System for detecting ice or snow on surface which specularly reflects light

• US 5,838,239 A
• Filed: 09/10/1996
• Issued: 11/17/1998
• Est. Priority Date: 10/20/1992
• Status: Expired due to Fees

• Current Assignee: Rosemount Aerospace, Inc. (Rtx Corporation)
• Original Assignee: Robotic Vision Systems, Inc. (Omron Corporation)
• Inventors: Stern, Howard, Schaefer, John, Maali, Fereydoun
• Primary Examiner(s): MULLEN, THOMAS J
• Application Number:
  US08/712,059
• Time in Patent Office: 798 Days
• Field of Search: 340/583, 340/962, 340/511, 340/601, 340/602, 356/381, 356/382, 356/369, 73/170.26, 244/134 F, 348/128, 348/143
• US Class Current: 340/583
• CPC Class Codes: B64D 15/20 Means for detecting icing or initiating de-icing
• CPC Class Codes: B64F 5/20 Ground installations for de-icing aircraft
• CPC Class Codes: G08B 19/02 Alarm responsive to formation or anticipated formation of ice

Abstract

A presence of a polarization altering substance on a specular surface is detected by transmitting light from a single strobed light source to the surface over a transmitting path and receiving the transmitted light from the surface. An intensity of the light is measured in both an optical non-isolator state and an isolator state by a same detector by delaying the non-isolated return light for a definite period of time before measuring it with the detector. The measured isolated and non-isolated intensities are converted to logarithmic form, range corrected, and compared to reference data established for the specific specular surface being investigated to detect the presence or absence of the polarization altering substance. Attenuation and backscattering effects of scattering and/or absorbing interference in the transmitted light are compensated so that the reference table is entered at the correct point. Using different intensities of transmitted light increases the dynamic range of the system.

Claims

1. Apparatus for detecting, on a surface which specularly reflects light, the presence of a polarization altering substance on said surface comprising:

means for transmitting a pulse of light over a transmitting path to said surface;

means for receiving transmitted light;

a receiving path for said transmitted light from said surface and from said substance to said means for receiving;

means for splitting said transmitted light into a non-isolated portion and an isolated portion;

means for delaying one of said non-isolated portion and said isolated portion relative to another thereof to produce a first-to-arrive signal and a second-to-arrive signal;

said first-to-arrive signal being completed at an output of said means for delaying before said second-to-arrive signal arrives at said output;

means for measuring a first intensity of said first-to-arrive signal and outputting a first signal;

means for measuring a second intensity of light of said second-to-arrive signal and outputting a second signal; and

means for comparing said first and second intensities of light to reference data to detect the presence of said substance on said surface.

2. Apparatus as in claim 1, further comprising:

means for outputting a first logarithmic signal from said first signal;

means for outputting a second logarithmic signal from said second signal;

means, responsive to a length of said receiving path, for range-correcting said first and second logarithmic signals to produce a range-corrected first logarithmic signal and a range-corrected second logarithmic signal;

means for comparing said range-corrected second logarithmic signal to said range-corrected first logarithmic signal and outputting a ratio signal;

means for calculating a threshold signal; and

means for comparing said ratio signal to said threshold signal.

3. Apparatus as in claim 2, wherein said ratio signal represents said second range-corrected logarithmic signal subtracted from said first range-corrected logarithmic signal.

4. Apparatus as in claim 1, wherein said reference data are in logarithmic form.

5. Apparatus as in claim 1, further comprising means for establishing said reference data by measuring said first and second intensities at a reference distance from said surface when said surface is a known surface with said polarization altering substance absent from said known surface.

6. Apparatus as in claim 5, wherein said means for establishing said reference data further comprises:

means for calculating a first ratio of said second intensity to said first intensity and making a first comparison of said first ratio to said second intensity when said polarization altering substance is absent from said known surface;

means for calculating a second ratio of said second intensity to said first intensity and making a second comparison of said second ratio to said second intensity when said polarization altering substance is present on said surface; and

means for determining a threshold to establish a difference between said first and second comparisons, said threshold representing different conditions of the surface being investigated.

7. Apparatus as in claim 6, wherein one of said conditions of said surface is the presence of one of ice and snow and another condition an absence thereof.

8. Apparatus as in claim 5, wherein said transmitting path and said receiving path are substantially a same length as said reference distance used by said means for establishing reference data.

9. Apparatus as in claim 5, wherein said transmitting path and said receiving path are substantially a different length from said reference distance and said means for comparing includes means for correcting for said different length.

