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A system for detecting ice or water within an area of interest having a detection system measuring radiance or reflectance of the area of interest when exposed to shortwave infrared radiation having a wavelength in the range containing a crossover point between the curves representing the absorption

A system for detecting ice or water within an area of interest having a detection system measuring radiance or reflectance of the area of interest when exposed to shortwave infrared radiation having a wavelength in the range containing a crossover point between the curves representing the absorption of electromagnetic radiation by ice and water. The detection system measures the radiance or reflectance in a first band having a wavelength in a spectral band on a first side of the crossover point and outputting a first band signal, and further measures the radiance or reflectance in a second band having a wavelength in a spectral band on a second opposing side of the same crossover point and outputting a second band signal. A processing unit determines a ratio of the first band signal and the second band signal and compares the ratio to a predetermined critical ratio and outputs a determination signal indicating presence of ice or water.

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1. A system for detecting ice and/or water within an area of interest, said system comprising: a detection system measuring radiance of the area of interest when exposed to electromagnetic radiation having wavelengths in a spectral band containing a crossover point in the curves describing the absor

1. A system for detecting ice and/or water within an area of interest, said system comprising: a detection system measuring radiance of the area of interest when exposed to electromagnetic radiation having wavelengths in a spectral band containing a crossover point in the curves describing the absorption of electromagnetic radiation by ice and water, said detection system measuring said radiance in a first band having wavelengths in a spectral band on a first side of said crossover point (band λ1) and outputting a first band signal (Rλ1), said detection system measuring said radiance in a second band having wavelengths in a spectral band on a second opposing side of said crossover point (band λ2) and outputting a second band signal (Rλ2); anda processing unit determining a ratio of said first band signal and said second band signal (γ=Rλ1/Rλ2), said processing unit comparing said ratio to predetermined critical ratio ranges and outputting a determination signal indicating at least one of presence of ice when said ratio is within a first range of said predetermined critical ratio ranges and presence of water when said ratio is within a second range of said predetermined critical ratio ranges. 2. The system according to claim 1, further comprising: a temperature sensor determining the temperature of the area of interest and outputting a temperature signal,wherein said processing unit comparing said temperature signal to a predetermined critical temperature range and outputting said determination signal in response thereto. 3. The system according to claim 1 wherein said processing unit determines existence of specular reflection in the area of interest, said processing unit outputting said determination signal in response to said specular reflection. 4. The system according to claim 1, further comprising: an auxiliary camera imaging the area of interest and outputting an auxiliary camera output,wherein said processing unit determines existence of specular reflection in the area of interest based on said auxiliary camera output, said processing unit outputting said determination signal in response to said specular reflection. 5. The system according to claim 1 wherein said processing unit calculates an effective radius of water droplets detected within the area of interest and outputs said determination signal in response thereto. 6. The system according to claim 1, further comprising: a second detection system measuring radiance in a non-absorbing spectral band, for example in the range of about 0.5 μm to about 0.7 μm, and outputting a second detection system signal,wherein said processing unit uses said second detection system signal, said first band signal, and said second band signal to verify detection and to calculate an effective radius of water droplets detected within the area of interest and outputs said determination signal in response thereto. 7. The system according to claim 1, further comprising: a second detection system measuring radiance in an absorbing spectral band, for example in the range of about 3.0 μm to about 5.0 μm, and outputting a second detection system signal,wherein said processing unit uses said second detection system signal, said first band signal, and said second band signal to verify detection and to calculate an effective radius of water droplets detected within the area of interest and outputs said determination signal in response thereto. 8. The system according to claim 1 wherein said detection system comprises one or more detectors, each of said one or more detectors being sensitive to said electromagnetic radiation having said wavelength in a spectral band covering said crossover point. 