detected, the direction is detected, and the spectrum is compared with the calculated threshold. By comparing the calculated pulse width with a preset pulse width and determining a second threshold value when the pulse width is shorter than the preset pulse width. Can be achieved.

  According to the present invention, it is possible to provide a pulse detection device that can reduce the false alarm probability even for noise with a large instantaneous power and can calculate with high accuracy while maintaining the detection probability without increasing the system scale.

It is a functional block diagram of a pulse detector. It is a figure explaining background noise. It is a functional block diagram of a pulse detection processing unit. It is a figure explaining a 2nd threshold value.

  Embodiments of the present invention will be described below with reference to screens using examples. The same reference numerals are assigned to substantially the same parts, and the description will not be repeated.

  The configuration of the pulse detection device will be described with reference to FIG. In FIG. 1, the pulse detection device 1 includes a wave receiving unit 2, a receiving unit 3, and a pulse detection processing unit 4. The wave receiving unit 2 receives incoming sound waves from underwater. The wave receiving unit 2 converts sound waves into electric signals. The receiving unit 3 performs phasing processing of received data and band limitation. The receiving unit 3 outputs a left beam and a right beam split beam. When a burst pulse exists in the input signal sequence, the pulse detection processing unit 4 outputs the arrival direction, the pulse frequency, and the pulse width.

  The background noise will be described with reference to FIG. In FIG. 2, the horizontal axis represents time and the vertical axis represents signal level. It can be estimated that there is a noise portion before and after the signal portion, and that the noise portion is also superimposed on the background of the signal portion.

  The configuration of the pulse detection processing unit will be described with reference to FIG. In FIG. 3, the pulse detection processing unit 4 includes a spectrum detection unit 41, a background noise calculation unit 42, a threshold determination unit 43, an orientation detection unit 44, a pulse detection unit 45, and a second threshold determination unit 46. It is configured.

  The spectrum detection unit 41 cuts out a data window having a preset length from the sum of the left and right split beams as the input signal sequence. The spectrum detection unit 41 performs frequency analysis on the window. The spectrum detection unit 41 outputs the frequency analysis result (frequency spectrum level) of the window to the background noise calculation unit 42.

  The background noise calculation unit 42 calculates background noise from the input data string. When calculating background noise, it is common to use a value obtained by integrating received data in order to suppress noise variation. However, as shown in FIG. 2, when integrated background noise is used, there is a possibility that the background noise may be set higher than the actual estimated value by cutting out the signal portion. In this case, the background noise is estimated to be larger than the actual estimated value, and the target detection probability is lowered.

  Therefore, considering that the background noise estimation result is not affected by the signal, the background noise uses the median value of the received data. The background noise using the median is N (f) as the background noise at the frequency f, k as the time when the spectrum levels of the received data are arranged in ascending order, and X (f, k) as the time at the frequency f. If the spectral level is k, it is calculated by Equation 1. The background noise calculation unit 42 outputs the calculated background noise to the threshold value determination unit 43.

  The threshold determination unit 43 calculates a threshold from the background noise input from the background noise calculation unit 42. The threshold value determination unit 43 compares the frequency spectrum of each data window input from the spectrum detection unit 41 with the threshold value, and detects a spectrum exceeding the threshold value. Assuming that the detection threshold is DT, the threshold T (f) at the frequency f is obtained by Equation 2.

When the spectrum is detected, the threshold determination unit 43 outputs the detection result to the direction detection unit 44.
The azimuth detector 44 uses a split beam output signal that is an output of the receiver 3. The azimuth detecting unit 44 obtains the phase difference from the complex signal after the split beam correlation with respect to the azimuth angle, and obtains the phase difference from the phase difference, the frequency, the sound speed, and the inter-beam distance. The azimuth detecting unit 44 obtains the phase difference φ from the real part Re and the imaginary part Im of the complex signal using Equation 3.

  Based on the phase difference φ, the signal frequency f, the sound velocity c, and the inter-beam distance d, the azimuth detecting unit 44 obtains the arrival azimuth angle θ of the received signal by Expression 4. The direction detection unit 44 outputs the obtained arrival azimuth angle to the pulse detection unit 45.

