RU2533528C2 - Object location or detection method - Google Patents

Abstract

FIELD: physics, optics.

SUBSTANCE: invention relates to optical instrument making. A method of locating or detecting an object using an active pulsed device, which includes a receiving electro-optical converter (EOC) and a laser emitter which generates short pulses for illuminating an object, reflections from the object of which are summed in a frame of the EOC, wherein after each generation of a short pulse for illuminating an object with a given duration τ, the method comprises periodically turning on the EOC for a time π through a given delay time t₃ with frequency f_g=1/(π+τ) for a given time θ, wherein the number of instances of turning the EOC per pulse is selected not greater than a value K_max=(t_3Kmax-t₃)/(τ+π), where t_3Kmax=(1/f-π) is the maximum delay time for turning on the EOC for the laser emitter which generates short pulses for illuminating an object with frequency f, t₃ is the delay time of turning on the EOC until the beginning of the period of time θ.

EFFECT: obtaining image definition and brightness with a high scene depth.

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Description

The invention relates to optical instrumentation, in particular to the observation of objects in low light, and more particularly to methods for determining the location or detection of an object using an active-pulse device.

A known method of observing objects at low light, according to which the object is illuminated by a pulsed light source, receive the light reflected from the objects by the optical image receiver, synchronizing the operation of its controlled shutter with the emission of pulsed light. A device for implementing this method comprises a pulsed light source with transmitting optics, an optical image receiver with a controlled pulsed shutter (European patent N 03263735). By adjusting the delay between the moment of light emission and the moment the shutter of the device is opened, an image of objects located in the most interesting zone is obtained.

A disadvantage of the known method and device is that when using one source and one camera, it is possible to obtain information about objects located only in a fairly narrow visibility zone. To expand the visibility range, it is possible to use several simultaneously working sources (or several pulses) with different delays to form one frame or cameras (each camera operates at its own range), followed by the summation of video signals, which leads to a significant increase in hardware costs (European patent N 0468175) .

The use of three cameras operating at different ranges, with the corresponding color coding of the images obtained by these cameras to determine the distance to objects (European patent N 0531722) allows us to estimate the range only approximately, especially when working in a muddy environment (fog, smoke, dust, etc. .). For example, if there is a fog band in the foreground (red) and an object in the background (blue), the resulting image will be magenta, making it difficult to estimate the distance to the object. For people who do not correctly perceive colors, determining the range using such a device will be impossible.

A device is known according to UK patent N 1052178. The device includes illumination of objects with a pulsed light source, receiving an optical image receiver reflected from objects of light, the receiver design making it possible to vertically change the relative position of images of objects depending on their distance.

The brightness of objects located at different distances from the device will be different and if there are a large number of objects at close range, the images of the latter will mask the images of distant objects. A similar masking effect of deleted images will occur when working in a cloudy environment (fog, snow, smoke, etc.).

Common to the above sources of information is the use of an active-pulse device consisting of an electron-optical converter (EOC), a television camera (TC), optically coupled with an EOC, an input lens projecting a scene image onto the photocathode of an EOP, electronic control units of the image intensifier tube and laser emitter generating short pulses of light.

Active-pulse devices, built on the basis of an electron-optical converter and laser illumination, provide observation of objects with high quality on the ground almost regardless of the level of natural illumination, and can also work in conditions of light, meteorological and artificial interference. An example may be a device claimed in US patent: Ofer David, Yehuda Borenstein US 7,733464B2, MKI G01C 3/08, 06/08/2010, which is an analogue of the proposed technical solution. The principle of operation of the device is reflected in figure 2. Designations:

1 - laser pulse of duration τ;

2 - open state of a tube with a duration of θ;

3, 4 - time dependence of the distance L = 0.5c to the object from which the leading and trailing edges of the laser pulse were reflected, respectively ∆L = 0.5c (τ + θ) is the depth of the scene viewed;

n = f · T _k is the number of laser pulses of frequency f during the frame time T _k ;

t ₃ is the delay time for switching on the image intensifier tubes

c is the speed of light.