9. The system according to claim 8 wherein said one or more detectors comprises at least two detectors, a first of said at least two detectors being sensitive to a first spectrum range on said first side of said crossover point and a second of said at least two detectors being sensitive to a second spectrum range on said second opposing side of said crossover point, said first spectrum range and said second spectrum range being at least partially different. 10. The system according to claim 1 wherein said detection system comprises at least one camera, said at least one camera being sensitive to said electromagnetic radiation having said wavelength in a spectral band containing said crossover point. 11. The system according to claim 10 wherein said detection system further comprises two or more spectral filters operably coupled to said at least one camera, a first of said two or more spectral filters being sensitive in a spectral band on said first side of said crossover point (band λ1) and a second of said at least two detectors being sensitive in a spectral band on said second opposing side of said crossover point (band λ2), said first spectrum range and said second spectrum range being at least partially different. 12. The system according to claim 1, further comprising: a data display system displaying an indicia in response to said determination signal. 13. The system according to claim 1, further comprising: a deice or anti-icing system of an airborne-based vehicle being responsive to said determination signal. 14. The system according to claim 1, further comprising: a flight control system of an airborne-based vehicle being responsive to said determination signal. 15. The system according to claim 1, further comprising: a brake control system of a ground-based vehicle being responsive to said determination signal. 16. The system according to claim 1, further comprising: a light source outputting light energy at the spectral bands of interest, for example from about 2.05 μm to about 2.30 μm, said light source illuminating the area of interest. 17. The system according to claim 16 wherein said light source is selected from the group consisting of a laser, halogen light, infrared light, and light-emitting diode. 18. A method for detecting ice within an area of interest, said method comprising: measuring a first radiance of the area of interest at a first spectral band in a spectral band on a first side of a crossover point (Rλ1);measuring a second radiance of the area of interest at a second spectral band on a second opposing side of said crossover point (Rλ2);calculating a radiance ratio of said first radiance and said second radiance (γ=Rλ1/Rλ2);outputting an ice-present warning in response to said radiance ratio being within a predetermined critical radiance ratio range (γcrit1<γ<γcrit2); andoutputting a specular reflection-present warning in response to said first radiance being greater than a predetermined critical radiance. 19. A method for detecting supercooled liquid water droplets within an area of interest, said method comprising: measuring a first radiance of the area of interest at a first spectral band in a spectral band on a first side of a crossover point (Rλ1);measuring a second radiance of the area of interest at a second spectral band on a second opposing side of said crossover point (Rλ2);calculating a radiance ratio of said first radiance and said second radiance (γ=Rλ1/Rλ2);determining whether said radiance ratio is within a predetermined critical radiance ratio range (γcrit1<γ<γcrit2),measuring a temperature of the area of interest; andoutputting a supercooled-liquid-water-droplets-present warning in response to said radiance ratio being within said predetermined critical radiance ratio range and said temperature being within a predetermined critical temperature range. 20. A method for detecting supercooled large droplets (SLD) within an area of interest, said method comprising: measuring a first radiance of the area of interest at a first spectral band on a first side of a crossover point (Rλ1);measuring a second radiance of the area of interest at a second spectral band on a second opposing side of said crossover point (Rλ2);calculating a radiance ratio of said first radiance and said second radiance (γ=Rλ1/Rλ2);determining whether said radiance ratio being greater than a predetermined critical radiance ratio range (γcrit1<γ<γcrit2),calculating a droplet effective radius; andoutputting a supercooled-large-droplets-present warning in response to said radiance ratio being within said predetermined critical radiance ratio range and said droplet effective radius being greater than a predetermined critical droplet radius. 21. A method for detecting water substance within an area of interest, said method comprising: measuring a first radiance of the area of interest at a first spectral band (band λ1) on a non-absorbing band (Rλ1);measuring a second radiance of the area of interest at a second spectral band (band λ2) on an absorbing band (Rλ2);calculating a radiance ratio of said first radiance and said second radiance (γ=Rλ1/Rλ2); andoutputting a signal indicating the presence of ice, liquid water or snow in response to said radiance ratio being within a predetermined critical radiance ratio ranges (γcrit1<γ<γcrit2) of ice, liquid water or snow.