Increasing measurement rate in time of flight measurement apparatuses

• US 20090122295A1
• Filed: 04/04/2006
• Published: 05/14/2009
• Est. Priority Date: 03/07/2006
• Status: Active Grant

• Current Assignee: Leica Geosystems AG (Hexagon AB)
• Original Assignee: Leica Geosystems AG (Hexagon AB)
• Inventors: Eaton, Robert B.
• Granted Patent: US 7,944,548 B2
• Time in Patent Office: Days
• US Class Current: 356/5.10
• CPC Class Codes: G01C 11/025 by scanning the object
• CPC Class Codes: G01S 17/86 Combinations of lidar systems with systems other than lidar, radar or sonar, e.g. with direction finders
• CPC Class Codes: G01S 17/87 Combinations of systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 19/47 the supplementary measurement being an inertial measurement, e.g. tightly coupled inertial
• CPC Class Codes: G01S 7/483 Details of pulse systems
• CPC Class Codes: Y02A 90/10 Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Abstract

An apparatus for measuring distance to a surface is disclosed. The apparatus transmits at least one subsequent pulse of light prior to receiving a reflection of a previously sent pulse of light. Thus, multiple pulses of light are in-flight at a given time. The embodiments are applicable to terrain mapping, bathymetry, seismology, detecting faults, biomass measurement, wind speed measurement, temperature calculation, traffic speed measurement, military target identification, surface to air rangefinding, high definition survey, close range photogrammetry, atmospheric composition, meteorology, distance measurement, as well as many other applications. 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, terrain, and/or objects.

Claims

1. A time of flight measurement apparatus comprising:

a laser configured to transmit light;

an optical receiver configured to receive light;

laser control circuitry configured to cause the laser to transmit a first pulse of light prior to a second pulse of light, the laser control circuitry further configured to cause the 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; and

elapsed time circuitry configured to measure an elapsed time between transmission of the first pulse of light by the laser and reception of the reflected portion of the first pulse of light by the optical receiver.

2. A time of flight measurement apparatus according to claim 1, further comprising:

a data processing device configured to calculate a distance between the apparatus and a surface based at least in part on the elapsed time.

5. A time of flight measurement apparatus according to claim 35, wherein the timing circuitry is further configured to sample electronic signals from the optical receiver during a second time interval approximating a time during which the reflected portion of the second pulse of light is estimated to be received by the optical receiver based at least in part on the range of distances from the laser ranging system to the surface and a scan angle of the second pulse of light.

6. A time of flight measurement apparatus according to claim 1, further comprising sampling electronics configured to receive characteristics of a discrete return reflection pulse, multiple reflection pulses, or an entire return reflection pulse waveform from the optical receiver.

7. A time of flight measurement apparatus according to claim 1, wherein the laser control circuitry is further configured to cause the laser to transmit at least one additional pulse of light after the first pulse of light is transmitted but prior to the time at which the reflected portion of the first pulse of light is received by the optical receiver.

8. A time of flight measurement apparatus according to claim 1, wherein the elapsed time circuitry is further configured to calculate a time between transmission of the second pulse of light by the laser and reception of a reflected portion of the second pulse of light by the optical receiver, wherein the reflected portion of the first pulse of light is received by the optical receiver prior to the reception of the reflected portion of the second pulse of light by the optical receiver.

9. A laser ranging system comprising a time of flight measurement apparatus according to claim 1, the laser ranging system further comprising:

at least one of, or any combination of, the members of a set consisting of;

a vehicle supporting the laser ranging system;

a position measurement unit;

an inertial measurement unit; and

a scanning subsystem.

10. A laser scanner comprising the time of flight measurement apparatus set forth in claim 1.

34. A time of flight measurement apparatus according to claim 1, further comprising:

a scanning subassembly configured to direct the first and second pulses of light transmitted by the laser at different scan angles.

35. A time of flight measurement apparatus according to claim 1, further comprising:

timing circuitry coupled to the optical receiver, the timing circuitry configured to sample electronic signals from the optical receiver during a first time interval, the first time interval approximating a time during which the reflected portion of the first pulse of light is estimated to be received by the optical receiver based at least in part on a range of distances from the laser ranging system to the surface and a scan angle of the first pulse of light.

3. (canceled)

4. (canceled)

11. A system for collecting information describing terrain, the system comprising:

a laser imaging detection and ranging (LIDAR) system configured to transmit at least one subsequent pulse of light prior to receiving a reflected portion of a previously emitted pulse of light.

