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

• US 6,069,565 A
• Filed: 10/09/1998
• Issued: 05/30/2000
• Est. Priority Date: 10/20/1992
• Status: Expired due to Fees

• 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: Schaefer, John, Stern, Howard, Maali, Fereydoun
• Primary Examiner(s): MULLEN, THOMAS J
• Application Number:
  US09/169,619
• Time in Patent Office: 599 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, 348/143, 348/128
• 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;

means for storing reference data, said reference data including first and second measurements, said first and second measurements corresponding to said first and second intensities respectively measured at an initial time;

means for storing current data, said current data including third and fourth measurements, said third and fourth measurements corresponding to said first and second intensities respectively measured at a subsequent time; and

means for comparing said current data to said reference data to detect the presence of said substance on said surface at said subsequent time.

2. An apparatus for detecting as in claim 1, wherein said current data and said reference data are in logarithmic form.

3. An apparatus for detecting as in claim 1, further comprising:

means for calculating a threshold signal from said reference data; and

said means for comparing compares said current data to said threshold signal.

4. An apparatus for detecting as in claim 1, further comprising:

means for calculating a threshold signal from a ratio of said first and second measurement;

means for computing a ratio signal from said third and fourth measurements;

said means for comparing compares said ratio signal to said threshold signal.

5. An apparatus for detecting as in claim 1, further comprising:

means for calculating a threshold signal from a ratio of said first and second measurement;

said means for storing said reference data being a memory for storing said threshold signal at said initial time;

means for computing a ratio signal from said third and fourth measurements;

said means for comparing compares said ratio signal to said threshold signal stored in said memory at said subsequent time.

6. An apparatus as in claim 1 wherein one of said conditions of said surface is the presence of one of ice and snow and another condition an absence thereof.

7. 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 storing a plurality of reference data, each of said plurality of reference data includes first and second measurements, said first and second measurements correspond to said first and second intensities respectively measured when said surface is in a known condition, such that at least one reflection characteristic of said surface is characterized by said plurality of reference data;

means for storing a plurality of current data, each of said plurality of current data includes third and fourth measurements, said third and fourth measurements corresponding to said first and second intensities respectively measured at a later time; and

means for comparing said current data to said reference data to detect the presence of said substance on said surface at said subsequent time.

8. An apparatus as in claim 7 wherein said at least one reflection characteristic stored in said plurality of reference data includes a plurality of reflection characteristics from said surface corresponding to a plurality of angles with respect to a normal of said surface.

9. An apparatus as in claim 7 wherein said at least one reflection characteristic stored in said plurality of reference data includes a plurality of reflection characteristics from said surface corresponding to a plurality of materials on said surface.

10. An apparatus as in claim 9 wherein said plurality of materials includes paints and surface treatments.

11. An apparatus as in claim 7 wherein said at least one reflection characteristic stored in said plurality of reference data includes a plurality of reflection characteristics from said surface corresponding to said surface being a plurality of materials.

12. An apparatus as in claim 7 wherein said at least one reflection characteristic stored in said plurality of reference data includes a plurality of reflection characteristics from said surface corresponding to a plurality of angles with respect to a normal of said surface and said surface being a plurality of materials.

13. An apparatus as in claim 7 wherein said polarization altering substance is one of ice, snow and an absence thereof.

14. Apparatus for detecting the presence of a polarization altering substance on a surface comprising:

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

means for receiving a reflected pulse of light;

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 said blocking component;

a reference pulse being transmitted by said means for transmitting at an initial time;

means for storing reference data, said reference data being first and second measured amplitudes from said means for measuring at said initial time, said first and second amplitudes corresponding to said blocking and said non-blocking component respectively; and

means for comparing third and fourth measured amplitudes from said means for measuring with said first and second amplitudes at a subsequent time, said third and fourth measured amplitudes corresponding to said blocking and said non-blocking component respectively measured at said subsequent time whereby a presence of said polarization altering substance on said surface can be detected by comparing said third and fourth measured amplitudes to said reference data which is stored by said means for storing when no polarization altering substance is on said surface.