Three dimensional interferometric synthetic aperture radar terrain mapping with unambiguous phase unwrapping employing subset bandwidth processing
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 pathrepeatedly detecting the position of the moving platform,repeatedly transmitting a radar signal having a predetermined bandwidth 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 of said predetermined bandwidth 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 of said predetermined bandwidth received by the second antenna employing plural transmitted radiant signals;
determining a first phase difference between said first and second synthetic aperture complex image data for each resolution cell;
forming third synthetic aperture complex image data for a plurality of resolution cells in slant range and Doppler frequency from radar reflections of a first subset of said predetermined bandwidth received by the first antenna employing plural transmitted radiant signals;
forming fourth synthetic aperture complex image data for a plurality of resolution cells in slant range and Doppler frequency from radar reflections of said first subset said predetermined bandwidth received by the second antenna employing plural transmitted radiant signals;
determining a second phase difference between said third and fourth synthetic aperture complex image data for each resolution cell;
resolving circular ambiguities in said first phase difference employing said second phase difference thereby forming a circular ambiguity resolved phase difference; and
computing the elevation and ground range for each resolution 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 said circular ambiguity resolved phase difference between said first and second synthetic aperture complex image data for that platform path.
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Abstract
Synthetic aperture radar data is used to produce a terrain map. Two synthetic radar antennas are placed on an aircraft, which moves in a set of substantially parallel flight paths. At least one antenna repeatedly transmits radar signals whose return echoes are received by both the antennas. The echo signals are processed conventionally to yield slant range and Doppler frequency data for plural resolution cells. The measured phase difference for each resolution cell provides an ambiguous measure of slant range difference to the two antennas needed to determine terrain elevation and correct ground range. As in the prior art, the radar transmissions employ an extended bandwidth of wavelengths. The received echo data is reprocessed using less than the entire bandwidth of the radar transmission to achieve additional center wavelengths. This produces a differing ambiguity interval and permits unambiguous determination of the slant range difference.
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Citations
34 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 transmitting a radar signal having a predetermined bandwidth 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 of said predetermined bandwidth 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 of said predetermined bandwidth received by the second antenna employing plural transmitted radiant signals; determining a first phase difference between said first and second synthetic aperture complex image data for each resolution cell; forming third synthetic aperture complex image data for a plurality of resolution cells in slant range and Doppler frequency from radar reflections of a first subset of said predetermined bandwidth received by the first antenna employing plural transmitted radiant signals; forming fourth synthetic aperture complex image data for a plurality of resolution cells in slant range and Doppler frequency from radar reflections of said first subset said predetermined bandwidth received by the second antenna employing plural transmitted radiant signals; determining a second phase difference between said third and fourth synthetic aperture complex image data for each resolution cell; resolving circular ambiguities in said first phase difference employing said second phase difference thereby forming a circular ambiguity resolved phase difference; and
computing the elevation and ground range for each resolution 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 said circular ambiguity resolved phase difference between said first and second synthetic aperture complex image data for that platform path. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. 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 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 having a predetermined bandwidth via said at least one of said first and second antennas; a first complex image formation apparatus 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 of said predetermined bandwidth received by said first antenna employing plural transmitted radar signals; a second complex image formation apparatus 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 of said predetermined bandwidth received by said second antenna employing plural transmitted radar signals; a first phase detector connected to said first and second complex image formation apparatuses for determining the phase angle difference between said complex image data of said first and second complex image formation apparatuses for each resolution cell thereby producing a first phase difference signal; a third complex image formation apparatus connected to said first antenna for forming third synthetic aperture complex image data for plural resolution cells in slant range and Doppler frequency from reflections of a first subset of said predetermined bandwidth received by said first antenna employing plural transmitted radar signals; a fourth complex image formation apparatus 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 of said first subset of said predetermined bandwidth received by said second antenna employing plural transmitted radar signals; a second phase detector connected to said third and fourth complex image formation apparatuses for determining the phase angle difference between said complex image data of said third and fourth complex image formation apparatuses for each resolution cell thereby producing a second phase difference signal; a phase disambiguity circuit connected to said first and second phase detectors for resolving circular ambiguities in said first phase difference signal employing said second phase difference signal thereby forming a circular ambiguity resolved phase difference signal; and a terrain map formation means connected to said position detector, said first complex image formation apparatus and said phase disambiguity circuit 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 said circular ambiguity resolved phase difference signal for each resolution cell. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
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Specification