The operation of the device is as follows: the laser generates a pulse of light of duration τ, which propagates into the depth of the scene. Part of the pulse energy is reflected from objects located at different distances from the emitter, it is returned and gets to the photocathode of the image intensifier tube. If, in this case, the image intensifier tube is turned on for a time θ with a predetermined time delay t ₃ , then an image of a scene segment with a depth of ∆L = 0.5c (τ + θ) located at a distance of ∆L 0.5s t ₃ will be recorded. If we repeat this process with a frequency f, then it turns out n = f T _k (T _k is the frame duration) of the images of the scene section with depth ∆L and at a distance L, which are summed in one frame.

This method of observation is practically independent of the illumination on the ground, as its effect on the receiver is attenuated by a number of times equal to 1 / f · θ. For example, at f = 10 ³ Hz and θ = 10 ^-7 sec, the attenuation is 10 ⁴ times. Under such conditions, the device can work in daylight conditions, as well as in the presence of powerful spotlights: headlights, bonfires, lighting lights, etc.

Turning on the image intensifier for a short time ensures registration of only the laser radiation stream reflected from the object. The radiation flux scattered in the atmosphere is not detected by the receiving channel of the device. As a result, the device allows observation in weather conditions: snow, fog, smoke, rain, etc.

The disadvantage of this technical solution is that the advantages of the device described above are realized only at very small values of τ and θ of the order of 10 ^-8 ÷ 10 ^-6 sec, which corresponds to ∆L from 1.5 m to 150 m. This limitation makes it difficult to detect objects observation, preliminary target designation and knowledge of the distance to the object is required.

The ∆L value can be increased by increasing θ, but the device will lose its immunity to interference.

This disadvantage can be eliminated if applied, as is done in the prototype of the proposed technical solution (US patent: Jeffrey Thomas femillaed, willes H. Weber US 6,730,913 B2, MKI G01J 5/00, 4.05. 2004), scanning mode according to the depth of the scene.

The principle of operation of the device is reflected in figure 3.

Designations:

π is the duration of the switching of the image intensifier tube (π <θ);

t _3i - programmable delay time for the i-th laser pulse of n pulses per frame, the rest is the same as in figure 2.

In this mode, the device operates as follows (figure 3). During the frame time (standard 25 Hz), a delay time t _3i is set for each laser pulse, and the image intensifier tube is turned on for the time π <θ: so that different sections of the scene are viewed for each laser pulse, the image of these sections are summed in the frame . This control mode provides a sufficiently large depth of the viewed scene: ∆L _max = 0.5c (τ + π) · f · T _k , where T _k is the frame duration while maintaining selectivity.

However, if we compare the operation schemes of the prototype and analogue, then at the same stage depth and the same parameters of laser pulses, the irradiation of objects in the case of an analogue is f · T _k times higher than for the prototype. This is due to the fact that during the frame (T _k ) the signal from the object is recorded once in the case of the prototype, and f · T _k times in the case of the analog.

The disadvantage of this technical solution is that to compensate for these losses in the prototype it is proposed to change (increase) the amplitude of the laser pulses or increase the gain of the image intensifier. Such compensation methods are not effective: for f = 10 ³ Hz and T _k = 25 · 10 ^-3 sec, the amplitude of the laser pulse must be increased by 25 times, which is not acceptable in practice. The same applies to amplification of an image intensifier tube, the value of which should be optimal for obtaining a high-quality image with minimal fluctuations. In addition, in the prototype, the maximum depth of the scene is limited by ∆L _max .

The technical result of the proposed technical solution is to provide clarity and brightness of the image with an increased scene depth by increasing the irradiance of objects while simplifying the equipment used.

The specified technical result is achieved in a method for determining the location or detection of an object using an active-pulse device including a receiving electron-optical converter (EOC) and a laser emitter that generates short object backlight pulses, the reflections of which from the object are then summed in the image intensifier frame, the fact that after each generation of a short pulse of illumination of an object with a given duration τ, the image intensifier tubes are periodically turned on for a time π after a specified delay time t ₃ s frequency f _g = 1 / (π + τ) for a given time θ, and the number of turns of the image intensifier tube per pulse of illumination of the object is chosen no more than K _max = (t _3Kmax -t ₃ ) / (τ + π),

where t _3Kmax = (1 / f-π) is the maximum delay time for switching on the image intensifier tube for a laser emitter generating short illumination pulses of an object with a frequency f,

t ₃ is the delay time for switching on the image intensifier tube until the beginning of the time period θ.

