Multiple beam lidar system for wind measurement

• US 6,646,725 B1
• Filed: 07/10/2002
• Issued: 11/11/2003
• Est. Priority Date: 07/11/2001
• Status: Active Grant

• Current Assignee: Iowa Research Foundation
• Original Assignee: Iowa Research Foundation
• Inventors: Krieger, John R., Eichinger, William E.
• Primary Examiner(s): Buczinski, Stephen C.
• Application Number:
  US10/193,723
• Time in Patent Office: 489 Days
• Field of Search: 356/28, 738/610.6, 738/61, 738/610.2
• US Class Current: 356/28
• CPC Class Codes: G01P 13/02 Indicating direction only, e.g. by weather vane
• CPC Class Codes: G01P 5/26 by measuring the direct influence of the streaming fluid on the properties of a detecting optical wave
• CPC Class Codes: G01S 17/87 Combinations of systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/95 for meteorological use
• CPC Class Codes: G01S 7/4814 of transmitters alone
• CPC Class Codes: G01S 7/486 Receivers
• 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 system for measuring components of the velocity of wind along two axes that are transverse to the line of sight of the system includes first and second light emitter arrays disposed along crossed first and second axes, respectively, for illuminating the distribution with light, a detector for receiving light backscattered from the distribution, and a controller to activate the arrays, receive detector signals, and calculate the projections of the velocity of the distribution onto the first and second axes. The light emitters of each array can be positioned at irregular distances and provide the system with the capability of discerning the direction of movement of the distribution along the two axes.

Claims

1. A system for measuring a first axis projection and a second axis projection of a velocity of a distribution of particulate matter, the system comprising:

at least three first light emitters disposed along the first axis at irregular distances from one another and aimed substantially perpendicular to the first axis for aiming at and illuminating the distribution to cause a first light signal to be reflected from the distribution;

at least three second light emitters disposed along the second axis at irregular distances from one another and aimed substantially perpendicular to the second axis for aiming at and illuminating the distribution to cause a second light signal to be reflected from the distribution;

a detector for receiving the first light signal to produce a first detector signal and for receiving the second light signal to produce a second detector signal;

a controller coupled to the first light emitters, the second light emitters, and the detector, the controller programmed or adapted to calculate the first axis projection and the second axis projection of the velocity of the distribution in response to the first and second detector signals.

2. The system claimed in claim 1, wherein the controller alternately activates the first and second light emitters.

3. The system claimed in claim 1, wherein the first axis is substantially perpendicular to the second axis.

4. The system claimed in claim 1, wherein the irregular distances of the first light emitters are different from the irregular distances of the second light emitters.

5. The system claimed in claim 1, wherein the first light emitters are divergently aimed to illuminate the distribution.

6. The system claimed in claim 1, wherein the detector comprises a telescope oriented to collect at least the first light signal and a photomultiplier optically coupled to the telescope.

7. The system claimed in claim 1, wherein the first axis crosses the second axis at a position between two of the first light emitters and between two of the second light emitters.

8. The system claimed in claim 1, the controller comprising a data storage device for storing data representing the first detector signal and the second detector signal.

9. The system claimed in claim 1, further comprising a first light source optically coupled to each of the first light emitters, wherein at least one of the first light emitters comprises a beam splitter.

10. The system claimed in claim 9, wherein the first light source comprises a first laser.

11. The system claimed in claim 9, further comprising a second laser optically coupled to each of the second light emitters, wherein at least one of the second light emitters comprises a beam splitter.

12. A system for measuring the projection of a velocity of a distribution of particulate matter along an axis, the system comprising:

at least three first light emitters disposed along the axis at irregular distances from one another and aimed substantially perpendicular to the axis for aiming at and illuminating the distribution to cause a light signal to be reflected from the distribution;

a detector for receiving the light signal to produce a detector signal;

a controller coupled to light emitters and to the detector, the controller programmed or adapted to calculate the projection of the velocity of the distribution along the axis in response to the detector signal.

13. The system claimed in claim 12, wherein the light emitters are divergently aimed to illuminate the distribution.

14. The system claimed in claim 12, wherein the detector comprises a telescope oriented to collect at least the light signal and a photomultiplier optically coupled to the telescope.

15. The system claimed in claim 12, wherein the controller comprises a data storage device for storing data representing the first detector signal.

16. The system claimed in claim 12, further comprising a light source optically coupled to each of the light emitters, and wherein at least one of the light emitters comprises a beam splitter.

17. The system claimed in claim 16, wherein the light source comprises a laser.

18. A system for measuring a first axis projection and a second axis projection of a velocity of a distribution of particulate matter, the system comprising:

means for illuminating the distribution with first send pulses, each first send pulse comprising at least three first light beams disposed along the first axis at irregular distances from one another and aimed substantially perpendicular to the first axis for aiming at and illuminating the distribution to cause a first light signal to be reflected from the distribution;

means for illuminating the distribution with second send pulses, each second send pulse comprising at least three second light beams disposed along the second axis at irregular distances from one another and aimed substantially perpendicular to the second axis for aiming at and illuminating the distribution to cause a second light signal to be reflected from the distribution;

means for detecting the first light signal and producing a first detected signal and means for detecting the second light signal and producing a second detected signal;

means for calculating the first axis projection and the second axis projection of the velocity of the distribution in response to the first and second detected signals.

19. The system claimed in claim 18, further comprising means for alternately activating the first and second send pulses.

