System for profiling objects on terrain forward and below an aircraft utilizing a cross-track laser altimeter

• US 20040141170A1
• Filed: 01/21/2003
• Published: 07/22/2004
• Est. Priority Date: 01/21/2003
• Status: Active Grant

• Current Assignee: Rosemount Aerospace, Inc. (Rtx Corporation)
• Original Assignee: Rosemount Aerospace, Inc. (Rtx Corporation)
• Inventors: Ray, Mark D., Jamieson, James R., Pesik, Joseph T.
• Granted Patent: US 7,095,488 B2
• Time in Patent Office: Days
• US Class Current: 356/5.01
• CPC Class Codes: G01S 17/42 Simultaneous measurement of distance and other co-ordinates indirect measurement G01S17/46
• CPC Class Codes: G01S 17/89 for mapping or imaging
• CPC Class Codes: G01S 17/933 of aircraft or spacecraft
• CPC Class Codes: G01S 7/4811 common to transmitter and receiver
• CPC Class Codes: G01S 7/4817 relating to scanning
• CPC Class Codes: G01S 7/483 Details of pulse systems
• CPC Class Codes: G01S 7/499 using polarisation effects

Abstract

A forward looking cross-track laser altimeter comprises: a first configuration of optical elements for guiding pulsed laser beams along a first optical path; a mirror element coupled to a scanner and disposed in the first optical path, the scanner operative to oscillate the mirror element to sweep the reflected laser beams back and forth across a line at a predetermined frequency; the scanner and mirror element configurable to reflect the pulsed laser beams along paths forward and downward at a predetermined angle to the flight path of the aircraft, wherein the pulsed laser beam paths are caused to be line swept across a ground track forward the aircraft; the mirror element for receiving returns of the pulsed laser beams from the terrain and objects on the terrain forward the aircraft and reflecting the returns along a second optical path to a light detector which produces a return signal in response thereto; a first circuit governed by the return signals for measuring times-of-flight of the returns and generating time-of-flight signals corresponding thereto; the scanner for generating a line sweep position signal; and a second circuit for generating for each return a data profile comprising range and line sweep position thereof based on the corresponding time-of-flight and position signals.

Claims

1. A forward looking cross-track laser altimeter disposable on-board an aircraft for profiling objects on terrain forward of the aircraft, said laser altimeter comprising:

a laser source for generating pulsed laser beams at a predetermined rate;

a first configuration of optical elements for guiding the pulsed laser beams along a first optical path;

a scanner;

a mirror element coupled to said scanner and disposed in the first optical path to reflect the pulsed laser beams, said scanner operative to oscillate the mirror element to sweep the reflected laser beams back and forth across a line at a predetermined frequency;

said scanner and mirror element configurable to reflect the pulsed laser beams along paths forward and downward at a predetermined angle to the flight path of the aircraft, wherein the pulsed laser beam paths are caused to be line swept across a ground track forward the aircraft;

said mirror element for receiving returns of said pulsed laser beams from the terrain and objects on the terrain forward the aircraft and reflecting said returns along a second optical path;

a light detector;

a second configuration of optical elements for guiding said returns from said second optical path to said light detector which produces a return signal in response to a detection of each return;

a first circuit coupled to said light detector and governed by the return signals for measuring times-of-flight of said returns and generating time-of-flight signals corresponding thereto;

said scanner for generating a position signal representative of a position of the laser beam in the line sweep; and

a second circuit coupled to said scanner and first circuit for generating for each return a data profile comprising range and line sweep position thereof based on the corresponding time-of-flight and position signals.

2. The laser altimeter of claim 1 wherein the second circuit is operative to receive a signal representative of aircraft position in latitude and longitude and to include the aircraft'"'"'s position in the data profiles.

3. The laser altimeter of claim 1 wherein the second circuit is operative to receive a signal representative of the inertial state of the aircraft and to include the aircraft'"'"'s inertial state in the data profiles.

