JP2002350541A - Active sonar apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a self Doppler erasure system of an active sonar apparatus for improving the decrease in accuracy for the Doppler measurement of a target echo. SOLUTION: A transmission signal generation section 2 generates the transmission source signal of two different kinds of basic frequencies F1 and F2, and transmits the sound wave of the two kinds of basic frequencies in a specific azimuth from an arrangement transducer 1 via a transmission control section 3 and a transmission/reception switcher 4. The sound wave being received by the arrangement transducer 1 is outputted to filter sections 5 and 12 via the transmission/reception switcher 4. Then, the amounts of frequency change ΔF1 and ΔF2 of each reverberation are calculated by an F1 phase-adjusting section 6, an FFT section 9, and a reverberation peak frequency detection section 10, and F2 phase-adjusting section 13, an FFT section 14, and a reverberation peak frequency detection section 15. A correction coefficient calculation section 11 calculates a correction coefficient required for erasing own Doppler using the ΔF1, ΔF2, F1, and F2 for outputting to an own Doppler erasure section 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an active sonar device, and more particularly to an improvement in a self-Doppler canceling system.

[0002]

2. Description of the Related Art An active sonar device which transmits sound waves into the sea and receives and detects a reverberation sound from a target (hereinafter referred to as a target echo), and which is mounted on a ship or the like and which itself moves with itself, is known. In addition, the frequency characteristics of the transmitted and received sound waves change due to the Doppler effect accompanying the own movement. This frequency change due to the movement of the self is called self-Doppler, and when Doppler measurement of a target echo is performed, erasure of the self-Doppler becomes important.

[0003] When measuring the Doppler of the target echo, the frequency characteristic of the target echo is detected, and the difference between the detected frequency, the transmitted frequency, and the frequency change due to the own Doppler is measured. This is because the calculation error leads to a Doppler measurement error of the target echo.

[0004] An example of a conventional self-Doppler erasing method of an active sonar device is described in Japanese Patent Application Laid-Open No. 4-208889. FIG. 5 shows a schematic functional block thereof.

[0005] A transmission signal generator 52 generates a transmission source signal of a basic frequency and outputs the signal to a self-Doppler erasure unit 53. The self-Doppler elimination unit 53 inputs the sound speed, the self-speed, and the moving direction at the time when the transmission source signal is input, calculates the frequency change of the transmission azimuth by the self-Doppler, and sets the transmission source signal as a basic at the time of reception. The frequency shift corresponding to the frequency change is performed so that the frequency becomes a certain frequency, and the result is output to the transmission control unit 54. Frequency F after frequency shift (= f
0-ΔF) [Hz] is given by equation (1). F = [(cv · cos θ) / (c + v · cos θ)] × f0 (1) where c is the sound speed in the sea [m / s], and v is the own speed [m
/ S], θ is the relative value [°] of the transmission azimuth as viewed from its own movement azimuth, and f0 is the basic frequency [Hz] of the transmission source signal.
It is.

The transmission control section 54 receives the output signal (frequency F) of the self-Doppler erasing section 53, performs phasing processing for forming a beam in the transmission direction, and performs amplification for obtaining a required transmission output. , Via the transmission / reception switch 55
It outputs to the array transducer 51.

[0007] The arrayed transducer 51 is provided with the transmission control unit 54.
Input signal is converted to sound waves and transmitted underwater.
The arrayed transducer 51 further receives a reverberation sound from the sea from the end of transmission and outputs it to the filter unit 56 via the transmission / reception switch 55. After selecting a desired frequency from the received reverberation signals in the filter unit 56, the phasing unit 57 forms a reception beam.

In the above publication, as a conventional example, a self-Doppler canceling unit is arranged on the receiving side, and the sound velocity measured at the time when the transmission source signal is input to the receiving beam formed by the phasing unit, A configuration for performing correction for self-Doppler elimination (frequency shift) according to the self-speed and the moving direction is also described.

An active sonar device that transmits a sound wave into the sea and receives and detects a target echo receives not only the target echo but also a reverberation signal generated as backscatter from plankton or the sea surface in the sea at all times. , Traditionally,
Prior to the target search, there has been proposed a method of eliminating a Doppler frequency shift component caused by the own traveling speed and transmission frequency by using the received reverberation signal frequency.