20. The system claimed in claim 18, wherein the first axis is substantially perpendicular to the second axis.

21. The system claimed in claim 18, wherein the irregular distances of the first light beams are different from the irregular distances of the second light beams.

22. The system claimed in claim 18, wherein the first light beams are divergently aimed to illuminate the distribution.

23. The system claimed in claim 18, wherein the means for detecting the first light signal and producing the first detected signal comprises a first telescope oriented to collect at least the first light signal and a first photomultiplier optically coupled to the first telescope.

24. The system claimed in claim 23, wherein the means for detecting the second light signal and producing the second detected signal comprises the first telescope and the first photomultiplier.

25. The system claimed in claim 18, wherein the first axis crosses the second axis at a position between two of the first light beams and between two of the second light beams.

26. The system claimed in claim 18, further comprising data storage means for storing data representing the first detected signal and the second detected signal.

27. The system claimed in claim 18, wherein the means for illuminating the distribution with first send pulses comprises a first laser.

28. The system claimed in claim 27, wherein the means for illuminating the distribution with first send pulses comprises a beam splitter.

29. The system claimed in claim 27, wherein the means for illuminating the distribution with second send pulses comprises the first laser.

30. A method of measuring a first axis projection and a second axis projection of a velocity of a distribution of particulate matter, the method comprising the steps of:

a) repeatedly generating first send pulses, each first send pulse comprising at least three first light beams disposed along the first axis at irregular distances from one another, the first light beams substantially perpendicular to the first axis and aimed at the distribution to repeatedly cause first return pulses to be reflected from the distribution, each first return pulse corresponding to a particular first send pulse;

b) repeatedly receiving the first return pulses with a detector and repeatedly producing first detector signals, each first detector signal representing a particular first return pulse;

c) repeatedly generating second send pulses, each second send pulse comprising at least three second light beams disposed along the second axis at irregular distances from one another, the second light beams substantially perpendicular to the second axis and aimed at the distribution to repeatedly cause second return pulses to be reflected from the distribution, each second return pulse corresponding to a particular second send pulse;

d) repeatedly receiving the second return pulses with the detector and repeatedly producing second detector signals, each second detector signal representing a particular second return pulse; and

e) calculating the first axis projection and the second axis projection of the velocity of the distribution in response to the repeatedly produced first and second detector signals.

31. The method claimed in claim 30, wherein steps a and c are performed together in alternating fashion with steps c and d performed together.

32. The method claimed in claim 30, wherein the irregular distances of the first light beams are different from the irregular distances of the second light beams.

33. The method claimed in claim 30, further comprising storing data representing the first detector signals and the second detector signals.

34. The method claimed in claim 30, wherein repeatedly producing first detector signals comprises producing a net first detector signal using a background function.

35. The method claimed in claim 30, wherein repeatedly receiving the first return pulses comprises sampling each first return pulse at a plurality of predetermined time intervals following the corresponding first send pulse, and wherein repeatedly receiving the second return pulses comprises sampling each second return pulse at a plurality of time intervals following the corresponding second send pulse, and wherein calculating the first axis projection and the second axis projection comprises calculating a plurality of first axis projections and second axis projections, wherein each projection is calculated in response to a plurality of the first and second return pulses sampled at the same time interval as eachother, whereby each time interval corresponds to an altitude at which the projections are calculated.

36. The method claimed in claim 30, wherein calculating the first axis projection and the second axis projection comprises calculating the logarithm of the ratio of the Fourier transform of the first detector signal to the Fourier transform of the second detector signal.

37. The method claimed in claim 30, wherein calculating the first and second axis projections comprises determining best-fit values fitted over all relevant frequencies for the reciprocals of the apparent velocities of the distribution along the first and second axes using a formula, the formula comprising:

$\ln <br><br>\left[\frac{F<br><br>\left[S_x<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(t\right)\right]}{F<br><br>\left[S_y<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(t\right)\right]}<br><br>\text{\hspace{1em}<br><br>}<br><br>R^{\&<br><br>1}\right]\ni <br><br>\underset{n\ni <br><br>0}{\overset{\mathrm{\infty <br><br>}}{\sum <br><br>}}<br><br>\text{\hspace{1em}<br><br>}<br><br>\frac{{\left(\&<br><br>\text{\hspace{1em}<br><br>}<br><br>i<br><br>\text{\hspace{1em}<br><br>}<br><br>\mathrm{\omega <br><br>}\right)}^n}{n!}<br><br>\text{\hspace{1em}<br><br>}<br><br>\left(c_x^n<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\kappa <br><br>}}_{n,x}\&<br><br><br><br>\text{\hspace{1em}<br><br>}<br><br>c_y^n<br><br>\text{\hspace{1em}<br><br>}<br><br>{\mathrm{\kappa <br><br>}}_{n,y}\right)$

wherein;

F[S_x(t)] represents the Fourier transform of the first detector signal, F[S_y(t)] represents the second detector signal, R represents the ratio of the sum total intensity of the first light beams to the sum total intensity of the second light beams, κ

_n,x represents statistical cumulants of the low order moments of the first array, κ

_n,y represents statistical cumulants of the low order moments of the second array, c_x represents the reciprocal of the apparent velocity of the distribution along the first axis, c_y represents the reciprocal of the apparent velocity of the distribution along the second axis, and ω

represents one of the relevant frequencies.