JPH05302849A - Apparatus for detecting change in frequency of underwater acoustic signal - Google Patents

Abstract

PURPOSE:To detect the change in frequency of an underwater acoustic signal in a passive sonar without delay. CONSTITUTION:A peak detecting circuit 3 detects the respective peak signals based on the frequency analysis data S2 from a frequency analysis circuit 1 and the frequency analysis data S3 immediately before from a memory circuit 2. A difference circuit 4 obtains the difference between the peak frequencies. A comparing circuit 5 judges the fact that the frequency of an underwater acoustic signal S1 is changed when the difference between the peak frequencies is larger than the threshold S7 from a threshold input terminal 8.

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 frequency change detecting device, and more particularly to an underwater acoustic signal frequency change detecting device for detecting a frequency change of an underwater acoustic signal in a passive sonar.

[0002]

2. Description of the Related Art A passive sonar device detects a frequency change of an underwater acoustic signal obtained from a hydrophone by using a detection device. A conventional detection device of this type analyzes a frequency spectrum of an underwater acoustic signal at regular time intervals and integrates frequency spectra obtained one after another for each of a plurality of frequency cells. Then, the cell change of the peak frequency cell having the maximum level of the integrated plurality of frequency cells, that is, the change of the peak frequency is compared with a preset threshold, and there is a change of the peak frequency exceeding the threshold. For example, it was considered that the frequency of the underwater acoustic signal changed.

[0003]

In the above-mentioned conventional detecting device, even if the signal-to-noise ratio (S / N) of the underwater acoustic signal is good, this signal is obtained after integrating the underwater acoustic signal for each frequency cell. The frequency change of is detected. Therefore, after the frequency of the underwater acoustic signal actually changes,
There is a problem in that it takes time until the integrated value of the changed frequency cell is detected as a peak frequency cell, which causes a delay in the frequency change detection of the underwater acoustic signal.

Accordingly, it is an object of the present invention to provide an underwater acoustic signal frequency change detecting device for a passive sonar device which detects a frequency change of an underwater acoustic signal without delay.

[0005]

The underwater acoustic signal frequency change detecting device of the present invention is a frequency analysis means for decomposing an underwater acoustic signal from a hydrophone into a plurality of frequency cell components per unit time to generate frequency analysis data. A storage unit for storing the new frequency analysis data generated by the frequency analysis unit and outputting the frequency analysis data stored immediately before, and a maximum from each of the frequency analysis data from the frequency analysis unit and the storage unit. Peak frequency detecting means for detecting a peak frequency representative of the frequency cell of the level, difference means for calculating a difference between the two peak frequencies to generate a difference frequency signal, preset threshold value and the difference frequency signal And when the difference frequency signal exceeds the threshold value, the underwater acoustic signal And a comparing means for determining that there is a frequency change.

[0006]

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. This underwater acoustic signal frequency change detection device is part of a passive sonar device. FIG. 2 is a partial signal waveform diagram in the embodiment of FIG.

Referring to FIGS. 1 and 2 together, the underwater acoustic signal frequency change detecting device is configured such that a hydrophone (not shown) obtains an underwater acoustic signal S1 (see FIG. 1, at time t0) obtained from an underwater target. (S1 has a frequency change) from the input terminal 6 to the frequency analysis circuit 1. The frequency analysis circuit 1 calculates the underwater acoustic signal S for each unit time Δt.
1 is subjected to frequency spectrum analysis, that is, this underwater acoustic signal S
1 is decomposed into a plurality of frequency cell components, and the frequency analysis data S2 as the result of the component decomposition is supplied to the peak detection circuit 3. This frequency analysis data S2 is the peak detection circuit 3
It is also supplied to the memory circuit 2 simultaneously with the supply to the memory circuit 2. Then, the memory circuit 2 stores the newly supplied frequency analysis data S2 and simultaneously outputs the previously stored frequency analysis data S3 to the peak detection circuit 3. The peak detection circuit 3 detects the frequency cell having the maximum (peak) level for each of the frequency analysis data S2 and S3, and the peak frequency of the frequency F (t + Δt) representing the maximum level frequency cell at the time (t + Δt). Signal S
4, and the peak frequency signal S5 of the frequency F (t) obtained at the frequency spectrum analysis time t one time before the time (t + Δt) is supplied to the difference circuit 4. Difference circuit 4 takes the difference between the peak frequency signals S4 and S5, calculates the difference frequency ΔF = F (t + Δt) -F (t), and generates difference frequency signal S6 representing this difference frequency ΔF. .. The comparison circuit 5 compares the difference frequency signal S6 with the level of the threshold S7 supplied to the threshold input terminal 8 (see FIG. 2, the difference frequency signal as early as the time t1 = t0 + Δt during the frequency change of the underwater acoustic signal S1). When the level of the signal S6 exceeds the threshold S7) and the difference frequency signal S6 exceeds the threshold S7, an output signal S8 indicating that the frequency change of the underwater acoustic signal S1 is detected is generated at the output terminal 7.

[0009]

As described above, the present invention compares the peak frequency obtained by the previous frequency spectrum analysis with the peak frequency obtained by the new frequency spectrum analysis for each frequency spectrum analysis of the underwater acoustic signal. Since the frequency change of the underwater acoustic signal is detected, the frequency change can be detected without delay.

[Brief description of drawings]

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

FIG. 2 is a partial signal waveform diagram in the embodiment of FIG.

[Description of symbols] 1 frequency analysis circuit 2 memory circuit 3 peak detection circuit 4 difference circuit 5 comparison circuit 6 input terminal 7 output terminal 8 threshold input terminal S1 underwater acoustic signal S2, S3 frequency analysis data S4, S5 peak frequency signal S6 difference Frequency signal S7 threshold S8 output signal

Claims (1)

[Claims] 1. A frequency analysis means for decomposing an underwater acoustic signal from a hydrophone into a plurality of frequency cell components per unit time to generate frequency analysis data, and new frequency analysis data generated by the frequency analysis means are stored. Storage means for outputting the frequency analysis data stored immediately before, and peak frequency detection for detecting a peak frequency representative of the frequency cell at the maximum level from each of the frequency analysis data from the frequency analysis means and the storage means. Means for calculating a difference between the two peak frequencies to generate a difference frequency signal, and comparing the difference frequency signal with a preset threshold value, and the difference frequency signal exceeds the threshold value. And comparing means for determining that there is a frequency change of the underwater acoustic signal. Underwater acoustic signal frequency change detection device.