JP2012173224A - Reverberation filter, active sonar device, reverberation removing method, and reverberation removing program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reverberation filter and the like that can accurately remove reverberation from a reflection wave.SOLUTION: The reverberation filter 10 includes reflection wave detection means 101 for detecting whether a level L of the reflection wave exceeds a level threshold Lth; duration measurement means 102 for measuring a duration T in which the level L of the reflection wave continues to exceed the level threshold Lth when the reflection wave detection means 101 detects that the level L of the reflection wave exceeds the level threshold Lth; and target echo determining means 103 for detecting whether the duration T measured by the duration measurement means 102 exceeds a duration threshold Tth, determines that a reflection wave in which the duration T exceeds the duration threshold Tth is a reverberation, and determines that a reflection wave in which the duration T does not exceed the duration threshold Tth is a target echo.

Description

  The present invention relates to a reverberation filter that removes reverberation contained in a reflected wave, a reverberation removal method, a reverberation removal program, and the like.

  An active sonar device measures the time, direction of arrival, and Doppler frequency until a reflected sound (echo) from a target reaches the receiver by emitting a sound wave from the transmitter to the underwater target. Thus, the device calculates the position and speed of the target. There are mainly CW (Continuous Wave) and LFM (Linear Frequency Modulated Pulse) as transmission signal forms used in the active sonar apparatus. CW is excellent in Doppler resolution and can easily extract a frequency by Fourier transform, but has a characteristic that it is vulnerable to reverberation. The method based on LFM and replica correlation processing is excellent in reverberation resistance because the power per unit frequency is small, but has a feature that it is inferior in Doppler resolution compared to CW.

  FIG. 8 is a block diagram showing an active sonar device described in Patent Document 1. In FIG. FIG. 9 is a graph showing the principle of echo signal detection by replica correlation. Hereinafter, description will be given based on these drawings.

  This type of active sonar device 1a includes a transmission signal generation unit 2 that generates and outputs a transmission signal, a transmission unit 4 that transmits the transmission signal amplified by the transmission signal amplification unit 3 as a sound wave, and a target. A wave receiving unit 5 that outputs a reflected sound wave including a target echo and other noise as a reception signal, and is amplified, filtered, and A / D converted by a reception signal amplification unit 6, a band filtering unit 7, and an A / D conversion unit 8. And a signal processing unit 12 for processing the received signal. The active sonar device 1a further includes a detection unit 13 that detects an echo signal from the received signal, and a display unit 14 that displays data output from the detection unit 13 on a screen or the like.

  Even if the received signal when the LFM signal is used is simply Fourier-transformed, the level of each frequency is lower than that of the CW signal and is difficult to extract. Therefore, the signal processing unit 12 generates a replica signal equivalent to the transmission signal, and performs so-called replica correlation processing using the replica signal to extract an echo signal. Replica correlation is a signal processing method for calculating the degree of correlation between a received signal and a sample signal (replica signal) while shifting the time with respect to the received signal, and is also called cross-correlation. The signal processing unit 12 calculates the degree of correlation with the reception signal using the transmission signal as a replica signal.

  FIG. 9 shows a conceptual diagram of echo signal detection by replica correlation. As shown in the figure, by obtaining the correlation with the replica signal R while shifting the time with respect to the received signal G, the peak p of the correlation degree appears at the time when the waveform is most similar. The time te ′ at which the echo arrives at the highest correlation.

  Specifically, the signal processing unit 12 that performs the signal processing as described above is a replica based on the received signal Fourier transform unit 121 and the transmission signal data sent from the transmission signal generation unit 2 as shown in FIG. A replica signal generating means 122 for generating a signal, a Fourier transform means 123 for the replica signal, a multiplying means 124 for multiplying one of the complex conjugates after the Fourier transform of the received signal and the replica signal, and an inverse Fourier transform of the product of the multiplying means 124. And an inverse Fourier transform means 125 for transforming.

  The signal processing unit 12 obtains the product of the received signal and the replica signal by the multiplying unit 124 while shifting the time, and inverse Fourier transforms this by the inverse Fourier transforming unit 125, as shown in FIG. Replica correlation is obtained. As shown in FIG. 9, the echo signal E is detected from the cross-correlation between the replica signal R and the received signal G.

