Three dimensional interferometric synthetic aperture radar terrain mapping employing altitude measurement
First Claim
1. A method of terrain mapping employing a platform including first and second antennas, the first and second antennas 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 the interferometer baseline along a set of substantially parallel platform paths;
for each such platform path;
repeatedly detecting the position of the moving platform,repeatedly detecting the distance above the terrain of the moving platform via a radiant ranging sensor,repeatedly transmitting a radar signal via at least one of the first and second antennas,receiving reflections of each of said transmitted radar signals via the predetermined field of view of at least one of the first and second antennas,forming first synthetic aperture complex image data for a plurality of resolution cells in slant range and Doppler frequency from radar reflections received by the first antenna 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 radar reflections received by the second antenna employing plural transmitted radiant signals;
determining the phase difference between said first and second synthetic aperture complex image data for each resolution cell;
computing the elevation and ground range for eachresolution cell within a selected one of said first and second synthetic aperture complex image data for each of said set of platform paths employing the detected position of the moving platform and the phase difference between said first and second synthetic aperture complex image data for that platform path; and
computing a corrected elevation and ground range for each resolution cell for each of said set of platform paths corrected for interferometer baseline roll angle employing said detected distance above the terrain of the moving platform of a corresponding adjacent platform path where the moving platform passed above the terrain imaged in said selected one of said first and second synthetic aperture complex image data
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Abstract
Synthetic aperture radar data is used in conjunction with altimeter data to produce a terrain map corrected for platform roll angle. The technique uses two synthetic radar antennas and a ranging altimeter placed on an aircraft. The aircraft is moved in a set of substantially parallel flight paths where each flight is directly over the strip of terrain viewed by the synthetic aperture radar of an adjacent flight. During each flight the at least one antenna repeatedly transmits radar signals whose return echoes are received by both the first and second antennas. Conventional synthetic aperture radar processing yields a terrain map uncorrected for roll angle. The uncorrected terrain map data from one flight are compared with the altimeter data taken during an adjacent flight. This permits the altimeter data to be used to determine the roll angle when the corresponding synthetic radar data was taken. This roll angle measure is then used to correct the height and ground range of nearby points in the uncorrected terrain map. The result is a terrain map corrected for roll angle in a manner more accurate than can be obtained by direct measurement of the roll angle.
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Citations
30 Claims
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1. A method of terrain mapping employing a platform including first and second antennas, the first and second antennas 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 the interferometer baseline along a set of substantially parallel platform paths; for each such platform path; repeatedly detecting the position of the moving platform, repeatedly detecting the distance above the terrain of the moving platform via a radiant ranging sensor, repeatedly transmitting a radar signal via at least one of the first and second antennas, receiving reflections of each of said transmitted radar signals via the predetermined field of view of at least one of the first and second antennas, forming first synthetic aperture complex image data for a plurality of resolution cells in slant range and Doppler frequency from radar reflections received by the first antenna 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 radar reflections received by the second antenna employing plural transmitted radiant signals; determining the phase difference between said first and second synthetic aperture complex image data for each resolution cell;
computing the elevation and ground range for eachresolution cell within a selected one of said first and second synthetic aperture complex image data for each of said set of platform paths employing the detected position of the moving platform and the phase difference between said first and second synthetic aperture complex image data for that platform path; and computing a corrected elevation and ground range for each resolution cell for each of said set of platform paths corrected for interferometer baseline roll angle employing said detected distance above the terrain of the moving platform of a corresponding adjacent platform path where the moving platform passed above the terrain imaged in said selected one of said first and second synthetic aperture complex image data - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A terrain mapping apparatus used with a moving platform having an axis of motion, said apparatus comprising:
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a position detector disposed on the moving platform for repeatedly detecting the position of the moving platform; a radiant ranging altimeter disposed on the moving platform for repeatedly detecting the distance above the terrain of the moving platform; a first radar antenna disposed on the moving platform having a predetermined field of view off the axis of motion of the moving platform; a second radar antenna disposed on the moving platform a predetermined distance from said first radar antenna having said predetermined field of view, said first and second radar antennas forming an interferometer baseline substantially perpendicular to the axis of motion; a transmitter disposed on the moving platform and connected to at least one of said first and second antennas for repeatedly transmitting a radar signal via said at least one of said first and second antennas; a first receiver disposed on the moving platform and connected to said first antenna for forming first synthetic aperture complex image data for plural resolution cells in slant range and Doppler frequency from reflections received by said first antenna employing plural transmitted radar signals; a second receiver disposed on the moving platform and connected to said second antenna for forming second synthetic aperture complex image data for plural resolution cells in slant range and Doppler frequency from reflections received by said second antenna employing plural transmitted radar signals; a phase detection means disposed on the moving platform and connected to said first and second receivers for determining the phase difference between said first and second synthetic aperture complex image data for each resolution cell; a terrain map means connected to said position detector, said first receiver and said phase detection means for computing the elevation and ground range for each resolution cell within said first synthetic aperture complex image data for each of said set of platform paths employing the detected position of the moving platform and the phase difference between said first and second synthetic aperture complex image data for each resolution cell; and a terrain map correction means connected to said radiant ranging altimeter and said terrain map means for computing corrected elevation and ground range for each resolution cell for each of said set of platform paths employing said detected distance above the terrain of the moving platform for a corresponding adjacent platform path. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30)
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Specification