[0010]

In the conventional system described in the above publication, a calculation for eliminating self-Doppler is performed using sound speed, own speed and moving direction information measured at the time of transmission. In the sea, the sound speed, self-velocity, and moving direction are not always constant and may change during reception. In addition, the self-motion that causes self-Doppler generation is three-dimensional in the actual sea, so that the transmission and reception beams are It is very difficult to measure the velocity vector in the center direction accurately and without time delay.

For this reason, if the sound speed, own speed, and moving direction change after transmission of a sound wave and before reception, the self-Doppler erasure function cannot sufficiently cope with the change.
Since it is difficult to completely eliminate the Doppler component generated by the own motion due to the measurement error of the velocity vector information, there is a problem that the Doppler measurement accuracy of the target echo decreases.

Further, in the conventional example in which the Doppler frequency shift component caused by the own traveling speed and the transmission frequency is eliminated by using the received reverberation signal frequency, the underwater plankton or the sea surface which is the source of the reverberation signal is stationary. Since the frequency change of the reverberation signal becomes equal to the frequency change due to the self-Doppler, if the peak frequency of the reverberation signal is detected and corrected so that the peak frequency becomes 0, the self-Doppler cancellation is performed. Although it is possible, in the actual sea, because the underwater plankton and the sea surface are moving due to the influence of the tidal current and the like, the Doppler component due to the movement becomes an error, and the Doppler measurement accuracy of the target echo is reduced. There's a problem.

SUMMARY OF THE INVENTION An object of the present invention is to provide a self-Doppler elimination system for an active sonar device which can improve the decrease in Doppler measurement accuracy of a target echo in view of such a problem.

[0014]

According to the present invention, the same motion is obtained by transmitting and receiving, at two different fundamental frequencies, and detecting the frequency change of the reverberation signal observed as the sum of the Doppler of the self-Doppler and the reverberation itself. However, if the fundamental frequency is different, the amount of frequency change due to self-Doppler and reverberation Doppler is different, and the difference in the amount of frequency change is
The difference between the fundamental frequencies is multiplied by a constant (hereinafter referred to as a correction coefficient) obtained from the moving speed and sound speed in the beam center direction at the time of transmission and the moving speed and sound speed in the beam center direction during reception. Utilizing, without directly measuring the moving speed in the direction of the center of the beam and the sound velocity, the self-Doppler is calculated and the self-Doppler is eliminated by calculating the correction coefficient at the time of reception. And

More specifically, the self-Doppler elimination method of the active sonar device according to the present invention corresponds to transmission signal generating means for simultaneously generating transmission source signals at two different fundamental frequencies, and corresponds to the two fundamental frequencies. Phasing means for simultaneously processing received signals, reverberation peak frequency detection means for detecting peak frequencies of reverberation levels corresponding to the two types of frequencies, and a correction coefficient necessary for self-Doppler cancellation from the two reverberation peak frequencies. A correction coefficient calculating means for calculating and a self-Doppler erasing means for erasing self-Doppler using the correction coefficient are provided.

In another embodiment of the present invention, instead of the reverberation peak frequency detecting means and the correction coefficient calculating means, target echo peak frequency detecting means for detecting a peak frequency of a target echo, and detecting at each frequency. Target Doppler calculating means for directly inputting the peak frequency of the target echo and directly calculating the Doppler of the target echo.

According to the present invention, there is an effect equivalent to measuring the moving speed and the sound speed in the direction of the beam center measured at each reception time, and the moving speed and the sound speed in the direction of the beam center are directly measured. Since it is not necessary to use the calculated value, the self-Doppler can be accurately erased, and the Doppler measurement accuracy of the target echo can be improved.

In the present invention, since the correction coefficient for self-Doppler cancellation is expressed as a difference between two reverberation frequency changes, a Doppler frequency change component of a reverberation signal due to movement of the plankton or the sea surface in the sea due to a tidal current or the like. Can also be eliminated.