  Patent Documents 2 and 3 disclose the following active sonar apparatus.

  The active sonar device of Patent Document 2 includes a transmitter, a receiver that receives a reflected wave of a sound wave transmitted from the transmitter as a received signal, and a seabed that represents the depth of the seabed at a position on a map. Based on the depth data and the obstacle data indicating the position of obstacles on the seabed, the detection / removal sea area extraction unit that extracts the sea area where the topography where reflection easily occurs is detected and removed, and the level of the received signal is calculated. A signal processing unit, a signal detection unit for detecting, as an echo signal, a received signal in which a level calculated by the signal processing unit of the received signal exceeds a preset threshold value, and a signal detection unit A detection / removal determination unit that removes echo signals reflected by the detection / removal sea area extracted by the detection / removal sea area extraction unit from the detected echo signals as reverberation;

  The active sonar device of Patent Document 3 is an active sonar device including a transmitter and a receiver that receives a reflected wave of a sound wave transmitted from the transmitter as a received signal. And a plotting processing unit configured to set a sea area where the topography where the sound wave is likely to be reflected on the bottom of the sea is plotted as a detection and removal sea area, and an echo from the received signal received by the receiver. A dereverberation unit that detects a signal and removes, as the reverberation, an echo signal reflected in the detection and removal sea area from the detected echo signal.

JP 2008-21605 A (FIGS. 13, 14, etc.) JP 2009-068989 A (summary etc.) JP 2009-150824 A (summary etc.)

  As described above, CW is inherently vulnerable to reverberation. On the other hand, LFM is more excellent in reverberation resistance than CW, but further reverberation resistance is desired. For example, in an active sonar device using an LFM signal, LFM is inferior in Doppler resolution compared to CW, so it is difficult to separate echoes from a moving target from reflected waves (reverberation) of the seabed, seamount, shipwreck, etc. is there. This becomes a cause of a false alarm when the LFM is used.

  Therefore, an object of the present invention is to provide a reverberation filter or the like that can remove reverberation from reflected waves with high accuracy.

The reverberation filter according to the present invention is:
Reflected wave detecting means for detecting whether or not the level of the reflected wave exceeds a level threshold;
When the reflected wave detection means detects that the level of the reflected wave exceeds the level threshold, a duration measuring means for measuring a duration during which the level of the reflected wave continues to exceed the level threshold; and
Detecting whether or not the duration time measured by the duration measurement means exceeds a duration threshold, and determining that the reflected wave is reverberation when the duration exceeds the duration threshold; Target echo determination means for determining that the reflected wave is the target echo when the duration does not exceed the duration threshold;
It is provided with.

The active sonar device according to the present invention is
A transmission signal generator for generating and outputting a transmission signal;
A transmission unit for transmitting the transmission signal output from the transmission signal generation unit as a sound wave;
A wave receiving unit that receives a reflected wave including a target echo generated by reflecting the sound wave transmitted from the wave transmitting unit at a target, and outputs the received wave as a received signal;
A signal processing unit that calculates a level of the reflected wave based on the received signal output from the wave receiving unit, and outputs the level of the reflected wave;
A reverberation filter according to the present invention for inputting the level of the reflected wave output from the signal processing unit,
It is provided with.

The dereverberation method according to the present invention includes:
Detect whether the level of the reflected wave exceeds the level threshold,
When it is detected that the level of the reflected wave exceeds the level threshold, the duration for which the level of the reflected wave continues to exceed the level threshold is measured,
It is detected whether the duration exceeds a duration threshold, and when the duration exceeds the duration threshold, it is determined that the reflected wave is reverberant, and the duration exceeds the duration threshold. If the reflected wave is not the target echo,
It is characterized by that.

The dereverberation program according to the present invention includes:
Reflected wave detection means for detecting whether or not the level of the reflected wave exceeds a level threshold;
When the reflected wave detection means detects that the level of the reflected wave exceeds the level threshold, a duration measuring means for measuring a duration during which the level of the reflected wave continues to exceed the level threshold; and
Detecting whether or not the duration time measured by the duration measurement means exceeds a duration threshold, and determining that the reflected wave is reverberation when the duration exceeds the duration threshold; Target echo determination means for determining that the reflected wave is the target echo when the duration does not exceed the duration threshold,
It is for making a computer function as.

