Aircraft ground velocity determination system
First Claim
1. Apparatus for determining the ground velocity of an aircraft comprising:
- means for detecting from the aircraft a first radiant energy contour of a first area of the earth'"'"'s surface and, after a time delay, a second radiant energy contour of a second area of the earth'"'"'s surface, which second area overlaps in part with the first area;
means for comparing said first contour with said second contour to produce a position shift signal which represents the relative contour position shift necessary to obtain the maximum degree of correlation between said first contour and said second contour;
means for producing an altitude correction signal;
means for multiplying said position shift signal by said altitude correction signal so as to produce a distance signal; and
means for dividing said distance signal by said time delay to obtain a ground velocity signal of the aircraft.
2 Assignments
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Accused Products
Abstract
A system for determining the ground velocity of an aircraft is disclosed. The system includes a CCD linear optical image sensor carried by the aircraft for forming a first and second substantially instantaneous light intensity contour of the optical image of the surface of the earth lying below the aircraft. The two contours are delayed in time with respect to each other. A computer, included in the system, compares the two contours to determine the relative position shift between the two contours by utilizing cross-correlation techniques. The computer then corrects the contour position shift for the aircraft altitude and divides the corrected position shift by the time delay between the two contours to obtain the aircraft ground velocity. A signal indicative of the aircraft ground velocity is output by the system.
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Citations
31 Claims
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1. Apparatus for determining the ground velocity of an aircraft comprising:
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means for detecting from the aircraft a first radiant energy contour of a first area of the earth'"'"'s surface and, after a time delay, a second radiant energy contour of a second area of the earth'"'"'s surface, which second area overlaps in part with the first area; means for comparing said first contour with said second contour to produce a position shift signal which represents the relative contour position shift necessary to obtain the maximum degree of correlation between said first contour and said second contour; means for producing an altitude correction signal; means for multiplying said position shift signal by said altitude correction signal so as to produce a distance signal; and means for dividing said distance signal by said time delay to obtain a ground velocity signal of the aircraft. - View Dependent Claims (2, 3, 4, 5)
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6. Apparatus for determining the ground velocity of an aircraft comprising:
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at least one optical image sensor, which includes a plurality of image forming elements, carried by the aircraft; means for enabling said elements to form a first optical image of a first area of the earth'"'"'s surface and, after a time delay, enabling said elements to form a second optical image of a second area of the earth'"'"'s surface which overlaps in part with said first area; means for controlling the length of time said elements are enabled and said time delay; means for comparing said first image with said second image to produce a position shift signal representing the relative image position shift necessary to obtain the maximum degree of correlation between said first and second images; means for generating an altitude correction signal; means for multiplying said position shift signal by said altitude correction signal so as to produce a distance signal; and means for dividing said distance signal by said time delay to obtain a signal representing the ground velocity of the aircraft. - View Dependent Claims (7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. Apparatus for determining the ground velocity of an aircraft comprising:
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a plurality of light sensitive elements which generate electrical signals in response to incident light; means for enabling a first set of said elements to form a first light contour from incident light emitted and reflected from a first area of the earth'"'"'s surface and, after a time delay, enabling a second set of said elements to form a second light contour from incident light emitted and reflected from a second area of the earth'"'"'s surface which partially overlaps the first area, said elements of said second set being interspersed among said elements of said first set; means for storing said first and second light contours; means for comparing said first and second stored light contours to produce a position shift signal representing the relative contour position shift necessary to obtain the maximum degree of correlation between said first and second stored light contours; means for generating an altitude correction signal; means for multiplying said position shift signal by said altitude correction signal to produce a ground distance signal; means for dividing said distance signal by said time delay to obtain an aircraft ground velocity signal. - View Dependent Claims (17, 18, 19, 20, 21, 22, 23)
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24. An apparatus for determining the ground velocity of an aircraft comprising:
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a sensor which includes a plurality of photodetector pixels, each pixel generating an electrical signal which has its magnitude proportional to the intensity of incident radiant energy; means for enabling less than all the pixels to generate signals which represent a first light intensity contour of a first area of the earth'"'"'s surface, and after a time delay, enabling the pixels which do not form part of said first light contour to generate signals which represent a second light intensity contour of a second area of the earth'"'"'s surface which partially overlaps said first area, wherein said pixels forming said first contour are interspersed among said pixels forming said second contour; means for adjusting the time delay to control the degree of overlap between said first and second areas; means for controlling the exposure time of said pixels as a function of the time delay, aircraft altitude, and intensity of a light contour; means for registering said first and second contours; means for digitizing the magnitude of the signals representing said first and second contours; means for storing said first and second digitized contours; means for arranging said first and second digitized contours in an initial pixel-to-pixel orientation with respect to each other and for incrementally shifting said first digitized contour to a plurality of successive pixel-to-pixel positions relative to said second digitized contour; means for multiplying the values of the corresponding pixels of said first and second digitized contours and for summing the products of all corresponding pixels of said first and second digitized contours for each orientation of said plurality of positions; means for storing the sums of said products means for identifying the greatest sum obtained over said plurality of position shifts; means for producing a signal representing the number of successive position shifts necessary to obtain said greatest sum; means for generating an altitude correction signal; means for multiplying said number of shifts signal by said altitude correction signal to generate a ground distance signal of the aircraft; and means for dividing said distance signal by said time delay to generate an aircraft ground velocity signal. - View Dependent Claims (25, 26)
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27. A method for determining the ground velocity of an aircraft comprising:
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detecting from the aircraft a radiant energy contour of a first area of the earth'"'"'s surface; after a time delay, detecting from the aircraft a radiant energy contour of a second area of the earth'"'"'s surface which partially overlaps the first area; comparing the first contour with the second contour to produce a signal representing the relative contour position shift necessary to obtain the maximum degree of correlation between the first and second contours; producing an altitude correction signal; multiplying the contour position shift signal by the altitude correction signal to produce a distance signal; and dividing the distance signal by the time delay to generate a ground velocity signal.
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28. A method for determining the ground velocity of an aircraft comprising:
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enabling a first set of photosensors mounted on the aircraft to form a first light intensity contour in response to light emitted and reflected from a first area of the earth'"'"'s surface; after a time delay, enabling a second set of photosensors mounted on the aircraft to form a second light intensity contour in response to light emitted and reflected from a second area of the earth'"'"'s surface which partially overlaps the first area; adjusting the time delay to control the degree of overlap of the first and second areas; controlling the time the photosensors are enabled as a function of the time delay, aircraft altitude, and average intensity of a previously formed contour; comparing the first and second contours to produce a signal representing the relative contour position shift necessary to attain the maximum degree of correlation between the first and second contours; generating an altitude correction signal; multiplying the relative contour shift signal by the altitude correction signal to produce a ground distance signal; and dividing the ground distance signal by the time delay to generate a ground velocity signal. - View Dependent Claims (29, 30, 31)
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Specification