10. Apparatus as in claim 5, wherein said means for establishing said reference data includes means for measuring said first and second intensities when said surface is a known surface with said polarization altering substance absent from said known surface at a plurality of angles with respect to a normal of said surface.

11. Apparatus as in claim 5, wherein said means for establishing said reference data includes means for measuring said first and second intensities at a plurality of angles with respect to a normal of said surface when said surface is a known surface with said polarization altering substance present.

12. Apparatus as in claim 1, wherein:

said means for transmitting light includes only one transmitter; and

said means for receiving transmitted light includes only one receiver.

13. Apparatus as in claim 1, wherein said means for delaying one of said non-isolated portion and said isolated portion includes optical fiber.

14. Apparatus as in claim 1, wherein said means for measuring a first intensity, said means for measuring a second intensity, and said means for comparing said first and second intensities are separated from said means for splitting by said means for delaying one of said non-isolated portion and said isolated portion.

15. Apparatus for detecting, on a surface which specularly reflects light, the presence of a polarization altering substance on said surface comprising:

means for transmitting a pulse of polarized light onto said surface;

means for receiving said pulse reflected from said surface;

means for directing said reflected pulse onto a non-blocking optical path to a detector;

means for directing said reflected pulse onto a blocking optical path to said detector; and

one of said blocking and non-blocking optical paths having a delay exceeding a pulse length of said pulse, whereby responses of said detector to said reflected pulse directed onto said blocking and non-blocking optical paths are separated.

16. Apparatus as in claim 15, further comprising optical fiber effective for producing said delay.

17. Apparatus as in claim 15, wherein said detector comprises:

means for measuring a first intensity of said reflected pulse directed onto one of said blocking and non-blocking optical paths not having said delay and outputting a first signal; and

means for measuring a second intensity of said reflected pulse directed onto another one of said blocking and non-blocking optical paths having said delay and outputting a second signal.

18. Apparatus as in claim 17, further comprising means for comparing said first and second intensities to reference data to detect the presence of said substance on said surface.

19. Apparatus as in claim 17, further comprising:

means for outputting a first logarithmic signal from said first signal;

means for outputting a second logarithmic signal from said second signal;

means, responsive to a length of one of said non-blocking and blocking optical paths, for range-correcting said first and second logarithmic signals to produce a range-corrected first logarithmic signal and a range-corrected second logarithmic signal;

means for comparing said range-corrected second logarithmic signal to said range-corrected first logarithmic signal and outputting a ratio signal;

means for calculating a threshold signal; and

means for comparing said ratio signal to said threshold signal.

20. Apparatus as in claim 19, wherein said ratio signal represents said second range-corrected logarithmic signal subtracted from said first range-corrected logarithmic signal.

21. Apparatus as in claim 18, wherein said reference data are in logarithmic form.

22. Apparatus as in claim 18, further comprising means for establishing said reference data by measuring said first and second intensities at a reference distance from said surface when said surface is a known surface with said polarization altering substance absent from said known surface.

23. Apparatus as in claim 22 wherein said means for establishing said reference data further comprises:

means for calculating a first ratio of said second intensity to said first intensity and making a first comparison of said first ratio to said second intensity when said polarization altering substance is absent from said known surface;

means for calculating a second ratio of said second intensity to said first intensity and making a second comparison of said second ratio to said second intensity when said polarization altering substance is present on said surface; and

means for determining a threshold to establish a difference between said first and second comparisons representing different conditions of the surface being investigated.

24. Apparatus as in claim 23 wherein one of said conditions of said surface is the presence of one of ice and snow and another condition an absence thereof.

25. Apparatus as in claim 18 wherein said means for establishing said reference data includes means for measuring said first and second intensities when said surface is a known surface with said polarization altering substance absent from said known surface at a plurality of angles with respect to a normal of said surface.

26. Apparatus as in claim 18 wherein said means for establishing said reference data includes means for measuring said first and second intensities at a plurality of angles with respect to a normal of said surface when said surface is a known surface with said polarization altering substance present.

27. Apparatus as in claim 18 wherein said means for measuring a first intensity, said means for measuring a second intensity, and said means for comparing said first and second intensities are separated from said means for receiving by one of said means for directing said reflected pulse onto said non-blocking optical path and said means for directing said reflected pulse onto said blocking optical path.

