Method of correcting for errors in radar imaging
First Claim
1. In a radar system including at least first and second stages for processing radar echo signals over a plurality of time samples of a single radar look, said radar echo signals being conditioned at each time sampling period by deramping in doppler and compressing into a plurality of range cells, said first stage for deriving from said conditioned radar echo signals at each time sample a set of complex signals of point-like targets according to a coarse azimuth resolution for each range cell of said plurality to form a time history of complex signals corresponding to said plurality of time samples for each point-like target, said second stage for deriving from said time histories of point-like targets a final azimuth resolution thereof to form a final radar image with improved resolution from a single radar look, a method of enhancing the focus of said final radar image by correcting focus errors developed in said time signal history data derived by said first stage prior to processing in said second stage, said method comprising the steps of:
- coherently combining the complex signals of time histories selected from the time histories derived by said first stage to generate a set of correction signals corresponding to said time samples of said first stage derived time histories; and
correcting the time histories derived by said first stage with respectively corresponding correction signals of said set prior to being processed in said second stage.
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Abstract
A method of correcting for focus errors or higher order errors, or various combinations thereof, in the final image effected by the processing of a radar. With regard to correcting focus errors, the method coherently combines the signal focus data from selected target time histories derived by a first stage processor of the radar to form a complex signal representative of the average focus error of the radar image. From the phase of the complex signal is derived a set of focus error compensation signals which are used to compensate for focus errors in the target time histories derived by the first stage processor. With regard to the higher order error correction, the method coherently combines the signal data from selected target time histories derived by the first stage processor by shifting the phase and frequency centroids of each complex signal thereof to a common value. Light filtering may be provided to remove wide band noise with a linear phase filter. Accordingly, the coherently combined and filtered error correction signals are point wise inverted and thereafter used to correct the complex signals of the time histories derived by the first stage processor. An additional embodiment is provided to permit both the focus error and higher order error correction methods to be performed at an intermediate stage in the radar processing.
62 Citations
12 Claims
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1. In a radar system including at least first and second stages for processing radar echo signals over a plurality of time samples of a single radar look, said radar echo signals being conditioned at each time sampling period by deramping in doppler and compressing into a plurality of range cells, said first stage for deriving from said conditioned radar echo signals at each time sample a set of complex signals of point-like targets according to a coarse azimuth resolution for each range cell of said plurality to form a time history of complex signals corresponding to said plurality of time samples for each point-like target, said second stage for deriving from said time histories of point-like targets a final azimuth resolution thereof to form a final radar image with improved resolution from a single radar look, a method of enhancing the focus of said final radar image by correcting focus errors developed in said time signal history data derived by said first stage prior to processing in said second stage, said method comprising the steps of:
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coherently combining the complex signals of time histories selected from the time histories derived by said first stage to generate a set of correction signals corresponding to said time samples of said first stage derived time histories; and correcting the time histories derived by said first stage with respectively corresponding correction signals of said set prior to being processed in said second stage. - View Dependent Claims (2, 3, 4)
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5. In a radar system including at least first and second stages for processing radar echo signals over a plurality of time samples of a single radar look, said radar echo signals being conditioned at each time sampling period by deramping in doppler and compressing into a plurality of range cells, said first stage for deriving from said conditioned radar echo signals at each time sample a corresponding set of complex signals of point-like targets according to a coarse azimuth resolution for each range cell of said plurality to form a time history of complex signals, corresponding to said plurality of time samples, for each point-like target, said second stage for deriving from said time histories of point-like targets a final azimuth resolution thereof to form a final radar image with improved resolution from a single radar look, a method of improving the final radar image by correcting for higher order errors developed in said time signal history data derived by said first stage prior to processing in said second stage, said method comprising the steps of:
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selecting a first subset of complex signal target time histories from said time histories derived by said first stage; deriving first and second complex signals for each target time history of said first subset using the complex signals respectively corresponding thereto, said first and second complex signals being representative respectively of the average doppler frequency and average doppler phase of their corresponding target time histories; adjusting the complex signals of said selected time histories as a function of their correspondingly derived first and second complex signals to form a second subset of frequency and phase adjusted complex signal time histories; coherently combining the complex signals of said second subset in accordance with common time samples of the time histories thereof to form a single time history of combined complex signals; generating a time history of error correction signals as a function of the corresponding time samples of said combined complex signal time history; and correcting the complex signals of the time histories derived by said first stage with corresponding signals of said derived time history of error correction signals. - View Dependent Claims (6, 7, 8, 9, 10, 11)
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12. In a radar system including at least first and second stages for processing radar echo signals over a plurality of time samples of a single radar look, said radar echo signals being conditioned at each time sampling period by deramping in doppler and compressing into a plurality of range cells, said first stage for deriving from said conditional radar echo signals at each time sample a corresponding set of complex signals of point-like targets according to a coarse azimuth resolution for each range cell of said plurality to form a time history of complex signals, corresponding to said plurality of time samples, for each point-like target, said second stage for deriving from said time histories of point-like targets a final azimuth resolution thereof to form a final radar image with improved resolution from a single radar look, a method of improving the final radar image by measuring and correcting for focus and higher order errors developed in said time signal history data derived by said first stage prior to processing in said second stage, said method comprising the steps of:
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selecting a first subset of complex signal target time histories from said time histories derived by said first stage; coherently combining the complex signals of a time history of said first subset for each time history thereof to generate a set of focus correction signals corresponding to the time samples of said selected time histories; correcting the complex signals of the time histories of said first subset with respectively corresponding focus correction signals of said set to form a second subset of focus corrected selected target time histories; deriving first and second complex signals for each target time history of said second subset using the complex signals respectively corresponding thereto, said first and second signals being representative respectively of the average doppler frequency and average doppler phase of their corresponding target time histories; adjusting the complex signals of the time histories of said second subset as a function of their correspondingly derived first and second complex signals to form a third subset of frequency and phase adjusted complex signal time histories; coherently combining the complex signals of said third subset in accordance with common time samples of the time histories thereof to form a single time history of combined complex signals; generating a time history of higher order error correction signals as a function of the corresponding time samples of said combined complex signal time history; and correcting the complex signals of the time histories derived by said first stage with corresponding signals of both of said focus error and higher order error correction signal time histories.
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Specification