4. The laser altimeter of claim 1 wherein the second circuit is operative to output the generated data profiles sequentially in an order corresponding to each line sweep of the pulsed laser beam.

5. The laser altimeter of claim 1 wherein the second circuit is operative to generate the data profiles sequentially in real time as the corresponding return signals are being produced.

6. The laser altimeter of claim 5 wherein the second circuit is operative to output the data profiles sequentially in real time as they are being generated.

7. The laser altimeter of claim 1 wherein the laser source comprises a passively Q switched microchip laser autonomously operative to generate the pulsed laser beams at the predetermined rate.

8. The laser altimeter of claim 1 wherein the laser source is operative to generate the pulsed laser beams at a rate in the approximate range of eight thousand to ten thousand pulses per second.

9. The laser altimeter of claim 1 including a beam expander disposed in the first optical path for expanding the beam by a predetermined magnification.

10. The laser altimeter of claim 9 wherein the beam expander includes optical elements folded into a penta-prism configuration.

11. The laser altimeter of claim 1 wherein the first and second configurations of optical elements are fixedly aligned in a mono-static configuration.

12. The laser altimeter of claim 1 wherein the first configuration of optical elements guides a portion of the pulsed laser beams along an optical path to the light detector which produces initial signals in response thereto;

and wherein the first circuit is governed by the initial and return signals for measuring times-of-flight of said returns.

13. The laser altimeter of claim 1 wherein the scanner comprises a resonant scanner.

14. The laser altimeter of claim 1 wherein the scanner is operative to oscillate the mirror element to sweep the reflected laser beams back and forth across the line at a frequency of approximately one-hundred hertz.

15. The laser altimeter of claim 1 wherein the elements of the laser altimeter are disposed within an enclosed housing which has a windowed area on one side for passing the reflected pulsed light beams from the housing.

16. The laser altimeter of claim 15 wherein the enclosed housing is mountable to the skin of the aircraft in an orientation in which the windowed area side is directed downward towards the terrain.

17. The laser altimeter of claim 1 wherein the scanner and mirror element are configurable to reflect the pulsed laser beams along paths directly downward from the aircraft, wherein the pulsed laser beam paths are caused to be line swept across a ground track directly below the aircraft;

and wherein the mirror element receives returns of the pulsed laser beams from the terrain and objects on the terrain directly below the aircraft.

18. A laser-based system disposed on-board an aircraft for profiling objects on the terrain forward of the aircraft during flight for use in the guidance and control of the aircraft, said system comprising:

a forward looking cross track laser altimeter operative to emit pulsed laser beams at a predetermined rate along line swept paths forward and downward at a predetermined angle to the flight path of the aircraft, said pulsed laser beams being line swept back and forth across a ground track forward the aircraft and as the aircraft moves along its flight path, said line sweeps serpentining an area of terrain forward the aircraft, said laser altimeter for receiving returns of said pulsed laser beams from the terrain and objects on the terrain in said area forward the aircraft;

said laser altimeter operative to measure times-of-flight and line sweep positions of said returns and generate for each return a data profile comprising range and line sweep position thereof based on the corresponding time-of-flight and position measurements, said data profiles being output from the laser altimeter;

a first unit coupled to the laser altimeter for receiving said return data profiles and for assembling the data profiles of a predetermined number of consecutive line sweeps to form composite data of a three-dimensional image of a first predetermined area of terrain forward the aircraft, said composite data of the three dimensional image including data of terrain contours and object profiles on the terrain;

a memory storing a terrain contour data base;

a second unit coupled to said first unit for accessing said memory to retrieve terrain contour data comprising terrain contour data of a second predetermined area substantially consistent with the boundaries of the first predetermined area, and for comparing data of the first and second predetermined areas to identify object profiles on the terrain in the first predetermined area for use in the guidance and control of the aircraft.

19. The system of claim 18 wherein the laser altimeter is operative to receive a signal representative of aircraft position in latitude and longitude and to include the aircraft'"'"'s position in the return data profiles.

