JPH0766050B2 - Direction measurement method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a direction measuring system,
In particular, it relates to an azimuth measuring method for measuring the arrival azimuth of a target signal received by a directional sonobuoy.

[0002]

2. Description of the Related Art Directional sonobuoys used to measure the arrival direction of a target signal have an OMNI hydrophone having a uniform directivity in all directions and an 8-shaped directivity having a maximum receiving sensitivity in the north-south direction. It has an NS hydrophone and an EW hydrophone that has a maximum sensitivity of 8 in the east-west direction. The directivity of each of these hydrophones is shown in FIG.
As shown in.

That is, the OMNI hydrophone is shown in FIG.
As shown in FIG. 2, the NS hydrophone has a uniform directivity in all directions, so-called OMNI directivity. As shown in FIG. 2 (b), the NS hydrophone has a so-called N-shaped maximum sensitivity axis of the 8-shaped directivity in the north-south direction.
The EW hydrophone has the S directivity, and has the so-called EW directivity, which is the maximum sensitivity axis of the 8-shaped directivity in the east-west direction, as shown in FIG.

The target to be acquired by passive reception with a directional sonobuoy having such a directivity is 360 °.
2 exists in any azimuth, but in FIG. 2, the target exists in the angular direction in which the azimuth B is tilted from the magnetic north N to the east E in the first quadrant.

Now, let A be the strength of the target signal, N _OM ,
If N _NS and N _EW are the intensities of underwater noise received by the OMNI hydrophone, NS hydrophone and EW hydrophone, respectively, the received signal of the OMNI hydrophone is O.
The MNI reception signal R _OM is represented by the equation (1), the NS reception signal R _NS which is the reception signal of the NS hydrophone is represented by the equation (2), and the EW reception signal R which is the reception signal of the EW hydrophone.
_EW is expressed by equation (3).

R _OM = A + N _OM (1) R _NS = A cos B + N _NS (2) R _EW = A sin B + N _EW (3) Conventional direction measuring method for measuring the arrival direction of the target signal received by the directional sonobuoy For example, as shown in FIG. 3, it is configured to include a quadrant determination unit 1 and an orientation determination unit 2.

In the quadrant determination unit 1, the directivity sonobuoy is set to O.
Upon receiving the MNI received signal R _OM , the NS received signal R _NS, and the EW received signal R _EW , the phase determination of R _NS and R _{EW with} respect to R _OM is performed, and the determination result is used as the quadrant output Q to determine the azimuth determination unit 2
Output to.

The quadrant output Q is determined based on the following four phase relationships. That is, (1) R _NS and R _EW are R _OM
When in phase with Q = 0 °, the first quadrant, (2) R _NS is R
When in phase with _OM , Q = 90 ° and second quadrant, (3) R _NS
The third quadrant Q = 180 ° when the R _EW are both R _OM reverse phase, (4) when R _NS is at R _OM in phase R _EW of R _OM and opposite phase Q = 270 ° The arrival azimuth of the target signal is determined by adding and setting the fourth quadrant and the angles at which each quadrant starts, and adding and setting an apparent azimuth that does not take the quadrant into consideration.

The azimuth determining section 2 outputs the quadrant output Q and OMNI.
Received signal R _OM , NS received signal R _NS , and EW received signal R _EW
Based on the above, the following equation (4) is executed to calculate the arrival azimuth angle B _A of the target signal.

[0010]

Symbols of numerator and denominator in parentheses in equation (4)
OMNI received signal R _OM to EW received signal R _EW and NS
It represents the time average value of the _product of the received signal R _NS . The time average values of these numerator and denominator are (5) and
It is shown by the equation (6).

[0012]

[0013]

The symbols − included in the equations (4) and (5) also represent time average values.

[0015]

In the above conventional azimuth measuring method, when the underwater noises N _OM , N _NS and N _EW included in the equations (1), (2) and (3) are uncorrelated with each other. Is obtained by setting the averaging time in equations (5) and (6) to be sufficiently long, so that A · N _EW , N _OM · AsinB, N _OM ·
The time averages of N _EW , A · N _NS , N _OM · Acos B, and N _OM · N _NS are asymptotic to zero because the statistical mean of the underwater noises N _OM , N _EW, and N _NS is zero.

Therefore, the equation (4) can be approximated to the equation (7) by averaging for a predetermined average time, and the arrival direction B _A of the target signal is calculated.