[0019]

FIG. 1 is a processing block diagram showing a first embodiment of the present invention. In the present embodiment, in addition to the conventional arrayed transducer 1, transmission control unit 3, transmission / reception switching unit 4 and Doppler processing unit 8, transmission sources of two different fundamental frequencies F 1 and F 2 are newly added. A transmission signal generator 2 for generating a signal, and the two different fundamental frequencies F
1 and F2, a filter unit 5, an F1 phasing unit 6, an FFT unit 9, and a reverberation peak frequency detecting unit 10 for supporting the fundamental frequency F1.
And a filter unit 12 corresponding to the fundamental frequency F2.
An F1 phasing unit 13, an FFT unit 14, a reverberation peak frequency detecting unit 15, a correction coefficient calculating unit 11 for calculating a correction coefficient for self-Doppler elimination, and a self-Doppler erasing unit 7 for performing self-Doppler elimination. And

Next, the operation of the first embodiment of the present invention shown in FIG. 1 will be described.

A transmission signal generator 2 generates transmission source signals of two different fundamental frequencies F1 and F2, and a transmission controller 3
Output to The transmission control unit 3 receives the transmission source signals of the two fundamental frequencies, performs phasing processing for forming a transmission beam in a predetermined direction, and performs amplification for obtaining a desired transmission output. Array transducer 1 via 4
Output to

The arrayed transducer 1 receives the output of the transmission control unit, converts it to acoustic energy, and moves the acoustic energy to a predetermined direction.
Transmits sound waves of various fundamental frequencies. In the present embodiment, the arrayed transducers 1 are a planar array in which transducers are arranged in a plane, but the invention is also applicable to other array shapes such as a cylindrical array and a line array.

The arrayed transmitter / receiver 1 further receives a sound wave immediately after transmission, converts a received signal into an electric signal, and passes through the transmission / reception switch 4 to the filter unit 5 and the filter unit 12.
Output to

The filter section 5 is a band-pass filter of a band W centered on the frequency F 1, and selects the F 1 signal from the received signals output from the arrayed transducer 1. F1
The phasing unit 6 forms a reception beam in a predetermined direction with respect to the signal of the selected frequency F1.

The FFT unit 9 performs a Fourier transform on the output signal of the F1 phasing unit to convert it into a frequency domain signal. The reverberation peak frequency detector 10 detects the frequency of the reverberation level peak value of the frequency domain signal, and calculates a frequency difference ΔF1 from the transmission fundamental frequency F1.

The filter section 12 is a band-pass filter of a band W centered on the frequency F2, and selects a signal of F2 from the reception signals output from the arrayed transducers 1. F
The two-phase adjusting unit 13 forms a reception beam in a predetermined direction with respect to the signal of the selected frequency F2.

The FFT unit 14 performs a Fourier transform on the output signal of the F2 phasing unit to convert the signal into a frequency domain signal. The reverberation peak frequency detector 15 detects the frequency of the reverberation level peak value of the frequency domain signal, and calculates a frequency difference ΔF2 from the transmission fundamental frequency F2.

The correction coefficient calculating section 11 receives the frequency differences ΔF1 and ΔF2 from the reverberation peak frequency detection section 10 and the reverberation peak frequency detection section 15 to calculate correction coefficients, and self-Doppler-eliminates the calculated correction coefficients. Part 7
Output to The self-Doppler elimination unit 7 eliminates a frequency change of the F1 phasing unit output signal due to the self-Doppler using the correction coefficient, and outputs the signal to the Doppler processing unit 8.

FIG. 2A shows an FFT of the fundamental frequency F1 system.
FIG. 2 is a conceptual diagram of a frequency-domain signal output from a unit 9;
(B) is a conceptual diagram of a frequency domain signal output from the FFT unit 14 of the fundamental frequency F2 system. Hereinafter, the operation of self-Doppler erasure in the present embodiment will be described with reference to FIG.

