A multi-look identification method known as score-level fusion is found to be capable of achieving very high
identification accuracy, even when low quality target signatures are used. Analysis using measured ground vehicle radar
signatures has shown that a 97% correct identification rate can be achieved using this multi-look fusion method; in
contrast, only a 37% accuracy rate is obtained when single target signature input is used. The results suggest that
quantity can be used to replace quality of the target data in improving identification accuracy. With the advent of sensor
technology, a large amount of target signatures of marginal quality can be captured routinely. This quantity over quality
approach allows maximum exploitation of the available data to improve the target identification performance and this
could have the potential of being developed into a disruptive technology.
When target motion is confined to a two-dimensional plane during coherent processing intervals, the adaptive joint time-frequency algorithm is shown to be an effective method for achieving rotational motion compensation in ISAR imaging. We illustrate the algorithm using both simulated and measured experimental radar data sets. The results show that the adaptive joint time-frequency algorithm performed very well in achieving a focused image of the target. Results also demonstrate that adaptive joint time-frequency techniques can significantly improve the distorted ISAR image over what can be achieved by conventional Fourier transform methods when the rotational motion of the target is confined to a two-dimensional plane. This study also adds insight into the distortion mechanisms that affect the ISAR images of a target in motion.
Gross distortion on ISAR images due to small perturbed target motion is experimentally verified. Quantitative results obtained under controlled experimental conditions on the target's motion have confirmed that large distortion in the ISAR image of the target can occur. The distortion is a consequence of the phase modulation effect in the radar return signal, as a result of small fluctuating perturbed motion of the target. This gives rise to distortion of the image in the cross-range direction. The distortion can be refocused by applying time-frequency analyiss. The Short-Time Fourier transform is used in this paper to examine some of the issues in refocusing distorted ISAR images.
ISAR images of moving targets are susceptible to distortion, for example, blurring due to small random fluctuation in the targets' motions. Small perturbation in the pitch, roll or yaw motions of an in-flight aircraft can introduce significant distortion to the ISAR images of in-flight aircraft. In this paper, experimental results on the distortion produced by small perturbed yaw motion of a target will be discussed. Numerical simulations of the distorted motions are compared with experimental results. This comparative analysis allows one to characterize the distortion mechanism and to gain some insights into the distortion process in radar imaging. It is found that even very small perturbation in the motion can be sufficient enough to introduce sizeable distortion to the radar images. The distortion can be attributed to the temporal phase modulation effect in the imaging process.
Small random rotational motion of an aircraft can affect the fidelity of the target's High Range Resolution (HRR) profile. A multiple scattering point-source model has been developed to investigate the distorting effect on a simulated target. Results indicate that even when the target possesses a very small amount of random motion during radar interrogation using a stepped frequency waveform (SFWF) scan, sizeable distortion in the target's range profile can still occur, making target identification more difficult. The well known range walk effect of the target during the SFWF radar scan offers a partial explanation for the distortion of the target's range profile. A more interesting situation emerges when the rotational motion is time-varying; a more severe distortion can occur as a result, leading to a broadening phenomenon and spurious peaks appearing in the target's range profile.
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