[0017]

On the other hand, if there is any correlation between the underwater noise N _OM and N _NS and N _EW , including the occurrence of marine conditions and marine life, the average time in equations (5) and (6) is If taken long enough, A ・ N _EW , N _OM , AsinB, A ・ N _NS
And the time average values of N _OM · sinB are asymptotic to zero for the same reason as described above, but the time average values of N _OM · N _EW and N _OM · N _NS are asymptotic to the values determined by the respective degrees of correlation.
Expression (4) in which the asymptotic arrival values are C _EW and C _NS can be expressed by the following Expression (8).

[0019]

From the equation (8), the target signal and the arrival azimuth angle B _A are the true target azimuth B due to the influence of the time average value of C _EW and C _NS.
However, there is a problem that the generated error cannot be improved by extending the average time.

The object of the present invention is to solve the above-mentioned problems,
An object of the present invention is to provide an azimuth measuring method in which the occurrence of error is significantly suppressed even when there is some correlation between the underwater noise N _OM and N _NS and N _EW .

[0022]

According to the method of the present invention, an OMNI hydrophone having a uniform directivity in all directions, an NS hydrophone having a figure-eight directivity in the north-south direction, and an OMNI hydrophone in the east-west direction. In a directional sonobuy azimuth measuring method that includes an EW hydrophone having a V-shaped directivity and is capable of knowing the direction of arrival of a target, a frequency signal is received by the OMNI hydrophone, the NS hydrophone, and the EW hydrophone. On the basis of the outputs of the bispectrum estimation unit that analyzes the components and estimates the bispectrum of each received signal by paying attention to the two frequencies of the analyzed frequency components in which the phase has little temporal variation. A quadrant determining unit that determines the quadrant of an incoming sound wave for the directional sonobuoy and sends it out as a quadrant output; And it has a configuration in which a direction determination unit that determines the orientation of the incoming waves to said directional sonobuoy based on force and the output of the bispectral estimator.

According to the method of the present invention, the quadrant output output from the quadrant determination unit is the reception of the NS hydrophone and the EW hydrophone with respect to the bispectrum of the reception signal of the OMNI hydrophone output from the bispectrum estimation unit. The configuration is such that the determination is made based on a combination of states in which the phases of the bispectrum of the signals are in-phase or opposite-phase.

Further, according to the method of the present invention, the azimuth determination of the incoming sound wave in the azimuth determining unit is performed in the quadrant designated by the quadrant output of the quadrant determining unit, with the NS hydrophone output from the bispectrum estimating unit and the quadrant. The azimuth angle in the quadrant of the incoming sound wave is determined based on the ratio of the bispectral output of the received signal by the EW hydrophone.

[0025]

In general, underwater noise is Gaussian and there is no correlation between different frequency components.

On the other hand, the signal emitted by the target often has a correlation between a plurality of frequency components, such as a frequency component caused by interference between the fundamental wave and a harmonic or between a plurality of frequency components.

The bispectrum estimated by the bispectrum estimator, which is a component of the present invention, expresses the correlation between a plurality of frequency components described above, and the target signal is frequency-analyzed to have a substantially constant phase. It is expressed as a value including the product of the spectral intensity of the two frequencies and the conjugate spectral intensity of the sum of the two frequencies and the bispectral noise, and is statistically zero for the underwater noise having Gaussianity,
The target signal having the above-described correlation has a property of having a constant value.

In the present invention, by utilizing the property of the bispectrum, the underwater noises N _OM , N _NS and N _EW are reduced as compared with the target signal, and the influence of the correlation between the underwater noises is suppressed,
The azimuth error caused by this influence is reduced.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In addition to the conventional quadrant judging unit 1 and azimuth determining unit 2 shown in FIG. 3, a bispectral estimating unit directly related to the present invention is provided. 3 is provided.

OM input to the bispectrum estimation unit 3
The NI reception signal R _OM , the NS reception signal R _NS, and the EW reception signal R _EW are expressed by equations (1), (2), and (3), respectively.

The bispectral estimator 1, based on these received signals, calculates the bispectral B _EW bispectral B _OM, the NS received signal by spectrum B _NS and EW received signals OMNI received signal. These bispectrums B _OM and B _EW are respectively expressed by equation (9) and equation (1
0) and equation (11).

