Synthetic aperture radar system having a third order tuned auto compensator for residual antenna motion and method for its use
First Claim
1. In a SAR system that receives reflections of radar signals from a target region, wherein such signals are combined with position signals from a motion sensor indicating antenna position, with the reflected signals and the position signals being integrated into range lines that may be combined to form a radar image, and wherein there may be residual motion between the antenna and the motion sensor, a method of correcting the position signals from the motion sensor to compensate for the amplitude and phase of antenna residual motion that may cause phase corruption in the radar image, the method comprising the steps of:
- a. transforming a received radar signal into a range line having a plurality of azimuth positions,b. transforming said received signal into a frequency spectrum f indicating the reflectivity of point reflectors at said azimuth positions, wherein one point reflector is located at each azimuth position, and wherein each point reflector is represented by a complex number having a certain magnitude and phase angle;
c. sampling the range line for substantially symmetric sets of point reflectors separated consecutively from each other by a distance corresponding to a frequency θ
, wherein said frequency corresponds to a mode of residual vibration of the antenna, and wherein said substantially symmetric set includes a main lobe point reflector, a pair of first order point reflectors, and a pair of second order point reflectors, each of said point reflectors being represented by a complex number, with said main lobe point reflector being centrally positioned between said pairs of first and second order point reflectors,d. calculating a product of a predetermined threshold with the greater magnitude of the two complex numbers f(x-θ
) and f(x+θ
), representing the pair of first order point reflectors,e. comparing the product with the magnitude of the complex number f(x) representing the main lobe point reflector,f. establishing first and second criteria of a symmetry relation, depending upon whether the magnitude of the complex number representing the main lobe point reflector is greater or less than the product of the predetermined threshold with the greater magnitude of the two complex numbers representing the pair of first order point reflectors,g. determining whether the complex numbers representing the main lobe point reflector, the pair of first order point reflectors, and the pair of second order point reflectors meet the first or second symmetry relation, depending upon the result of the comparison of step e,h. calculating estimates of the amplitude and phase of the antenna residual motion, depending upon the result of the comparison of step e,i. generating an antenna residual motion signal therefrom, andj. combining the antenna residual motion signal with the position signals from the motion sensor, to correct for antenna residual motion between the motion sensor and the antenna.
1 Assignment
0 Petitions
Accused Products
Abstract
In a SAR system a method is provided for compensating for antenna residual motion relative to a motion sensor, wherein such residual motion causes phase corruption in a radar image produced by the SAR system. Residual motion compensation is provided by first correlating a received radar signal to a range line having a plurality of azimuth positions. Such signal is transformed into a frequency spectrum indicating the reflectivity of point reflectors at the various azimuth positions. Then, the range line is sampled for symmetric sets of sequential point reflectors positioned along the range line at a consecutive distance from each other corresponding to a specified frequency associated to a mode of residual vibration of the antenna. The amplitude and phase angle of said mode of the antenna residual motion may be obtained from such symmetric sets.
-
Citations
15 Claims
-
1. In a SAR system that receives reflections of radar signals from a target region, wherein such signals are combined with position signals from a motion sensor indicating antenna position, with the reflected signals and the position signals being integrated into range lines that may be combined to form a radar image, and wherein there may be residual motion between the antenna and the motion sensor, a method of correcting the position signals from the motion sensor to compensate for the amplitude and phase of antenna residual motion that may cause phase corruption in the radar image, the method comprising the steps of:
-
a. transforming a received radar signal into a range line having a plurality of azimuth positions, b. transforming said received signal into a frequency spectrum f indicating the reflectivity of point reflectors at said azimuth positions, wherein one point reflector is located at each azimuth position, and wherein each point reflector is represented by a complex number having a certain magnitude and phase angle; c. sampling the range line for substantially symmetric sets of point reflectors separated consecutively from each other by a distance corresponding to a frequency θ
, wherein said frequency corresponds to a mode of residual vibration of the antenna, and wherein said substantially symmetric set includes a main lobe point reflector, a pair of first order point reflectors, and a pair of second order point reflectors, each of said point reflectors being represented by a complex number, with said main lobe point reflector being centrally positioned between said pairs of first and second order point reflectors,d. calculating a product of a predetermined threshold with the greater magnitude of the two complex numbers f(x-θ
) and f(x+θ
), representing the pair of first order point reflectors,e. comparing the product with the magnitude of the complex number f(x) representing the main lobe point reflector, f. establishing first and second criteria of a symmetry relation, depending upon whether the magnitude of the complex number representing the main lobe point reflector is greater or less than the product of the predetermined threshold with the greater magnitude of the two complex numbers representing the pair of first order point reflectors, g. determining whether the complex numbers representing the main lobe point reflector, the pair of first order point reflectors, and the pair of second order point reflectors meet the first or second symmetry relation, depending upon the result of the comparison of step e, h. calculating estimates of the amplitude and phase of the antenna residual motion, depending upon the result of the comparison of step e, i. generating an antenna residual motion signal therefrom, and j. combining the antenna residual motion signal with the position signals from the motion sensor, to correct for antenna residual motion between the motion sensor and the antenna. - View Dependent Claims (2, 3, 4, 5, 6)