In FIG. 2A, F1t (f) 23 represents a frequency domain signal of the fundamental frequency F1 system at time t and frequency f. ΔF1 (22) is the frequency change of the reverberation signal caused by its own movement, tide, etc.
This is as in equation (4). ΔF1 = [(ΔC + ΔV) / (Cx-Vx × cosθx)] × F1 + ΔFz (2) ΔC = Cr-Cx (3) ΔV = Vr × cosθr + Vx × cosθx (4) In Equations (2) to (4), Cx is the sound speed [m / s] in the sea at the time of transmission, and Vx is the own speed [m / s] at the time of transmission.
s] and θx are the relative azimuths [°] of the transmission beam center as viewed from the moving azimuth of the vehicle at the time of transmission, Cr is the sound speed [m / s] in the sea at the time of reception, and Vr is the own speed [m /
s] and θr are the relative azimuths of the transmitted beam center [°] as viewed from its own azimuth at the time of reception. [Hz].

Further, (ΔC + ΔV) / (Cx−Vx × cos) in the equation (2)
θx) is a correction coefficient for self-Doppler erasure. In FIG. 2A, T24 represents the pulse width of the transmission waveform, and it is determined whether the peak of the reverberation level or the peak of the target echo depends on whether the continuity of the detected peak is longer, equal, or shorter than T24. Used for

2 (b) is the same as the description of FIG. 2 (a), and F1 in FIG.
ΔF2 (26) is obtained by equation (5).

ΔF2 = [(ΔC + ΔV) / (Cx−Vx × cos θx)] × F2 + ΔFz (5) Reverberation frequency change ΔF1 (22) detected by reverberation peak frequency detector 10 in FIG. And the reverberation frequency change ΔF2 (26) detected by the reverberation peak frequency detector 15 in FIG. 1, ie, ΔFz is eliminated from the equations (2) and (5) to correct the correction coefficient (ΔC + ΔV). / (Cx−Vx × cosθx), the correction coefficient = (ΔF2-ΔF1) / (F2-F1) (6) In the self-Doppler elimination unit 7 in FIG. The frequency change due to the self-Doppler is canceled by inputting the output of the F1 phasing unit 6 using the equation (7).

[Erase frequency] = [Correction coefficient] × F1 (7) Accordingly, in the present embodiment, the reverberation peak frequency ΔF1,
If ΔF2 can be detected, the speed of sound in the sea or its own speed,
The correction coefficient can be obtained from equation (6) without measuring the moving azimuth and the like, and self-Doppler erasure can be performed according to equation (7).

FIG. 3A shows an example of a processing flow of reverberation peak frequency detection, and FIG. 3B shows a conceptual diagram of peak frequency detection. Hereinafter, the operation of reverberation peak frequency detection in the present embodiment will be described with reference to the processing flow of FIG. FIG. 3 shows the case where the fundamental frequency is the F1 system, but the same applies to the F2 system.

The signal F1t (f) 23 obtained by converting the received signal into the frequency domain by the FFT unit 9 shown in FIG. 1 is input at 31, and the amplitude corresponding to the frequency is sequentially read. Here, since the input signal F1t (f) 23 is limited to the band W centered on the frequency F1 by the filter unit 5 in FIG. 1, as shown at 32, only in the range of F1-W / 2 to F1 + W / 2. Increase the frequency f.

Next, at 33, it is detected whether or not f is a frequency at which the signal F1t (f) 23 has a peak. This is because, as shown in FIG. 3B, the amplitude F1t (f) 23 of the frequency f of interest and the amplitudes F1t (f-1) 37 and F1t (f +) of the preceding and following frequencies f-1 and f + 1, respectively.
1) 38 is compared, and F1t (f) 23 is changed to F1t (f−
1) If it is larger than either 37 or F1t (f + 1) 38, it is determined that the peak is present, otherwise, it is determined that it is not a peak.

If not, the amplitude for the next frequency is checked. If it is a peak, it is determined at 34 whether the peak is a reverberation or a target echo, based on whether the peak continues longer in time than the transmission pulse width T.

That is, when the peak is the target echo, the peak detection time is longer than the transmission pulse width T and is not continuously detected. Then, the detected peak frequency is determined to be the reverberation peak frequency, and at 35, the difference between the detected reverberation peak frequency and the transmission fundamental frequency is obtained, and output to the correction coefficient calculation unit 11 of FIG. 1 as the reverberation frequency change ΔF1. . 3 if not determined as the reverberation peak frequency
2, the next peak frequency is detected.

