APPARATUS AND METHODS FOR A SYNTHETIC APERTURE RADAR WITH SELF-CUEING
A synthetic aperture radar (SAR) system and method of operation advantageously implements dynamic self-cueing or autonomous cueing of successive high-resolution SAR data collection based on previously collected wide-swath SAR data, for instance without the intervention of ground-based resources. For example, target detection may be performed on-board a spaceborne or airborne SAR platform using wide-swath SAR data acquired via a first beam at a first frequency band, the first beam pointed at a first angle relative to an along-track direction. Subsequent activities are cued by the platform based on the previously collected wide-swath SAR data. For instance, the SAR platform may cue subsequent acquisition of SAR data via a second beam at a second frequency band, the second beam pointed at a second angle relative to an along-track direction. The SAR platform may advantageously employ a multi-band SAR antenna.
1 . A method of operation of a synthetic aperture radar (SAR) system comprising at least one SAR antenna, a SAR processor, a SAR controller, and a communication antenna, the method comprising:
acquiring, by a first beam of the at least one SAR antenna, wide-swath SAR data at a first frequency band, the first beam of the at least one SAR antenna pointed at a first angle relative to an along-track direction;
processing, by the SAR processor, at least a portion of the wide-swath SAR data;
detecting, by the SAR processor, a target in the wide-swath SAR data;
cueing, by the SAR controller, acquisition of high-resolution SAR data, the high-resolution SAR data including data backscattered by the target; and
in response to cueing, by the SAR controller, acquisition of high-resolution SAR data, acquiring, by a second beam of the at least one SAR antenna, high-resolution SAR data at a second frequency band, the second beam of the at least one SAR antenna pointed at a second angle relative to an along-track direction.
2 . The method of claim 1 wherein acquiring, by a second beam of the at least one SAR antenna, high-resolution SAR data at a second frequency band includes acquiring, by a second beam of the at least one SAR antenna, high-resolution SAR data at a second frequency band, the second frequency band different from the first frequency band.
3 . The method of claim 2 wherein acquiring, by a first beam of the at least one SAR antenna, wide-swath SAR data at a first frequency band includes acquiring, by a first beam of a shared-aperture multi-band SAR antenna, wide-swath SAR data at a first frequency band, and acquiring, by a second beam of the at least one SAR antenna, high-resolution SAR data at a second frequency band includes acquiring, by a second beam of the shared-aperture multi-band SAR antenna, high-resolution SAR data at a second frequency band.
4 . The method of claim 3 wherein acquiring, by a first beam of a shared-aperture multi-band SAR antenna, wide-swath SAR data at a first frequency band includes acquiring, by a first beam of a planar phased array antenna, wide-swath SAR data at a first frequency band, and acquiring, by a second beam of the shared-aperture multi-band SAR antenna, high-resolution SAR data at a second frequency band includes acquiring, by a second beam of the planar phased array antenna, high-resolution SAR data at a second frequency band.
5 . The method of claim 1 further comprising:
processing, by the SAR processor, at least a portion of the high-resolution SAR data to form an image of the target; and
transmitting, by the communication antenna, to a receiving terminal at least one of the high-resolution SAR data and the image of the target; wherein acquiring, by the second beam, high-resolution SAR data at a second frequency band occurs without interruption to acquiring, by the first beam, wide-swath SAR data at a first frequency band.
6 . The method of claim 1 wherein acquiring, by a first beam of the at least one SAR antenna, wide-swath SAR data at a first frequency band includes pointing the first beam at a first angle relative to an along-track direction.
7 . The method claim 6 wherein pointing the first beam at a first angle relative to an along-track direction includes pointing the first beam forward of broadside.
8 . The method of claim 7 wherein pointing the first beam forward of broadside includes dynamically steering the first beam.
9 . The method of claim 1 wherein acquiring, by a second beam of the at least one SAR antenna, high-resolution SAR data at a second frequency band includes pointing the second beam at a second angle relative to an along-track direction.
10 . The method of claim 9 wherein pointing the second beam at a second angle relative to an along-track direction includes pointing the second beam aft of the first beam.
11 . The method of claim 10 wherein pointing the second beam aft of the first beam includes pointing the second beam aft of broadside.
12 . The method of claim 10 wherein pointing the second beam aft of the first beam includes dynamically steering the second beam.
13 . The method of claim 1 wherein acquiring, by the second beam of the at least one SAR antenna, high-resolution SAR data at a second frequency band includes acquiring, by the second beam of the at least one SAR antenna, high-resolution SAR data at a second frequency band, the second frequency band including a radar frequency higher than the first frequency band.
14 . The method of claim 1 wherein processing, by the SAR processor, at least a portion of the wide-swath SAR data includes performing range compression and azimuth compression.
15 . The method of claim 1 wherein detecting, by the SAR processor, a target in the wide-swath SAR data includes at least one of a single-feature-based method, a multi-feature-based method, or an expert-system-oriented method.
16 . The method of claim 1 wherein identifying, by the SAR processor, a target in the wide-swath SAR data includes performing a constant false alarm rate (CFAR) detection.
17 . The method of claim 1 wherein detecting, by the SAR processor, a target in the wide-swath SAR data includes detecting, by the SAR processor, at least one of a natural feature, a man-made structure, or a vehicle, the target situated on a land surface or a water surface of the Earth.
18 . The method of claim 1 wherein transmitting, by the communication antenna, to a receiving terminal includes transmitting, by the communication antenna, to a ground terminal, the ground terminal situated on one of a land surface of the Earth, a water surface of the Earth, or in the Earth's atmosphere.
19 . The method of claim 1 wherein acquiring, by a first beam of the at least one SAR antenna, wide-swath SAR data at a first frequency band includes acquiring, by a first beam of the at least one SAR antenna, wide-swath SAR data at a first frequency band with a swath width exceeding 50 km.
20 . The method of claim 1 wherein acquiring, by a second beam of the at least one SAR antenna, high-resolution SAR data at a second frequency band includes acquiring, by a second beam of the at least one SAR antenna, high-resolution SAR data at a second frequency band with a swath width less than 50 km.
21 . The method of claim 1 wherein acquiring, by a second beam of the at least one SAR antenna, high-resolution SAR data at a second frequency band includes acquiring, by a second beam of the at least one SAR antenna, high-resolution SAR data at a second frequency band, the second frequency band the same as the first frequency band.
22 . A synthetic aperture radar (SAR) system comprising at least one SAR antenna, a SAR processor, a SAR controller, and a communication antenna, the SAR system operable to perform operations comprising:
acquiring, by first beam of the at least one SAR antenna, wide-swath SAR data at a first frequency band, the first beam at east one antenna pointed at a first angle relative to an along-track direction;
processing, by the SAR processor, at least a portion of the wide-swath SAR data;
detecting, by the SAR processor, a target in the wide-swath SAR data;
cueing, by tai e SAR controller, acquisition of high-resolution SAR data, the high-resolution SAR data including data backscattered by the target; and
in response to cueing, by the SAR controller, acquisition of high-resolution SAR data, acquiring, by a second beam of the at least one SAR antenna, high-resolution SAR data at a second frequency band, the second beam of the at least one SAR antenna pointed at a second angle relative to an along-track direction.
23 . The SAR system of claim 22 wherein the SAR processor, the SAR controller, and the communication antenna are co-located on a spaceborne or airborne SAR platform.
24 . The SAR system of claim 23 wherein the spaceborne SAR platform is a free-flying spacecraft.
25 . The SAR system of claim 22 wherein the at least one SAR antenna comprises a plurality of sub-arrays, each sub-array pre-steered to a respective selected steering angle.