28. Apparatus for detecting on a surface which specularly reflects light, the presence of a polarization altering substance on said surface comprising:

means for transmitting light over a transmitting path to said surface;

means for receiving transmitted light;

a receiving path for said transmitted light from said surface and from said substance to said means for receiving;

optical means in at least one of said transmitting path and said receiving path;

means for alternating said optical means between an optical non-isolator state and an optical isolator state;

said means for receiving including means for measuring a first intensity of light received at said means for receiving when said optical means is in said optical non-isolator state, and means for measuring a second intensity of light received at said means for receiving when said optical means is in said optical isolator state;

means for compensating said measured first intensity of light for effects of scattering and/or absorbing interference of said transmitted light; and

means for comparing said compensated first intensity and said second intensity of light to a plurality of reference data to detect the presence of said substance on said surface.

29. Apparatus as in claim 28, wherein said reference data are in logarithmic form.

30. Apparatus as in claim 28, further comprising means for establishing said reference data by measuring said first and second intensities at a reference distance from said surface when said surface is a known surface with said polarization altering substance absent from said known surface.

31. Apparatus as in claim 30 wherein said means for establishing said reference data further comprises:

means for calculating a first ratio of said first intensity to said second intensity and making a first comparison of said first ratio to said first intensity when said polarization altering substance is absent from said known surface;

means for calculating a second ratio of said first intensity to said second intensity and making a second comparison of said second ratio to said first intensity when said polarization altering substance is present on said surface; and

means for determining a threshold to establish a difference between said first and second comparisons representing different conditions of the surface being investigated.

32. Apparatus as in claim 31 wherein one of said conditions of said surface is the presence of one of ice and snow and another condition an absence thereof.

33. Apparatus as in claim 30 wherein:

said transmitting path and said receiving path are substantially a same length as said reference distance used by said means for establishing reference data.

34. Apparatus as in claim 30 wherein said transmitting path and said receiving path are substantially a different length from said reference distance and said means for comparing includes means for correcting for said different length.

35. Apparatus as in claim 30 wherein said means for establishing said reference data includes means for measuring said first and second intensities when said surface is a known surface with said polarization altering substance absent from said known surface at a plurality of angles with respect to a normal of said surface.

36. Apparatus as in claim 30 wherein said means for establishing said reference data includes means for measuring said first and second intensities at a plurality of angles with respect to a normal of said surface when said surface is a known surface with said polarization altering substance present.

37. Apparatus as in claim 28 wherein:

said means for transmitting light includes only one transmitter; and

said means for receiving transmitted light includes at least one receiver.

38. Apparatus as in claim 28 wherein:

said means for transmitting light includes at least one transmitter; and

said means for receiving transmitted light includes only one receiver.

39. Apparatus as in claim 28 wherein:

said means for transmitting light includes at least one transmitter; and

said means for receiving transmitted light includes at least one receiver.

40. Apparatus for detecting on a surface which specularly reflects light, the presence of a polarization altering substance on said surface comprising:

means for transmitting light over a transmitting path to said surface;

means for receiving transmitted light;

a receiving path for said transmitted light from said surface and from said substance to said means for receiving;

optical means in at least one of said transmitting path and said receiving path;

means for alternating said optical means between an optical non-isolator state and an optical isolator state;

means for measuring a first intensity of light received at said means for receiving when said optical means is in said optical non-isolator state and outputting a first signal;

means for compensating said first signal for effects of scattering and/or absorbing interference of said transmitted light and outputting a compensated first signal;

means for measuring a second intensity of light received at said means for receiving when said optical means is in said optical isolator state and outputting a second signal;

means, responsive to a length of said receiving path, for range-correcting said first compensated signal and said second signal;

means for comparing said range-corrected second signal to said range-corrected compensated first signal and outputting a ratio signal;

means for calculating a threshold signal; and

means for comparing said ratio signal to said threshold signal.

41. Apparatus according to claim 40, wherein:

said means for comparing said range-corrected second signal to said range-corrected compensated first signal includes a computer; and

said means for comparing said ratio signal to said threshold signal includes said computer.