The bispectrum estimation unit 3 receives the input OM.
The NI reception signal R _OM , the NS reception signal R _NS, and the EW reception signal R _EW are each subjected to Fourier transform processing to be converted into frequency domain data, and the phase variation is small among the frequency components included in these frequency domain data, and S / The bispectrum B of the OMNI received signal is based on the two frequencies f ₁ and f ₂ which are selected by focusing on the one having a relatively good N, and the spectrum and noise of the three frequency components of the sum f ₁ + f ₂ of these two frequencies. _OM , NS bi-spectral of received signal B _NS and E
The bispectrum B _EW of the W received signal is estimated as in the following equations (9), (10) and (11).

B _OM = X (f ₁ ) ^× X (f ₂ ) ^× X (f ₁ + f ₂ ) + N _BOM (9) B _NS = X (f ₁ ) ^× X (f ₂ ) ^× X ( f ₁ + f ₂ ) cos ³ B + N _BNS (10) B _EW = X (f ₁ ) · X (f ₂ ) · X ^* (f ₁ + f ₂ ) sin ³ B + N _BEW (11) Formulas (9) and (9) In 10) and (11), X (f1
), X (f2) and X (f1 + f2) represent the spectral intensities of the target signal intensity A at frequencies f1, f2 and f1 + f2, respectively, and the symbol * indicates conjugation.
Further, N _BOM , N _BNS and N _BEW each represent a noise component.

That is, the bispectrum is represented by the two frequencies estimated to be emitted by the target, the spectral intensities and conjugate spectral intensities of the frequency of the sum of these two frequencies, and the noise related to these frequency components. Further, the bispectral level noises N _BOM , N _BNS, and N _BEW are expressed by equations (12), (13), and (14), respectively. _{N BOM = X (f 1)} X * (f 1 + f 2) N OM (f 2) + X (f 2) X * (f 1 + f 2) N OM (f 1) + X * (f 1 + f 2) N _OM (f ₁ ) N _OM (f ₂ ) + X (f ₁ ) X (f ₂ ) N _OM ^* (f ₁ + f ₂ ) + X (f ₁ ) N _OM (f ₂ ) N _OM ^* (f ₁ + f ₂ ) + X (f ₂ ) N _OM (f ₁ ) N _OM ^* (f ₁ + f ₂ ) + N _OM (f ₁ ) N _OM (f ₂ ) N _OM ^* (f ₁ + f ₂ ) ... (12) _NBNS = (X (F ₁ ) X ^* (f ₁ + f ₂ ) N _NS (f ₂ ) + X (f ₂ ) X ^* (f ₁ + f ₂ ) N _NS (f ₁ ) + X (f ₁ ) X (f ₂ ) N ^* _NS (f ₁ + f ₂ )) cos ² B + (X ^* (f ₁ + f ₂ ) N _NS (f ₁ ) N _NS (f ₂ ) + X (f ₁ ) N _NS (f ₂ ) N ^* _NS (f ₁ + f ₂ ) + X (f ₂ ) N _NS (f ₁ ) N ^* _NS (f ₁ + f ₂ )) cosB + N _NS (f ₁ ) N _NS (f ₂ ) N ^* _NS (f ₁ + f ₂ ) ... (13) N _BEU = (X (f ₁ ) X ^* (f ₁ + f ₂ ) N _EW (f ₂ ) + X (f ₂ ) X ^* (f ₁ + f ₂ ) N _EW (f ₁ ) + X (F ₁ ) X (f ₂ ) N ^* _EW (f ₁ + f ₂ )) sin ² B + (X ^* (f ₁ + f ₂ ) N _EW (f ₁ ) N _EW (f ₂ ) + X (f ₁ ) N _EW (f ₂ ) N ^* (f ₁ + f ₂ ) + X (f ₂ ) N _EW (f ₁ ) N ^* (f ₁ + f ₂ )) sinB + N _EW (f ₁ ) N _EW (f ₂ ) N ^* _EW ( f ₁ + f ₂ ) ... (14) Here, N _OM (f), N _NS (f) and N _EW (f) are included in the OMNI received signal R _OM , NS received R _NS and EW received signal R _EW , respectively. It is the spectrum intensity at frequency f of underwater noise N _OM , N _NS and N _EW .

The quadrant judging unit 1 is a bispectral estimating unit 3
From the OMNI received signal, NS received signal and EW received signal bispectrum B _OM , B _NS and B _EW ,
The quadrant determination is performed based on the determination whether the phases of B _NS and B _{EW with} respect to the bispectrum B _OM of the received signal are in-phase or anti-phase, and the determination result is output to the azimuth determination unit 2 as a quadrant output Q.

