Rear-looking apparatus and method for detecting contrails
First Claim
1. An airborne system for indicating that a contrail is forming at a distance behind an aircraft, said contrail having an onset which normally occurs within a predetermined contrail onset range behind the aircraft, said system comprising:
- means carried by the aircraft for directing a lidar signal behind the aircraft into intersection with at least the onset of a contrail which has formed behind the aircraft, the onset of the contrail being within the contrail onset range, said lidar signal being scattered back toward the aircraft by the contrail to form a return signal having an amplitude related to said distance at which the contrail forms behind the aircraft, said directing means modulating the lidar signal according to a pseudorandom pattern, the return signal having a pattern related to said pseudorandom pattern; and
means carried by the aircraft for cross correlating said pattern of the return signal and the lidar signal to generate a profile of the amplitude of the return signal according to said distance from the aircraft, said profile having a peak within the onset range and corresponding to said distance of the onset behind the aircraft for indicating that the contrail is being formed behind the aircraft.
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Abstract
Contrail detection aft of an aircraft is provided by a rear-looking ranging system carried by the aircraft. A randomly modulated laser beam is directed into a detection volume aft of the aircraft for scatter back toward a detector on the aircraft. Bistatic mounting of a laser and a telescope of the detector preclude sensing of the scattered beam forward of the detection volume. Processing of the detected scattered beam includes cross correlation and analysis to indicate the formation of the contrail aft of the aircraft.
50 Citations
26 Claims
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1. An airborne system for indicating that a contrail is forming at a distance behind an aircraft, said contrail having an onset which normally occurs within a predetermined contrail onset range behind the aircraft, said system comprising:
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means carried by the aircraft for directing a lidar signal behind the aircraft into intersection with at least the onset of a contrail which has formed behind the aircraft, the onset of the contrail being within the contrail onset range, said lidar signal being scattered back toward the aircraft by the contrail to form a return signal having an amplitude related to said distance at which the contrail forms behind the aircraft, said directing means modulating the lidar signal according to a pseudorandom pattern, the return signal having a pattern related to said pseudorandom pattern; and means carried by the aircraft for cross correlating said pattern of the return signal and the lidar signal to generate a profile of the amplitude of the return signal according to said distance from the aircraft, said profile having a peak within the onset range and corresponding to said distance of the onset behind the aircraft for indicating that the contrail is being formed behind the aircraft. - View Dependent Claims (2, 3, 4)
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5. A system for detecting a contrail resulting from operation of an aircraft at high altitude, wherein the contrail forms along an axis at a distance behind the aircraft within a contrail onset range generally close but not immediately behind the aircraft and has an onset within the onset range, said system comprising:
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means for generating a continuous-wave output signal having a pseudorandom output sequence; means for mounting said generating means on said aircraft to direct the output laser signal into intersection with a contrail extending along the axis behind the aircraft, said signal being scattered back toward the aircraft by the contrail onset to form a return signal having an amplitude related to said distance and having a sequence related to the output sequence; means for temporally grouping the return signal; means for cross correlating the output sequence with the temporally grouped return signal to generate an output indicative of the amplitude of the return signal with respect to distance relative to the aircraft from which the return signal was scattered back toward the aircraft; and means for determining whether there is a peak in the amplitude of the return signal corresponding to a first distance from the aircraft which is within the onset range to indicate that a contrail is resulting from operation of the aircraft. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12)
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13. A system for detecting a contrail which results from operation of an engine of an aircraft, the contrail forming at a distance behind the aircraft and having an onset corresponding to a front portion of the contrail, the onset generally being within a maximum distance from said aircraft, said maximum distance being short relative to the distance at which the contrail extends behind the aircraft, the front portion having a definable shape, said system comprising:
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means for generating an output lidar signal; means for modulating the lidar signal according to a pseudorandom pattern; means for storing a cross correlation pattern corresponding to the pseudorandom pattern; means for mounting said generator means on said aircraft to direct said output lidar signal into any contrail which forms within the maximum distance so that said signal is scattered back toward the aircraft and forms a return signal having amplitude and a pattern related to the pseudorandom pattern; means carried by the aircraft for detecting the return signal and generating a count signal; means responsive to the count signal for resolving the count signal into temporal bins to form a histogram; and means for cross correlating said cross correlation pattern with the histogram to define a profile of the amplitude of the return signal as a function of the distance from the aircraft, said profile having a peak at one such distance within the maximum distance to indicate that a contrail has formed as a result of operation of said engine. - View Dependent Claims (14)
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15. A system for indicating that there is a contrail resulting from operation of an engine of an aircraft, said system indicating that the contrail has formed behind the engine in a detection volume having a selected dimension starting at a given distance aft of the engine and extending rearwardly of the engine, the contrail having an onset at which a front portion of the contrail is positioned, the onset generally being within a maximum distance from the aircraft, said maximum distance being short relative to the distance at which the contrail extends behind the engine and long relative to the given distance, the front portion having a definable shape, said system comprising:
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means for generating a lidar output signal; means for modulating the lidar signal according to a pseudorandom pattern; means for storing a cross correlation pattern corresponding to the pseudorandom pattern; means for mounting said generating means on the aircraft offset from the engine by a first offset distance and for directing said lidar signal transversely of said selected dimension to intersect any contrail onset which forms within said detection volume so that said lidar signal is scattered back toward the engine and forms a return signal having amplitude and a pattern related to the pseudorandom pattern; means for tracking the location of said contrail, said tracking means being mounted on the aircraft offset from the engine by a second offset distance, the second distance being different from the first offset distance, said tracking means being responsive to the return signal for resolving the return signal into temporal bins to form a histogram; and means for cross correlating the cross correlation pattern with the histogram to define a profile of the amplitude of the return signal as a function of distance from the aircraft, the profile having a peak at a distance within the selected dimension of the detection volume to indicate that a contrail has formed as a result of said engine. - View Dependent Claims (16, 17, 18, 19, 20, 21)
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22. A method of determining whether a contrail is forming behind an aircraft, wherein the contrail may be in or adjacent to a cloud, comprising the steps of:
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directing a lidar beam rearward of the aircraft; defining a first zone immediately aft of the aircraft, a second zone immediately aft of the first zone and in which no contrail normally forms, and a third zone immediately aft of the second zone and in which a contrail normally forms; detecting a return signal backscattered by said contrail if said contrail is forming and by any such cloud in said second zone; obtaining a cloud signal representing the average value of the return signal returned from the second zone; obtaining a first contrail signal representing a peak in the value of the return signal returned from a contrail in the third zone; obtaining a second contrail signal representing the average of the return signal returned from the third zone; and comparing the cloud signal to the second contrail signal and determining, if the value of the cloud signal is greater than the value of the second contrail signal, that no contrail is forming behind the aircraft. - View Dependent Claims (23, 24, 25, 26)
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Specification