ISAR imaging radar system
AssigneeTexas Instruments Incorporated
InventorSherman H. Tsao
Life of this patent
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Abstract
A method for removing range migration effects that produce doppler smearing in Inverse Synthetic Aperture Radar (ISAR) system (20) image of moving target (50) first generates a synthetic aperture radar image in the zero doppler cells from the target by summing a plurality of ISAR radar data points. Next, the method and system compensate each of the data points by a factor representing the effect of non-zero doppler frequency shift in said data points. Further, the method and system compensate the generated ISAR image for non-zero doppler frequency shift from the target using the compensated data points. This method and system may be used in an ISAR system doppler processor to reduce or eliminate doppler smearing in ISAR images.
Claims25
A method for improving ISAR imaging radar signal processing to compensate for range migration effects in the ISAR signal from a moving reflector, comprising the steps of:
- measuring the sampled return, f(.xi..sub.i, t.sub..kappa.) where i is the range bin index of the ISAR signal and .kappa. is the ISAR signal PRI index, according to the formula, ##EQU23## for i=0, 1, . . . , N-1, .kappa.=0, 1, . . . , M-1, and h representing a point source of the reflector;
- resampling said return according to the formula ##EQU24## for i=0, 1, . . . , N-1;
- and .kappa.=0, 1, . . . , M-1, for positive doppler frequency shift cells, 0<s.ltoreq.M/2-1, and computing the ISAR image from said cell compensations according to the formula ##EQU25## for i=0, 1, . . . , N-1;
- and resampling said return according to the formula ##EQU26## for i=0, 1, . . . , N-1;
- and .kappa.=0, 1, . . . , M-1, for negative doppler frequency shift cells, M/2.ltoreq.s.ltoreq.M-1, and computing the ISAR image from said cell compensations according to the formula ##EQU27## for i=0, 1, . . . , N-1;
- where:
- .xi. is the wave coordinate variable
- t=time
- D is the initial displacement between the reference reflector and the arbitrary reflector
- s is n integer variable indexing discrete speed
- .kappa. indexes the pulse number within the aperture
- .lambda. is the wave length of the radar signal
- c is the speed of wave propagation
- i indexes the sample number within one pulse return
- P(.xi.) is the complex envelope of the transmitted pulse
- P'(.xi..sub.i) is a sampled version of P(.xi.).
A method for removing range migration effects from an inverse synthetic aperture radar image of a moving object, comprising the steps:
- (a) generating a synthetic aperture radar image in the zero doppler cells of the object by summing a plurality of imaging synthetic aperture radar data points from the object;
- (b) compensating each of said data points by a factor representing the effect of non-zero doppler frequency shift on said data points;
- (c) compensating said generating synthetic aperture radar image for non-zero doppler frequency shift from the object using said compensating data points, thereby removing from said synthetic aperture radar image said range migration effects.
An improved ISAR system for removing range migration effects from an ISAR image from a moving object, comprising
- circuitry for generating a synthetic aperture radar image without regard for doppler frequency shift of the object by summing a plurality of imaging synthetic aperture radar points from the object;
- circuitry for compensating each of said data points by a factor representing the effect of non-zero doppler frequency shift on said data points and;
- circuitry for compensating said generated synthetic aperture radar image for non-zero doppler frequency shift from the object using said compensated data points, thereby removing from said synthetic aperture radar image said range migration effects.
Dependencies are inferred from the claim text.