42. Apparatus for detecting, on a surface which specularly reflects light, the presence of a polarization altering substance on said surface comprising:

means for transmitting a pulse of light over a transmitting path to said surface;

means for receiving transmitted light;

a receiving path for said transmitted light from said surface and from said substance to said means for receiving;

means for splitting said transmitted light into a non-isolated portion and an isolated portion;

means for delaying one of said non-isolated portion and said isolated portion relative to another thereof to produce a first-to-arrive signal and a second-to-arrive signal;

said first-to-arrive signal being completed at an output of said means for delaying before said second-to-arrive signal arrives at said output;

means for measuring a first intensity of said first-to-arrive signal and outputting a first signal;

means for measuring a second intensity of light of said second-to-arrive signal and outputting a second signal;

means for compensating said first signal for effects of scattering and/or absorbing interference of said transmitted light and outputting a compensated first signal; and

means for comparing said compensated first signal and said second signal to reference data to detect the presence of said substance on said surface.

43. Apparatus as in claim 42, further comprising:

means for compensating said second signal for effects of scattering and/or absorbing interference of said transmitted light and outputting a compensated second signal;

means for comparing said compensated second signal to said compensated first signal and outputting a ratio signal;

means for calculating a threshold signal; and

means for comparing said ratio signal to said threshold signal.

44. Apparatus as in claim 42, wherein said reference data are in logarithmic form.

45. Apparatus as in claim 42, further comprising means for establishing said reference data by measuring said first and second intensities at a reference distance from said surface when said surface is a known surface with said polarization altering substance absent from said known surface.

46. Apparatus as in claim 45, wherein said means for establishing said reference data further comprises:

means for calculating a first ratio of said second intensity to said first intensity and making a first comparison of said first ratio to said second intensity when said polarization altering substance is absent from said known surface;

means for calculating a second ratio of said second intensity to said first intensity and making a second comparison of said second ratio to said second intensity when said polarization altering substance is present on said surface; and

means for determining a threshold to establish a difference between said first and second comparisons, said threshold representing different conditions of the surface being investigated.

47. Apparatus as in claim 46, wherein one of said conditions of said surface is the presence of one of ice and snow and another condition an absence thereof.

48. Apparatus as in claim 45, wherein said transmitting path and said receiving path are substantially a same length as said reference distance used by said means for establishing reference data.

49. Apparatus as in claim 45, wherein said transmitting path and said receiving path are substantially a different length from said reference distance and said means for comparing includes means for correcting for said different length.

50. Apparatus as in claim 45, wherein said means for establishing said reference data includes means for measuring said first and second intensities when said surface is a known surface with said polarization altering substance absent from said known surface at a plurality of angles with respect to a normal of said surface.

51. Apparatus as in claim 45, wherein said means for establishing said reference data includes means for measuring said first and second intensities at a plurality of angles with respect to a normal of said surface when said surface is a known surface with said polarization altering substance present.

52. Apparatus as in claim 42, wherein:

said means for transmitting light includes only one transmitter; and

said means for receiving transmitted light includes only one receiver.

53. Apparatus as in claim 42, wherein said means for delaying one of said non-isolated portion and said isolated portion includes optical fiber.

54. Apparatus as in claim 42, wherein said means for measuring a first intensity, said means for measuring a second intensity, and said means for comparing said first and second intensities are separated from said means for splitting by said means for delaying one of said non-isolated portion and said isolated portion.

55. Apparatus for detecting, on a surface which specularly reflects light, the presence of a polarization altering substance on said surface comprising:

means for transmitting a pulse of polarized light onto a surface;

means for receiving said pulse reflected from said surface;

means for directing said reflected pulse onto a non-blocking optical path to a detector;

means for directing said reflected pulse onto a blocking optical path to said detector;

one of said blocking and non-blocking optical paths having a delay exceeding a pulse length of said pulse, whereby responses of said detector to said reflected pulse directed onto said blocking and non-blocking optical paths are separated; and

means for compensating said reflected pulse for effects of scattering and/or absorbing interference of said transmitted light.

56. Apparatus as in claim 55, further comprising optical fiber effective for producing said delay.

57. Apparatus as in claim 55, wherein said detector comprises:

means for measuring a first intensity of said reflected pulse directed onto one of said blocking and non-blocking optical paths not having said delay and outputting a first signal; and

means for measuring a second intensity of said reflected pulse directed onto another one of said blocking and non-blocking optical paths having said delay and outputting a second signal.

58. Apparatus as in claim 57, wherein said means for compensating includes:

means for measuring said first signal at a time when a backscattering effect of said scattering and/or absorbing interference of said transmitted light is near a maximum;

means for filtering said first signal to remove said backscattering effect from said first signal; and

means for determining a distance from said means for transmitting to said surface.

