JPS6352346B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sonar target display device, and more particularly to a sonar target display device that processes sonar echoes received by a split beam and displays them as video signals on a CRT or the like.

When receiving a sonar target signal, the outputs of multiple electroacoustic transducers, that is, receivers, are phased to form a plurality of split beams having two equal reception beams on the left and right sides in any direction. The split beam reception method is well known these days.

FIG. 1 is a diagram showing the principle of operation of the split beam reception system.

In order to explain the operating principle, Fig. 1 takes as an example a set of split beams consisting of two left and right reception beams, but the number of split beams is , can be set in any number and in any direction as desired.

In Figure 1, T1, T2, T3, T4 and T1', T2', T3', T4' indicate receiver groups arranged in an equicircular arrangement and at equal intervals, and the reference direction of the receiver group is Y. Assume that they are arranged symmetrically about the '-Y'' axis, for example, four on each side.
It indicates a direction perpendicular to the Y'' axis, and this intersection point O is the center point of the arrangement of the above-mentioned receiver group.

In principle, these receiver groups may be arranged in a circular arrangement, a linear arrangement, or any other arrangement state, and the number thereof can be set arbitrarily.
The receiver group on the right half centered on the Y'-Y'' axis, i.e., T1, T2, T3, T4, and the receiver group on the left half, i.e., T1', T2', T3', T4' are the same. For example, for the outputs of receivers T1, T2, T3, and T4,
The output is phased by adding a time delay difference caused by a delay circuit or weighting by a weighting function, etc., depending on the distance difference from the X″ axis, that is, the phase difference when receiving the input. Instrument group T1, T2, T
3. The combined reception directivity of T4 is as shown in A, and in exactly the same way, the receiver groups T1', T2', T3', T
The combined received wave directivity obtained by 4' is as shown in B,
The reception directivity characteristics are shown with O' and O'' having a distance of d on the X'-X'' axis as the respective reception center points.

Clearly, the receive beams from the two receive directivity have a common beam range, and the incoming echoes received by this common portion are subjected to cross-correlation processing as described below.

In this case, two receiver groups T1, T2, T3, T4 and T4 are used to form the two split beams.
1', T2', T3', and T4' are used independently on the left and right sides as in a, but they can be used in a way such that one or more receivers overlap each other, as in b. But of course I couldn't use my index finger to support it. As will be described later, the interval d is related to the azimuth accuracy with respect to the sonar target, and if the phasing contents are the same, it is determined by how the receiver group is used, the number, etc. Incidentally, as described above, any plurality of such split beams can be formed in all desired directions.

Reception using such a split beam has the following characteristics compared to reception using a single receiving beam normally used in sonar reception.

In other words, in addition to target amplitude information, phase difference information is obtained by cross-correlation calculation of the received signals using the common range of the two receiving beams directed toward the target, and the calculation accuracy of this information depends only on the processing accuracy of the processing circuit. Therefore, it is easy to improve the detection accuracy of sonar targets.

In addition, the phase difference information obtained with this split beam includes the motion of the sonar target, the multipath effects of the reflected echoes from the sonar target, the motion of the platform on which the sonar is mounted, and the effects of the sonar target echoes. Although fluctuations that occur in response to the S/N ratio of signal S to noise N are added, these are small in the case of the phase difference value of the sonar target, and are small in the case of the phase difference value of reverberation and noise. It has the characteristic that it is usually much larger, and by utilizing these characteristics, it is possible to construct a receiving apparatus having a detection function superior to that of the ordinary one-beam receiving system.

However, in this type of conventional split beam receiver, the amplitude information is obtained by adding the amplitude information of the left and right receiving beams of the split beam, and the azimuth information is obtained by detecting phase difference information between the left and right receiving beams. Since processing is performed only by displaying the echo on the screen using the input sonar target echo, reverberation and noise input are output with the same processing content, and these are displayed as a large number of pseudo echoes. This has the disadvantage that it often appears on the display surface, deteriorating the degree of signal discrimination on the display surface, so-called recognition differential, and making it extremely difficult to detect the target.

