Laser radar

• US 5,715,044 A
• Filed: 02/22/1989
• Issued: 02/03/1998
• Est. Priority Date: 08/14/1987
• Status: Expired due to Fees

• Current Assignee: Boeing North American Incorporated (The Boeing Co.)
• Original Assignee: Boeing North American Incorporated (The Boeing Co.)
• Inventors: Hayes, Cecil L.
• Primary Examiner(s): Hellner, Mark
• Application Number:
  US07/312,523
• Time in Patent Office: 3,268 Days
• Field of Search: 356/5, 356/5.09, 356/5.11, 342/129
• US Class Current: 356/5.09
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 7/483 Details of pulse systems

Abstract

The inventive laser radar uses a multiple frequency processing technique for the purpose of extracting relative range information from a received signal by transmitting and receiving two frequencies that are derived from a reference signal source modulated by two modulators that are driven by a different frequency, the reference frequency source also serving as a local oscillator.

Claims

1. A laser radar for scanning a target aperture having a predetermined array of locations comprising:

a laser means having a power source and a resonator cavity containing a lasing medium, said laser means providing a SINGLE FREQUENCY LIGHT SOURCE (FO);

means for dividing said SINGLE FREQUENCY LIGHT SOURCE into FIRST and SECOND REFERENCE FREQUENCY BEAMS;

control means for providing APERTURE DIRECTION SIGNALS and a FIRST and SECOND FREQUENCY CONTROL SIGNAL;

frequency shifting means responsive to said FIRST and SECOND FREQUENCY CONTROL SIGNAL for frequency shifting said FIRST REFERENCE FREQUENCY BEAM and said SECOND REFERENCE FREQUENCY BEAM to form a respective FIRST FREQUENCY SHIFTED BEAM and a respective SECOND FREQUENCY SHIFTED BEAM;

scanner means responsive to said APERTURE DIRECTION SIGNALS for combining and directing said FIRST FREQUENCY SHIFTED BEAM and said SECOND FREQUENCY SHIFTED BEAM to each predetermined target aperture location and for receiving a combined REFLECTED FIRST FREQUENCY SHIFTED BEAM SIGNAL and a REFLECTED SECOND FREQUENCY SHIFTED BEAM SIGNAL from said target;

detector means for combining and detecting a sample of said SECOND REFERENCE FREQUENCY BEAM in combination with said REFLECTED FIRST FREQUENCY SHIFTED BEAM SIGNAL and said REFLECTED SECOND FREQUENCY SHIFTED BEAM SIGNAL to provide a RANGE CARRIER SIGNAL;

monitor means for combining and detecting a sample of said FIRST FREQUENCY SHIFTED BEAM and said SECOND FREQUENCY SHIFTED BEAM to form a DEMODULATION REFERENCE SIGNAL;

phase demodulation means referenced to said DEMODULATION REFERENCE SIGNAL and responsive to said RANGE CARRIER SIGNAL for demodulating said RANGE CARRIER SIGNAL to provide a RELATIVE RANGE SIGNAL; and

signal processor and display means responsive to said RELATIVE RANGE SIGNAL and to the APERTURE DIRECTION SIGNALS for quantizing and storing the digital value of the amplitude of the corresponding relative phase delay between the RELATIVE RANGE SIGNAL and said DEMODULATION REFERENCE SIGNAL for each respective location in said target aperture.

2. The laser radar of claim 1 wherein said means for dividing said SINGLE FREQUENCY LIGHT SOURCE into FIRST and SECOND REFERENCE FREQUENCY BEAMS further comprises:

a first beamsplitter having at least a first input port and reflected and transmitting output ports;

said input port being positioned to be responsive to said SINGLE FREQUENCY LIGHT SOURCE (Fo), said reflect output port being characterized to provide said FIRST REFERENCE FREQUENCY BEAM and said output port being characterized to provide a SECOND REFERENCE FREQUENCY BEAM.

3. The laser radar of claim 1 wherein said control means further comprises:

a digital controller for providing a recurring sequence of DIGITIZED APERTURE DIRECTION SIGNALS; and

a signal conditioner and drive amplifier for conditioning and scaling said DIGITIZED APERTURE DIRECTION SIGNALS to provide scanner drive motor signals characterized to drive said scanner means to reflect said FIRST and SECOND FREQUENCY SHIFTED BEAMS to each target aperture location to be illuminated by said combined FIRST and SECOND FREQUENCY SHIFTED BEAMS.

4. The laser radar of claim 1 wherein said scanner means further comprises:

a scanner reflector means responsive to said combined FIRST and SECOND FREQUENCY SHIFTED BEAMS for reflecting said beams to a target and for continuously receiving said combined REFLECTED FIRST and SECOND FREQUENCY SHIFTED BEAM signals from said target; and

gimbal and drive motor assembly responsive to said drive motor signals for driving said reflector means laterally and vertically to sequentially point said combined FIRST and SECOND FREQUENCY SHIFTED BEAMS at each successive target aperture location in response to said SCANNER DRIVE MOTOR SIGNALS and to receive said combined REFLECTED FIRST and SECOND FREQUENCY SHIFTED BEAM signals from each said target aperture location.

5. The laser radar of claim 1 wherein said detector means further comprises:

a beamsplitter responsive to a sample of said SECOND REFERENCE FREQUENCY BEAM, said combined REFLECTED FIRST and SECOND FREQUENCY SHIFTED BEAM for combining said beams to provide a RECEIVED SIGNAL BEAM; and

diode detector and amplifier means responsive to said RECEIVED SIGNAL BEAM for mixing said beam signals to provide said RANGE CARRIER SIGNAL.

