Method for controlling a light source in a night vision surveillance system

• US 6,603,507 B1
• Filed: 06/09/1999
• Issued: 08/05/2003
• Est. Priority Date: 04/12/1999
• Status: Expired due to Term

• Current Assignee: National Chung-Shan Institute of Science and Technology
• Original Assignee: Chung-Shan Institute of Science & Technology Armaments Bureau MND (Government of The Republic of China)
• Inventors: Lin, Chunn-Yenn, Jiang, Shiaw-Shiang, Liou, Guang-Hann
• Primary Examiner(s): Garber, Wendy R.
• Assistant Examiner(s): TOPPIN, CATHERINE J
• Application Number:
  US09/328,982
• Time in Patent Office: 1,518 Days
• Field of Search: 348/216.1, 348/370, 348/371
• US Class Current: 348/216.1
• CPC Class Codes: H04N 23/56 provided with illuminating means

Abstract

A method for controlling a light source in a night vision system is provided. The method first computes a pulse width T_p=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.

Claims

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 T_p of a light beam emitted from the pulsed light illuminator, in which T_p=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 T_p/(T_p+T_2d), where T_2d=2d/c;

the pulsed active-light illuminator emitting light pulses with the pulse width T_p and an emitting period (T_p+T_2d); 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 T_2d.

2. The method of claim 1, wherein the d₁ is set to be in a range of about 0.01d to 0.99d.

3. The method of claim 1, wherein the duty cycle is set to $D=\frac{T_p}{T_p+T_{2}}$

d=1-d1d2-d1d.

4. A night vision system to observe an object at an observing distance d from the night vision system, the night vision system comprising:

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 T_p 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 $D=\frac{T_P}{T_P+T_{2<br><br>\text{\hspace{1em}<br><br>}<br><br>d}}=\frac{1-\frac{d_1}{d}}{2-\frac{d_1}{d}},$

where d₁=d−

(T_p/2)c and T_2d=2d/c, so that the illuminating control signal controls the pulsed light source to emit the light pulses in an emitting period of (T_p+T_2d) 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 T_2d.

5. The night vision system of claim 4, wherein the d₁ is the shortest distance of the light beam to the sensor, at which back-scattering lights can enter the gated sensor.

6. The night vision system of claim 4, wherein the d₁ is in a range of about 0.001d to 0.99d.

7. The night vision system of claim 4, wherein the gated light sensor comprises a gated low-light-level camera.

8. The night vision system of claim 4, wherein the pulsed light source comprises a pulsed laser illuminator.

9. The night vision system of claim 4, wherein the pulsed light source and the gated light sensor have parallel optical axes.

10. The night vision system of claim 9, wherein the pulsed light source and the gated light sensor are put sufficiently close so as to have a substantially equal distance to the object along the parallel optical axes.