Method for controlling a light source in a night vision surveillance system
First Claim
1. A method for controlling a light source in a night vision system, which comprises a pulsed light illuminator and a gated light sensor, the method comprising:
- estimating or measuring a desired observing distance d of an object;
setting a shortest distance d1 for back-scattering lights to enter the light sensor;
determining a pulse width Tp of a light beam emitted from the pulsed light illuminator, in which Tp=2(d−
d1)/c, where c represents a light speed;
determining a duty cycle D for the pulsed light illuminator, wherein D is equal to Tp/(Tp+T2d), where T2d=2d/c;
the pulsed active-light illuminator emitting light pulses with the pulse width Tp and an emitting period (Tp+T2d); and
the light sensor receiving the light pulses which are reflected by the object, wherein the light sensor has a sensing period identical to the emitting period but with a delay time of T2d.
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Abstract
A method for controlling a light source in a night vision system is provided. The method first computes a pulse width Tp=2(d−d1)/c, where c is the light speed, according to parameters of a desired observing distance d and a shortest distance d1 of the back-scattering light that enters the light sensor, such as a low-light-level camera. According to the definition of duty cycle D, it is determined by D=(1−d1/d)/(2−d1/d). According to the parameters of the desired observing distance and the pulse width, control signals are generated by a pulse signal controller to control a pulsed active-light illuminator with proper emitting period and a gated light sensor with proper gated-on period.
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Citations
10 Claims
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1. A method for controlling a light source in a night vision system, which comprises a pulsed light illuminator and a gated light sensor, the method comprising:
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estimating or measuring a desired observing distance d of an object;
setting a shortest distance d1 for back-scattering lights to enter the light sensor;
determining a pulse width Tp of a light beam emitted from the pulsed light illuminator, in which Tp=2(d−
d1)/c, where c represents a light speed;
determining a duty cycle D for the pulsed light illuminator, wherein D is equal to Tp/(Tp+T2d), where T2d=2d/c;
the pulsed active-light illuminator emitting light pulses with the pulse width Tp and an emitting period (Tp+T2d); and
the light sensor receiving the light pulses which are reflected by the object, wherein the light sensor has a sensing period identical to the emitting period but with a delay time of T2d. - View Dependent Claims (2, 3)
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4. A night vision system to observe an object at an observing distance d from the night vision system, the night vision system comprising:
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a pulsed light source used to periodically emit light pulses, each of the light pulses comprises a light beam with respect to a pulse width Tp for each of the light pulses;
a gated light sensor used to periodically receive the light pulses reflected by the object; and
a pulse signal controller to produce an illuminating signal and a receiving control signal to respectively control the pulsed light source and the gated light sensor so as to periodically emitting and receiving the light beam, wherein each of the light pulses is controlled to have a duty cycle of where d1=d−
(Tp/2)c and T2d=2d/c, so that the illuminating control signal controls the pulsed light source to emit the light pulses in an emitting period of (Tp+T2d) and the receiving control signal controls the gated light sensor to receive the reflected light pulses in a receiving period which is identical to the emitting period but has a delay of T2d.- View Dependent Claims (5, 6, 7, 8, 9, 10)
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Specification