59. Apparatus as in claim 58, further comprising means for comparing said first and second signals to reference data to detect the presence of said substance on said surface.

60. Apparatus as in claim 59, further comprising:

means for outputting a ratio signal from said first and second signals;

means for calculating a threshold signal; and

means for comparing said ratio signal to said threshold signal.

61. Apparatus as in claim 59, wherein said reference data are in logarithmic form.

62. Apparatus as in claim 59, further comprising means for establishing said reference data by measuring said first and second intensities at a reference distance from said surface when said surface is a known surface with said polarization altering substance absent from said known surface.

63. Apparatus as in claim 62 wherein said means for establishing said reference data further comprises:

means for calculating a first ratio of said second intensity to said first intensity and making a first comparison of said first ratio to said second intensity when said polarization altering substance is absent from said known surface;

means for calculating a second ratio of said second intensity to said first intensity and making a second comparison of said second ratio to said second intensity when said polarization altering substance is present on said surface; and

means for determining a threshold to establish a difference between said first and second comparisons representing different conditions of the surface being investigated.

64. Apparatus as in claim 63 wherein one of said conditions of said surface is the presence of one of ice and snow and another condition an absence thereof.

65. Apparatus as in claim 59 wherein said means for establishing said reference data includes means for measuring said first and second intensities when said surface is a known surface with said polarization altering substance absent from said known surface at a plurality of angles with respect to a normal of said surface.

66. Apparatus as in claim 59 wherein said means for establishing said reference data includes means for measuring said first and second intensities at a plurality of angles with respect to a normal of said surface when said surface is a known surface with said polarization altering substance present.

67. Apparatus for detecting, on a surface which specularly reflects light, the presence of a polarization altering substance on said surface comprising:

means for transmitting a pulse of polarized light onto a surface;

means for receiving said pulse reflected from said surface;

means for directing said reflected pulse onto a non-blocking optical path to a detector;

means for directing said reflected pulse onto a blocking optical path to said detector;

one of said blocking and non-blocking optical paths having a delay exceeding a pulse length of said pulse, whereby responses of said detector to said reflected pulse directed onto said blocking and non-blocking optical paths are separated,

said detector including means for measuring a first intensity of said reflected pulse directed onto one of said blocking and non-blocking optical paths not having said delay and outputting a first signal, and means for measuring a second intensity of said reflected pulse directed onto another one of said blocking and non-blocking optical paths having said delay and outputting a second signal;

means for establishing thresholds for said first and second signals; and

means, responsive to said means for establishing thresholds, for controlling an intensity of said transmitted pulse.

68. Apparatus as in claim 67, further comprising:

means for compensating said first and second signals for said intensity of said transmitted pulse to produce first and second compensated signals; and

means for comparing said first and second compensated signals to reference data to detect the presence of said substance on said surface.

69. Apparatus as in claim 68, further comprising:

means for outputting a ratio signal from said first and second compensated signals;

means for calculating a threshold signal; and

means for comparing said ratio signal to said threshold signal.

70. Apparatus as in claim 67 further comprising means for compensating said reflected pulse for effects of scattering and/or absorbing interference of said transmitted light.

71. Apparatus as in claim 70, wherein said means for compensating said reflected pulse for effects of scattering and/or absorbing interference of said transmitted light includes:

means for measuring said first signal at a time when a backscattering effect of said scattering and/or absorbing interference of said transmitted light is near a maximum;

means for filtering said first signal to remove said backscattering effect from said first signal; and

means for determining a distance from said means for transmitting to said surface.

72. Apparatus for measuring horizontal visibility, comprising:

means for transmitting a pulse of polarized light onto a reference surface;

means for receiving said pulse reflected from said reference surface;

means for directing said reflected pulse on a non-blocking optical path to a detector to isolate a non-blocking component of said reflected pulse;

means for directing said reflected pulse on a blocking optical path to said detector to isolate a blocking component of said reflected pulse;

means for measuring an amplitude of said non-blocking component and/or said blocking component;

means for determining an attenuation coefficient by comparing said measured amplitude to a reference amplitude; and

means for calculating the horizontal visibility based on the attenuation coefficient.

73. Apparatus as in claim 72, wherein one of said blocking and non-blocking optical paths has a delay exceeding a pulse length of said pulse, whereby responses of said detector to said reflected pulse directed onto said blocking and non-blocking optical paths are separated in time.

74. Apparatus as in claim 72, wherein said means for transmitting said pulse includes means for controlling an intensity of said pulse.