  The pulse detector 45 arranges the detection results of the spectrum exceeding the threshold in time series. The pulse detection unit 45 performs pulse detection from the continuity of frequency and the continuity of arrival azimuth. The pulse detector 45 sets a section in which the spectrum detection results are continuous as a pulse width. The pulse detector 45 uses the detected spectrum frequency as the pulse frequency and the pulse width as the pulse detection result. The pulse detection unit 45 outputs the pulse detection result to the second threshold value determination unit 46.

  The second threshold value determination unit 46 determines a short pulse according to a condition set in advance from the pulse detection unit result. When the short pulse is not determined, the second threshold determination unit 46 outputs the pulse detection result as a signal as it is.

  On the other hand, when it determines with a short pulse, the 2nd threshold value determination part 46 implements 2nd threshold value determination with the threshold value according to the pulse width. The second threshold determination unit 46 determines that a signal is greater than or equal to the second threshold, and noise is less than or equal to the second threshold. If the detection threshold corresponding to the pulse width is DT2, and the second threshold at frequency f is T2 (f), the second threshold determination unit 46 calculates T2 (f) from Equation 5.

  The second threshold value will be described with reference to FIG. In FIG. 4, the horizontal axis represents time and the vertical axis represents signal level. The second threshold value determination unit 46 applies the (first) threshold value to a pulse whose pulse width exceeds Wsp. On the other hand, the second threshold value determination unit 46 applies the second threshold value to a pulse having a pulse width equal to or less than Wsp. Therefore, the second threshold determination unit 46 captures a pulse at time A whose pulse width exceeds Wsp as a signal. The second threshold determination unit 46 captures the pulse at time B having a pulse width equal to or less than Wsp as noise. That is, the second threshold determination unit 46 determines the pulse at time B as clutter noise. On the other hand, the second threshold determination unit 46 captures a pulse at time C having a pulse width equal to or less than Wsp as a signal. Note that the second threshold determination unit 46 adaptively changes Wsp.

  It is well known that the pulse width detected by the pulse detector is wide when the target sound source is a long distance and narrow when the target sound source is a short distance. Since there is a clear relationship between the spectrum level and the pulse width, the signal and noise can be discriminated more accurately by setting the relationship between the spectrum level and the pulse width in advance.

  As described above, according to the present embodiment, the second threshold determination in consideration of the relationship between the pulse width and the spectrum level is applied to the problem of erroneously detecting noise having a large instantaneous power such as clutter noise as a pulse due to a change in the surrounding environment. Therefore, it is possible to reduce the false alarm probability even for noise with a large instantaneous power and to calculate with high accuracy.

  DESCRIPTION OF SYMBOLS 1 ... Pulse detection apparatus, 2 ... Reception part, 3 ... Reception part, 4 ... Pulse detection process part, 41 ... Spectrum detection part, 42 ... Background noise calculation part, 43 ... Threshold determination part, 44 ... Direction detection part, 45 ... pulse detection unit, 46 ... second threshold value determination unit.

Claims (3)

In a pulse detection device for detecting a burst pulse by a digital signal from a signal sequence received by a device for receiving a pulse sound emitted from a sound source,
Means for frequency-analyzing the input signal sequence and calculating a spectrum;
Means for calculating a threshold from background noise;
Comparing the means for detecting the azimuth with the spectrum and the calculated threshold value, and detecting the spectrum exceeding the threshold value, the means for determining that there is a pulse for the section exceeding the threshold value;
A pulse detecting device comprising: a means for comparing the calculated pulse width with a preset pulse width and determining a second threshold when the calculated pulse width is shorter than the preset pulse width. The pulse detection device according to claim 1,
A pulse detection device that performs a second threshold determination process from a relationship between a preset pulse width and a spectrum level. The pulse detection device according to claim 2,
2. A pulse detection apparatus, wherein background noise using a median value calculated for each spectrum is applied to the second threshold determination process.

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