The reverberation frequency change ΔF2 is obtained in the same manner, and is output to the correction coefficient calculation section 11 in FIG. The correction coefficient calculation unit 11 obtains a correction coefficient from the input reverberation frequency changes ΔF1 and ΔF2 and the fundamental frequencies F1 and F2 by calculating the equation (6), and outputs the correction coefficient to the self-Doppler elimination unit 7.

As described above, in the above embodiment, two different
Transmit and receive at different fundamental frequencies, and change the frequency of the reverberation signal generated by the active sonar due to self-Doppler,
Since the correction coefficient used in self-Doppler elimination is calculated based on the difference between the two frequencies, the effect equivalent to measuring the actual moving speed and sound speed in the beam center direction at each reception time is obtained. In addition, the effect of Doppler frequency change caused by the movement of submarine plankton and the sea surface due to tidal currents, which cause reverberation, can be eliminated, so self-Doppler can be accurately eliminated and Doppler measurement accuracy of target echo is improved It has the effect of being let.

FIG. 4 is a block diagram showing a second embodiment of the present invention. Although the basic configuration of the present embodiment is the same as that of the first embodiment, the present embodiment is devised so as to directly perform target Doppler measurement without performing self-Doppler erasure.

In FIG. 4, since the components from the arrayed transducers 1 to the FFT unit 14 are the same as in the first embodiment, here, the target echo peak frequency detection units 41 and 42 and the target Doppler calculation unit 43 are described. I will explain only.

The target echo peak detecting section 41 determines that the reverberation signal is not reverberant in the reverberation signal determination performed at 34 in FIG. 3A in the first embodiment, and determines the target echo as (8). ΔF which is the sum of the frequency change due to self-Doppler and the target Echo Doppler shown in equations (10) to (10)
1 is calculated.

ΔF1 = [(ΔC + ΔV) / (Cx-Vx × cosθx)] × F1 + ΔFT (8) ΔC = Cr-Cx (9) ΔV = Vr × cosθr + Vx × cosθx (10) In the formulas (8) to (10), Cx is the sound speed [m / s] in the sea at the time of transmission, and Vx is the own speed [m / s] at the time of transmission.
s] and θx are the relative azimuths [°] of the transmission beam center as viewed from the moving azimuth at the time of transmission, Cr is the sound speed [m / s] in the sea at the time of reception, and Vr is the own speed [m] at the time of reception. /
s] and θr represent the relative azimuth [°] of the center of the transmission beam viewed from its own moving azimuth at the time of reception, and ΔFT represents the Doppler frequency [Hz] of the target echo.

The target echo detecting section 42 is the same except that F1 of the target echo detecting section 43 is read as F2, and the equation (8) becomes the equation (11).

ΔF2 = [(ΔC + ΔV) / (Cx−Vx × cos θx)] × F2 + ΔFT (11) The target Doppler calculator 43 inputs the ΔF1 and ΔF2, and calculates the equation (8) and From the equation (11), the correction coefficient (ΔC + ΔV) /
(Cx−Vx × cosθx) was deleted, and ΔFT was solved (1
2) The target Doppler ΔFT is calculated using the equation.

ΔFT = (ΔF1 × F2-ΔF2 × F1) / (F2-F1) (12) As described above, in this embodiment, the Doppler of the target echo detected at two different frequencies is directly measured. Therefore, a further effect that the self-Doppler erasing unit 7 can be reduced can be obtained.

[0049]

According to the present invention, the transmission and reception are performed at two different fundamental frequencies, and the frequency change of the reverberation signal generated by the active sonar due to the self-Doppler is detected for each of the two types of frequencies. Since the correction coefficient used in the erasure is calculated, there is no need to use the measured values of the moving speed and sound velocity in the direction of the beam center measured at each reception time to obtain the correction coefficient. And the accuracy of Doppler measurement of the target echo can be improved.

Further, even if its own speed and moving direction change after transmission, self-Doppler erasure can be performed with high accuracy, and Doppler measurement accuracy can be improved.

According to the second embodiment of the present invention,
Since the Doppler of the target echo detected at two different frequencies can be directly measured, the effect of reducing the number of self-Doppler canceling parts can be obtained.

