JPS6411151B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sonar target display device, and in particular, the deviation angle from the center azimuth of each target point, which is determined from the phase characteristics of the cross-correlation circuit output of two received beam outputs directed toward the target, is calculated by 1. By approximating with the following equation, recalculating the deviation angle using this linear equation, finding the spread in the target azimuth direction from the deviation angle, and further superimposing the amplitude of the cross-correlation circuit output on this and displaying it. The present invention relates to a sonar target display device that makes it possible to clearly determine the shape of a target and the direction (opposition) of the target as seen from an observation point.

Conventionally, this type of target display device performs a cross-correlation calculation of the output of two received beams directed toward the target.
The azimuthal spread of the target was directly determined and displayed from the phase value. However, the above-mentioned cross-correlation phase value has disturbances due to the effects of noise, reverberation, differences in propagation paths, etc., and errors in the receiving circuit and arithmetic circuit.

For this reason, as shown in Figure 1, the output display results show that the targets are scattered and their shapes cannot be clearly determined. This method has the disadvantage that even if a straight line is drawn, an accurate slope cannot be obtained.

The present invention provides a phase fitting circuit that approximates the deviation angle from the center azimuth of each target point obtained from the phase characteristics of the output of the cross-correlation circuit using a linear equation, and a spread calculation circuit that calculates the spread in the azimuth direction using the approximated deviation angle. By providing an amplitude superimposing circuit that superimposes and displays the amplitude of the output of the cross-correlation circuit on the spread in the azimuth direction, scattering of the target of the calculation results is prevented, thereby solving the above-mentioned drawbacks.

Next, one embodiment of the present invention will be described with reference to the drawings.

FIG. 2 is a block diagram of an embodiment of the present invention. In FIG. 2, a sound wave from a target is converted into an electric signal by an acoustic-electric converter 1, and sent to a preamplifier circuit and an analog-to-digital (A/D) converter circuit 2, where it is converted into a digital signal. The digitized received signal is formed in a phasing circuit 3 into two receiving beams, left and right, each having the same characteristics for one direction, and sent to a cross-correlation calculating circuit 5 via a filter circuit 4.

Now let the left and right beam outputs l _L and l _R represent l _L = x _L + jz _L ...(1) l _R = x _R + jz _R ... (2) where j is (j) ² = -1. The cross-correlation output l _RL of the left and right beams is obtained from the following formula l _LR = _L・_R ^* = 1/2 ( _L + _L ) ( _R
- _R ) = 1/2 ( _L・_R + _L・_R ) +j1/2 ( _R・_L − _L・_R )=x _LR +j
z _LR ...(3) However, l _R ^* represents the complex conjugate of l _R , and the symbol ^- represents the time average.

Letting the phases of the left and right beam outputs be φ _L and φ _R , respectively, tanφ _L = z _L /x _L ……(4) tanφ _R = z _R /x _R ……(5) Also, the phase of the correlation output φ _LR is It is expressed as

Considering the phase difference φ _L −φ _R between the left and right beam outputs, tan(φ _L −φ _R )=tanφ _L −tanφ _R /1+tanφ
_L tanφ _R = ZL/XL-ZR/XR/1+ZL/XL・ZR/XR=x _R・z
_L −x _L・z _R ／x _L・x _R +z _L・z _R ...(7) If we average equation (7) and compare it with equation (6), ( _L − _R ) = tanφ _LR ...(8 ), and the amplitude of the correlation between the left and right beams and the phase difference between the left and right beam outputs can be obtained as the output of the cross-correlation circuit 5.

Next, it will be explained with reference to FIG. 3 that the phase difference between the left and right beam outputs represents the opposition of the target.

In FIG. 3, points L and R are the receiving points of the left and right beams, respectively, and AB is the target. However, target AB is L,
With respect to R, it is assumed that the reflected sound waves from any point on AB are sufficiently far away at points L and R to be considered as plane waves.

Now, the reflected sound wave from one end A of target AB is at point L,
Considering the case where the reflected sound wave is incident on R, the reflected sound wave is considered to be a plane wave, so it is incident on the surface LR with a deviation angle of θ, and the incident wave at point L is smaller than the incident wave at point R (φ _L −
The phase is delayed by φ _R ). This phase difference (φ _L
-φ _R ) can be obtained from the cross-correlation output of the left and right beam outputs as described above.

If (φ _L −φ _R ) is found, (φ _L −φ _R )=2πdsinθ/λ ...(9) Therefore, the deviation angle θ from the central direction is θ=sin ^-1 {λ(φ _L − It can be obtained as φ _R )/2πd} ...(10). However, λ is the wavelength of the signal. From this, the extent L _X of the target point A in the azimuth direction can be determined from the distance L _Y of the point A determined from the propagation time of the sound wave using the following equation. distance here
L _Y is the distance between the observation point (the center of points L and R) and point A, as shown in FIG.

