Laser radar device and method

• US 20070171396A1
• Filed: 05/18/2005
• Published: 07/26/2007
• Est. Priority Date: 05/19/2004
• Status: Active Grant

• Current Assignee: Qinetiq Limited (QinetiQ Group PLC)
• Original Assignee: Qinetiq Limited (QinetiQ Group PLC)
• Inventors: Harris, Michael, Smith, David, Coffey, Adrian
• Granted Patent: US 7,391,506 B2
• Time in Patent Office: Days
• US Class Current: 356/28
• CPC Class Codes: G01S 17/95 for meteorological use
• CPC Class Codes: G01S 7/493 Extracting wanted echo signals
• 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

A coherent laser radar or lidar device (2;20;84;90) for measuring wind speed is described that comprises a transmitter for transmitting a beam of light to a remote probe volume (6;54), a receiver for detecting back-scattered light and an analyser for calculating wind velocity at the remote probe volume from the Doppler shift in frequency of the detected back-scattered light. The analyser is arranged to monitor for the presence of, and/or to ensure the calculated wind speed is corrected for, any Doppler frequency components of the detected back-scattered light that arise from back-scatter off cloud located at a range greater than the range of the remote probe volume. It is described how the lidar (2;20;84;90) may be scanned and wind velocity components calculated by fitting the scanned line of sight velocity values to a predetermined function. Furthermore, it is outlined how an initial fit may be performed to determine which points are to be used in this calculation. The incorporation of a back scatter profiling means, such as ceilometer (82), is also described. A wind turbine (902) incorporating such a device (90) is also described.

Claims

1. A coherent laser radar device for atmospheric wind speed measurement comprising:

a transmitter arranged to focus a beam of light to a remote probe volume,

a receiver arranged to detect back-scattered light, and

an analyser arranged to calculate wind speed at the remote probe volume from the Doppler shift in frequency of the detected back-scattered light,

wherein the analyser is arranged to monitor for the presence of, and/or to ensure the calculated wind speed is corrected for, any Doppler frequency components of the detected back-scattered light that arise from back-scatter off cloud located at a range greater than the range of the remote probe volume.

2. A device according to claim 1 wherein the transmitter comprises a variable focus mechanism.

3. A device according to claim 2 that is arranged to sequentially measure wind speed at a plurality of measurement remote probe volumes, wherein each of said plurality of measurement remote probe volumes is at range less than a first range limit.

4. A device according to claim 3 wherein the transmitter is additionally arranged to focus the beam of light to at least one reference remote probe volume, said at least one reference remote probe volume being at a range greater than said first range limit.

5. A device according to claim 4 wherein the Doppler frequency characteristics of the back-scattered light detected when the transmitter is focussed to said at least one reference remote probe volume are used by the analyser during the calculation of wind speed at each of said plurality of measurement remote probe volumes.

6. A device according to claim 5 wherein the analyser is arranged to produce Doppler spectra comprising the intensity of the detected back-scattered light as a function of Doppler shift frequency for each measurement at each of said measurement and reference remote probe volumes, wherein the calculation of wind speed comprises subtracting at least one reference Doppler spectrum from each of the measurement Doppler spectra.

7. A device according to claim 1 wherein the analyser is arranged to monitor the intensity of the detected back-scattered light as a function of Doppler shift frequency for the presence of two or more discrete intensity peak.

8. A device according to claim 7 wherein, in the presence of two or more discrete intensity peaks, the wind velocity at the associated remote probe volume is determined from the intensity peak at the lower Doppler shift frequency.

9. A device according to claim 1 further comprising an atmospheric back-scatter profiler arranged to measure the back-scatter cross-section of the atmosphere as a function of range.

10. A device according to claim 9 wherein the analyser is arranged to take the back-scatter profile measured by the atmospheric back-scatter profiler and to use said profile to ensure the calculated wind speed is corrected for any Doppler frequency components of the detected back-scattered light that arise from back-scatter off cloud located at a range greater than the range of the remote probe volume.

11. A device according to claim 1 wherein scanning means are provided to scan the beam of light transmitted by the transmitter within the remote probe volume.

