Laser radar wire detection

• US 5,151,747 A
• Filed: 10/11/1991
• Issued: 09/29/1992
• Est. Priority Date: 10/11/1991
• Status: Expired due to Term

• Current Assignee: OL Security LLC (Intellectual Ventures LLC)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Nourrcier, Charles E.
• Primary Examiner(s): Hellner, Mark
• Application Number:
  US07/774,914
• Time in Patent Office: 354 Days
• Field of Search: 356/5, 356/4.5, 356/28.5
• US Class Current: 356/5.09
• CPC Class Codes: G01S 17/32 using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 17/933 of aircraft or spacecraft
• CPC Class Codes: G01S 7/4917 superposing optical signals in a photodetector, e.g. optical heterodyne detection
• CPC Class Codes: G06V 10/255 Detecting or recognising potential candidate objects based on visual cues, e.g. shapes

Abstract

A laser radar detection system (10) is provided for detecting targets located within a detection field and discriminating between unresolved and resolved detected objects (32,34). The detection system (10) employs a laser radar sensor (12) for transmitting a frequency modulated optical transmit signal (22) which scans a desires field and receiving a return signal (24) from objects located therein. The laser radar sensor (12) includes a photo mixer (20) for providing the difference between the return signal (24) and a local oscillator (LO) signal (26) derived from the transmit signal (22). A processor (14) is employed for receiving the difference signal and provides a fourier transform thereof to thereby provide a power spectrum in the frequency domain. The processor (14) analyzes the power spectrum to determine whether the transformed signal contains side lobes (40) and is therefore clutter or does not contain side lobes (40) and therefore indicates the detection of an unresolved object (32).

Claims

1. A laser radar detection system which discriminates between unresolved and resolved detected objects, said system comprising:

a laser radar sensor for transmitting an optical scanning transmit signal within a desired field and receiving reflected signals from objects located therein;

said laser radar sensor including a photo mixer for receiving both said reflected signals and a local oscillator (LO) signal derived from said transmit signal and providing the difference therebetween as an output signal; and

processing means for receiving the output signal of said photo mixer and discriminating between resolved and unresolved signals detected therein said processing means comprising;

fourier transform means for providing an unweighted fourier transform of the received signal to thereby provide a power spectrum in the frequency domain; and

signal processing means for determining whether the power spectrum of said signal contains side lobes representing clutter or does not contain side lobes representing an unresolved object.

2. The system as defined in claim 1 wherein said signal processing means includes:

measurement means for detecting an amplitude which indicates a gaussian envelope or a main pulse of said power spectrum and measuring the pulse width thereof; and

detection means for detecting an amplitude representative of side lobes existing on either side of said gaussian envelope or main pulse.

3. The system as defined in claim 2 wherein said fourier transform means comprises:

an expansion surface acoustic wave (SAW), said expansion SAW receiving an impulse from an impulse generator connected thereto;

a compression SAW; and

a mixer for providing the difference between the expansion SAW output and the output of said photo mixer, said mixer output being provided to said compression SAW.

4. The system as defined in claim 2 wherein said transmit signal is transmitted within a beam having a cross-sectional detection area and a width.

5. The system as defined in claim 4 wherein said resolved signals are representative of detected objects having a width that is less than half the width of the beam, said unresolved signals being representative of detected objects having a width larger than the width of said beam.

6. The system as defined in claim 2 wherein said processing means further comprises:

second fourier transform means for providing a weighted fourier transform of said signal, said second fourier transform means producing a power spectrum without side lobes and further checking for less obvious unresolved targets hidden within the side lobes of the power spectrum for a resolved target.

7. A laser radar detection system which discriminates between unresolved and resolved detected objects, said system comprising:

a laser radar sensor for transmitting an optical scanning transmit signal within a desired field and receiving reflected signals from objects located therein;

said laser radar sensor including a photo mixer for receiving both said reflected signals and a local oscillator (LO) signal derived from said transmit signal and providing the difference therebetween as an output; and

processing means for receiving the output of the photo mixer and discriminating between resolved and unresolved signals detected therein, said processing means including first fourier transform means for providing an unweighted fourier transform of said signal to obtain a power spectrum and signal processing means for determining whether the power spectrum of said signal contains side lobes and is therefore clutter or does not contain side lobes and therefore indicates an unresolved object.

8. The system as defined in claim 7 wherein said signal processing means includes:

measurement means for detecting an amplitude which indicates a gaussian envelope or a main pulse of said power spectrum and measuring the pulse width thereof; and

detection means for detecting an amplitude representative of side lobes existing on either side of said gaussian envelope or main pulse.

9. The system as defined in claim 8 wherein said processing means further includes an unweighted surface acoustic wave (SAW) comprising:

an expansion surface acoustic wave (SAW), said expansion SAW receiving an impulse from an impulse generator connected thereto;

a compression SAW; and

a mixer for providing the difference between the expansion SAW output and the output of said photo mixer, said mixer output being applied to said compression SAW.

10. The system as defined in claim 9 wherein said processing means further comprises:

second fourier transform means for providing a weighted fourier transform of said signal, said second fourier transform means producing a power spectrum without side lobes and further checking for less obvious unresolved targets hidden within the side lobes of the power spectrum for a resolved target.

11. A method for detecting objects within a desired field with a laser radar detection sensor and discriminating between unresolved and resolved objects located therein, said method comprising:

transmitting an optical laser radar signal and scanning a desired field therewith;

receiving reflected signals from objects located within the field scanned;

comparing a local oscillator signal derived from the transmitted radar signal with the reflected signal and providing the difference therebetween as a difference signal;

transforming said difference signal to a frequency domain with an unweighted fourier transform to thereby provide a power spectrum;

determining whether the power spectrum of the detected signal contains side lobes; and

discriminating between unresolved and resolved signals, said resolved signals having side lobes located thereon and unresolved signals having essentially no side lobes.

12. The method as defined in claim 11 wherein the step of determining whether the power spectrum contains side lobes further comprises the steps of:

detecting any amplitude which indicates a gaussian envelope or a main pulse of said power spectrum;

measuring the pulse width of said gaussian envelope or said main pulse; and

checking for any amplitude outside of said pulse width, said amplitude indicating a side lobe.

13. The method as defined in claim 12 further comprising the steps of:

transforming said difference signal to a power spectrum with a weighted fourier transform;

eliminating any side lobes from said power spectrum; and

checking for less obvious unresolved targets hidden within the side lobes of the power spectrum for a resolved target.