JPH03242576A - Method for distinguishing underwater sound source - Google Patents

Abstract

PURPOSE:To automatically distinguish an underwater sound source from a surface sound source by placing an underwater microphone located at a distance within three times a depth of water from a water bottom directly under the sound source and using time difference wherein autocorrelation of an acoustic signal received by the microphone is maximum. CONSTITUTION:An underwater microphone 1 is located at a distance L three times a depth of water D from a position directly under a sound source 6. A signal S(t) 4 of the sound source received by the underwater microphone 1 is input to a correlation unit 2. The correlation unit 2 calculates an absolute value ¦R(t)¦ 5 of autocorrelation according to an equation. A distinguishing unit 3 calculates tau for which the absolute value of the autocorrelation ¦R(tau)¦ is a maximum, and when the value is larger than D/C, the sound source is determined to be on the surface and when the value is smaller than D/C, the sound source is determined to be in the water. C refers to the velocity of sound in the water.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an underwater sound source discrimination method, particularly an underwater sound source that automatically discriminates between an underwater sound source and an above-water sound source when the sound source passes through a narrow channel zone such as a strait. Concerning sound source discrimination method.

[Conventional technology]

Conventionally, this type of discrimination has been performed visually or by confirming the presence or absence of an underwater sound source using radar.

[Problem to be solved by the invention]

The conventional underwater sound source discrimination method described above is based on visual or
The problem is that it is not possible to automatically distinguish between underwater sound sources and overwater sound sources based only on acoustic signals.

[Means to solve the problem]

The underwater sound source discrimination method of the present invention is an underwater sound source discrimination method for discriminating whether a sound source existing in an area shallower than 1/2 of the water depth exists on the water surface or underwater, and comprises: An underwater microphone that is grounded on the bottom of the water at a distance within three times the water depth from the position; a correlation unit that calculates the autocorrelation of the acoustic signals received by the underwater microphone; and a determination unit that determines whether the water is present in the water or in the water.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of the underwater sound source discrimination method of the present invention, FIG. 2 is an explanatory diagram of the sound propagation path of the sound source in the embodiment of FIG. 1 when the sound source is above the water surface, and FIG. The figure is the first
FIG. 3 is an explanatory diagram of the sound propagation path of the sound source in the illustrated embodiment when the sound source is underwater;

In FIG. 2, the sound from the sound source 6 on the water surface is directly received by the underwater microphone 7 through a path Psn, and is also reflected from the bottom and the water surface through a path PSR and received.

In Fig. 2, the path R3R is the one with the best S/N (signal-to-noise ratio) among the reflection paths of the sound waves emitted from the sound source 6 that reach the underwater microphone. , P that divides the water bottom and water surface into three parts,
It is reflected at Q point. Setting the underwater microphone 1 at a distance three times the depth of the water from directly below the sound source 6 was chosen as a nearly limit distance beyond which an effective S/N ratio could not be secured.

Now, the received sound is obtained by receiving the signals generated by the sound source 6 via the paths PSD and PSR, and adding them with the time difference shown by equation (1).

Here, C is the speed of sound in water.

Equation (1) can be easily derived from the fact that the PSD is clearly J1 shift 12, the PSR is 3a, and a = D' + (there are 3 houses).

In Fig. 3, the sound of underwater sound source 6 is transmitted by underwater microphone 1.
The reflected path sound that is directly received through the path PDD and input into the underwater microphone 1 with the best S/N is the line connecting the mirror image point R of the underwater microphone 1 on the water surface and the sound source 6 and the water surface. It is specularly reflected at the intersection S and is input via the path PDR. Therefore, the received sound is the sum of the signals generated by the sound source 6 with these two time differences. The time difference in this case is expressed by the following equation (2).

Obviously, τ is the reception time difference shown in equation (1) or (2) (2) where A is the water depth of the sound source 6.

In equation (2), PDR is the distance between the sound source 6 and point R, and its guidance is clear from FIG. 3 as well as PDD.

Next, the embodiment shown in FIG. 1 will be described with reference to FIGS. 2 and 3.

The sound source signal S (t
) 4 is input to the correlation section 2. In correlation part 2 (3)
The absolute value of autocorrelation IR(t]5 is determined by the formula.

R(τ)1=l÷S 5(1)・5(t−τ)dtl・
(3) Here, T is the integration time and is a number greater than 0. The absolute value 5 of the autocorrelation is the time difference in equation (1) when the sound source 6 is above the water surface, and (
2) The maximum value is taken when τ matches the time difference in the equation.

The determining unit 3 changes IR(τ)1 of the absolute value 5 of the autocorrelation by τ, and determines τ at which the value becomes the maximum. Koru. As shown in Figure 4, when the distance between the underwater microphone position and the underwater microphone installation position is within 3 times the water depth (3D or less), the sound source water depth A is the water depth + the absolute value of autocorrelation IR (τ). 1
The water source is determined to be underwater when τ is the maximum.

〔Effect of the invention〕

As explained above, the present invention includes an underwater microphone installed at a distance within three times the water depth from the bottom position directly below the sound source, a correlation section that calculates the autocorrelation of the acoustic signal received by the underwater microphone, and a correlation unit that calculates the autocorrelation of the acoustic signal received by the underwater microphone. By having a discriminating part that discriminates whether the sound source is on the water surface or underwater based on the maximum time difference, it is possible to discriminate whether the sound source is on the water surface or underwater only by the acoustic signal.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the underwater sound source discrimination method of the present invention, FIG. 2 is an explanatory diagram showing the sound wave propagation path in the embodiment of FIG. 1 when the sound source is on the water surface, and FIG. Fig. 4 is an explanatory diagram showing the sound wave propagation path when the sound source is underwater in the embodiment shown in Fig. 1, and Fig. 4 shows the time difference giving the maximum absolute value of autocorrelation in the embodiment shown in Fig. It is a figure which shows the relationship with the distance between. 1... Underwater microphone, 2... Correlation section, 3... Discrimination section, 4... Received sound wave S (t) of underwater microphone, 5... ... Absolute value of autocorrelation, A ... Water depth of the sound source, D ...
...Water depth, L...Distance between the water bottom position directly below the sound source and the installation position of the underwater microphone.

Claims (1)

[Claims] This is an underwater sound source discrimination method that determines whether a sound source existing in an area shallower than 1/2 of the water depth exists on the water surface or underwater, the method comprising:
An underwater microphone installed on the bottom of the water within twice the distance,
A correlation unit that calculates an autocorrelation of the acoustic signal received by the underwater microphone, and a discrimination unit that determines whether the sound source is on the water surface or underwater based on the time difference at which the autocorrelation is maximum. This underwater sound source discrimination method is characterized by: