Covert surveillance system for tracking light sensitive tagged moving vehicles

• US 6,465,787 B1
• Filed: 08/07/2000
• Issued: 10/15/2002
• Est. Priority Date: 08/07/2000
• Status: Expired due to Term

• Current Assignee: Aerospace Corporation
• Original Assignee: Aerospace Corporation
• Inventors: Klein, Christopher F., Coulter, John K.
• Primary Examiner(s): Hannaher, Constantine
• Assistant Examiner(s): Israel, Andrew
• Application Number:
  US09/633,319
• Time in Patent Office: 799 Days
• Field of Search: 250/341.3, 250/568, 250/566, 356/364, 356/368
• US Class Current: 250/341.3
• CPC Class Codes: G02B 27/28 for polarising used in stereoscopes G02B30/25

Abstract

A surveillance system uses pulsed laser near infrared light to illuminate a retroreflecting tag attached to a target for providing a return image that pulsates and that can be monitored by a camera for covert tracking of a target. The surveillance system may instead use pulsed near infrared polarized laser light to illuminate a transparent ¼ waveplate tag affixed to a moving vehicle or transitory containers for monitoring enhanced return images reflected from the tags serving to change the polarization of the illuminating laser beam so as to provide a co-located camera with return images that pulsate relative to background images for enhanced viewing and surveillance of the vehicle or container.

Claims

1. system for surveiling a target, the system comprising,

a ¼

wavelength tag affixed to the target,

a laser for providing pulsed polarized laser light for illuminating the ¼

wavelength tag for rotating the polarization of the pulsed polarized laser light and for providing a tag image of the pulsed rotated polarized light within a background image, the tag image and the background image form a return image, the background image surrounding the tag image,

a polarizer for receiving the return image, for communicating the tag image and for blocking the background image, and

a camera for receiving the tag image.

2. The system of claim 1 wherein the laser, polarizer and camera are rigidly attached colocated together as a surveillance camera.

3. The system of claim 1 wherein the pulsed laser light is near infra red pulsed laser light having a wavelength between 700 nm and 950 nm.

4. The system of claim 1 further comprising,

a filter for filter out sunlight having differing wavelengths than a wavelength of the pulse laser light.

5. The system of claim 1, wherein,

the target is a motor vehicle,

the tag is disposed over a license plate tag location.

6. The system of claim 1 wherein the laser comprises,

a laser diode for providing laser light,

a pulser for pulsing the laser light into pulsed laser light, and

a polarizer for polarizing the pulsed laser light into the pulse polarized light.

7. The system of claim 1 wherein the laser comprises,

a laser diode providing continuous polarized laser light, and

a laser pulser for pulsing the laser diode to providing the pulsed polarized laser light.

8. The system of claim 1 wherein,

the tag is a plurality of tags providing a respective plurality of return tag images, and

the camera is for receiving the plurality of tag images.

9. The system of claim 1 wherein the tag comprises,

a ¼

wave plate, and

a retroreflector.

10. A system for surveillance imaging of a target, the system comprising,

a first laser for providing a first pulsed polarized light,

a second laser for providing a second pulse polarized light, the first and second pulsed polarized light are orthogonally polarized respecting each other, the first and second pulsed polarized lights are alternately pulsed respecting each other,

a ¼

waveplate tag attached to the target for rotating the polarization of the first pulsed polarized light and for not rotating the second pulsed polarized light, and for providing a return tag image of the first rotated pulsed polarized light and the second unrotated pulsed polarized light, the target serving to reflect the first rotated pulsed polarize light and to reflect the second unrotated pulsed polarized light,

a polarizer for receiving the return tag image, the polarizer for passing one and blocking the other one of the reflected first rotated pulsed polarized light and reflected second unrotated pulsed polarized light as a passed image and as a blocked image, respectively, and

a camera for receiving the passed image, the passed image flickering as the first and second pulsed polarized light are alternately turned on and off.

11. The system of claim 10 further comprising a laser lens for focusing the pulsed laser light on the retroreflecting tag.

12. The system of claim 10 further comprising a camera lens for focusing the camera onto the return image.

13. The system of claim 10 further comprising a recorder for recording the return image over time.

14. The system of claim 10 wherein the tag comprises,

a ¼ wave plate, and

a retroreflector.

15. The system of claim 10 wherein the ¼

wave plate is made of transparent cellophane adhesive tape.