The quadrant output Q has the following four output contents. (1) When B _NS and B _EW are in agreement with B _OM , Q
= 0 first quadrant °, (2) B _NS second quadrant in the Q = 90 ° when B _EW in B _OM and opposite phase of the B _OM in phase, (3) B
Q = 180 ° when _NS and B _EW both have opposite phases to B _OM, and (4) Q = 270 ° when B _NS has the same phase as B _OM and B _EW has opposite phases to B _OM . Specify each of the 4th quadrants with.

The azimuth determining unit 2 executes the calculation of the equation (15) based on the quadrant output Q, the bispectrum B _NS of the NS received signal, and the bispectrum B _EW of the EW received signal to determine the arrival direction of the target signal. Calculate BA.

[0039]

Here, the symbol-indicates the time average value of the bispectrum of the EW and NS received signals.

By the way, the target generates signals of frequencies f ₁ and f ₂ , and these two signals interfere with each other to generate the sum frequency f ₁
When + f ₂ is generated, or when the harmonic components are when f ₁ and f ₂ are equal, f ₁ , f ₂ and f ₁
There is a substantially constant phase relationship between the three frequency components + f ₂ and, therefore, X in equations (9), (10) and (11)
The time average value of (f ₁ ) · X (f ₂ ) · X ^* (f ₁ + f ₂ ) gradually approaches a constant value as the average time lengthens.

Further, underwater noise generally has Gaussianity, and noise components at different frequencies have no correlation. Therefore, the average time of noise represented by the equations (12), (13) and (14) is average. It asymptotically approaches zero with the extension of time. Therefore, by averaging for a predetermined time, the formula (1
5) can be approximated to the equation (16), and the arrival direction of the target signal is calculated.

[0043]

In this way, in the measurement of the target azimuth by the bispectrum, the measurement result is not affected regardless of the correlation between the underwater noises N _OM , N _NS and N _EW .

[0045]

As described above, the present invention remarkably suppresses the influence of underwater noise on the azimuth measurement by utilizing the bispectrum for calculating the arrival direction of the target signal.
This has the effect of significantly reducing the azimuth measurement error.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an azimuth measuring method according to an embodiment of the present invention.

FIG. 2 Directional Sonobui OMNI directivity (a), NS
It is a figure which shows directivity (b) and EW directivity.

FIG. 3 is a block diagram showing a configuration of a conventional azimuth measuring method.

[Explanation of symbols]

 1 quadrant determination unit 2 azimuth determination unit 3 bispectral estimation unit

Claims (3)

[Claims] 1. An OMNI hydrophone having a uniform directivity in all directions, an NS hydrophone having an 8-shaped directivity in the north-south direction, and an EW hydrophone having an 8-shaped directivity in the east-west direction. In the directional sonobuy direction measuring method for determining the direction of arrival of a target, the respective frequency components are analyzed by receiving the reception signals from the OMNI hydrophone, NS hydrophone and EW hydrophone, and the analyzed frequency components Of these, a bispectrum estimation unit that estimates the bispectrum of each received signal by focusing on two frequencies whose phase fluctuations are small, and a quadrant of an incoming sound wave for the directional sonobuoy based on the output of the bispectrum estimation unit. A quadrant determining unit for determining and transmitting as a quadrant output, an output of the quadrant determining unit and a bispectral estimating unit. An azimuth measuring method, comprising: an azimuth determining unit that determines the azimuth of an incoming sound wave with respect to the directional sonobuoy based on the output. 2. The quadrant output output by the quadrant determining section is:
The NS for the bispectrum of the received signal of the OMNI hydrophone output by the bispectrum estimation unit
The azimuth measuring method according to claim 1, wherein the determination is made based on a combination of states in which the phases of the bispectrum of the reception signals of the hydrophone and the EW hydrophone are in-phase or in-phase. 3. The azimuth determination of the incoming sound wave in the azimuth determination unit is performed by the NS output from the bispectral estimation unit in a quadrant designated by the quadrant output of the quadrant determination unit.
The azimuth measuring method according to claim 1, wherein the azimuth measuring method is performed by setting an in-quadrant azimuth angle of an incoming sound wave determined based on a ratio of a bispectral output of a reception signal by the hydrophone and the EW hydrophone.