The purpose of the present invention is to eliminate the above-mentioned drawbacks, to sequentially sample the phase difference information obtained by the split beam reception method at time intervals that can be arbitrarily specified in advance based on the operational conditions of the sonar, and to analyze the phase difference information for each of these specific time intervals. Display of pseudo echoes due to reverberation and noise can be achieved by providing a simple means of determining the interval error variance of phase difference information, determining the presence or absence of echo input from the sonar target from this value, and displaying this only when an echo is input. To provide a sonar target display device which greatly improves the recognition differential and makes it extremely easy to detect a sonar target.

The device of the present invention is a sonar target display device that receives and displays a sonar target signal, in which the outputs of a plurality of electroacoustic transducers are phased to have equal reception directivity in any direction. a split beam forming means for forming a plurality of left and right reception beams (split beams); a correlation calculation means for calculating a correlation between the left and right reception beam outputs obtained by the split beam formation means; a phase difference detection means for determining the phase difference of the sonar target signal from the output obtained by the calculation means; an output detection means for outputting the azimuth and amplitude of the sonar target from the phase difference obtained by the phase difference detection means; an interval error variance calculation means for sequentially sampling and outputting the error variance on the time axis of the phase difference obtained by the phase difference detection means in time intervals that can be arbitrarily specified in advance from sonar operating conditions, etc.; Compare the interval error variance output by the variance calculation means with a threshold value that can be specified in advance from sonar operating conditions, etc., and perform the above-mentioned only when the sonar target signal is input such that the interval error variance is equal to or less than this threshold level. and threshold setting means for displaying the output of the output detection means.

Next, the present invention will be explained in detail with reference to the drawings.
FIG. 2 is a block diagram showing one embodiment of the present invention.

The transducer 1 for transmitting and receiving waves has N electroacoustic transducer elements arranged in equal circles and at regular intervals, and in the case of receiving waves, these N electroacoustic transducers are used to form a split beam. The conversion elements are connected to output the same number of N outputs corresponding to the right and left receiving beams of the split beam for each specific direction. The number of outputs M of the electroacoustic transducer elements corresponding to the specific direction and right and left receiving beams that form this split beam depends on the characteristics of the split beam to be formed, the arrangement conditions of the electroacoustic transducer elements, etc. It can be determined arbitrarily. The output electrical signals that these electroacoustic transducers operate as receivers are sent to the transducer 1.
After being amplified to the required level by the built-in input amplification circuit of the split beam, S receiver output groups 101-1M (R ), 101-2M
(R), 101-3M (R), ......101-SM
(R) and M for left receive beamforming, respectively.
S receiver output group 101 including S receiver outputs
-1M(L), 101-2M(L), 101-3M(L),...
. . . is sent to the split beam forming circuit 2 as 101-SM(L), etc. In this case, for example, the receiver outputs 101-1M(R) and 101-1M(L) are
As shown in FIG. 1, each consists of the outputs of M receivers that form the right and left beams of the split beam formed in the reference direction of the transducer 1, and in this embodiment, such M The individual receiver outputs are combined in all directions of the transducer 1 so that all directions are covered by the split beam.

The total circumference of 360 degrees of the transducer 1 is divided by the overlapping angle of the right and left receiving beams of one split beam formed by combining the M right and left receivers determined in this way. The number S corresponds to the total number of split beams consisting of a pair of right and left receive beams. Therefore, the outputs S101-SM(R) and S101-SM(L) of the transducer 1 are S101-SM(R) and S101-SM(L).
This becomes the output for the second split beam formation.

The split beam forming circuit 2 includes an A-D converter that converts these analog input signals into digital signals, as well as a phasing circuit, a bandpass filter, etc. for forming the split beam. The received signal is filtered by a bandpass filter whose passband is the used bandwidth as an output corresponding to the two left and right receiving beams with equal characteristics formed in the phasing circuit. Input 101-1M
(L) is the right (R) receiving beam output 201-1 respectively.
A, left (L) is sent to the correlation calculation circuit 3 as a received beam output 201-1B. Other inputs of split beam forming circuit 2, 101-2M(R), 101-
2M(L), 101-3M(R), 101-3M(L),...
... 101-SM (R), 101-SM (L), etc., in exactly the same way, right (R) and left, respectively.
(L) receiving beam output 201-2A, 201-2
B, 201-3A, 201-3B, 201
The output signals are sent to the correlation calculation circuit 3 as S split beam output pairs such as -SA and 201-SB. This split beam forming circuit 2 has a phasing circuit for split beam forming, and this phasing circuit has a phasing circuit for forming a split beam. It has a built-in delay circuit that provides a delay amount corresponding to the phase difference determined by the arrangement conditions of the By setting the above-mentioned delay amount, weighting function value, etc., a split beam having desired characteristics can be arbitrarily formed.

