Fog piercing ranging apparatus and method

• US 5,781,147 A
• Filed: 05/09/1997
• Issued: 07/14/1998
• Est. Priority Date: 01/28/1997
• Status: Expired due to Term

• Current Assignee: Kama-Tech (HK) Limited
• Original Assignee: Laser Technology Incorporated (Laser Technology)
• Inventors: Elliott, Scott, Dunne, Jeremy G., Miller, Eric A.
• Primary Examiner(s): Sotomayor, John B.
• Application Number:
  US08/853,609
• Time in Patent Office: 431 Days
• Field of Search: 342/23, 342/54, 342/94, 342/95, 342/41
• US Class Current: 342/54
• CPC Class Codes: G01S 13/60 wherein the transmitter and receiver are mounted on the moving object, e.g. for determining ground speed, drift angle, ground track G01S13/64 takes precedence
• CPC Class Codes: G01S 13/865 Combination of radar systems with lidar systems
• CPC Class Codes: G01S 13/874 Combination of several systems for attitude determination in general G01C, control of attitude G05D1/49
• CPC Class Codes: G01S 13/937 of marine craft
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 17/18 wherein range gates are used
• CPC Class Codes: G01S 7/003 Transmission of data between radar, sonar or lidar systems and remote stations

Abstract

An apparatus and method for accurately determining a target distance in adverse weather conditions utilizing both LASER and RADAR is disclosed. The radar signals are used to determine an approximate range which is then used as a gating window for the determination of which laser reflection is from the actual target as opposed to a reflection from the atmospheric interference. The method basically comprises the steps of initiating a radar pulse in the direction of a target and receiving a reflection, transmitting a laser signal and receiving a plurality of reflections, determining an approximate range based on the radar signals, and using this approximate range to ascertain which of the laser reflections is from the target. This determination is preferably made by generating a gating signal and gate width from the radar signals and passing the set of laser range signals through the gate to eliminate the false signals and select the signal that survives the gate as the accurate target range.

Claims

1. An apparatus for range finding comprising:

a radar transceiver adapted to send a radio frequency signal toward said target and receive at least one reflected signal from said target and produce radar data representative of said transmitted and reflected radar signals;

a laser transceiver adapted to transmit a laser light signal toward an expected target, receive at least one reflected laser light signal and produce laser data representative of said transmitted and reflected laser signals; and

a computer coupled to said laser transceiver and to said radar transceiver receiving said radar data and said laser range data, wherein said computer determines an approximate range from said radar data and utilizes said approximate range to provide a laser gating window to determine a laser range from said laser data.

2. The apparatus according to claim 1 wherein said computer determines a radar range gating window from said laser range and determines an accurate radar range utilizing said radar range gating window and said radar data.

3. The apparatus according to claim 1 further comprising a display device coupled to said computer for providing a display of said laser range or said radar range.

4. The apparatus according to claim 3 wherein said computer determines speed from successive determinations of laser range from sequentially received sets of laser range data.

5. An apparatus for range finding comprising:

a radar transceiver adapted to send a radio frequency signal toward said target and receive at least one reflected signal from said target and produce radar data representative of said transmitted and reflected radar signals;

a radar computer coupled to said radar transceiver having a processor determining a radar range from said radar data and computing a laser gating signal;

a laser transceiver adapted to transmit a laser light signal toward an expected target, receive at least one reflected laser light signal and produce laser data representative of said transmitted and reflected laser signals; and

a laser computer coupled to said laser transceiver receiving said laser data and said laser gating signal, wherein said laser computer determines a laser range from said laser data and said laser gating signal.

6. The apparatus according to claim 5 further comprising said laser computer determining a radar gating signal from said laser range and coupling said radar gating signal to said radar computer to refine said radar range.

7. The apparatus according to claim 6 further comprising a display device coupled to one of said computers for displaying either said radar range or said laser range.

8. A method for laser range finding during inclement weather conditions utilizing a radar transceiver and a laser transceiver comprising the steps of:

issuing a radar chirp from said radar transceiver in the direction of an anticipated target;

receiving a plurality of reflected radar signals;

issuing a laser light pulse from said laser transceiver in the direction of said anticipated target;

receiving a plurality of reflected laser light signals;

selecting one of said plurality of reflected radar signals as a target reflection;

determining a radar range from said target reflection and said radar chirp;

determining a laser gating signal from said radar range;

setting a laser gating window to said laser gating signal plus a gate width;

applying said window to said reflected laser signals to determine a selected laser signal that passes through said window;

converting said selected laser signal to a laser range; and

displaying said laser range.

9. The method according to claim 8 further comprising the steps of:

determining a radar gating signal from said laser range; and

applying said radar gating signal to said radar reflections to determine said radar target reflection.

10. The method according to claim 8 wherein said steps of selecting, determining, setting, applying and converting are performed by a computer coupled to said radar transceiver and said laser transceiver.

11. The method according to claim 8 wherein said steps of selecting and determining are performed by a computer in said radar transceiver.

12. The method according to claim 8 wherein said steps of setting, applying and converting are performed by a computer in said laser transceiver.

13. The method according to claim 10 wherein said transceivers are housed in a single enclosure with said computer.

14. A method of determining an accurate range to a target during adverse weather conditions comprising the steps of:

sending a first radar signal from a radar transceiver toward said expected location of said target;

receiving a first set of reflected radar signals from said target;

determining from said transmitted and reflected radar signals an approximate range to said target;

sending a laser signal from a laser transceiver toward an expected location of a target;

receiving a first set of reflected laser signals in said laser transceiver;

determining from said transmitted laser signal and said first set of reflected laser signals a set of potential target ranges; and

selecting from said set of potential target ranges a range closest to said approximate range to said target as said accurate range.

15. The method according to claim 14 wherein said step of determining from said transmitted and reflected radar signals includes setting a laser gating window equal to a value equivalent to said approximate range.

16. The method according to claim 15 wherein said step of determining from said transmitted laser signal and said first set of reflected laser signals includes comparing said set of reflected laser signals to said laser gating window and said step of selecting includes selecting a laser signal.

17. The method according to claim 15 wherein said selected one of said potential target ranges is provided to said radar transceiver as a gate to improve accuracy of said approximate range determined by said radar transceiver.

18. A vessel docking aid system for providing approach speed and range information to operating personnel comprising:

a first sensor unit having a radar transceiver and a laser transceiver therein, mounted on one of said dock or said vessel;

a second sensor unit having a second radar transceiver and a second laser transceiver therein; and

at least one computer coupled to said sensor units for analyzing data transmitted from said first and second transceivers, said computer receiving reflection signals from both said radar and laser transceivers and determining radar target ranges and a laser target ranges therefrom, said computer utilizing said determined radar target range to select one of said laser ranges as an accurate laser target range.

19. The system according to claim 18 wherein said computer converts said radar range to a laser gating window for determining said laser range to said target.

20. The system according to claim 19 wherein said computer utilizes said laser range to generate a radar gate for determining said radar target range.