JPS5848878A - Object discriminating system for active sonar - Google Patents

Abstract

PURPOSE:To easily specify the shapes and positions of objects by periodically projecting pulse-like sound waves to a specific object while changing its bearing slightly, and displaying the objects as spots by the modulation of luminance. CONSTITUTION:An object 4 is properly selected from a PPI display and its distance and bearing are previously informed. Pulse-like sound waves are directionally projected from a sonar. The sound waves are projected to the object 4 from the wave transmitter 3 and the reflected waves from the object 4 are received by a wave receiver 7. A signal received from a phase adjuster 8 adjusting the phases of signals from each receiving element is processed by a received signal processing circuit 9 to obtain a luminance modulating signal to a cathode- ray tube (CRT) display circuit 10. The CRT circuit 10 displays spots on the CRT in accordance with the shape and position of the object on the basis of horizontal and vertical synchronous signals from a control circuit 5.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an active sonar target identification system in which the shape and posture of a target are roughly displayed using brightness modulation.

For example, when detecting the presence or absence of any object in seawater, a sonar as an ultrasonic radar is an effective detection means, but conventionally, even if an object is detected, the detection display is not displayed. Since the appearance was simply a dot-like or rectangular spot, the shape of the object was known! A handful of ml<,
L, therefore, there is a drawback that it is not possible to identify the object.

That is, in the one type of act-up sonar according to the prior art, the correlation between the transmitted wave and the reflected wave from the target object (so-called received echo wave) is calculated, and the correlation output is processed using an appropriate threshold value. The presence or absence of a target was determined by this.

1) Received waves from a great object are displayed as dots or rectangular spots in the PI display image improvement, but such a display shows that the shape of the target is almost TH. It is something.廿/ko, threshold straight (+11 What is 1? The number of spots is not necessarily limited to one, but generally multiple spots are displayed on the screen, but in such a case, which spot is true? It is difficult to determine whether the object is a target object, and in some cases, there is a risk that something other than the true 1'' object may be mistakenly determined as such.

Furthermore, the conventional PPI display also has the disadvantage that when the distance to the interstitial object is short, the spots become densely packed, making it almost useless.

These shortcomings are mostly due to the signal power to 4KI sound power ratio (SN
The cause can be found in the fact that the presence/absence of the target object was completely determined by rough processing using the magnitude of the signal power to residual power ratio (SR ratio) as a clue. In other words, if only the SN ratio or SR ratio, which is a macroscopic ridge, is used, there is a limit to object identification (1), and it is almost impossible to know the general shape of the object, and therefore the nature of the object. It is something.

Therefore, it is an object of the present invention to provide an active sonar target identification method in which the shape and posture of a target can be roughly known.

For this purpose, the present invention provides the following advantages: 1) Since the direction and distance of each target object can be known in advance from the PI light display, when any target object is selected, the direction of the target object is determined in order to scan the target object. A pulsed sound wave is emitted in an appropriate state, and the wave reflected from the target object in response to the sound wave example contains information about the longitudinal shape and posture of the target object. The luminance modulation display allows an outline of the target to be selected to be known.

The present invention will be explained below with reference to FIGS. 1 to 3.

First, FIG. 1 shows a schematic configuration of a sonar according to the present invention together with a target object. In this case, the target 4 is of course selected appropriately from those displayed on the PI), and the distance to the target 4 and its direction d are known in advance.
On the premise that the target object 4 is the target object 4, the sonar is designed to radiate a beam-like sound wave with directionality to the target object 4 in order to capture the target object 4. Of course, the sound wave emission in this case is carried out while changing the azimuth angle by an appropriate magnitude within a predetermined azimuth angle range, and, more importantly, the wavelength of the sound wave is adjusted appropriately considering the distance to the target object 4-. It is set to be determined.