The right and left receiving beams of this split beamforming circuit 2 are output pairs, e.g. 201-1A and 201-1B are complex functions E _R and
It can be expressed as E _L and shown by the following equations (1) and (2). This means that the other receive beam power 2
01-2A, 201-2B, 201-3A, 20
The same applies to 1-3B, 201-SA, 201-SB, etc.

E _R =X _R +jY _R …(1) E _L =X _L +jY _L …(2) In equations (1) and (2), X _R and X _L are real parts, jY _R ,
jY _L indicates the imaginary part.

The correlation calculation circuit 3 performs a cross-correlation calculation of the right and left receiving beam outputs as shown in equations (1) and (2), which corresponds to the common range of the split beams shown in Figure 1. This corresponds to performing multiplication. In addition, such cross-correlation calculations are performed using (1) and
Processing can be carried out by multiplying one of the complex functions shown in equation (2) by the _complex conjugate function of the other complex function. It has a function generation circuit, a multiplication circuit, an integration circuit, etc., and these perform cross-correlation of the right and left receiving beam outputs by multiplying the complex conjugate functions of E _R and E _L.

The complex conjugate function E _L ^* of E _L can be expressed by the following equation (3).

E _L ^* = X _L −jY _L …(3) Therefore, the right and left receiving beam outputs 201-1A
And the cross-correlation output L _RL of 201-1B etc. is as follows
It is shown by equation (4).

l _RL = _R・_L ^* = ( _R + _R ) ( _L − _L ) = ( _{R L} + _{R L} ) + j ( _{R L} − _{R L} ) = X _RL + jY _RL …(4) In equation (4), X _RL and Y _RL are respectively ( _R
X _L + Y _R Y _L ) and ( _{R L} − _{R L} ) are shown. From this equation (4), the phase angle _RL of l _RL can be expressed by the following equation (5).

In equations (4) and (5), the symbol - indicates time average. The output of the correlation calculation circuit 3 is shown in the above equation (4), for example, the inputs 201-1A and 201-
A correlation output signal 301-1 is obtained as a correlation output signal for 1B, and a correlation output signal 30 corresponding to other input signals is obtained.
1-2, 301-3, . . . 301-S are output in exactly the same manner and sent to the phase difference detection circuit 4.

For example, the correlation output signal 301-1 is calculated by the division circuit of the phase difference detection circuit 4 according to equation (4).
l Perform division in equation (5) using the real and imaginary parts of _RL to obtain tan _RL , further calculate arctan of this value using a functional calculation circuit, and use this as the phase difference signal 401-1B. The signal is sent to the output detection circuit 5 and the interval error dispersion calculation circuit 6 as a signal. Phase difference signals 401-2B, 401- obtained by input signals 301-2, 301-3, 301-S
The same applies to 3B, 401-SB.

In order to investigate the relationship between this _RL and the phases of the right and left receiving beam outputs, the phases of the right and left receiving beam outputs E _R and E _L shown in equations (1) and (2) are calculated as φ _R and φ _L , this phase difference φ _R −φ _L can be expressed as in the following equation (6) using the real part and imaginary part of equations (1) and (2).

Equations (5) and (6) obviously have the same value, and therefore the following equations (7) and (8) are obtained.

tan _RL = tan(φ _R −φ _L ) …(7) _RL =φ _R −φ _L …(8) In other words, the phase difference _RL of the phase difference signal 401-1B etc. output from the phase difference detection circuit 4 is a split beam. is equal to the phase difference between the right and left receive beam outputs.

Figure 3 shows the electrical phase difference between the received signals by the right and left receiving beams forming a split beam, and
FIG. 3 is a diagram showing the relationship between the split beam phase difference and the incident angle of the received signal, showing the relationship with the incident angle of the received signal.