6. The laser radar of claim 1 wherein said detecting means further comprises:

a bias and amplifier means for biasing said detector diode, and for amplifying said low level RANGE CARRIER SIGNAL, the gain and bandwidth of said amplifier being characterized to provide said RANGE CARRIER SIGNAL having an amplitude in a predetermined range.

7. The laser radar of claim 1 wherein said phase demodulator means further comprises:

differencing means responsive to said RANGE CARRIER SIGNAL to provide a PROCESSED RANGE CARRIER SIGNAL;

filter means responsive to said PROCESSED RANGE CARRIER SIGNAL for filtering said PROCESSED RANGE CARRIER SIGNAL within a predetermined band-pass to provide a FILTERED RANGE SIGNAL; and

a synchronous phase demodulator responsive to said FILTERED RANGE SIGNAL and to said DEMODULATOR REFERENCE SIGNAL for providing said RELATIVE RANGE SIGNAL.

8. The laser radar of claim 7 wherein said differencing means further comprises:

a DIFFERENCE NETWORK HAVING an input responsive to said RANGE CARRIER SIGNAL, said output providing said PROCESSED RANGE CARRIER SIGNAL containing the a signal containing the frequency difference between said REFLECTED FIRST and SECOND FREQUENCY SHIFTED BEAM.

9. The laser radar of claim 1 wherein said signal processor and display means further comprises:

a display means for displaying an image of the scene scanned by said scanner as an array of illuminated pixels (picture elements), the intensity of each pixel being controlled by the stored amplitude value of said RELATIVE RANGE SIGNAL, the color of each pixel being controlled by the stored value of the relative phase delay between the RELATIVE RANGE SIGNAL and said DEMODULATION REFERENCE SIGNAL.

10. The laser radar of claim 1 wherein said signal processor and display means further comprises:

a display means for displaying a perspective image of the scene scanned by said scanner as an array of illuminated pixels (picture elements), the location and intensity of each pixel being controlled by the respective APERTURE DIRECTION SIGNAL and the corresponding stored amplitude value of said RELATIVE RANGE SIGNAL and the color of each pixel being controlled by the stored value of the corresponding relative phase delay between the RELATIVE RANGE SIGNAL and said DEMODULATION REFERENCE SIGNAL.

11. The laser radar of claim 1 wherein said PHASE DEMODULATOR MEANS further comprises:

means responsive to said range carrier signal for measuring the absolute time for light to move from the laser radar to the target and return.

12. A laser radar for scanning a target aperture having a predetermined array of locations comprising:

a laser means having a power source and a resonator cavity containing a lasing medium, said laser means providing a SINGLE FREQUENCY LIGHT SOURCE (FO);

means for dividing said SINGLE FREQUENCY LIGHT SOURCE into FIRST and SECOND REFERENCE FREQUENCY BEAMS;

control means for providing APERTURE DIRECTION SIGNALS and for providing a FIRST and SECOND FREQUENCY CONTROL SIGNAL;

frequency shifting means responsive to said FIRST and SECOND FREQUENCY CONTROL SIGNAL for frequency shifting said FIRST REFERENCE FREQUENCY BEAM and said SECOND REFERENCE FREQUENCY BEAM to form a respective FIRST FREQUENCY SHIFTED BEAM and a respective SECOND FREQUENCY SHIFTED BEAM;

scanner means responsive to said APERTURE DIRECTION SIGNALS for combining and directing said FIRST FREQUENCY SHIFTED BEAM and said SECOND FREQUENCY SHIFTED BEAM to each predetermined target aperture location and for receiving a combined REFLECTED FIRST FREQUENCY SHIFTED BEAM SIGNAL and a REFLECTED SECOND FREQUENCY SHIFTED BEAM SIGNAL from said target;

detector means for combining and detecting a sample of said SECOND REFERENCE FREQUENCY BEAM in combination with said REFLECTED FIRST FREQUENCY SHIFTED BEAM SIGNAL and said REFLECTED SECOND FREQUENCY SHIFTED BEAM SIGNAL to provide a RANGE CARRIER SIGNAL;

monitor means for combining and detecting a sample of said FIRST FREQUENCY SHIFTED BEAM and said SECOND FREQUENCY SHIFTED BEAM to form a DEMODULATION REFERENCE SIGNAL;

phase demodulator means referenced to said DEMODULATION REFERENCE SIGNAL and responsive to said RANGE CARRIER SIGNAL for squaring said RANGE CARRIER SIGNAL to form a SQUARED RANGE CARRIER SIGNAL and for band pass filtering and demodulating said SQUARED RANGE CARRIER SIGNAL to provide a RELATIVE RANGE SIGNAL; and

signal processor and display means responsive to said DEMODULATION REFERENCE SIGNAL, said RELATIVE RANGE SIGNAL and to the APERTURE DIRECTION SIGNALS for quantizing and storing the digital value of the amplitude of the corresponding RELATIVE RANGE SIGNAL and for quantizing and storing the value of the corresponding relative phase delay between the RELATIVE RANGE SIGNAL and said DEMODULATION REFERENCE SIGNAL for each respective location in said target aperture.

13. The laser radar of claim 12 wherein said phase demodulator means referenced to said DEMODULATION REFERENCE SIGNAL and responsive to said RANGE CARRIER SIGNAL for processing said RANGE CARRIER SIGNAL to form a PROCESSED RANGE CARRIER SIGNAL and for band pass filtering and demodulating said SQUARED RANGE CARRIER SIGNAL to provide a RELATIVE RANGE SIGNAL further comprises:

means responsive to said range carrier signal for measuring the absolute time for light to move from the laser radar to the target and return.