Interferometric synthetic aperture detection of sparse non-surface objects
First Claim
1. A method of detecting non-surface objects employing a platform including first and second transducers, the first and second transducers each having a predetermined field of view and together forming an interferometer baseline, said method comprising the steps of:
- moving the platform substantially perpendicular to a line though the first and second transducers,repeatedly transmitting a radiant signal via at least one of the first and second transducers;
receiving reflections of each of the transmitted radiant signals via the predetermined field of view of at least one of the first and second transducers;
forming first synthetic aperture complex image data for a plurality of resolution cells in slant range and Doppler frequency from radiant reflections received by the first transducer employing plural transmitted radiant signals;
forming second synthetic aperture complex image data for a plurality of resolution cells in slant range and Doppler frequency from radiant reflections received by the second transducer employing plural transmitted radiant signals;
determining the complex phase factor between said first and second synthetic aperture complex image data for each resolution cell in the absence of non-surface objects;
multiplying one of said first and second synthetic aperture complex image data of each resolution cell by the complex conjugate of the complex image data of the corresponding resolution cell of said complex phase factor, thereby forming a first product signal for each resolution cell; and
subtracting said first product signal of each resolution cell from the other of said first and second synthetic aperture complex image data of the corresponding resolution cell, thereby forming a difference signal for each resolution cell which is substantially zero except in the presence of a non-surface object.
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Abstract
A technique for detecting non-surface objects from a moving platform using radiant ranging. The platform moves perpendicular to a line through a pair of first and second transducers. A transmitter repeatedly transmits a radiant signal via a first transducer. The return reflection signals in both transducers include return reflection signals from sparse non-surface objects in the presence of surface clutter reflections. Respective synthetic aperture complex images of resolution cell in slant range and Doppler frequency are formed from the received reflections of the two transducers. The complex phase factor between received reflections for each resolution cell in the absence of non-surface objects is determined. This is feasible because the non-surface objects are sparse, that is rare and generally encountered individually. Each resolution cell of the first synthetic aperture complex image is multiplied with the complex conjugate of the corresponding resolution cell of said complex phase factor. The resulting product signal is subtracted from the second synthetic aperture complex image. The resulting signal is non-zero (except for second order effects) only in the presence of a non-surface reflecting target. The technique may employ a third transducer permitting detection of non-surface objects at otherwise blind heights.
64 Citations
25 Claims
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1. A method of detecting non-surface objects employing a platform including first and second transducers, the first and second transducers each having a predetermined field of view and together forming an interferometer baseline, said method comprising the steps of:
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moving the platform substantially perpendicular to a line though the first and second transducers, repeatedly transmitting a radiant signal via at least one of the first and second transducers; receiving reflections of each of the transmitted radiant signals via the predetermined field of view of at least one of the first and second transducers; forming first synthetic aperture complex image data for a plurality of resolution cells in slant range and Doppler frequency from radiant reflections received by the first transducer employing plural transmitted radiant signals; forming second synthetic aperture complex image data for a plurality of resolution cells in slant range and Doppler frequency from radiant reflections received by the second transducer employing plural transmitted radiant signals; determining the complex phase factor between said first and second synthetic aperture complex image data for each resolution cell in the absence of non-surface objects; multiplying one of said first and second synthetic aperture complex image data of each resolution cell by the complex conjugate of the complex image data of the corresponding resolution cell of said complex phase factor, thereby forming a first product signal for each resolution cell; and subtracting said first product signal of each resolution cell from the other of said first and second synthetic aperture complex image data of the corresponding resolution cell, thereby forming a difference signal for each resolution cell which is substantially zero except in the presence of a non-surface object. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A non-surface object detection apparatus used with a moving platform comprising:
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a first transducer having a predetermined field of view off the axis of motion of the moving platform; a second transducer a predetermined distance from the first transducer having said predetermined field of view; a transmitter connected to at least one of the first and second transducers for repeatedly transmitting a radiant signal via said at least one of said first and second transducers; a first receiver connected to said first transducer for forming first synthetic aperture complex image data for each of a plurality of resolution cells in slant range and Doppler frequency from reflections received by said first transducer employing plural transmitted radiant signals; a second receiver connected to said second transducer for forming second synthetic aperture complex image data for each of a plurality of resolution cells in slant range and Doppler frequency from reflections received by said second transducer employing plural transmitted radiant signals; a complex phase factor means connected to said first and second receivers for determining the complex phase factor between said first and second and second complex image data for each resolution cell in the absence of non-surface objects, thereby producing a complex phase factor signal for each resolution cell; a complex conjugate means connected to said complex phase factor means for forming the complex conjugate of said complex phase factor signal of each resolution cell, thereby forming a complex conjugant signal of each resolution cell; a product means connected to said first receiver and said complex conjugate means for multiplying said complex conjugate signal of each resolution cell by said first synthetic aperture complex image data of the corresponding resolution cell, thereby forming a product signal for each resolution cell; and a difference means connected to said second receiver and said product means for subtracting said product signal of each resolution cell from said second synthetic aperture complex image data of the corresponding resolution cell, thereby forming a difference signal for each resolution cell which is substantially zero except in the presence of a non-surface object. - View Dependent Claims (15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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Specification