  According to the present invention, it is possible to remove reverberation from a reflected wave with high accuracy by determining whether the reflected wave is reverberation or a target echo based on a duration time during which the level of the reflected wave continues to exceed the level threshold. .

It is a block diagram which shows Embodiment 1 of the reverberation filter and active sonar apparatus which concern on this invention. It is a block diagram which shows an example of the computer which functions as each means of the reverberation filter of FIG. It is sectional drawing which shows the usage example of the active sonar apparatus of FIG. It is a graph which shows the sound wave which reached | attained the receiving part in the usage example of FIG. It is a graph which shows the correlation degree of the target echo in FIG. 4, and a seabed reflected wave. It is a flowchart which shows an example of the operation | movement in the reverberation filter of FIG. It is a block diagram which shows Embodiment 2 of the reverberation filter and active sonar apparatus which concern on this invention. It is a block diagram which shows the active sonar apparatus of patent document 1. It is a graph which shows the principle of the echo signal detection by replica correlation.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as “embodiments”) will be described with reference to the accompanying drawings. In the present specification and drawings, the same reference numerals are used for substantially the same components.

  FIG. 1 is a block diagram showing Embodiment 1 of a reverberation filter and an active sonar device according to the present invention. FIG. 2 is a block diagram illustrating an example of a computer that functions as each unit of the reverberation filter of FIG. Hereinafter, description will be given based on this drawing.

  The reverberation filter 10 according to the first embodiment includes a reflected wave detection unit 101 that detects whether or not the level L of the reflected wave exceeds the level threshold Lth, and the reflected wave that the level L of the reflected wave exceeds the level threshold Lth. When the detection means 101 detects, the duration measurement means 102 that measures the duration T during which the level L of the reflected wave continues to exceed the level threshold Lth, and the duration T measured by the duration measurement means 102 is the duration threshold. It is detected whether or not Tth is exceeded, and when the duration T exceeds the duration threshold Tth, it is determined that the reflected wave is reverberation, and when the duration T does not exceed the duration threshold Tth, the reflection is determined. And target echo determination means 103 for determining that the wave is the target echo.

  As an example, a case where a sound wave is transmitted into the sea and a reflected wave is received will be described. In this case, the reverberation is mainly a sea bottom reflected wave. Since the seabed is extremely large compared to the target, the reflected seabed wave is received for a longer time than the target echo. Therefore, according to the reverberation filter 10, the duration T during which the level L of the reflected wave continues to exceed the level threshold value Lth is measured, and if the duration T exceeds the duration threshold value Tth, the reflected wave is determined to be reverberant. If the duration T does not exceed the duration threshold Tth, the reverberation can be removed from the reflected wave with high accuracy by determining that the reflected wave is the target echo. In particular, when a sound wave is transmitted from the sea surface to the sea or from the sea to a deeper sea, the number of reflected waves on the sea floor increases so that this effect becomes more remarkable. The same effect can be obtained not only when sound waves are transmitted into the sea but also when sound waves are transmitted in the air.

  Even when radio waves are transmitted in the air, the reverberation mainly becomes ground reflected waves or sea surface reflected waves, so that the same effect as described above can be obtained by using the reverberant filter 10. When radio waves are transmitted from the air to the air, particularly when radio waves are transmitted from the air to lower air, the ground reflected waves or the sea surface reflected waves become very large, and this effect becomes more remarkable. Therefore, the reverberation filter 10 can be applied to a radar apparatus.

  During the measurement of the duration T, the duration measuring means 102 continues to exceed the level threshold Lth even if the level L of the reflected wave falls below the level threshold Lth within a certain time. The duration time T may be measured as follows. In this case, even if the level L temporarily decreases due to the influence of noise, the influence can be eliminated, so that noise resistance can be improved.

  The target echo determination means 103 provides a second duration threshold Tth2 that is shorter than the duration threshold Tth, detects whether the duration T exceeds the second duration threshold Tth2, and the duration T is the second duration. When the threshold value Tth2 is not exceeded, the reflected wave may be determined as noise. In this case, even if the level L is temporarily increased due to the influence of noise, the influence can be eliminated, so that noise resistance can be improved.

  Each value of the level threshold value Lth, the duration threshold value Tth, and the second duration threshold value Tth2 may be predetermined theoretically or experimentally, and may be appropriately changed during use of the reverberation filter 10. The reflected wave to be processed may be any signal, for example, an LFM signal or a CW signal.