12. A system according to claim 11, further comprising at least one of, or any combination of, the members of a set consisting of:

a vehicle carrying the LIDAR system, GPS, and IMU;

a global positioning system (GPS); and

an inertial measurement unit (IMU).

13. A system according to claim 11, further comprising:

a global positioning system (GPS);

an inertial measurement unit (IMU); and

a vehicle carrying the LIDAR system, GPS, and IMD.

14. A system according to claim 12, wherein the LIDAR system further comprises:

a laser configured to emit the pulses of light;

an optical receiver configured to receive a reflected portion of the previously emitted pulse of light after the at least one subsequent pulse of light is transmitted; and

elapsed time circuitry configured to calculate an elapsed time between transmission of the first pulse of light and reception of the reflected portion of the first pulse of light by the optical receiver.

15. A system according to claim 11, wherein the GPS receives signals from multiple satellites and calculates positional data of the vehicle from the signals received from the satellites, wherein the positional data includes latitude, longitude, and elevation data;

and wherein the IMU calculates attitude data of the vehicle, the attitude data including heading data, pitch data, and roll data.

16. A system according to claim 11, further comprising:

a data processing unit configured to receive range data from the LIDAR, the data processing unit further configured to receive pitch, roll, and heading data from the IMU, the data processing unit further configured to receive latitude, longitude, and altitude data from the GPS.

17. A system according to claim 16, wherein the data processing unit further includes computer executable instructions stored on a computer readable medium, the computer executable instructions configured to cause the data processing unit to create a digital terrain model (DTM) or point cloud describing terrain based at least in part on the data received from the LIDAR, IMU, and GPS.

18. A method performed by a LIDAR system including at least one laser for transmitting light and at least one receiver for receiving light reflected from a surface, the LIDAR system being configured for acquiring data describing the surface, the method 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.

19. A method according to claim 18, further comprising:

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

determining a time of flight of the second pulse of light including determining a time between the transmission of the second pulse of light and a time of reception of the reflected portion of the second pulse of light.

20. A method according to claim 18, further comprising:

calculating a distance of travel of the first pulse of light; and

calculating a distance of travel of the second pulse of light.

21. A method according to claim 18, wherein the pulses of light are transmitted using a laser.

23. A method according claim 18, further comprising modulating or polarizing the first pulse of light.

24. A method according to claim 23, further comprising associating the reflected portion of the first pulse of light with the transmitted first pulse of light based on the modulation or polarization of the reflected portion of the first pulse of light.

25. A method according to claim 23, further comprising modulating or polarizing the second pulse of light differently than the first pulse of light.

26. A method according to claim 18, wherein the pulses of light are transmitted by a laser imaging detection and ranging (LIDAR) system, the method further comprising:

receiving a signal from the LIDAR describing a time of flight of the first pulse of light;

receiving a signal from a global positioning system (GPS) describing a position of a vehicle in which the LIDAR unit and GPS are carried; and

receiving a signal from an inertial measurement unit (IMU) describing changes in attitude of the vehicle.

27. A method according to claim 26, further comprising:

creating a digital terrain model (DTM) based at least in part on the information received from the LIDAR, GPS, and IMD.

28. A method according to claim 18, further comprising:

creating a digital terrain model (DTM), a digital surface model (DSM), or a point cloud model describing the surface.

29. A method according to claim 18, further comprising:

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

30. A method according to claim 18, further comprising:

performing analysis of a waveform of a reflected portion of the first pulse of light.

31. A method according to claim 18, further comprising:

mapping terrain, performing bathymetry, performing seismology, detecting faults, measuring biomass, measuring wind speed, taking ozone measurements, calculating temperature, measuring traffic speed, identifying a target, performing surface to air rangefinding, surveying, performing close range photogrammetry, analyzing the atmosphere, performing meteorology, or measuring distance.

32. A computer readable medium having computer executable instructions stored on the computer readable medium, the computer executable instructions configured to cause a computer to create the DTM, DSM, or point cloud model of claim 28.

33. Circuitry configured to control the transmission of light by at least one laser according to the method of claim 18.

36. A method according to claim 18, wherein the reflected portions are sampled during predetermined time periods, wherein the duration and timing of the predetermined time periods are calculated based at least in part on a maximum and minimum distance between an aircraft and the ground below the aircraft and a scan angle of the first and second pulses of light.

22. (canceled)