20. The system of claim 19 wherein the laser altimeter is operative to include the aircraft'"'"'s position with each line sweep of the return data profiles.

21. The system of claim 18 wherein the laser altimeter is operative to receive a signal representative of an inertial state of the aircraft and to include the aircraft'"'"'s inertial state in the data profiles.

22. The system of claim 18 wherein the laser altimeter is operative to output the return data profiles in a data stream having a sequential order corresponding to each line sweep of the pulsed laser beam.

23. The system of claim 18 wherein the laser altimeter is operative to generate the data profiles sequentially in real time as the corresponding return signals are being produced.

24. The system of claim 23 wherein the laser altimeter is operative to output the data profiles sequentially in real time as they are being generated.

25. The system of claim 18 wherein the first unit is operative to assemble the data profiles of the most recent predetermined number of consecutive line sweeps to form composite data of a three-dimensional image of the first predetermined area of terrain which becomes a sliding window area of terrain along the ground track of the aircraft during flight.

26. The system of claim 25 wherein the laser altimeter is operative to receive a signal representative of instantaneous aircraft position in latitude and longitude and to include the aircraft'"'"'s position in the return data profiles;

and wherein the first unit is operative to establish a geographical location and latitude and longitude boundaries of the first predetermined area based on return data profiles and associated instantaneous aircraft position thereof.

27. The system of claim 26 including a global positioning system (GPS) receiver for providing a signal representative of the instantaneous position of the aircraft for use by the laser altimeter.

28. The system of claim 26 wherein the second unit is operative to access the memory to retrieve terrain contour data of the second predetermined area based substantially on the established geographical location and latitude and longitude boundaries of the first predetermined area.

29. The system of claim 18 including a third unit coupled to the second unit for defining a safe flight volume forward the aircraft based on the identified object profiles of the first predetermined area.

30. The system of claim 29 wherein the aircraft is an unmanned air vehicle (UAV) including a flight control director unit for autonomous control of the UAV based on the safe flight volume data from the third unit.

31. The system of claim 29 including an air-to-air collision avoidance system for determining other aircraft in a volume of space surrounding the aircraft, said collision avoidance system being coupled to the third unit for use in defining the safe flight volume.

32. The system of claim 29 including a laser obstacle avoidance system for detecting obstacles in proximity to the flight path of the aircraft, said laser obstacle avoidance system coupled to the third unit for use in defining the safe flight volume.

33. The system of claim 18 including a laser wind speed sensor for determining the wind speed surrounding the aircraft for use in the guidance and control of the aircraft.

34. The system of claim 18 wherein the second unit is operative to integrate the data of the first and second predetermined areas to form composite terrain and object on terrain data for use in the guidance and control of the aircraft.

35. The system of claim 34 wherein the aircraft is an unmanned air vehicle (UAV) including a flight control director unit for autonomous control of the UAV based on the composite terrain and object on terrain data from the second unit.

36. The system of claim 18 including a third unit for identifying a target concealed by a common object on the terrain forward the aircraft, said third unit being operative to collect return data profiles of said common object from each of a plurality of different approach aircraft flight paths and to integrate said return data profiles to form a composite three dimensional image of said common object from which to identify said concealed target.

37. A laser-based system disposed on-board an aircraft for identifying a target concealed by a common object on the terrain from a plan view of the common object from the aircraft during flight, said system comprising:

a forward looking cross track laser altimeter operative to emit pulsed laser beams at a predetermined rate along line swept paths forward and downward at a predetermined angle to the flight path of the aircraft, said pulsed laser beams being line swept back and forth across a ground track forward the aircraft and as the aircraft moves along its flight path, said line sweeps serpentining an area of terrain forward the aircraft, said laser altimeter for receiving returns of said pulsed laser beams from said common object, said target concealed thereby and surrounding terrain in said area forward the aircraft;