While the sound waves are emitted from the transmitter 3 toward the target 4,
The reflected wave from the target object 4 is received by the wave receiver 7, and the sound waves used in this case are, for example, hyperbolic FM waves. This is a type of FM wave with a constant amplitude and a time function whose frequency is inversely proportional to time, and is known to be unaffected by the Doppler effect. A high-voltage hyperbolic FM signal of one fixed time length is obtained from the hyperbolic FM wave generator 1 at a period To, and when this is applied to the line array type transmitter 3 via the analog shift register 2, a sound wave is generated. It is radiated in a predetermined azimuth direction. Therefore, for example, when the analog shift register 2 is composed of BBD+CCD, if the delay time is changed by controlling the shift clock frequency periodically (To), the sound waves are transmitted within a predetermined azimuth angle range in a so-called sector scanning manner. That is why it is done. Regarding sector scanning, since this is already known as a basic scanning method in ultrasonic inspection, no further explanation is required.

FIG. 2(a) schematically shows a hyperbolic FM wave radiated from the transmitter 3 in time series in accordance with the azimuth. The size of the azimuthal angle change step is a matter directly related to the azimuth resolution, which is given by 0.5, for example. Therefore, if the value of n is 2(), the viewing angle in terms of direction is 0° (-0, 5°×20).

By the way, since the pink interval as the period To has a large depth depending on the attitude state of the target object 4, its value needs to be set appropriately. This is because if there is a depth, the length of time the reflected wave exists will be large. For example, if the length of target 4 is 75m, the ping interval is H1Oms.
It is necessary to set the above. Furthermore, the distance over which the reflected wave from the target object 4 can be received is limited by the near field of the transmitter 3 and the propagation loss that is constant depending on the wavelength λ used. ), the limit value of distance L and azimuth resolution Δθ are expressed by formula (1),
It is given by (2). 1r, -D"/'λ (
-) ... (1) Δθ= D/L
(r a d) −(2) However, D indicates the resolution width in the azimuth direction. Therefore, if L Th 1
000m, Δθ=yr/aao (= o, s) If it is run ann, D and λ are approximately 8m and 7tyn, respectively.
(The frequency is approximately 20 KHz). In this case, the propagation loss of sound waves in seawater is about 65 dB per one way, and it is considered that the waves can be received sufficiently, but if the length of the target 4 is short, for example 75 m, it is difficult to understand the outline. It can be said that this is insufficient. If D = 4 m to improve resolution, the above formula (1),
From (2), the azimuth resolution and wavelength are 0.004 radian (-o, 2a°) and 1.6 cm (frequency is about 94 KHz), respectively, but the attenuation per one way is about 80 dB.
Since this is close to the reception limit, the resolution should be set appropriately.

When a sound wave is appropriately radiated from the wave transmitter 3 to the target object 4, the sound wave is reflected by the target object 4, and the reflected wave is received by the wave receiver 7. The receiver 7 may be non-directional. However, it is possible to improve the spatial S/N ratio by providing a directivity width that can at least cover the beam sweep width during transmission. When the receiver 7 is constructed as a litho array type, the received signals from each receiver must be adjusted by the phaser 8 so that their phases match. The phaser 8 is composed of an analog shift register, and its delay time is controlled by changing the shift clock frequency to fl+ as in the analog shift register 2.
! This is done by controlling I.

tl+l control circuit In addition to controlling the operation of the 5-digit hyperbolic Ii'M wave generator 1, it also controls the frequency of the shift clock signal given to the analog shift register 2 and phasing device 8, and will be further described later. It also controls the received vibration signal processing circuit 9, the cathode ray tube display circuit 10.1-IJ gas generator 6, etc.

