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Compared to conventional radars, arc array synthetic aperture radar (SAR) enables wide-area observation under ideal conditions. However, helicopters carrying arc array SAR platforms are generally smaller in size and more sensitive to vibration, which has a greater impact on the imaging quality. In this paper, the vibration error of the arc array SAR platform is investigated, and a vibration error model of the arc array SAR platform is established. Based on the study of the vibration error model, a vibration phase estimation and compensation algorithm based on the delayed conjugate multiplication method is proposed. In the first step, distance pulse pressure processing is performed on the echo signal. In the second step, the pulse pressure signals and their delays in the same distance unit are subjected to conjugate multiplication, and the phase of the signal after conjugate multiplication is extracted. The extracted phase is then amplitude- and phase-compensated to estimate the vibration phase. In the third step, the vibration phase is compensated in the azimuthal direction of the distance pulse pressure signal, and the pairwise echo is eliminated, which completes the compensation of the airborne arc array SAR vibration platform. [ABSTRACT FROM AUTHOR]

Compared to conventional radars, arc array synthetic aperture radar (SAR) enables wide-area observation under ideal conditions. However, helicopters carrying arc array SAR platforms are generally smaller in size and more sensitive to vibration, which has a greater impact on the imaging quality. In this paper, the vibration error of the arc array SAR platform is investigated, and a vibration error model of the arc array SAR platform is established. Based on the study of the vibration error model, a vibration phase estimation and compensation algorithm based on the delayed conjugate multiplication method is proposed. In the first step, distance pulse pressure processing is performed on the echo signal. In the second step, the pulse pressure signals and their delays in the same distance unit are subjected to conjugate multiplication, and the phase of the signal after conjugate multiplication is extracted. The extracted phase is then amplitude- and phase-compensated to estimate the vibration phase. In the third step, the vibration phase is compensated in the azimuthal direction of the distance pulse pressure signal, and the pairwise echo is eliminated, which completes the compensation of the airborne arc array SAR vibration platform.

Platform vibration introduces sinusoidal modulation in inverse synthetic aperture lidar (ISAL) imaging, which causes paired echoes in ISAL imaging. In this paper, a varying amplitude vibration phase suppression algorithm is proposed. Working without prior knowledge, the proposed algorithm can suppress paired echoes under the condition of varying vibration amplitude and will not introduce new phase errors. Furthermore, the method is suitable for the imaging scene without isolated points. Both the simulated and real experiment results of ISAL turntable data demonstrate the effectiveness of the proposed algorithm.

The helicopter-borne synthetic aperture radar (SAR) system suffers high-frequency vibrations caused by the rotor rotation. This micro-vibration induces phase modulation, which gives rise to paired echoes and seriously degrades the quality of SAR images due to the unexpected ghost phenomenon. In this letter, a nonparametric paired echo suppression method for helicopter-borne SAR imaging is proposed. By constructing a modified vibration error model and introducing the autofocus method for the vibration phase error estimation, it can suppress the paired echoes directly, which avoids the complex vibration parameter estimation in the traditional methods. The effectiveness of the proposed method is demonstrated via simulations and real data processing. [ABSTRACT FROM AUTHOR]

The amplitude and phase distortions of radar echo signal will cause the emergence of undesirable ghost scattering points, which degrade the quality of terahertz (THz) radar images. In this paper, a physics-based procedure is presented to predict the atmospheric attenuation and dispersion characteristics at THz frequencies, which is mainly based on the line-by-line calculation method with a specific modification in phase-shift prediction. The line-by-line parameters provided by the high-resolution transmission spectroscopic database and atmospheric condition parameters obtained from the Air Force Geophysics Laboratory reference atmospheric constituent profiles are adopted to predict the atmospheric transmittance and the phase shift for specific transfer paths. The results are compared with measured data to demonstrate the accuracy, while the proposed procedure is used to analyze the impacts of atmospheric transfer characteristics on radar imaging via the high-resolution range profile simulation. The signal distortion is interpreted in terms of paired echoes to illustrate the importance of frequency band selection for high-resolution imagery at THz frequencies. [ABSTRACT FROM AUTHOR]

Paired echoes are the typical manifestation of Doppler characteristics caused by vibrating targets in high-resolution synthetic aperture radar (SAR). Conventional imaging algorithms produce smeared paired echoes. It results in not only the inconvenience of vibration parameter analysis but also the emergence of unwanted ghost targets to degrade SAR image quality. This paper proposes a method on paired echo focusing and suppression of vibrating targets. After demodulation and range compression, the signal is decomposed into the form of Bessel series in the azimuth direction. Then, the range walk is compensated in the 2-D frequency domain by Doppler keystone transform. Next, the range curvature is corrected in the range-Doppler domain by using range cell migration correction to achieve the focus of paired echoes. Compared with conventional SAR imaging algorithms, the focused paired echoes could reach system nominal resolution. Furthermore, this focusing method, which works without prior knowledge of vibrating targets, is suitable for various vibrating states of multiple targets. On the basis of paired echo focusing, the residual video phase of paired echoes is also eliminated. Then, vibration parameters, including vibration frequency, amplitude, and initial phase, are estimated. These parameters are used herein to construct the reference function to compensate the sinusoidal modulation phase in the range-Doppler domain. Finally, deghosted vibrating targets can be obtained. Simulations show that paired echoes could be successfully focused within one resolution unit as well as the robustness of its application. At last, the real SAR data from a moving truck are used to further validate the effectiveness of the proposed method. [ABSTRACT FROM PUBLISHER]

Paired echoes are the typical Doppler characteristics of vibrating targets in high resolution synthetic aperture radar ( SAR) . Conventional imaging algorithms produce smeared paired echoes which is not conductive to the analysis of vibrating parameters. A paired echoes focusing algorithm for vibrating targets is proposed. On the basis of the analytic formula derivation in 2-D frequency domain for vibrating targets, Keystone transform is employed to perform migration correction. Then the quadratic phase error is compensated in the Range-Doppler domain. Finally, the vibrating targets and the stationary targets can be well focused contemporaneously. The proposed algorithm needs no prior knowledge of vibrating targets, so it can be used for the imaging of multiple targets at different vibrating state. The simulation results validate the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]

Platform vibration introduces sinusoidal modulation in inverse synthetic aperture lidar (ISAL) imaging, which causes paired echoes in ISAL imaging. In this paper, a varying amplitude vibration phase suppression algorithm is proposed. Working without prior knowledge, the proposed algorithm can suppress paired echoes under the condition of varying vibration amplitude and will not introduce new phase errors. Furthermore, the method is suitable for the imaging scene without isolated points. Both the simulated and real experiment results of ISAL turntable data demonstrate the effectiveness of the proposed algorithm. [ABSTRACT FROM AUTHOR]