_{L _}
By calculating the spread in the azimuth direction using equation (11) from the reflected sound wave signals from each point of be able to.

However, the phase difference obtained from equation (6) includes disturbances due to noise, reverberation, propagation path differences, receiver circuit and calculation errors, etc., and if used as is, it will not reach the target as shown in Figure 1. It often does not show a clear form or correct countermeasure. Therefore, in the present invention, returning to FIG. 2, the amplitude of the correlation output, which is the output of the cross-correlation calculating circuit 5, and the phase difference between the left and right beam outputs are temporarily stored in the memory circuit 6, and then sent to the phase shifting circuit 7.

The phase fitting circuit 7 approximates the target deviation angle from the phase of the cross-correlation using a linear equation. In other words, since the target targeted by a sonar is generally considered to have a linear shape as shown in the example in Figure 3, the deviation angle determined from the left and right beam phase difference of the reflected waves at each target point also changes linearly. I think it can be approximated by a linear equation.

The phase fitting circuit 7 performs the following calculation using the amplitude and phase of the cross-correlation stored in the memory circuit 6, and approximates θ in equation (10) by a linear equation using the method of least squares.

θ(i)=sin ⁻¹ {λφ _LR (i)/2πd} (12) where the subscript i represents the i-th sampling of the digitized signal.

Now, if the number of samplings used for linear equation approximation is N, then θ'=aL _Y +b...(13) Then, a, b are a=ρσ _O '/σ _LY , b=-aμ _LY + μ _O ′, ρ is the correlation coefficient, σ _O ′ and σ _LY are the variances of O′ and L _Y , respectively, and μ _O ′ and μ _LY are the variances of O′ and L Y, respectively.
O′, is the average value of L _Y. Therefore, a and b are obtained as the following equations (14) and (15). Regarding these points, please refer to "Statistical Processing of Random Data" published by Baifukan, published by JS Bendatsu. Co-authored by AG Pearsol (translated by Hidekatsu Tokumaru et al.), pages 127-128.

b=-a・(1/N _h+N-1 〓 ^i=h L _Y (i)) +(1/N _h+N-1 〓 ^i=h θ(i)) ……(15) (13 ) and the amplitude of the correlation output are sent to the spread calculation circuit 8.

The spread calculating circuit 8 uses θ'(i) to calculate the spread of each target point in the azimuth direction according to the following equation.

_{L _} The amplitude of the cross-correlation circuit output expressed by the length of the screen in the vertical direction is superimposed on the spread of the data) in the azimuth direction, and the result is sent to the display 10 for display. The result is improved to clearly represent the shape of the target, as shown in the example of the display shown in FIG. 4, and to more accurately represent the opposing position of the target.

As explained above, the present invention aims to achieve two goals.
In a sonar display device that displays the shape of a target and its opposition using the cross-correlation output of two beams, the target deviation angle determined from the phase characteristics of the cross-correlation circuit output is
By adding a phase fitting circuit that approximates the following equation, a spread calculation circuit that calculates the spread in the azimuth direction from this approximate value, and an amplitude superimposition circuit that superimposes and displays the amplitude of the cross-correlation circuit output on the spread in the azimuth direction. This has the effect of clearly displaying the shape of the target and accurately displaying the opposing force of the target.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of a display by a conventional display device, where the X-axis and Y-axis both represent distance, and the length of the vertical line represents the magnitude of amplitude. Fig. 2 is a block diagram of an embodiment of the present invention, Fig. 3 is an explanatory diagram of a method for determining the spread of a target in the azimuth direction from the phase difference between two received beams, and Fig. 4 is an illustration of a method using the present invention. It is a figure showing an example of a display. DESCRIPTION OF SYMBOLS 1... Acoustic-electric conversion unit, 2... Preamplifier circuit and A/D conversion circuit, 3... Phaser circuit, 4... Filter circuit, 5... Cross-correlation calculation circuit, 6... Memory circuit, 7... Phase fitting circuit, 8...
Spread calculation circuit, 9... Amplitude superimposition circuit, 10...
display.

Claims (1)

[Claims] 1. In a sonar target display device that determines the position and orientation of a target by cross-correlating the outputs of two received beams directed toward the target, and displays the same,
A phase fitting circuit that approximates the deviation angle from the center azimuth of each target point obtained from the phase characteristics of the beam cross-correlation circuit output using a linear equation, and a spread calculation circuit that calculates the spread of the target in the azimuth direction from this approximated deviation angle. and an amplitude superimposition circuit that superimposes and displays the amplitude of the output of the cross-correlation circuit, so that the shape and direction of the target can be clearly determined.