  The dereverberation method of the first embodiment captures the operation of the reverberation filter 10 as a method invention, and includes the following steps. (1) A step of detecting whether or not the level L of the reflected wave exceeds the level threshold Lth. (2) A step of measuring a duration T during which the reflected wave level L continues to exceed the level threshold value Lth when it is detected that the reflected wave level L exceeds the level threshold value Lth. (3) It is detected whether or not the duration T exceeds the duration threshold Tth. When the duration T exceeds the duration threshold Tth, it is determined that the reflected wave is reverberation, and the duration T is the duration. Determining that the reflected wave is a target echo when the threshold value Tth is not exceeded.

  Each unit of the reverberation filter 10 may function in a computer 35 as shown in FIG. The dereverberation program according to the first embodiment is for causing the computer 35 to function each unit of the dereverberation filter 10. In other words, the dereverberation program according to the first embodiment reflects the fact that the reflected wave level L exceeds the level threshold value Lth. The reflected wave detection means 101 detects whether the reflected wave level L exceeds the level threshold value Lth. When the wave detection unit 101 detects, the duration measurement unit 102 that measures the duration T during which the level L of the reflected wave continues to exceed the level threshold value Lth, and the duration T measured by the duration measurement unit 102 continues. It is detected whether or not the time threshold Tth has been exceeded. When the duration T exceeds the duration threshold Tth, it is determined that the reflected wave is reverberant, and when the duration T does not exceed the duration threshold Tth. This is for causing the computer 35 to function as the target echo determination means 103 for determining that the reflected wave is the target echo.

  As shown in FIG. 2, the computer 35 may be a general computer including a CPU 31, a RAM 32, a ROM 33, an input / output interface 34, and the like. The CPU 31 reads out the dereverberation program from the RAM 32 or the ROM 33, interprets it, and executes it. The dereverberation program may be recorded on a non-transitory storage medium, such as an optical disk or a semiconductor memory. In this case, the dereverberation program is read from the recording medium by the computer 35 and executed.

  The dereverberation method and dereverberation program of the first embodiment can adopt various configurations in the same manner as the reverberation filter 10 in addition to the configurations described above. According to the dereverberation method and the dereverberation program of the first embodiment, the same operations and effects as the reverberation filter 10 are achieved.

  The active sonar device 1 according to the first embodiment includes a transmission signal generation unit 2 that generates and outputs a transmission signal 21, and a transmission unit 4 that transmits the transmission signal 21 output from the transmission signal generation unit 2 as a sound wave 22. Receiving the reflected wave 24 including the target echo 23 generated by the reflection of the sound wave 22 transmitted from the transmission unit 4 by the target, and outputting this as a reception signal 25; Based on the received signal 25 output from the unit 5, the reflected wave level L is calculated, the signal processing unit 12 that outputs the reflected wave level L, and the reflected wave level L output from the signal processing unit 12. And an input reverberation filter 10.

  The transmission signal 21 may be a CW signal or an LFM signal. That is, the active sonar device 1 has the following characteristics. The transmission signal 21 is an LFM signal. The signal processing unit 12 uses the transmission signal 21 output from the transmission signal generation unit 2 as a replica signal 26, calculates the degree of correlation 27 between the replica signal 26 and the reception signal 25 output from the reception unit 5, and calculates the correlation The degree 27 is output as the level L of the reflected wave.

  The active sonar device 1 is provided with a transmission signal amplification unit 3, a reception signal amplification unit 6, a band filtering unit 7, an A / D conversion unit 8, and a display unit 14. The reverberation filter 10 inputs the correlation degree 27 from the signal processing unit 12 as the reflected wave level L, and outputs display data 36 including data on the target echo and the reverberation to the display unit 14. The signal processing unit 12 includes a Fourier transform unit 121, a replica signal generation unit 122, a Fourier transform unit 123, a multiplication unit 124, and an inverse Fourier transform unit 125.

  FIG. 3 is a sectional view showing an example of use of the active sonar device of FIG. FIG. 4 is a graph showing a sound wave that reaches the wave receiving unit in the usage example of FIG. Hereinafter, a description will be given with reference to FIGS.

