SYSTEM AND METHOD OF MEASURING FLOW VELOCITY IN THREE AXES

• US 20030043364A1
• Filed: 09/04/2001
• Published: 03/06/2003
• Est. Priority Date: 09/04/2001
• Status: Active Grant

• Current Assignee: Rosemount Aerospace, Inc. (Raytheon Technologies Corporation d/b/a RTX)
• Original Assignee: Rosemount Aerospace, Inc. (Raytheon Technologies Corporation d/b/a RTX)
• Inventors: Meneely, Clinton T., Ray, Mark D., Jamieson, James R.
• Granted Patent: US 6,542,227 B2
• Time in Patent Office: Days
• US Class Current: 356/28.5
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 17/58 Velocity or trajectory determination systems; Sense-of-movement determination systems
• CPC Class Codes: G01S 17/87 Combinations of systems using electromagnetic waves other than radio waves
• CPC Class Codes: G01S 17/88 Lidar systems specially adapted for specific applications
• CPC Class Codes: G01S 17/933 of aircraft or spacecraft
• CPC Class Codes: G01S 7/4812 transmitted and received beams following a coaxial path
• CPC Class Codes: G01S 7/4813 Housing arrangements
• CPC Class Codes: G01S 7/4817 relating to scanning
• CPC Class Codes: G01S 7/483 Details of pulse systems

Abstract

A LIDAR system for measuring flow velocity in three axes comprises: a LIDAR arrangement of optical elements for generating a coherent beam of light and directing the coherent beam of light by at least one rotationally operated optical element from the system with a predetermined pattern, the at least one rotationally operated optical element also for receiving reflections from particles along the predetermined pattern and directing the beam reflections to a light detector which converts the beam reflections into representative electrical signals; and a processor for detecting bursts from the electrical signals which are representative of light beam reflections from at least one particle substantially at a corresponding position along the predetermined pattern, and for computing a Doppler frequency for each of a selected plurality of detected bursts from the signal content thereof. The processor also capable of associating the selected plurality of detected bursts with their corresponding positions along the predetermined pattern and for computing a three axis flow velocity measurement from at least three of the selected plurality of computed Doppler frequencies and their corresponding positions along the predetermined pattern. A method of measuring flow velocity in three axes is further disclosed.

Claims

1. A light detection and ranging (LIDAR) system for measuring flow velocity in three axes, said system comprising:

at least one rotationally operated optical element;

a LIDAR arrangement of optical elements for generating a coherent beam of light and directing said coherent beam of light substantially on a first optical path incident on said at least one rotationally operated optical element which directs said coherent beam of light from said system along a second optical path of a predetermined pattern, said at least one rotationally operated optical element also for receiving reflections of said coherent beam of light from particles along said predetermined pattern and directing said beam reflections to said LIDAR arrangement of optical elements;

a light detector;

said LIDAR arrangement of optical elements for directing said beam reflections to said light detector which converts said beam reflections into representative electrical signals;

processing means coupled to said light detector for detecting electrical signal bursts from said electrical signals, each signal burst being representative of light beam reflections from at least one particle substantially at a corresponding position along said predetermined pattern, and for computing a Doppler frequency for each of a selected plurality of detected electrical signal bursts from the signal content thereof,

said processing means for associating said selected plurality of detected electrical signal bursts with their corresponding positions along said predetermined pattern and for computing a three axis flow velocity measurement from at least three of the selected plurality of computed Doppler frequencies and their corresponding positions along said predetermined pattern.

2. The system of claim 1 wherein the processing means includes at least one digital processor, and means for digitizing the electrical signals from the light detector and providing said digitized electrical signals to said at least one digital processor.

3. The system of claim 2 wherein the at least one digital processor includes:

a first digital processor coupled to the digitizing means for receiving the digitized electrical signals, detecting the electrical signal bursts therefrom, and computing the Doppler frequency for each of the selected plurality of detected electrical signal bursts from the digitized signal content thereof, and

a second digital processor coupled to said first digital processor for receiving data words from said first signal processor, each data word being representative of the Doppler frequency of one of the selected plurality of detected electrical signal bursts, said second processor for associating said data words with their corresponding positions along said predetermined pattern and for computing a 3-axis flow velocity measurement from at least three of said data words and their corresponding positions along said predetermined pattern.

4. The system of claim 1 including a three orthogonal axis coordinate system with two of the orthogonal axes being in a plane of the predetermined pattern of the coherent beam of light and the third axis projected along a line of sight of the LIDAR system and substantially perpendicular to said plane;

and wherein one of the two orthogonal axes in said plane being a reference axis.

5. The system of claim 4 wherein the processing means includes means for determining angular positions of the particles, causing the detected electrical signal bursts, along the predetermined pattern in the plane based on the reference axis;

and means for selecting the at least three computed Doppler frequencies based on the relative angular positions of the corresponding particles along the predetermined pattern in the plane with respect to each other.

