JPH0693016B2 - Signal processing device for passive sonar - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a signal processing device for a passive sonar, and in particular, it improves S / N when detecting the arrival direction of underwater sound waves based on the received signals of at least two hydrophones. The present invention relates to a passive sonar signal processing device.

[Prior Art] A signal processing device of a passive sonar that arranges a plurality of hydrophones in consideration of operating conditions such as receiving directivity to be formed and determines a target azimuth based on a phase difference between the received signals is well known.

FIG. 2 is an explanatory diagram for detecting the arrival direction of a sound wave based on the phase difference between the reception signals of two hydrophones.

Now, assuming that the incoming sound waves from the sound source at the azimuth angle θ with respect to the reference azimuth are incident on the hydrophones A and B, respectively, the reception signals S _A and S _B of the hydrophones _A and _B are as follows (1),
It is shown by the equation (2).

S _A = Asin (ωt + φ) (1) S _B = Asin (ωt + φ + Δφ) (2) where A is amplitude, ω is angular frequency, φ is phase, and Δφ is phase difference.

In addition, the propagation time difference between the incoming sound waves of the hydrophones A and B is ΔT.
If the distance between the hydrophones A and B is d and the speed of sound is c, then ΔT = dsin θ / c from FIG. 2, so Δφ =
ωΔT = ωd · sin θ / c, and the following equation (3) is obtained.

Therefore, if the phase difference Δφ of the received signal and the frequency are known,
The azimuth angle θ can be easily obtained from the equation (3). In the above description, the case where there are two hydrophones is taken as an example, but even if there are two or more hydrophones, this is divided into two groups of the same number,
By subjecting the received signals to the phasing processing so as to eliminate the mutual phase difference based on the arrangement conditions for each group, basically the same processing as in the case of two hydrophones can be performed. In this way, the conventional azimuth detecting technology of this type phase-combines the reception signals of a plurality of hydrophones that are equal for each azimuth to provide one combined directivity as a whole, and the received signals based on these combined directivities. Many of them mutually detect the azimuth angle by using the equation (3).

By the way, when azimuth detection is performed using two or more hydrophones, the received signals of the hydrophones are often used while being time-integrated over a predetermined time. The purpose of this time integration is to increase the energy of signal components with high stationarity by integration, resulting in high S / N.
(Signal / Noise). In this case, the time length of time integration is usually several tens of seconds in consideration of the operating conditions of the passive sonar.

[Problems to be solved by the invention]

As described above, conventionally, for the purpose of obtaining high S / N in signal processing, time integration is performed on the received signal for each direction. However, due to such time integration effect
There is a limit to the improvement of S / N, and the integration effect of the signal component energy with high stationarity can be obtained, but the noise component energy suppression effect is small. The reason for this is basically considered to be due to the difference in the autocorrelation characteristics of the signal and noise.

That is, since the noise component energies are uncorrelated with each other, they can be expected to cancel each other out if they are integrated over a sufficiently long time, and since the signal component energies have self-relationship characteristics, the accumulation effect is obtained by integrating over a sufficiently long time. There is. However, the integration effect cannot be sufficiently obtained in a short time of about several tens of seconds.

An object of the present invention is to level the distance characteristic of the propagation loss of the incoming signal of each direction including noise by automatic gain control, and then set the spatial vector corresponding to the incoming direction and level of the sound wave to set time and space. By integrating, the integration time is several tens.
Another object of the present invention is to provide a passive sonar signal processing device capable of suppressing noise that is randomly generated even for about a second and remarkably improving S / N.