12. A device according to claim 11 wherein the analyser is arranged to determine a line of sight wind velocity value for a plurality of known scan positions within the remote probe volume and to calculate at least one wind velocity component at the remote probe volume by fitting the plurality of line of sight velocity values to a predetermined function.

13. A device according to claim 12 wherein the analyser is arranged to ensure that each calculated line of sight velocity value is corrected for any Doppler frequency components of the detected back-scattered light that arise from back-scatter off cloud located at a range greater than the range of the remote probe volume.

14. A device according to claim 12 wherein the analyser is arranged such that one or more line of sight velocity values acquired during the scan are omitted from the calculation of the at least one wind velocity component.

15. A device according to claim 1 wherein, during use, the focus of the receive beam is arranged to coincide with the focus of the transmit beam.

19. A device according to claim 1 that is arranged for ground based, upwardly directed, operation.

16-18. -18. (canceled)

20. A method for calculating atmospheric wind speed comprising the steps of (i) taking Doppler frequency data acquired by a coherent laser radar device from a remote probe volume and (ii) calculating wind velocity at the remote probe volume of the coherent laser radar device from said Doppler frequency data, characterised in that step (ii) comprises the step of monitoring said Doppler frequency data for the presence of, and/or ensuring the calculated wind speed is corrected for, any Doppler frequency components that arise from back-scatter off cloud located at a range greater than the range of the remote probe volume.

21. A method according to claim 20 wherein said Doppler frequency data comprises a plurality of Doppler spectra acquired from a plurality of remote probe volumes.

22. A method according to claim 21 wherein said plurality of Doppler spectra comprise a first set of Doppler spectra acquired from one or more measurement remote probe volumes at a range less than a first range limit and a second set of Doppler spectra acquired from one or more remote probe volumes at a range greater than said first range limit.

23. A method according to claim 22 wherein step (ii) comprises the step of using said second set of Doppler spectra to ensure the wind speed calculated from each of said first set of Doppler spectra is corrected for any Doppler frequency components that arise due to back-scatter off cloud.

24. A method according to claim 23 wherein the calculation of wind speed comprises the step of subtracting a Doppler spectrum of said second set from each Doppler spectra of said first set.

25. A method according to claim 20 and comprising the additional step of taking a back-scatter profile measured by an atmospheric back-scatter profiler located in the vicinity of the coherent laser radar device and using the back-scatter profile to monitor said Doppler frequency data for the presence of any Doppler frequency components that arises from back-scatter off cloud located at a range greater than the range of the remote probe volume.

26. A method according to claim 20 in which said Doppler frequency data comprises a plurality of Doppler spectra acquired from each remote probe volume, wherein each of said plurality of Doppler spectra are acquired from a known scan position within said remote probe volume.

27. A method according to claim 26 in which a line of sight velocity value is calculated from each Doppler spectra of each scan position within said remote probe, wherein the step of calculating wind velocity at a remote probe volume comprises the step of fitting at least some of said line of sight velocity values to a predetermined function.

28. A method according to claim 27 wherein the at least some line of sight velocity values selected for use in the step of calculating the at least one wind velocity component at a remote probe volume comprise line of sight velocity values having a deviation from an initial fit less than a predetermined amount.

29. A method according to claim 27 wherein the at least line of sight velocity values selected for use in the step of calculating the at least one wind velocity component at a remote probe volume exclude the N line of sight velocity values having the highest deviation from an initial fit, wherein N is a predetermined integer greater than or equal to one and less than the number of line of sight velocity values.

30. A method according to claim 20 in which the Doppler frequency data comprise the intensity of detected back-scattered light as a function of Doppler shift, wherein the step of calculating wind velocity at the remote probe volume comprises analysing said data for the presence of two or more discrete peaks at different Doppler frequencies, wherein the line of sight wind velocity at the remote probe volume is determined from the peak at the lower Doppler shift frequency.

31. A method according to claim 20 wherein step (i) comprises the step of using a coherent laser radar device to acquire Doppler frequency data from at least one remote probe volume.

32. A computer program for implementing the method of claim 20.

33. A computer program carrier containing in machine readable form a computer program suitable for implementing the method of claim 20.

34. A computer suitably programmed to implement the method of claim 20.

35. (canceled)