  Here, it is assumed that the wave transmitting unit 4 and the wave receiving unit 5 are floating on the sea surface 30 at a certain distance. When the sound wave 22 is transmitted from the transmission unit 4, the direct wave 20 and the reflected wave 24 are received by the reception unit 5. The direct wave 20 is a sound wave 22 that reaches the wave receiving unit 5 without hitting anything. The reflected wave 24 is a sound wave 22 that reaches the wave receiving unit 5 after hitting something, and includes a target echo 23 that hits the target 11 and a reflected sea wave 28 that hits the seabed 29.

  As shown in FIG. 4, the direct wave 20 first reaches the wave receiving unit 5. Since the direct wave 20 is not hit anywhere, the level is high because the attenuation is small. Thereafter, the target echo 23 arrives at the wave receiving unit 5, and the seabed reflected wave 28 arrives a little later than this.

  FIG. 5 is a graph showing the correlation between the target echo and the seafloor reflected wave in FIG. Hereinafter, a description will be given with reference to FIGS.

  In the reverberation filter 10, the correlation degree 27 corresponds to the level L, and the time during which the level L continues to exceed the level threshold Lth is handled as the duration T. FIG. 5 shows that there is a clear difference between the duration T1 of the target echo 23 and the duration T2 of the reflected sea wave 28. The duration T1 of the target echo 23 is determined by the size of the target 11 (length in the wavefront vertical direction). On the other hand, the duration T2 of the seafloor reflected wave 28 is considerably long because the reflected waves from a plurality of points with different distances continuously reach the wave receiving unit 5. Since the size of the search target of the active sonar device 1 is sufficiently small with respect to the seabed 29, there is a clear difference between the duration T1 of the target echo 23, the seabed reflected wave 28, and the duration T2.

  Therefore, the reverberation filter 10 can separate the target echo 23 and the seafloor reflected wave 28 with high accuracy by utilizing the difference between the duration T1 of the target echo 23 and the duration T2 of the seafloor reflected wave 28. That is, the time when the level L exceeds the level threshold value Lth is measured, and it is determined whether the duration time T is longer or shorter than the duration threshold value Tth, thereby performing filtering based on the duration time T. In the example shown in FIG. 5, since T1 ≦ Tth, the reflected wave 24 of the duration T1 is the target echo 23, and since T2> Tth, the reflected wave 24 of the duration T2 is the seabed reflected wave 28. Although T1 ≦ Tth and T2> Tth, T1 <Tth and T2 ≧ Tth are substantially the same.

  According to the active sonar device 1, by using the reverberation filter 10, the reflected sea wave 28 can be accurately removed, so that false alarms can be reduced and the target echo 23 can be easily identified. In particular, when the wave transmission unit 4 transmits the sound wave 22 from the sea surface 30 to the sea or from the sea to a deeper sea, the seafloor reflected waves 28 are extremely increased, and this effect becomes more remarkable.

  FIG. 6 is a flowchart illustrating an example of the operation in the reverberation filter according to the first embodiment. Hereinafter, description will be made with reference to FIGS. 1 and 6.

  First, the duration T is set to “0” (step 201), the degree of correlation 27 is input as the level L from the signal processing unit 12 (step 202), and the level L is compared with the level threshold Lth (step 203).

  If L ≦ Lth, the process returns to step 201, and if L> Lth, the sampling time Δt is added to the duration T to obtain a new duration T (step 204). Subsequently, the correlation degree 27 is input as a level L from the signal processing unit 12 (step 205), and the level L and the level threshold Lth are compared (step 206). If L ≦ Lth, the process proceeds to step 209. If L> Lth, the duration T is compared with the duration threshold Tth (step 207).

  If T ≦ Tth, the process returns to step 204. If T> Tth, the process proceeds to step 208. In step 208, since the duration T exceeds the duration threshold Tth, it is determined that the reflected wave corresponding to the duration T is reverberation. On the other hand, in step 209, since the duration T does not exceed the duration threshold Tth, it is determined that the reflected wave corresponding to the duration T is the target echo. Thereafter, if the process is continued, the process returns to step 201, and if the process is completed, the process is terminated (step 210).

  Steps 201 to 203 correspond to the operation of the reflected wave detection unit 101, steps 204 to 206 correspond to the operation of the duration measurement unit 102, and steps 207 to 210 correspond to the operation of the target echo determination unit 103. .