[Means for solving problems]

The signal processing device of the passive sonar of the present invention is a signal processing device of the passive sonar which detects the arrival direction of an underwater sound wave based on the reception signals of at least two hydrophones, and the signal processing device receives signals from the at least two hydrophones. Automatic gain control means for compensating the propagation loss for each predetermined processing time unit of the signal, and the predetermined processing time unit for the reception signals of the at least two hydrophones for which the propagation loss is compensated by the automatic gain control means. Frequency analysis means for respectively performing Fourier transform processing to output frequency domain data indicating a level versus frequency spectrum; and receiving the frequency domain data and corresponding to the maximum level value of the frequency spectrum for each predetermined processing time unit. At the frequency corresponding to the maximum level value while obtaining the frequency Note: An azimuth calculating means for calculating the azimuth of arrival of the underwater sound wave by obtaining a phase difference between at least two hydrophones, and a maximum level of the frequency spectrum with the azimuth of the underwater sound wave calculated by the azimuth calculating means as a direction. A vector calculation means for obtaining a vector amount having a value for each of the predetermined processing time units, and a target direction detection means for spatially integrating the vector amount for a predetermined time to detect the arrival direction of the underwater sound wave. .

〔Example〕

 The present invention will now be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the present invention. Here, hydrophones 1, 2 and AGC (Automatic Gain Contr
ol) circuits 3 and 4, frequency analysis circuits 5 and 6, azimuth / vector operation circuit 7, target azimuth detection circuit 8 and the like.

First, the essential points of the present invention will be described.

When viewed as a space vector corresponding to the arrival direction and level of the sound wave, the signal component that is the target of the signal processing has a small change in direction if the target that is the source of the sound wave is a long distance,
In many cases, it can be regarded as a vector having a substantially constant azimuth within a predetermined setting processing time. On the other hand, the noise component is so-called background noise, which is randomly generated both temporally and spatially such as biological sounds and waves in the sea, and thus can be regarded as an azimuth dispersion vector.

If such a received signal is integrated over a predetermined time,
The energy of the signal component coming from a specific direction is integrated, while the energy of the noise component cancels out and decreases, so that the S / N can be improved. In this case, in order to effectively reduce the noise in the target space, it is sufficient to eliminate the distance dependence of the propagation loss from the target which is the sound source to the hydrophone which is the receiving point, and to level it. The embodiment shown in (1) is also configured from this point of view.

Now, in FIG. 1, the hydrophones 1 and 2 are arranged at predetermined distance intervals, receive sound waves from an incoming target and background noise in the target space as input sound waves, convert them into electric signals, and convert them into an AGC circuit 3 And 4 respectively.

The AGC circuits 3 and 4 perform automatic gain control of a preset characteristic within a predetermined permissible fluctuation range for each predetermined reception processing time unit with respect to an input signal. The preset automatic gain control characteristic is a characteristic that compensates the propagation loss of the underwater acoustic wave that attenuates in inverse proportion to the square of the distance over the operating distance, that is, the characteristic opposite to the propagation loss characteristic. Therefore, the levels of the signals output from the AGC circuits 3 and 4 are normalized by the propagation loss and leveled. these
The outputs of the AGC circuits 3 and 4 are supplied to the frequency analysis circuits 5 and 6, respectively.

The frequency analysis circuits 5 and 6 perform frequency analysis on the output signals of the AGC circuits 3 and 4 for each reception processing time unit, and extract frequency information regarding the input sound waves acquired by the hydrophones 1 and 2. The frequency analysis is performed using FFT (Fast Fourier Transform), and frequency domain data 501 and 601 indicating the level versus frequency spectrum of the input signal are generated. The frequency domain data 501 and 601 are supplied to the azimuth / vector calculation circuit 7 as information for detecting the frequency of the incoming underwater sound wave.

The azimuth / vector calculation circuit 7 receives the frequency domain data 501 and 601 from the frequency analysis circuits 5 and 6, respectively, and calculates the arrival azimuth of the underwater sound waves arriving at the hydrophones 1 and 2 for each reception processing time unit based on these data. , Set the vector amount with the input level as the magnitude and the direction of arrival as the direction. In this case, the frequency corresponding to the maximum level value in the frequency spectrum provided from the frequency domain data 501 and 601 is obtained, and the azimuth angle is calculated based on the equation (3).
Then, the maximum level value is set as the magnitude, the calculated azimuth angle is set as the direction, and the vector amount with the reception point as the coordinate origin is set. As described above, since the calculation of the expression (3) is performed using the frequency corresponding to the maximum level value of the frequency spectrum of the input sound wave after the AGC processing, it is possible to calculate the accurate azimuth angle with less influence of noise components. In addition, the azimuth / vector operation circuit 7 sets the frequency domain data together with the set vector amount.
The frequency spectrum information provided by 501, 601 is supplied to the target orientation detection circuit 8.

