JP2535745B2 - Sonar signal detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a sonar used when the target signal is detected from a received signal which is a sonar output by transmitting a pulse signal with a sonar used for the sea surface, the seabed and the like. A sonar signal for separating and extracting only the target signal from the reflected sound (reverberation) and noise from the sea surface, seabed, thermocline (a layer where the water temperature sharply decreases in the depth direction), water mass, etc. that are received simultaneously at the output. It relates to a detection method.

(Summary of the Invention) The present invention is a sonar signal detection system in which a pulse signal is transmitted by a sonar used toward the sea surface, the seabed, etc., and a target signal is detected from a received signal that is a sonar output, and the received signal is a sample. Data string of sample values received before (simultaneously or earlier than) the sample value at the present time, which is the time when processing is performed on one sample value at a certain time By calculating a moving average value using a plurality of sample values of (the data string before the present time point) and performing the separation and extraction of the target signal while paying attention to the difference between the present time data and the moving average value, This is intended to improve the reliability of target detection.

(Prior Art and Problems to be Solved by the Invention) An active sonar transmits a pulse signal,
The distance from the target reflected in the received signal to the target is detected, and the reflected sound from the target in the multiple received signals received by the receivers at different positions is compared to determine the direction from the phase information. It is something to detect.

The received signal after transmitting the pulse signal from the sonar that detects the target almost vertically to the sea surface and the sea floor is the reverberation sound of the sound wave that is repeatedly reflected on the sea surface and the sea floor as shown in FIG. When the second pulse signal is transmitted from the sonar and received, the received signal is overlapped by the first transmitted signal as shown in FIG. 5, and the water temperature distribution in the depth direction is not uniform and changes. Then, the sound wave is reflected from the thermocline and becomes a reverberant received waveform. Therefore, the received signal contains the reflected sound from the target, the reverberant sound repeatedly reflected from the sea surface and the seabed, and the volume reverberant sound in the sea.

As a method of extracting only the pulse signal reflected from the target (that is, the target signal) from such a received signal and reading the phase of the short pulse signal, conventionally, the received signal is as shown in FIG. 6 (A). TVG (Time Variable Gain) processing was performed, and the level of the TVG processing output was treated as a target signal that was greater than a certain threshold level TH. As mentioned above, there is a reverberant sound in the received signal that is as loud as the reflected sound from the target, and this reverberant sound greatly interferes with detecting the reflected sound from the target. Phase information could not be detected. For example, the sixth
Both the non-target signal and the target signal are included in the TVG processing output of FIG. 6 (A), and both exceed the threshold level TH. Therefore, both of the target outputs are detected in the detection output of FIG. 6 (B). Signal appears.

In order to eliminate the above drawbacks, the present invention focuses on the point that the reflected sound from the target and the reverberant sound have different rising characteristics in time, as shown in FIG. Sample value of (the current point is the time when processing one sample value at a certain time)
And the difference between the moving average value calculated using the data string of the fixed length section based on the current time among the data strings of the sample values before the current time and only the reflected sound from the target can be accurately detected. It is an object to provide a sonar signal detection method.

(Means for Solving the Problems) In order to achieve the above object, the present invention transmits a pulse signal in water from a sonar wave transmitter and receives the sonar wave receiver including a reflected sound from a target. In a sonar signal detection method that separates and extracts a target signal from a signal, an A / D converter that creates a data string of sample values by sampling the received signal of the receiver at a certain sampling period, and at a certain time The time when processing one sample value as the target is the current time, and the moving average value is calculated using the data string of the constant length section based on the current time among the data strings before the one sample value of the current processing target Then, a moving average processor for calculating the difference between the sample value of the processing target and the moving average value, and a target in which the difference between the sample value of the processing target and the moving average value exceeds a predetermined threshold level. The estimated signal of A signal detection processor that detects the presence, a trigger signal generator that outputs a trigger signal at the output of the signal detection processor that indicates the presence of the signal estimated as the target, and a sample value that receives the trigger signal. It has a configuration including a hold circuit for holding.

It should be noted that here, the data string before the one sample value of the processing target may be considered as the past data string when the time when the sample value of the processing target is processed is the current time, and the past and current data may be considered. It may be considered to include both.

(Operation) In the present invention, the received signal is sampled at a certain sampling variable frequency to generate a sampled value d, which is processed in real time using the following equation (1) to extract only the reflected sound from the target. . Now, as shown in FIG. 7, the data at the time of processing the sampled value d, that is, the current data d _j is used, and the processing calculation result is Y _j.
Then, the principle formula in the present invention is as follows.