  In step 206, even if the level L of the reflected wave falls below the level threshold Lth within a certain time, the duration T may be measured assuming that the level L of the reflected wave continues to exceed the level threshold Lth. At this time, n (natural number) may be determined in advance, and the predetermined time may be set to n × Δt. That is, in step 206, the number of times L ≦ Lth is counted, and if the number is less than or equal to n, the duration T is measured assuming that the level L continues to exceed the level threshold value Lth.

  In step 207, a second duration threshold Tth2 shorter than the duration threshold Tth is provided, and it is detected whether the duration T exceeds the second duration threshold Tth2, and the duration T is set to the second duration threshold Tth2. When it does not exceed, the reflected wave may be determined as noise. At this time, n (natural number) may be determined in advance, and the second duration threshold value Tth2 may be set to n × Δt. That is, in step 207, the number of times T> Tth is counted, and if the number does not exceed n, it is determined that the reflected wave is noise.

  FIG. 7 is a block diagram showing Embodiment 2 of the reverberation filter and active sonar device according to the present invention. Hereinafter, description will be given based on this drawing.

  The reverberation filter 40 according to the second embodiment includes a position data input unit 401 that inputs position data on a map where a reflected wave is generated, and terrain data that inputs terrain data corresponding to the position data input by the position data input unit 401. It further includes an input unit 402 and a threshold value changing unit 403 that changes at least one of the level threshold value Lth and the duration threshold value Tth based on the terrain data input by the terrain data input unit 402. The threshold changing unit 403 may change at least one of the level threshold Lth, the duration threshold Tth, and the second duration threshold Tth2 based on the terrain data input by the terrain data input unit 402. Other configurations of the reverberation filter 40 are the same as those of the reverberation filter of the first embodiment.

  The active sonar device 1A of the second embodiment is different from the first embodiment except that the reverberation filter of the first embodiment is replaced by a reverberation filter 40 and that the position data acquisition unit 41 and the terrain data storage unit 42 are further provided. It is the same structure as 1 active sonar apparatus.

  The position data acquisition unit 41 is, for example, a GPS device or a keyboard, and automatically or artificially acquires data (such as latitude and longitude) on the map of the transmission unit 4 and the reception unit 5 on the map. The position data acquisition unit 41 outputs the current position data to the position data input unit 401 in response to a request from the position data input unit 401.

  The terrain data storage unit 42 is a general storage device such as an HDD, for example, and previously stores terrain data (such as a depth distribution) corresponding to a position on a map. The terrain data storage unit 42 outputs terrain data corresponding to the position data to the terrain data input unit 402 in response to a request from the terrain data input unit 402.

  A use example as shown in FIG. 3 will be described. Based on the terrain data input by the terrain data input unit 402, the threshold value changing unit 403 changes each threshold value as follows, for example. In general, the deeper the sea floor, the attenuated and weakened sea floor reflected waves. Therefore, the level threshold Lth is lowered so that a low level target echo can be detected. In general, the more the bottom of the seabed is, the more the seabed reflected wave comes from all directions and the duration T2 thereof becomes longer. Therefore, the duration threshold Tth is increased so that a target echo having a longer duration T1 can be detected. .

  According to the second embodiment, reverberation can be removed from the reflected wave with higher accuracy by changing each threshold according to the terrain. The other operations and effects of the second embodiment are the same as those of the first embodiment.

  Although the present invention has been described with reference to the above embodiments, the present invention is not limited to the above embodiments. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention. Further, the present invention includes a combination of some or all of the configurations of the above-described embodiments as appropriate.

  Although a part or all of the above embodiments can be described as the following supplementary notes, the present invention is not limited to the following configurations.