Points O′ and O″ are reception center points of the right and left beams with spacing d, point O is the midpoint of points O′ and O″,
Line segments X'-X'' and Y'-Y'' indicate the X and Y axes orthogonal to point O.

A sound wave incident from a sonar target P at an azimuth angle θ that is sufficiently far away from points O, O', O'', etc. becomes a plane wave, and therefore, as shown in Fig. 3, the incident waves w, are incident as w′ and w″. Sound wave incident on right beam receiving center point O′
w′ arrives at the left beam receiving center point O″ with a time delay corresponding to the distance O′D from the sound wave w″, which reaches the left beam receiving center point O″.
The time delay corresponding to this O′D is equal to the electrical phase difference φ _R −φ _L shown in equation (8), and O′D is equal to ∠O′O″D when θ
Therefore, it can be expressed as 2π·d·sinθ/λ (λ is the wavelength of the received sound wave), and the following equation (9) can be obtained from these relationships.

φ _R −φ _L =2π・d・sinθ/λ (9) From this equation (9), the incident angle of the sound wave, that is, the target azimuth angle φ can be expressed by the following equation (10).

θ=sin ^-1 {λ・(φ _R −φ _L )/2πd} …(10) In equation (10), λ and d are known values in advance,
Therefore, by knowing the electrical phase difference φ _R -φ _L of the echoes of the sonar target received by the right and left receiving beams forming a split beam, the azimuth angle θ of the target can also be determined.

The output detection circuit 5 includes a buffer memory, a numerical arithmetic circuit, a multiplication circuit, etc., and receives S phase difference signals 401 from the phase difference detection circuit 4 under the control of a built-in program. -1B,401
-2B, 401-3B, ......401-SB, that is, _RL for each direction and the corresponding amplitude information signals 401-1A, 401- shown by equation (4)
2A, 401-3A, ......401-SA are input one after another, stored in the buffer memory and read out, and the absolute value amplitude E ₀ of the input signal for each direction is calculated using the following equation (11). Calculate.

E ₀ =X _RL /cos _RL …(11) In this case, the phase difference _RL is calculated by the functional calculation circuit.
cos _RL and then 1/cos _RL , and then multiplied by X _RL in a multiplication circuit to calculate E ₀ .

In addition to the above-mentioned E ₀ obtained in this way, the output detection circuit 5 receives phase difference signals 401-1B, 40
1-2B, 401-3B, 401-SB, etc., using _{the RL} for each direction, that is, φ _R −φ _L , calculate the azimuth θ for each direction shown in equation (10) using a function calculation circuit, A multiplication circuit or the like calculates the output including these _E0 and θ for each direction as a video output signal 5.
01-1, 501-2, 501-3,...50
Output as 1-S.

However, these video output signals 501
-1,501-2,501-3,...501-
If S and the like are displayed as they are, reverberation and noise will be displayed along with the necessary signals, often making it extremely difficult to detect the target.

Therefore, in this embodiment, a gate circuit 8 is provided that sends the output of the output detection circuit 5 to the CRT 9 only when a desired signal is output, and in order to turn on the gate of this gate circuit 8 only when an echo is input, The error variance calculation circuit 6 and the threshold value setting circuit 7 are provided to eliminate the above-mentioned problems.

FIG. 4 is a received signal characteristic diagram showing general characteristics of the phase difference _RL of the received signal and the absolute amplitude E ₀ in split beam reception.

Figure 4A is a general characteristic diagram of phase difference _RL .
Diagram B shows a general characteristic diagram of the absolute value amplitude E ₀ . Each point shown in the diagram of FIG. 4A indicates a sample value of the phase difference _RL .

As mentioned above, when receiving a sonar echo, in addition to the desired echo, undesired signals such as reverberation and noise are simultaneously input, and among these, those having the same frequency band as the desired input echo are processed and output as is along with the echo. and is displayed as a pseudo echo.

In this case, the variation in the phase of the input data that is sampled one after another at a specific time interval,
That is, in terms of fractions, as a matter of course, echoes have the smallest dispersion, followed by reverberation that has coherence with the input echo, and then noise. Therefore, knowing the magnitude of dispersion means knowing the difference between echo and non-echo.