[Brief description of the drawings]

FIG. 1 is a processing block diagram showing a first embodiment of the present invention.

FIG. 2A is a conceptual diagram of a frequency domain signal of a fundamental frequency F1 system. (B) A conceptual diagram of a frequency domain signal of a fundamental frequency F2 system.

FIG. 3A is a flowchart illustrating an example of a reverberation peak frequency detection process. (B) It is a conceptual diagram of peak frequency detection.

FIG. 4 is a processing block diagram showing a second embodiment of the present invention.

FIG. 5 is a schematic functional block diagram of a conventional technique.

[Explanation of symbols]

 Reference Signs List 1 arrayed transmitter / receiver 2 transmission signal generator 3 transmission controller 4 transmission / reception switcher 5 filter unit 6 F1 phasing unit 7 self-Doppler elimination unit 8 Doppler processing unit 9 FFT unit 10 reverberation peak frequency detection unit 11 correction coefficient calculation unit 12 Filter section 13 F2 phasing section 14 FFT section 15 reverberation peak frequency detection section 21 reverberation peak frequency 22 ΔF1 23 F1t (f) 24 transmission time T 25 reverberation peak frequency 26 ΔF2 27 F2t (f) 31 frequency domain signal F1t (f) Input processing 32 Frequency increase, loop processing 33 Peak detection processing 34 Continuity determination processing 35 ΔF1 calculation processing 36 ΔF1 output processing 37 Frequency f-1 amplitude F1t (f-1) 38 Frequency f + 1 amplitude F1t (f + 1) 41 Target echo peak frequency Detector 42 Target echo peak frequency detector 43 th Reference Doppler calculation unit 51 Arrayed transducers 52 Transmission signal generator 53 Self-Doppler erasure unit 54 Transmission control unit 55 Transmission / reception switch unit 56 Filter unit 57 F1 phasing unit

Claims (6)

[Claims] 1. A transmission signal generating means for simultaneously generating transmission source signals at two different fundamental frequencies, a means for processing a received signal corresponding to the two fundamental frequencies, and a means corresponding to the two kinds of frequencies. Reverberation peak frequency detection means for detecting a peak frequency of a reverberation level, correction coefficient calculation means for calculating a correction coefficient required for self-Doppler elimination from the two reverberation peak frequencies, and self-Doppler erasure using the correction coefficient An active sonar device characterized by comprising a self-Doppler erasing means that performs the operation. 2. The reverberation peak frequency detection means receives a frequency domain signal as input, detects the peak frequency, and detects when the detected peak frequency is continuously generated for a transmission pulse time or longer. And a reverberation signal determining means for determining the detected peak frequency as a reverberation peak frequency, and means for calculating a difference between the reverberation peak frequency and a transmission fundamental frequency.
An active sonar device as described. 3. The peak frequency detecting means receives the frequency domain signal, reads the amplitude for each frequency, and compares the amplitude with a frequency before and after the frequency of interest. 2. The active sonar device according to claim 1, further comprising means for determining a peak frequency when the amplitude of the focused frequency is larger than both of the amplitudes of the frequencies. 4. A transmission signal generating means for simultaneously generating transmission source signals with two different fundamental frequencies, a means for processing a received signal corresponding to the two fundamental frequencies, and a means for processing the two kinds of frequencies. A target echo peak frequency detecting means for detecting a peak frequency of the target echo;
An active sonar device comprising: target Doppler calculating means for inputting two target echo peak frequencies and calculating Doppler of the target echo. 5. The target echo peak frequency detecting means receives the received frequency domain signal, detects peak frequency, and determines continuity of the detected peak frequency. A target echo signal determining unit that determines the detected peak frequency as a target echo peak frequency when the transmission echo time is equal to or shorter than the transmission pulse time, and a unit that calculates a difference between the target echo peak frequency and the transmission fundamental frequency. The active sonar device according to claim 4, characterized in that: 6. The peak frequency detecting means receives the frequency domain signal, reads the amplitude for each frequency, and compares the amplitude with frequencies before and after the frequency of interest. 5. The active sonar apparatus according to claim 4, further comprising means for determining a peak frequency when the amplitude of the frequency of interest is larger than both of the amplitudes of the frequencies.