[Appendix 1] Reflected wave detecting means for detecting whether or not the level of the reflected wave exceeds a level threshold value;
When the reflected wave detection means detects that the level of the reflected wave exceeds the level threshold, a duration measuring means for measuring a duration during which the level of the reflected wave continues to exceed the level threshold; and
Detecting whether or not the duration time measured by the duration measurement means exceeds a duration threshold, and determining that the reflected wave is reverberation when the duration exceeds the duration threshold; Target echo determination means for determining that the reflected wave is the target echo when the duration does not exceed the duration threshold;
A reverberation filter characterized by comprising:

[Appendix 2] The reverberation filter according to Appendix 1,
Position data input means for inputting position data on a map where the reflected wave is generated;
Terrain data input means for inputting terrain data corresponding to the position data input by the position data input means;
Threshold change means for changing at least one of the level threshold and the duration threshold based on the terrain data input by the terrain data input means;
A reverberation filter, further comprising:

[Appendix 3] The reverberation filter according to Appendix 1 or 2,
The duration measuring means includes
While measuring the duration, even if the level of the reflected wave falls below the level threshold within a certain time, the duration is measured assuming that the level of the reflected wave continues to exceed the level threshold. ,
Reverberation filter characterized by that.

[Supplementary Note 4] The reverberation filter according to any one of Supplementary notes 1 to 3,
The target echo determination means provides a second duration threshold that is shorter than the duration threshold, detects whether the duration exceeds the second duration threshold, and the duration is the second duration threshold. The reflected wave is determined to be noise when it does not exceed
Reverberation filter characterized by that.

[Supplementary Note 5] The reverberation filter according to any one of Supplementary notes 1 to 4,
The reflected wave is a sound wave and an LFM signal;
Reverberation filter characterized by that.

[Appendix 6] A transmission signal generator for generating and outputting a transmission signal;
A transmission unit for transmitting the transmission signal output from the transmission signal generation unit as a sound wave;
A wave receiving unit that receives a reflected wave including a target echo generated by reflecting the sound wave transmitted from the wave transmitting unit at a target, and outputs the received wave as a received signal;
A signal processing unit that calculates a level of the reflected wave based on the received signal output from the wave receiving unit, and outputs the level of the reflected wave;
The reverberation filter according to any one of supplementary notes 1 to 4, wherein the level of the reflected wave output from the signal processing unit is input;
An active sonar device characterized by comprising:

[Appendix 7] An active sonar device as set forth in Appendix 6,
The transmission signal is an LFM signal;
The signal processing unit uses the transmission signal output from the transmission signal generation unit as a replica signal, calculates a correlation between the replica signal and the reception signal output from the reception unit, and calculates the correlation. Output as the level of the reflected wave,
An active sonar device characterized by that.

[Appendix 8] An active sonar device according to appendix 6 or 7,
The wave transmitting section transmits the sound wave from the sea surface to the sea or from the sea to a deeper sea,
An active sonar device characterized by that.

[Appendix 9] Detecting whether the level of the reflected wave exceeds the level threshold,
When it is detected that the level of the reflected wave exceeds the level threshold, the duration for which the level of the reflected wave continues to exceed the level threshold is measured,
It is detected whether the duration exceeds a duration threshold, and when the duration exceeds the duration threshold, it is determined that the reflected wave is reverberant, and the duration exceeds the duration threshold. If the reflected wave is not the target echo,
A dereverberation method characterized by that.

[Supplementary Note 10] Reflected wave detection means for detecting whether or not the level of the reflected wave exceeds the level threshold value,
When the reflected wave detection means detects that the level of the reflected wave exceeds the level threshold, a duration measuring means for measuring a duration during which the level of the reflected wave continues to exceed the level threshold; and
Detecting whether or not the duration time measured by the duration measurement means exceeds a duration threshold, and determining that the reflected wave is reverberation when the duration exceeds the duration threshold; Target echo determination means for determining that the reflected wave is the target echo when the duration does not exceed the duration threshold;
Reverberation removal program to make the computer function as a computer.

  The present invention is applicable to, for example, a sonar device and a radar device.

DESCRIPTION OF SYMBOLS 1,1A, 1a Active sonar apparatus 2 Transmission signal generation part 3 Transmission signal amplification part 4 Transmission part 5 Reception part 6 Reception signal amplification part 7 Band-pass filtering part 8 A / D conversion part 10,40 Reverberation filter 101 Reflected wave detection Means 102 Duration measurement means 103 Target echo determination means 11 Target 12 Signal processing part 121 Fourier transform means 122 Replica signal generation means 123 Fourier transform means 124 Multiplication means 125 Inverse Fourier transform means 13 Detection part 14 Display part 20 Direct wave 21 Transmission signal 22 Sound wave 23 Target echo 24 Reflected wave 25 Received signal 26 Replica signal 27 Correlation 28 Seabed reflected wave 29 Seabed 30 Sea surface 31 CPU
32 RAM
33 ROM
34 I / O interface 35 Computer 36 Display data 401 Position data input means 402 Terrain data input means 403 Threshold change means 41 Position data acquisition part 42 Terrain data storage part L level Lth level threshold T, T1, T2 duration Tth duration threshold Tth2 Second duration threshold