In Figure 4A, the variance of the phase difference _RL is at time t ₀
The time t ₁ before and after receiving the echo is
and much smaller than for t ₂ . Figure 4A
In this case, the sample data of the phase difference information at time t ₀ clearly shows continuity, and the slope of the straight line formed by these data changes depending on the split beam direction and the target posture.

In addition, Figure 4B shows the temporal change in the absolute absolute value level. At time t ₀ when an echo is input, the amplitude value E ₀ shows the maximum value, but even at time t ₁ when no echo is input, due to reverberation, noise, etc. Some echoes with large amplitude values appear, and these are displayed as false echoes.

From these facts, it can be seen that it is sufficient to know the variance of the sampled input data and output and display it only during time _t0 , and that this variance can be obtained by knowing the variance of the phase difference _RL .

The interval error variance calculation circuit 6 in FIG. 2 includes a sampling circuit, a variance calculation circuit, a correlation coefficient calculation circuit, etc., and calculates and outputs the error variance of the phase difference _RL .

In this case, the phase difference _RL for each direction sent out from the phase difference detection circuit 4 is input one after another, and this is sampled at a time interval that can be arbitrarily specified from the operational conditions such as the sonar's transmission pulse width. Compute the interval error variance for each.

This interval error variance V is expressed by the following equation (12).

V=σ _y ² (1−ρ _xy ² ) …(12) As shown in equations (13) and (14) described later, in equation (12), σ _y ² is the interval variance of the phase difference, and ρ _xy is the time interval variance. The correlation coefficient between the time sample characteristics and phase difference characteristics of is shown. The value of ρ _xy differs greatly between when the phase difference _RL changes linearly with time, as at time t ₀ in FIG. 4A, and when it changes randomly, such as at times t ₁ and t ₂ . When time t ₀ changes linearly, the value of ρ _xy becomes maximum, that is, 1, and the value of V in equation (12) becomes significantly smaller than the values in the time domain at t ₁ and t ₂ before and after. . Therefore, by setting the value of V in advance to a threshold level that can be specified depending on the purpose, the dispersion of the phase difference _RL can be adjusted to the direction of the target, as at time t ₀ in Fig. 4A. , it is possible to determine that it is a straight line with an inclination determined by the body position, etc., and by gating the output of this time output detection circuit 5 on, it is possible to display the output only for echoes. .

σ _y ² and ρ _xy in equation (12) are each expressed as follows (13)
and (14).

In equations (13) and (14), n indicates the number of samples in any specified time interval, y _i is the phase information included in each time interval, and y i is the arithmetic mean value thereof.

Furthermore, in equation (14), σ _x is the standard deviation of the number of sample numbers corresponding to the elapsed time within the above-mentioned time interval or the order of the information to be inputted one after another, and σ _y is the phase information obtained in each time interval. standard deviation,
xi indicates the time corresponding to yi or the sampling number corresponding to the order of the next input information, and xi indicates the arithmetic mean value thereof.

The interval error variance calculation circuit 6 superimposes and samples the input phase difference signal _RL in a predetermined time interval and with a delay of a desired time at a time in a sampling circuit corresponding to the time series, and calculates these sample values. From this, the variance σ _y ² shown by equation (13) is obtained by calculation using a dispersion calculation circuit, etc., and the correlation coefficient xy shown by equation (14) is obtained by calculation by a correlation coefficient calculation circuit, etc., and from these, the correlation coefficient _xy is obtained by calculation by equation (12). Compute and output the interval error variance V.

This interval error variance V is generated by the interval error variance signal 601-
1,601-2,601-3,...601-S
etc. are input to the threshold value setting circuit 7.

The threshold value setting circuit 7 compares the preset threshold value and the input section error variance V by a comparison circuit,
A gate signal for this time period is formed only when the value falls below the threshold value as a result of this size determination, and this is used as the threshold value setting signal 701-1, 701-2, 701-3 corresponding to the split beam direction for each direction. ,...
...701-S and the like to the gate circuit 8.

The gate circuit 8 receives this input, turns on this gate circuit connected to the output circuit of the output detection circuit 5 only when an input echo is detected by the logic gate circuit, and outputs the video output signals 501-1, 501-.
2,501-3,...501-S etc.
Causes the CRT9 to transmit and display echoes.