According to the above calculation formula, the condition of j> n is required for the calculation of Y _j , and the calculation is started from the time of j−n.
Further, i is an integer from 1 to n, and d _j is m (where m>
It is a data string consisting of sample values of n). Also, Is the average value of sample values in a fixed length section (sample number n) based on the current time, and the sample value of the processing target is updated at each sampling cycle (the value of j increases by 1) and the average The fixed length section that takes is also moved for each sampling period, and is called a moving average value. When the received signal is processed by sequentially changing j in the equation (1), the reverberant non-target signal is suppressed, and only the target signal can be emphasized and detected, and FIG. ) State.

According to this calculation formula, as in the waveform of FIG. 2 (A) in which the non-target signal portion of FIG. 6 is enlarged, the reverberation sound with a gentle rising has the Y _j level smaller than the predetermined value K, and As in the waveform of FIG. 2 (B), which is an enlarged view of the target signal portion of FIG.
The size of Y _j level can be maintained, and Y _j > K (however, τ
Is the sampling period). Therefore, in the processing using this moving average processing method, only a reflected sound from the target can be automatically detected by providing a certain threshold level TH, as in a series of processing shown in FIG. The point at which the phase information is read can be clearly detected, and the target direction can be measured by combining the processing results of a plurality of received signals. In addition, according to the present invention, the moving average value is calculated by using the previous data of the current data, so that the processing can be performed in real time.

(Embodiment) An embodiment of the sonar signal detection method according to the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the present invention, in which 1 is a pulse signal generator that generates a transmission pulse signal, 2 is a transmitter, and 3 is a wave transmitter that transmits a sound wave of a transmission pulse into water. These make up the sonar transmission system.
The sound wave emission direction of the wave transmitter 3 is, for example, the sea surface or the sea bottom direction. 4 is an origin wave receiver for receiving reflected sound waves, 4X is an X axis wave receiver arranged at a position separated from the origin wave receiver in the X axis direction, and 4Y is an origin wave receiver. Is a Y-axis wave receiver arranged at a position separated from the Y axis direction. 5,5
X and 5Y are amplifiers for amplifying the reception signal of the wave receiver, and the wave receivers 4, 4X and 4Y and the amplifiers 5, 5X and 5Y form a sonar reception system. 6,6X, 6Y are A / D converters that sample the amplifier output, which is an analog signal, at a predetermined sampling frequency and convert it to a digital signal.7,7X, 7Y are TVG (Time Variable).
Gain) TVG processor, 8,8X, 8Y are hold circuits, 9X is a phase detector that detects the phase difference between the outputs of the hold circuits 8,8X, and 9Y is the phase difference between the output of the hold circuits 8 and 8Y. A phase detector for detection, 10 is an azimuth calculator for calculating the target azimuth from the outputs of both phase detectors 9X and 9Y. 11 is
The moving average process is performed on the data sequence before the present time (at the time when one particular sample value to be processed is processed) of the sampled data sequence which is the received signal after TVG processing, and Y _j of the equation (1) is calculated. A moving average processor to calculate, 12 detects a signal estimated as a target exceeding a predetermined threshold level using the processing result of the TVG processor, and a calculation result using the processing result of the moving average processor A signal detection processor for detecting a signal estimated as a target at which Y _j exceeds a predetermined threshold level, 13 receives the output of the signal detection processor, and performs the hold operation of the hold circuits 8, 8X, 8Y. It is a trigger signal generator that generates a trigger signal. The trigger signal generator 13 outputs a trigger signal only when detection of a signal estimated to be a target based on the TVG processing result and detection of a signal estimated to be a target based on the moving average processing result occur at the same time.

 Next, the above-mentioned embodiment and operation will be described with reference to FIG.

FIG. 3 (A) is a transmission start signal for pulse signal transmission in the active sonar, in which pulses are output every 0.5 seconds. A pulse signal is transmitted from the wave transmitter 3 into the water in synchronization with this transmission start signal.

After the pulse signal is transmitted, the received signal reflected from the target or the like, received by the wave receivers 4, 4X, 4Y and amplified by the amplifiers 5, 5X, 5Y is shown in FIG. 3 (B). The received signal contains reverberant sound in addition to the reflected sound from the target (target signal), and the received signal level changes with time.

FIG. 3 (C) shows the present signal after the received signal is converted into a digital signal by the A / D converters 6, 6X and 6Y, and the received signal level changes with time because the post-processing shows a small change. As it is (the gain is small for reflection from a short distance and increases as the distance increases)
The signals subjected to TVG processing by the TVG processors 7, 7X and 7Y according to the G curve are shown. Hold circuits 8, 8X, 8Y and moving average processor 1
The signal after the TVG processing of FIG. 3 (C) (that is, a data string of sample values) is added to 1.