6. The system of claim 5 wherein the processing means includes means for computing a single axis flow velocity measurement from each of the selected Doppler frequencies;

and means for computing the three axis flow velocity measurement using the three orthogonal axis coordinate system based on a function of the computed single axis flow velocity measurements and the angular positions of the corresponding particles along the predetermined pattern in the plane with respect to the reference axis.

7. The system of claim 6 wherein the processing means includes means for computing the three axis flow velocity measurement based on a function of the computed single axis flow velocity measurements, the angular positions of the corresponding particles along the predetermined pattern in the plane with respect to the reference axis, and an angle that the second optical path makes with the third axis.

8. The system of claim 5 wherein the predetermined pattern is cyclical;

including means for generating a signal at substantially the same point along the pattern cycle; and

wherein the reference axis is aligned by the generated signal substantially at said point along the predetermined pattern in the plane.

9. The system of claim 8 wherein the angular position determining means includes means for determining the angular positions along the predetermined pattern from the generated pattern cycle signals using time based measurement techniques.

10. The system of claim 1 wherein the at least one rotationally operated optical element also for scanning the predetermined pattern of the coherent beam of light azimuthally about a line of sight of the LIDAR system;

including means for determining the azimuth position of said scan and generating a signal representative thereof to the processing means; and

wherein the processing means includes means for computing three axis flow velocity measurements at various determined azimuth positions based on said generated azimuth position signals.

11. The system of claim 1 wherein the LIDAR system is operative on an aircraft which has a three axis coordinate system;

and wherein the processing means includes means for computing three axis flow velocity measurements based on a three axis coordinate system of the LIDAR system; and

means for converting the three axis flow velocity measurements of the LIDAR system coordinates to three axis flow velocity measurements based on the aircraft coordinates.

12. The system of claim 1 including a display unit coupled to the processing means;

and wherein the processing means includes means for controlling the display of the computed three axis flow velocity measurements on said display unit.

13. Method of measuring flow velocity in three axes, said method comprising the steps of:

generating a coherent beam of light and directing said coherent beam of light into space substantially along an optical path of a predetermined pattern;

receiving reflections of said coherent beam of light from particles in space along said predetermined pattern;

converting said light beam reflections into representative electrical signals;

detecting electrical signal bursts from said electrical signals, each signal burst being representative of light beam reflections from at least one particle substantially at a corresponding position along said predetermined pattern;

computing a Doppler frequency for each of a selected plurality of detected electrical signal bursts from the signal content thereof,

associating said selected plurality of detected electrical signal bursts with their corresponding positions along said predetermined path; and

computing a three axis flow velocity measurement from at least three of the selected plurality of computed Doppler frequencies and their corresponding positions along said predetermined path.

14. The method of claim 13 including the step of choosing a three orthogonal axis coordinate system with two of the orthogonal axes being in a plane of the predetermined pattern of the coherent beam of light and the third axis projected along a line of sight of the LIDAR system and substantially perpendicular to said plane;

and wherein one of the two orthogonal axes in said plane being a reference axis.

15. The method of claim 14 including the steps of:

determining angular positions of the particles, causing the detected electrical signal bursts, along the predetermined pattern in the plane based on the reference axis; and

selecting the at least three computed Doppler frequencies based on the relative angular positions of the corresponding particles along the predetermined pattern in the plane with respect to each other.

16. The method of claim 15 including the steps of:

computing a single axis flow velocity measurement from each of the selected Doppler frequencies; and

computing the three axis flow velocity measurement using the three orthogonal axis coordinate system based on a function of the computed single axis flow velocity measurements and the angular positions of the corresponding particles along the predetermined pattern in the plane with respect to the reference axis.

17. The method of claim 16 including the step of computing the three axis flow velocity measurement based on a function of the computed single axis flow velocity measurements, the angular positions of the corresponding particles along the predetermined pattern in the plane with respect to the reference axis, and an angle that the second optical path makes with the third axis.

18. The method of claim 15 wherein the predetermined pattern of the coherent beam of light is generated cyclical;

including the step of generating a signal at substantially the same point along the pattern cycle; and

aligning the reference axis by the generated signal substantially at said point along the predetermined pattern in the plane.

19. The method of claim 18 including the step of determining the angular positions along the predetermined pattern from the generated pattern cycle signals using time based measurement techniques.

20. The method of claim 13 including the steps of:

scanning the predetermined pattern of the coherent beam of light azimuthally about a line of sight;

determining the azimuth position of said scan;

computing three axis flow velocity measurements at various determined azimuth positions based on said determined azimuth position signals.

21. The method of claim 13 including the step of converting the three axis flow velocity measurements from one three axis coordinate system to another.

22. The method of claim 13 including the step of displaying the computed three axis flow velocity measurements on a display unit.