-
-
7. An autocompensator for an SAR system that receives reflections of radar signals from a target region, wherein such signals are combined with position signals from a motion sensor indicating antenna position, with the reflected signals and the position signals being integrated into range lines that may be combined to form a radar image, and wherein there may be residual motion between the antenna and the motion sensor, the autocompensator comprising:
-
means for transforming a received radar signal into a range line having a plurality of azimuth positions, means for transforming said received signal into a frequency spectrum f indicating the reflectivity of point reflectors at said azimuth positions, wherein one point reflector is located at each azimuth position, and wherein each point reflector is represented by a complex number having a certain magnitude and phase angle; means for sampling the range line for substantially symmetric sets of point reflectors separated consecutively from each other by a distance corresponding to a frequency θ
, wherein said frequency corresponds to a mode of residual vibration of the antenna, and wherein said substantially symmetric set includes a main lobe point reflector, a pair of first order point reflectors, and a pair of second order point reflectors, each of said point reflectors being represented by a complex number, with said main lobe point reflector being centrally positioned between said pairs of first and second order point reflectors,means for calculating a product of a predetermined threshold ε
with the greater magnitude of the two complex numbers f(x-θ
) and f(x+θ
), representing the pair of first order point reflectors,means for comparing the product with the magnitude of the complex number f(x) representing the main lobe point reflector, means for establishing first and second criteria of a symmetry relation, depending upon whether the magnitude of the complex number representing the main lobe point reflector is greater or less than the product of the predetermined threshold with the greater magnitude of the two complex numbers representing the pair of first order point reflectors, means for determining whether the complex numbers representing the main lobe point reflector, the pair of first order point reflectors, and the pair of second order point reflectors meet the first or second symmetry relation, depending upon the result of the comparison of the product with the magnitude of the complex number f(x) representing the main lobe point reflector, means for calculating estimates of the amplitude and phase of the antenna residual motion, depending upon the result of the comparison of the product with the magnitude of the complex number f(x) representing the main lobe point reflector, and means for generating an antenna residual motion signal therefrom, wherein the autocompensator corrects the position signals from the motion sensor to compensate for the amplitude and phase of antenna residual motion that may cause phase corruption in the radar image. - View Dependent Claims (8, 9, 10)
-
-
11. An SAR system, comprising:
-
means for transmitting radar signals to a target region; means for receiving the reflections of the radar signals from the target region; means for producing position signals from a motion sensor indicating antenna position; an autocompensator comprising; means for transforming a received radar signal into a range line having a plurality of azimuth positions, means for transforming said received signal into a frequency spectrum f indicating the reflectivity of point reflectors at said azimuth positions, wherein one point reflector is located at each azimuth position, and wherein each point reflector is represented by a complex number having a certain magnitude and phase angle, means for sampling the range line for substantially symmetric sets of point reflectors separated consecutively from each other by a distance corresponding to a frequency θ
, wherein said frequency corresponds to a mode of residual vibration of the antenna, and wherein said substantially symmetric set includes a main lobe point reflector, a pair of first order point reflectors, and a pair of second order point reflectors, each of said point reflectors being represented by a complex number, with said main lobe point reflector being centrally positioned between said pairs of first and second order point reflectors,means for calculating a product of a predetermined threshold ε
with the greater magnitude of the two complex numbers f(x-θ
) and f(x+θ
), representing the pair of first order point reflectors,means for comparing the product with the magnitude of the complex number f(x) representing the main lobe point reflector, means for establishing first and second criteria of a symmetry relation, depending upon whether the magnitude of the complex number representing the main lobe point reflector is greater or less than the product of the predetermined threshold with the greater magnitude of the two complex numbers representing the pair of first order point reflectors, means for determining whether the complex numbers representing the main lobe point reflector, the pair of first order point reflectors, and the pair of second order point reflectors meet the first or second symmetry duct with the magnitude of the complex number f(x) representing the main lobe point reflector, means for calculating estimates of the amplitude and phase of the antenna residual motion, depending upon the result of the comparison of the product with the magnitude of the complex number f(x) representing means for generating an antenna residual motion signal therefrom; and means for correcting the position signals from the motion sensor to compensate for the amplitude and phase of antenna residual motion that may cause phase corruption in the radar image. - View Dependent Claims (12, 13, 14, 15)
-
Specification