FIG. 3D shows the current signal before the moving average processing and the signal obtained by performing the moving average processing of the equation (1) on the current signal after the TVG processing by the moving average processor 11. Also, FIG. 3 (E) is a TV
An operation for detecting the presence of a received signal of a level higher than this by providing an appropriate threshold level TH1 for the G processing result, and FIG. 3 (F) shows the threshold level TH2 appropriate for the moving average processing result. The operation for detecting the presence of a received signal having a level higher than TH2 is provided, and FIG. 3 (G) is estimated to be a reflected sound from the target from the logical sum (multiplication) of FIGS. 3 (E) and (F). This is a situation where the presence of a signal is detected, and these operations are executed by the signal detection processor 12.

The trigger signal generator 13 is a signal detection processor 12 indicating the presence of a signal estimated to be a reflected sound from the target in FIG.
Then, the trigger signal is applied to the hold circuits 8, 8X, 8Y, and the result of detecting the phase of the reflected sound from the target is obtained by the hold operation of the hold circuit as shown in FIG. 3 (H). Since the phase of the target signal contained in the received signals received by the receivers 4, 4X, 4Y arranged at mutually different positions will be mutually deviated according to the target azimuth, it is for the reference origin The phase difference in the X-axis direction is detected by the phase detector 9X that receives the output of the hold circuit 8 corresponding to the wave receiver 4 and the hold circuit 8X corresponding to the X-axis wave receiver 4X, and similarly the origin wave reception Hold circuit 8 and Y-axis wave receiver
The phase detector 9Y which receives the output from the hold circuit 8Y corresponding to 4Y detects the phase difference in the Y-axis direction. Then, the target azimuth is calculated by the azimuth calculator 10 which receives the outputs of the phase detectors 9X and 9Y.

(Effects of the Invention) As described above, in the sonar signal detection method of the present invention, a sonar received signal is sampled at a certain sampling period to create a data string of sample values, and one sample value at a certain time Is set as the current time point, the moving average value is calculated for the data string before one sample value of the processing target at this time point, and the difference between the sample value of the processing target and the moving average value is sequentially calculated. Therefore, the level of data with a steep rise in time is preserved, but the data with a slow rise time is removed.Therefore, the rise time of the target signal is detected because it has a steep characteristic,
Reverberation sounds from the sea surface, the seabed, thermocline, water bodies, etc. can be removed because the level characteristics have a gradual rise in time. Thus, in the processing described in the present invention, the target signal and the reverberant sound can be separated, only the target signal can be automatically detected, and the phase information and the like can be cut out.
It is extremely useful when applied to a sonar device that requires automatic signal detection. Further, it can be applied to signal detection processing in various marine audio equipment, and is industrially effective.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a sonar signal detection system according to the present invention, FIG. 2 is an explanatory view of the principle of the present invention, FIG. 3 is an operation explanatory view of the embodiment of the present invention, and FIG. 4 is a pulse. Explanatory diagram showing a received signal waveform including reverberant sound reflected on the sea surface and the sea bottom after signal transmission, FIG. 5 is an explanatory diagram showing a received signal waveform when pulse signal transmission is repeated, and FIG. 6 is a conventional TVG processing FIG. 7 is an explanatory diagram showing the received waveform after that, and FIG. 7 is an explanatory diagram of the calculation method of the formula (1) showing the sampled value after sampling the sonar received signal. 1 ... Pulse signal generator, 2 ... Transmitter, 3 ... Wave transmitter, 4,4X, 4Y ... Receiver, 5,5X, 5Y ... Amplifier, 6,6X, 6Y
...... A / D converter, 7,7X, 7Y …… TVG processor, 8,8X, 8Y …… Hold circuit, 9X, 9Y …… Phase detector, 10 …… Direction calculator, 11 …… Moving average Processor, 12 ... Signal detection processor, 13
...... Trigger signal generator.

Claims (1)

(57) [Claims] 1. A sonar signal detection system for transmitting a pulse signal into water from a sonar wave transmitter, and separating and extracting a target signal from a reception signal of the sonar wave receiver including reflected sound from the target, The A / D converter that creates a sampled data string by sampling the received signal of the wave receiver at a certain sampling period, and the time at which one sampled value at a certain time is processed The moving average value is calculated by using the data string of the constant length section based on the current time among the data strings before the one sample value of the processing target in (1) and the difference between the sample value of the processing target and the moving average value. A moving average processor for calculating, a signal detection processor for detecting the presence of a signal estimated as a target in which the difference between the sample value of the processing target and the moving average value exceeds a predetermined threshold level, Presumed to be the target Sonar signal detection, comprising: a trigger signal generator that outputs a trigger signal at the output of the signal detection processor indicating the presence of a signal; and a hold circuit that receives the trigger signal and holds the sample value. method.