In this way, by displaying the azimuth angle and absolute amplitude information of the echo only in the time period corresponding to the echo input, it is possible to perform a display in which the effects of pseudo echoes due to reverberation and noise are significantly reduced.

The present invention sequentially samples target phase information obtained by a split beam reception method in time intervals that can be arbitrarily set in advance based on sonar operating conditions, etc., and calculates the interval error variance of the phase information for each of these specific time intervals. The basic feature is that the presence or absence of an echo input is determined based on this dispersion and the output is displayed only when an echo is input, and various modifications of this embodiment can be considered.

For example, in this embodiment, the right and left split receiving beams formed by the split beam forming circuit 2 utilize the left and right electroacoustic transducers of the transducer 1 independently. The input amplifier circuit built into the transducer 1, the A-D converter included in the split beam forming circuit 2, etc. can be used independently or integrated into independent structures. It is also possible to easily implement the following.

In addition, in this embodiment, the absolute value amplitude of the echo obtained by the output detection circuit 5 is calculated using equation (11), but this uses the X _RL and Y _RL of equation (4) and squares them respectively. It is clear that the same result can be obtained even if the sum is square rooted.

Further, the threshold value setting circuit 7 also sets the echo judgment level using one threshold value in this embodiment, but for example, this threshold value can be set to high,
It is clear that it is possible to easily set the error distribution to three levels, medium and low, and use the section error variance in accordance with the purpose of displaying the sonar signal.

It should be noted that video output signals 501-1, 501-2, 501-3, . . . are output from the output detection circuit 5.
...It is easy to use only the E ₀ shown in equation (11) included in 501-S to electronically switch and display these, or to add interpolation between the outputs of these E ₀ and display them. Furthermore, it is clear that it is also possible to easily implement a method in which the average value of the phase within the interval is determined by the least squares method in the interval error variance calculation circuit 6, and the variance of the deviation from this value is determined. All of the above can be easily implemented without detracting from the spirit of the present invention.

As explained above, according to the present invention, the phase information of the target obtained by the split beam reception method is sampled sequentially in time intervals that can be arbitrarily set in advance based on the operational conditions of the sonar, and By providing a simple method that calculates the interval error variance of the phase difference information, determines whether there is an echo input from the sonar target from this value, and displays this only when an echo is input, it is possible to eliminate false echoes caused by reverberation, noise, etc. This has the effect that it is possible to realize a sonar target display device that avoids display, significantly improves the recognition differential, and makes it extremely easy to detect sonar targets.

[Brief explanation of drawings]

Fig. 1 is an operating principle diagram showing the principle of operation of the split beam reception system, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 is a diagram showing the right side of the split beam in the embodiment of Fig. 2. and a diagram showing the relationship between the electrical phase difference between the left receiving beam and the received signal incident angle, and FIG. 4 shows the general characteristics of the phase difference and absolute value amplitude of the received signal due to split beam reception in the embodiment of FIG. 2. It is a signal characteristic diagram. In Fig. 2, 1... transducer, 2... split beam forming circuit, 3... correlation calculation circuit, 4...
...Phase difference detection circuit, 5...Output detection circuit, 6...
...Interval error variance calculation circuit, 7...Threshold value setting circuit,
8...Gate circuit, 9...CRT.

Claims (1)

[Claims] 1 In a sonar target display device that receives and displays a sonar target signal, the outputs of a plurality of electroacoustic transducers are phased to form two left and right reception beams each having equal reception directivity in any direction. split beam forming means for forming a plurality of split beams (split beams); a phase difference detection means for determining the phase difference of the sonar target signal from the output obtained; an output detection means for outputting the azimuth and amplitude of the sonar target from the phase difference obtained by the phase difference detection means; and the phase difference detection means. an interval error variance calculation means for sequentially sampling and outputting the error variance on the time axis of the phase difference obtained by the method in time intervals that can be arbitrarily specified in advance from sonar operating conditions, etc.; and an output of the interval error variance calculation means. The output detection means outputs the output of the output detection means only when the sonar target signal is input so that the interval error variance is compared with a threshold level that can be specified in advance from the sonar operating conditions, etc. 1. A sonar target display device comprising: threshold setting means for displaying a threshold value.