said laser altimeter operative to measure times-of-flight and line sweep positions of said returns and generate for each return a data profile comprising range and line sweep position thereof based on the corresponding time-of-flight and position measurements, said data profiles being output from the laser altimeter; and

a first unit coupled to the laser altimeter for receiving said return data profiles and for assembling the data profiles of a predetermined number of consecutive line sweeps to form composite data of a three-dimensional image of said common object and target concealed thereby for each of a plurality of different approach flight paths, wherein each three-dimensional image providing a view orientation of said common object and target concealed thereby based on the corresponding approach flight path associated therewith;

said first unit for integrating the composite data of said different viewed three-dimensional images to form a comprehensive three dimensional image of the common object and target concealed thereby, and for identifying the concealed target from said comprehensive three dimensional image.

38. The system of claim 37 wherein the first unit is operative to receive a signal representative of aircraft position in latitude and longitude and to determine a geographic location of the common object based on the aircraft position signal and data profiles of the common object;

and wherein the first unit is operative to assemble the data profiles of the predetermined number of consecutive line sweeps to form composite data of the three-dimensional image of the common object and target concealed thereby for each of a plurality of different approach flight paths based on the geographic location determined for the common object.

39. The system of claim 38 including a GPS receiver for providing the signal representative of the aircraft'"'"'s position.

40. The system of claim 37 wherein the common object comprises a tree and the target is concealed under a canopy of the tree.

41. A laser altimeter disposable on-board an aircraft for profiling objects on terrain forward of the aircraft during flight, said laser altimeter comprising:

a laser source for generating pulsed laser beams at a predetermined rate;

a first configuration of optical elements for guiding the pulsed laser beams along a first optical path and including an optical element configurable to direct the pulsed laser beams from the first optical path to paths forward and downward at a predetermined angle to the flight path of the aircraft, wherein the pulsed laser beam paths are guided along a path on the terrain forward the aircraft;

said optical element for receiving returns of said pulsed laser beams from the terrain and objects on the terrain along said terrain path forward the aircraft and directing said returns along a second optical path;

a light detector;

a second configuration of optical elements for guiding said returns from said second optical path to said light detector which produces a return signal in response to a detection of each return;

a first circuit coupled to said light detector and governed by the return signals for measuring times-of-flight of said returns and generating time-of-flight signals corresponding thereto; and

a second circuit coupled to said first circuit for generating data profiles for the returns, each data profile comprising a range based on the time-of-flight signal of the corresponding return.

42. The laser altimeter of claim 41 wherein the second circuit is operative to receive a signal representative of aircraft position in latitude and longitude and to include the aircraft'"'"'s position in the data profiles.

43. The laser altimeter of claim 41 wherein the second circuit is operative to receive a signal representative of the inertial state of the aircraft and to include the aircraft'"'"'s inertial state in the data profiles.

44. The laser altimeter of claim 41 including a beam expander disposed in the first optical path for expanding the beam by a predetermined magnification.

45. The laser altimeter of claim 44 wherein the beam expander includes optical elements folded into a penta-prism configuration.

46. The laser altimeter of claim 41 wherein the first and second configurations of optical elements are fixedly aligned in a mono-static configuration.

47. The laser altimeter of claim 41 wherein the first configuration of optical elements guides a portion of the pulsed laser beams along an optical path to the light detector which produces initial signals in response thereto;

and wherein the first circuit is governed by the initial and return signals for measuring times-of-flight of said returns.

48. The laser altimeter of claim 41 wherein the elements of the laser altimeter are disposed within an enclosed housing which has a windowed area on one side for passing the directed pulsed light beams from the housing.

49. The laser altimeter of claim 48 wherein the enclosed housing is mountable to the skin of the aircraft in an orientation in which the windowed area side is directed downward towards the terrain.

50. The laser altimeter of claim 41 wherein the optical element is configurable to direct the pulsed laser beams along a path directly downward from the aircraft;

and wherein the optical element receives returns of the pulsed laser beams from the terrain and objects on the terrain directly below the aircraft.