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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]