The received signals from each receiving element whose phase has been adjusted by the phaser 8 are combined in a complex manner at the final stage, and Figure 2 (1)) shows the received signals obtained in time series. . τ in the figure is the minimum time required for the sound wave to travel back and forth to the target object 4. After this time τ has elapsed, received signals are obtained almost periodically, and usually each received signal is Δτl Δτ2 ΔτB . . . relative to the corresponding transmitted signal.
. . . K can be obtained with a certain delay time. This is because the shape of the target is generally complex, and the target 4 has some depth when viewed from the transducer. Therefore, if there is a received signal relative to the transmitted signal, the outline of the target object 4 can be known by modulating the brightness based on the magnitude of the received signal and the delay time relative to the transmitted signal. . By the way, since the time in the trench where the received signal can be obtained is known in advance from the PPI scope display, the distance gate can be set. The distance gate setting is performed by the trigger generator 6, and by setting the distance gate, only the reflected waves from the target object 4 and its vicinity are received and processed, and the control circuit 5 also controls the timing at which the sweep starts in the cathode ray tube display circuit IO. When controlling this, it becomes possible to capture the target object 4 in the center of the screen while taking the depth into consideration while the sweep speed is high.

The brightness modulation signal to the cathode ray tube display circuit 10 is obtained by processing the received signal from the phaser 8 by the received signal processing circuit 9. Specifically, the details of the processing are as follows:
' This is a correlation calculation between the replica signal from the M-wave generator l. The replica signal referred to here corresponds to a copy of the transmitted signal, and in this example is given as a hyperbolic FM wave. This replica signal is the distance resolution width Δr(
m), and when the sound speed is C (m/s), Δr/
They are generated at a time interval ΔL satisfying cf and in a temporally overlapping state and given to the received signal processing circuit 9, but in the received signal processing circuit 9, when the timings of any of the replica signals and any of the received signals match. The maximum correlation output is output when the timing is off, so that if the timing is off, almost no correlation output will be obtained. FIG. 3(c) shows the correlation output thus obtained. If the correlation output obtained in this way is given to the cathode ray tube display circuit 10 as a luminance modulation signal, the cathode ray tube display circuit 10 can detect the target on the cathode ray tube based on the horizontal and vertical numbers (α) from the control circuit 5. It is designed to display a spot according to its shape and posture. On the other hand, if you start the direct sweep at a high speed [7], the horizontal and vertical axes will be The target object is displayed in multiple spots as direction and distance.
(c) shows an example of spot display on a cathode ray tube. However, the black circles indicate spots, and those with larger diameters indicate higher brightness than those with smaller diameters. The intensity of the reflected wave from the target object varies depending on the reflected portion, and the target object has a depth depending on its shape and posture, so that the spot pattern shown in the figure can be obtained. From this spot pattern, it is possible to estimate what the target object is, and if it is clear, it is possible to roughly know what kind of posture it is in.

As explained above, the present invention performs sector scanning by periodically emitting pulsed sound waves in all directions while slightly changing the direction and distance of a target object whose direction and distance are known in advance. The reflected wave from the target object is displayed as a spot by brightness modulation while controlling the starting point of 1-1% discount. According to the present invention, the shape and posture of the target object are also taken into consideration, and the target object is displayed in a plurality of spots in this state.
The effect of easy V determination is a) f.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the sonar structure and target object according to the present invention, and FIGS. 2(a), (b), (c)
Figure 3(a) is a diagram explaining the principles of sound wave transmission, reception, and reception processing by the sonar.
b) and (c) are diagrams showing examples of spot charts for targets. 1... Hyperbolic FM wave generator, 2... Analog noise 7
register, 3...transmitter, 4...[target, 5.
...Control circuit, 6...l-IJ Generator, 7...
Receiver, 8... Phaser, 9... Receiving signal processing circuit, ]
()...CRT display + r21 path. Masami Akimoto, 11-person patent attorney
J) υ@3 Figure (a) (b) (C) Direction e → 467-

Claims (1)

[Claims] Sector scanning is performed by periodically emitting pulsed sound waves to a target whose direction and distance are known in advance while slightly changing the direction. An act-up sonar target identification method characterized in that a spot display is performed by increasing the sweep speed by brightness modulation while the start time is controlled to be delayed by d.