HIGH-SPEED LASER RANGING SYSTEM INCLUDING A FIBER LASER

• US 20080192228A1
• Filed: 02/14/2007
• Published: 08/14/2008
• Est. Priority Date: 02/14/2007
• Status: Active Grant

• Current Assignee: Leica Geosystems AG (Hexagon AB)
• Original Assignee: Leica Geosystems AG (Hexagon AB)
• Inventors: Eaton, Robert B.
• Granted Patent: US 7,639,347 B2
• Time in Patent Office: Days
• US Class Current: 356/5.01
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 7/4818 using optical fibres

Abstract

Apparatuses and methods for gathering data describing a surface are disclosed. The apparatuses transmit pulses of light at a high rate using one or more fiber lasers. Examples of such apparatuses include laser ranging systems, such as light detection and ranging (LIDAR) systems, and laser scanners. Data received from the apparatus by a data processing unit can be used to create a data model, such as a point cloud, digital surface model or digital terrain model describing the surface. The surface can be the surface of terrain and/or objects, for example. Use of the fiber laser results in many advantages, such as improved vertical surface discrimination, increased pulse rate, safety benefits, as well as other advantages.

Claims

1. A laser ranging system comprising:

at least one fiber laser configured to transmit pulses of light to a surface at a rate of at least about 20,000 pulses of light per second, each fiber laser including an optical fiber as an active gain region, wherein the active gain region includes a rare-earth doped element;

laser control circuitry, wherein the laser control circuitry is configured to cause the at least one fiber laser to transmit the pulses of light at the rate of at least about 20,000 pulses of light per second;

an optical receiver configured to receive return signals comprising portions of the transmitted pulses of light reflected from the surface;

elapsed time circuitry configured to measure an elapsed time between transmission of at least one transmitted pulse of light by the fiber laser and reception of at least one corresponding return signal;

a position measurement unit configured to acquire position information corresponding to the position of the laser ranging system;

an inertial measurement unit configured to acquire pitch, roll, and heading information corresponding to movement of the laser ranging system; and

a scanning subassembly configured to direct the pulses of light at various scan angles.

2. A laser ranging system according to claim 1, further comprising:

processing circuitry configured to derive a digital model of the surface based at least in part on the measured elapsed time.

3. A laser ranging system according to claim 1, wherein the rare-earth doped element includes erbium, ytterbium, and/or neodymium.

4. A laser ranging system according to claim 1, further comprising circuitry configured to distinguish between multiple return signals corresponding to a single pulse of light reflected from multiple, vertically spaced objects on the surface.

5. A laser ranging system according to claim 1, wherein a width of the pulses generated by the fiber laser enables a vertical discrimination of less than 3.5 meters.

6. A laser ranging system according to claim 1, further comprising processing circuitry that includes a processor configured to calculate a distance between the laser ranging system and the surface based at least in part on each measured elapsed time.

7. A laser ranging system according to claim 1, further comprising sampling electronics configured to receive, from the optical receiver, characteristics of a discrete return pulse, reflection pulses, and/or an entire return reflection pulse waveform.

8. A laser ranging system according to claim 1, further comprising:

an aerial platform supporting at least the fiber laser, optical receiver, laser control circuitry, elapsed time circuitry, the position measurement unit, the inertial measurement unit, and scanning subassembly.

9. A laser ranging system according to claim 8, wherein the aerial platform includes an airplane or other aircraft.

10. A laser ranging system according to claim 1, wherein a wave length of the transmitted light is selected based on an eye-safety parameter.

11. A laser ranging system according to claim 10, wherein a wavelength of the transmitted light is between about 1.3-1.8 micron.

12. A laser ranging system according to claim 10, wherein a wavelength of the transmitted light is about 1.5 micron.

13. A laser ranging system according to claim 10, wherein a wavelength of the transmitted light is between about 1.535 and about 1.545 micron.

14. A laser ranging system according to claim 1, wherein the system has an associated maximum pulse rate of at least about 100 kilohertz.

15. A laser ranging system according to claim 1, wherein the system has an associated maximum pulse rate of at least about 150 kilohertz.

16. A laser ranging system according to claim 1, wherein a pulse waveform generated by the fiber laser at a rate of 20 kilohertz is substantially similar to a pulse waveform generated by the fiber laser at a rate of 100 kilohertz.

17. A laser ranging system according to claim 1, wherein the at least one fiber laser is configured to transmit pulses of light at a rate of about 100 kilohertz and the laser control circuitry causes the at least one fiber laser to transmit pulses of light at the rate of about 100 kilohertz.

18. A laser ranging system according to claim 1, wherein the at least one fiber laser is configured to transmit pulses of light at a rate of at least 150 kilohertz and the laser control circuitry causes the at least one fiber laser to transmit pulses of light at the rate of at least 150 kilohertz.

19. A laser ranging system according to claim 1, wherein the laser control circuitry is further configured to cause the fiber laser to transmit a first pulse of light prior to a second pulse of light, the laser control circuitry further configured to cause the fiber laser to transmit the second pulse of light prior to a time at which a reflected portion of the first pulse of light is received by the optical receiver.

20. A laser ranging system according to claim 1, wherein each pulse of light has a pulse width of about ten nanoseconds or less.

21. A laser ranging system according to claim 1, wherein the laser ranging system is capable of overlapping parallel or multi-pulse operation to approximately 36 kHz or faster at an altitude of 6000 m above ground level.