The proposed technical solution is illustrated by drawings.

Figure 1 shows a diagram of the principle of operation of an active-pulse device in accordance with the proposed technical solution.

Figure 2 shows the principle of operation of an active-pulse device in the analogue method.

Figure 3 shows the principle of operation of an active-pulse device with a controlled delay time in the prototype method.

Implement in practice a method for determining the location or detection of an object is quite simple. As in the analogue, prototype, and most examples of the prior art, an active-pulse device is used, which includes a receiving electron-optical converter (EOC) and a laser emitter that generates short illumination pulses of the object, the reflections of which from the object are then summed in the image intensifier frame . After each generation of a short illumination pulse of an object with a given duration τ, the image intensifier tubes are periodically turned on for a time π after a specified delay time t ₃ with a frequency f _g = 1 / (π + τ) for a given time θ, and the number of image intensifier turns on per illumination pulse no more than K _max = (t _3Kmax -t ₃ ) / (τ + π) are selected

where t _3Kmax = (1 / f-π) is the maximum delay time for switching on the image intensifier tube for a laser emitter generating short illumination pulses of an object with a frequency f,

t ₃ is the delay time for switching on the image intensifier tube until the beginning of the time period θ.

Thus, a more rational solution is proposed, the essence of which is illustrated by the diagram in figure 1, which indicates:

 T = (τ + π) is the switching period of the image intensifier,

t _3Kmax = (1 / f-π) is the maximum delay time for one pulsed laser,

_Kmax = (t _3Kmax -t _3i ) / (τ + π) is the maximum number of times the switching of the image intensifier tube per laser pulse,

K _slave - the working number of the inclusion of the image intensifier tube, determined by its sensitivity and power of laser radiation.

The remaining designations in accordance with figure 2 and 3.

For each laser pulse, after a predetermined delay time t ₃ , the generator is started, including the image intensifier tube for a time π with a frequency

f _g = 1 / π + θ, which provides viewing of the scene ∆L _max = 0.5c (π + θ) · f _g (1 / ft ₃ ).

For example, π = 100 ns, θ = 100 ns, t ₃ = 100 ns, f _g = 1/200 ns = 5 MHz, f = 5 kHz:

∆L _max = 30 · (5 · 10 ³ -0.5) ≈15 · 10 ⁴ m.

Such a great depth of scene is not achievable in practice. The actual ∆L _slave value is determined by the sensitivity of the image intensifier tube and the laser radiation power. This value, ceteris paribus, will always be greater than ∆L _max in the prototype.

In the case of the present invention, it is possible to level the delay time - t ₃ and to achieve increased irradiation for distant areas.

Thus, when using the proposed technical solution, it is possible to achieve a technical result in the form of obtaining clarity and brightness of the image with an increased scene depth by increasing the irradiation of objects while simplifying the equipment used.

Claims (1)

A method for determining the location or detection of an object using an active-pulse device, including a receiving electron-optical converter (EOC) and a laser emitter, generating short pulses of illumination of the object, the reflections of which from the object are then summed in the image intensifier frame, characterized in that after each generation of short pulse of illumination of the object with a predetermined duration τ performed periodically switch EOC for a time π through a preset delay time t ₃ at a frequency f ₌ 1 / (π + τ) within Target th time θ, and the number of inclusions per pulse EOC backlight object selected magnitude no more than K _max = (t _3Kmax -t ₃₎ / (τ + π),
where t _3Kmax = (1 / f-π) is the maximum delay time for switching on the image intensifier tube for a laser emitter generating short illumination pulses of an object with a frequency f,
t ₃ is the delay time for switching on the image intensifier tube until the beginning of the time period θ.

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