The target azimuth detection circuit 8 spatially integrates the vector amount output from the azimuth / vector calculation circuit 7 around the coordinate origin for a predetermined time, and the sound waves input to the hydrophones 1 and 2 are based on the integrated data. Whether or not the sound wave is from the desired target is determined, and when it is determined that the sound wave is from the desired target, the level and frequency of the incoming sound wave are determined. The processing contents are as follows.

That is, the dispersion of the azimuth angle appearing in the time characteristic of the azimuth angle obtained by integrating over a predetermined time is obtained, and when this dispersion is within the allowable range of the predetermined judgment threshold value,
It is determined that the sound wave providing this azimuth is the sound wave coming from the target. This means that the temporal change rate of the azimuth angle of the sound wave from the target that is sufficiently far away from the hydrophones 1 and 2 is obviously small, and shows a relatively regular change.
It is based on the fact that the dispersion of the azimuth angle is also small. In addition,
The judgment threshold value is set in advance based on a large number of operation records and design data.

In this way, the target direction is determined, while the vector quantity obtained by temporally and spatially integrating the input sound wave signal is obtained. This integrated vector quantity is
The noise canceling effect of the noise component vector, which is normalized by 3 and 4, and whose vector direction changes randomly, shows a significantly larger effect than the case of the conventional non-normalized time integration. The signal component vectors, which have small changes and can be regarded as essentially stationary, are accumulated with strong autocorrelation, so that the S / N is significantly improved.

The embodiment of FIG. 1 has been described by taking two hydrophones constituting a passive sonar arranged at a predetermined interval, but the same applies to a combination of two hydrophones other than each other. It is clear that this can be done. Further, it goes without saying that the two hydrophones may have directivity combined by using a plurality of two or more hydrophones.

〔The invention's effect〕

As described above, according to the present invention, after the propagation loss is compensated by the AGC circuit for the reception signals of at least two hydrophones, the Fourier transform processing is performed to determine the frequency of the maximum level value and the phase difference between the reception signals. Then, the arrival direction of the underwater sound wave is calculated for each predetermined processing time unit, the calculated arrival direction is set as a direction, and the vector amount having the maximum level value of the frequency spectrum is set for each predetermined processing time unit. By spatially integrating the quantity over a predetermined time, there is an effect that the S / N can be significantly improved and the arrival direction of the sound wave can be detected.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram for detecting a target azimuth from a phase difference between received signals by two hydrophones. 1,2 …… Hydrophone, 3,4 …… AGC circuit, 5,6 …… Frequency analysis circuit, 7 …… Direction / vector operation circuit, 8 …… Target direction detection circuit, 501,601 …… Frequency domain data.

Claims (1)

[Claims] 1. A signal processing device of a passive sonar for detecting an arrival direction of an underwater sound wave based on received signals of at least two hydrophones, wherein a predetermined processing time is applied to received signals from the at least two hydrophones. Automatic gain control means for compensating the propagation loss for each unit, and Fourier transform processing for each of the predetermined processing time units with respect to the reception signals of the at least two hydrophones whose propagation loss is compensated by the automatic gain control means. And frequency analysis means for outputting frequency domain data showing a level vs. frequency spectrum,
Receiving the frequency domain data, determining the frequency corresponding to the maximum level value of the frequency spectrum for each predetermined processing time unit, and determining the phase difference between the at least two hydrophones at the frequency corresponding to the maximum level value. Direction calculation means for calculating the arrival direction of the underwater sound wave, and a vector amount having the arrival direction of the underwater sound wave calculated by the direction calculation means as a direction and having a maximum level value of the frequency spectrum as the magnitude, the predetermined processing time unit A signal processing device for a passive sonar, comprising: vector calculation means for each of the above; and target direction detection means for spatially integrating the vector quantity over a predetermined time to detect the arrival direction of the underwater sound wave.