22. A light detection and ranging (LIDAR) system comprising:

a fiber laser configured to transmit pulses of light to a surface, each pulse of light having a pulse width of about five nanoseconds or less, the fiber laser including an optical fiber as an active gain region;

laser control circuitry configured to cause the fiber laser to transmit the pulses of light with a pulse width of five nanoseconds or less;

an optical receiver configured to receive return signals reflected from the surface;

circuitry configured to distinguish between multiple return signals corresponding to a single transmitted pulse of light;

elapsed time circuitry configured to measure an elapsed time between transmission of at least one pulse of light by the fiber laser and reception of at least one respective return signal;

circuitry configured to calculate a distance based at least in part on the elapsed time, wherein the distance calculation has a precision of about ten centimeters or less;

a position measurement unit configured to acquire information associated with a position of the LIDAR system, wherein the position measurement unit is configured to receive signals from multiple satellites and to calculate positional data from the signals received from the satellites, wherein the positional data includes latitude, longitude, and elevation data;

an orientation measurement unit configured to acquire information associated with a pitch, roll, and heading of the LIDAR system, wherein the orientation measurement unit is configured to calculate attitude data of the LIDAR system, the attitude data including heading data, pitch data, and roll data; and

a scanning subassembly configured to direct the pulses of light at various scan angles.

23. A LIDAR system according to claim 22, further comprising:

a data processing unit configured to receive range data from the circuitry configured to calculate a distance, the data processing unit further configured to receive pitch, roll, and heading data from the orientation measurement unit, the data processing unit further configured to receive latitude, longitude, and altitude data from the position measurement unit, wherein the data processing unit further includes computer executable instructions stored on a computer readable medium, the computer executable instructions being configured to cause the data processing unit to create a digital terrain model (DTM) describing terrain, or a point cloud describing terrain based at least in part on the data received from the circuitry configured to calculate a distance, position measurement unit, and orientation measurement unit.

24. A LIDAR system according to claim 22, wherein the position measurement unit includes a global positioning system (GPS) and the orientation measurement unit includes an inertial measurement unit (IMU).

25. A LIDAR system according to claim 22, wherein a wavelength characteristic of the transmitted light corresponds with an eye-safety parameter.

26. A LIDAR system according to claim 25, wherein a wavelength of the transmitted light is between about 1.3-1.8 micron.

27. A method for mapping terrain, performing bathymetry, performing seismology, detecting faults, measuring biomass, measuring wind speed, taking ozone measurements, calculating temperature, measuring traffic speed, identifying an object, surveying, performing close range photogrammetry, analyzing the atmosphere, performing meteorology, or measuring a distance, comprising:

using the LIDAR system of claim 22 to map terrain, perform bathymetry, perform seismology, detect faults, measure biomass, measure wind speed, take ozone measurements, calculate temperature, measure traffic speed, identify an object, survey, perform close range photogrammetry, analyze the atmosphere, perform meteorology, or measure a distance.

28. A method for acquiring data describing one or more surfaces, the method comprising:

transmitting pulses of light from at least one fiber laser at a rate of at least 20,000 pulses of light per second, the fiber laser including an optical fiber as an active gain region;

for at least one transmitted pulse of light, receiving at least one return signal;

for at least one return signal, determining a time of flight of the corresponding pulse of light based at least in part on an elapsed time between the transmission of the pulse of light and reception of the corresponding return signal;

calculating distances between a reference and the one or more surfaces;

receiving a signal associated with a position of the fiber laser;

receiving a signal associated with changes in attitude of the fiber laser; and

generating a three-dimensional digital data model using at least the calculated distances between the reference and the one or more surfaces.

29. A method according to claim 28, wherein the pulses of light are transmitted from the at least one fiber laser at a rate of at least 100,000 pulses of light per second.

30. A method according to claim 28, further comprising calculating distances to two surfaces from which a single pulse of light is reflected, wherein the distances calculated have a vertical discrimination between the vertical distance between two surfaces of less than 3.5 meters.

31. A method according to claim 28, wherein the three-dimensional digital data model generated includes a 3.5 meter or less vertical discrimination between surfaces.

32. A method according to claim 28, wherein the pulses transmitted have a width of ten nanoseconds or less.

33. A method according to claim 28, wherein the pulses transmitted have a width of five nanoseconds or less.

34. A method according to claim 28, wherein a waveform of the pulses of light transmitted at 20,000 pulses of light per second is substantially similar to a waveform of the pulses of light transmitted at 100,000 pulses of light per second.

35. A method according to claim 28, wherein the pulses of light are unattenuated.

36. A method according to claim 28, further comprising:

transmitting a first pulse of light;

transmitting a second pulse of light after the first pulse of light is transmitted;

receiving a reflected portion of the first pulse of light after the second pulse of light is transmitted; and

determining a time of flight of the first pulse of light by determining an elapsed time between the transmission of the first pulse of light and the time of reception of the reflected portion of the first pulse of light.

37. A method according to claim 28, wherein the three-dimensional digital data model includes a digital terrain model (DTM), a digital surface model (DSM), or a point cloud model describing the one or more surfaces from which the portions of the pulses of light are reflected.

38. A method according to claim 28, further comprising:

recording information in a computer readable medium, the information describing a discrete return reflection pulse, multiple reflection pulses, or an entire return reflection pulse waveform.

39. A method according to claim 28, further comprising:

performing an analysis of a waveform of the at least one return signal.