JPH0593772A - Detecting device for underwater acoustic signal - Google Patents

Abstract

PURPOSE:To obtain an underwater acoustic signal detecting device which can suppress a harmful influence according to a frequency component of other signals effectively. CONSTITUTION:A title item is provided with a storage means 1 which stores an azimuth information for each frequency component which is obtained at each certain time, a variance calculation circuit 2 as an azimuth variance value calculation means which calculates a variance value of an azimuth for each frequency component from an azimuth information of a past certain period, and a criterion circuit 3 as a signal criterion means which determines presence or absence of a signal with the azimuth variance value which is calculated by the variance calculation circuit 2 as a reference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an underwater acoustic signal detecting apparatus, and more particularly to an underwater acoustic signal detecting apparatus utilizing the direction of underwater acoustics and the level of frequency components.

[0002]

2. Description of the Related Art In a conventional underwater acoustic signal detection system, signal detection is performed by using only level information of direction and level information for each frequency component of underwater sound. That is, the following is performed in order to detect a signal having a level higher than the noise component. First, the average value Mp of the frequency components of the underwater sound is calculated by Equation 1. It is assumed that there are N cell frequency components and the frequency components are arranged in ascending order.

[0003]

[Equation 1]

Where α = P- (W / 2) -1; β = P
+ (W / 2) +1; Xi is the level of the i-th cell (i =
1 to N); Mp is the noise average value (p
= 1 to N); W indicates the number of cells used for noise average value calculation. In addition, "p <= W / 2" or "p> = N-W / 2"
, P = W / 2 + 2 and p = N−W / 2−, respectively.
A noise average value of 2 is used. In addition, a total of 3 cells centering on the cell for which the noise average is calculated are excluded from the calculation target.

Next, the threshold value Ti is calculated from the equation 2 based on the noise average value.

Ti = K · Mi; (where K: constant) Equation 2

Then, the threshold and the frequency component are compared with each other, and the signal exceeding the threshold is detected as a signal (see the equation 3).

“Signal: Xi> = Ti” “Non-signal: Xi <Ti” Equation 3

[0009]

In the conventional method, since the threshold is applied by using the levels of the frequency components in the vicinity, there is a drawback in that the detection is affected by other frequency components. For example, when the signal itself has a frequency spread of about W in Expression 1, the threshold becomes relatively high, which makes it difficult to detect the signal.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an underwater acoustic signal detecting apparatus capable of improving the disadvantages of the conventional example and, particularly, effectively suppressing the adverse effect due to the frequency components of other signals. To aim.

[0011]

According to the present invention, storage means for storing direction information for each frequency component obtained at fixed time intervals, and a dispersion value of the direction for each frequency component are calculated from the direction information for a fixed period in the past. The azimuth dispersion value calculating means and the signal determining means for determining the presence or absence of a signal based on the azimuth dispersion value calculated by the azimuth dispersion value calculating means are provided. This aims to achieve the above-mentioned object.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. The embodiment shown in FIG. 1 is a storage means 1 for storing direction information for each frequency component obtained at regular time intervals.
And a dispersion calculation circuit 2 as an azimuth dispersion value calculation means for calculating the dispersion value of the azimuths for each frequency component from the azimuth information in the past fixed period, and a signal based on the azimuth dispersion value calculated by the dispersion calculation circuit 2. And a determination circuit 3 as a signal determination means for determining the presence or absence of The determination circuit 3 has a function of detecting a stable frequency component of the arrival direction of the underwater acoustic signal. Then, from the input terminal 100, the envelope θi for each frequency component (i = f0, f1, ..., Fn ...,
fm) is input. These are stored in the storage circuit 1 and input to the distributed calculation circuit 2. Distributed calculation circuit 2
Then, the dispersion of the azimuth for each frequency component is calculated by Expression 4.

[0013]

[Equation 2]

However, the direction with respect to the frequency component fn at the time t is θfnt, and the frequency component in the time section tO to tT.
Let θfn be the average direction of fn.

The value calculated by the equation (4) is sent to the decision circuit (3), and it is decided whether it is a signal or not by comparing it with the constant (K) which can be arbitrarily changed according to the measurement condition by the equation (5).

“Signal: δfn <K” “Non-signal: δfn> K” ・ ・ ・ Equation 5

The dispersion of the azimuth of the signal becomes small unless the signal source suddenly changes the position in the time interval for calculating the dispersion. On the other hand, since the arrival direction of the noise component is not limited to a specific direction, the direction dispersion is large. Therefore, it is possible to detect the signal by appropriately selecting the constant K. The frequency cell number of the frequency component determined to be a signal is output from the output terminal 200.

[0018]

As described above, since the azimuth information for each frequency component according to the present invention is utilized, an unprecedented excellent underwater acoustic signal that can be detected without being affected by other frequency components. A detection device can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Storage circuit 2 Dispersion calculation circuit as dispersion value calculation means 3 Judgment circuit as signal judgment means 100 Input terminal 200 Output terminal

Claims (2)

[Claims] 1. Storage means for storing direction information for each frequency component obtained at fixed time intervals, and direction dispersion value calculation means for calculating a dispersion value of direction directions for each frequency component from direction information of a past fixed period. An underwater acoustic signal detecting apparatus comprising: a signal determining unit that determines the presence or absence of a signal based on the azimuth dispersion value calculated by the azimuth dispersion value calculating unit. 2. The underwater acoustic signal detecting apparatus according to claim 1, wherein the signal determining means has a function of detecting a stable frequency component of the arrival direction of the underwater acoustic signal.