Claims (10)

Reflected wave detecting means for detecting whether or not the level of the reflected wave exceeds a level threshold;
When the reflected wave detection means detects that the level of the reflected wave exceeds the level threshold, a duration measuring means for measuring a duration during which the level of the reflected wave continues to exceed the level threshold; and
Detecting whether or not the duration time measured by the duration measurement means exceeds a duration threshold, and determining that the reflected wave is reverberation when the duration exceeds the duration threshold; Target echo determination means for determining that the reflected wave is the target echo when the duration does not exceed the duration threshold;
A reverberation filter characterized by comprising: The reverberation filter according to claim 1,
Position data input means for inputting position data on a map where the reflected wave is generated;
Terrain data input means for inputting terrain data corresponding to the position data input by the position data input means;
Threshold changing means for changing at least one of the level threshold and the duration threshold based on the terrain data input by the terrain data input means;
A reverberation filter, further comprising: The reverberation filter according to claim 1 or 2,
The duration measuring means includes
While measuring the duration, even if the level of the reflected wave falls below the level threshold within a certain time, the duration is measured assuming that the level of the reflected wave continues to exceed the level threshold. ,
Reverberation filter characterized by that. The reverberation filter according to any one of claims 1 to 3,
The target echo determination means provides a second duration threshold that is shorter than the duration threshold, detects whether the duration exceeds the second duration threshold, and the duration is the second duration. When the threshold is not exceeded, the reflected wave is determined to be noise.
Reverberation filter characterized by that. The reverberation filter according to any one of claims 1 to 4,
The reflected wave is a sound wave and an LFM signal;
Reverberation filter characterized by that. A transmission signal generator for generating and outputting a transmission signal;
A transmission unit for transmitting the transmission signal output from the transmission signal generation unit as a sound wave;
A wave receiving unit that receives a reflected wave including a target echo generated by reflecting the sound wave transmitted from the wave transmitting unit at a target, and outputs the received wave as a received signal;
A signal processing unit that calculates a level of the reflected wave based on the received signal output from the wave receiving unit, and outputs the level of the reflected wave;
The reverberation filter according to any one of claims 1 to 4, wherein a level of the reflected wave output from the signal processing unit is input;
An active sonar device characterized by comprising: The active sonar device according to claim 6,
The transmission signal is an LFM signal;
The signal processing unit uses the transmission signal output from the transmission signal generation unit as a replica signal, calculates a correlation between the replica signal and the reception signal output from the reception unit, and calculates the correlation. Output as the level of the reflected wave,
An active sonar device characterized by that. The active sonar device according to claim 6 or 7,
The wave transmitting section transmits the sound wave from the sea surface to the sea or from the sea to a deeper sea,
An active sonar device characterized by that. Detect whether the level of the reflected wave exceeds the level threshold,
When it is detected that the level of the reflected wave exceeds the level threshold, the duration for which the level of the reflected wave continues to exceed the level threshold is measured,
It is detected whether the duration exceeds a duration threshold, and when the duration exceeds the duration threshold, it is determined that the reflected wave is reverberant, and the duration exceeds the duration threshold. Determining that the reflected wave is a target echo when there is not, and determining that the reflected wave whose duration does not exceed the duration threshold is a target echo;
A dereverberation method characterized by that. Reflected wave detection means for detecting whether or not the level of the reflected wave exceeds a level threshold;
When the reflected wave detection means detects that the level of the reflected wave exceeds the level threshold, a duration measuring means for measuring a duration during which the level of the reflected wave continues to exceed the level threshold; and
Detecting whether or not the duration time measured by the duration measurement means exceeds a duration threshold, and determining that the reflected wave is reverberation when the duration exceeds the duration threshold; Target echo determination means for determining that the reflected wave is the target echo when the duration does not exceed the duration threshold,
Reverberation removal program to make the computer function as a computer.

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