SAR Signal Processing Architecture and Effects of Motion Errors for mmWave and THz Frequencies

Batra, Aman; Wiemeler, Michael; Kreul, Theo; Goehringer, Diana; Kaiser, Thomas

doi:10.1109/iwmts.2019.8823730

Cited by 8 publications

(5 citation statements)

References 6 publications

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“…According to (9), the phase error of an echo signal caused by high-frequency vibration error in each range gate can be regarded as the SFM signal, which can be expressed as…”

Section: Lfrft-based High-frequency Vibration Error Estimation Methodsmentioning

confidence: 99%

“…However, a higher frequency also means that the imaging quality of THz-SAR is more sensitive to the vibration error of the motion platform. Although the high-frequency vibration error will not affect the track of THz-SAR, it will seriously influence the phase of the radar echo signal, thus worsening the image quality [8,9]. Therefore, high-frequency vibration error estimation and compensation is the key for THz-SAR ultrahigh resolution imaging.…”

Section: Introductionmentioning

confidence: 99%

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A Novel High-Frequency Vibration Error Estimation and Compensation Algorithm for THz-SAR Imaging Based on Local FrFT

Ding

Zheng

et al. 2020

Sensors

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Compared with microwave synthetic aperture radar (SAR), terahertz SAR (THz-SAR) is easier to achieve ultrahigh-resolution image due to its higher frequency and shorter wavelength. However, higher carrier frequency makes THz-SAR image quality very sensitive to high-frequency vibration error of motion platform. Therefore, this paper proposes a novel high-frequency vibration error estimation and compensation algorithm for THz-SAR imaging based on local fractional Fourier transform (LFrFT). Firstly, the high-frequency vibration error of the motion platform is modeled as a simple harmonic motion and THz-SAR echo signal received in each range pixel can be considered as a sinusoidal frequency modulation (SFM) signal. A novel algorithm for the parameter estimation of the SFM signal based on LFrFT is proposed. The instantaneous chirp rate of the SFM signal is estimated by determining the matched order of LFrFT in a sliding small-time window and the vibration acceleration is obtained. Hence, the vibration frequency can be estimated by the spectrum analysis of estimated vibration acceleration. With the estimated vibration acceleration and vibration frequency, the SFM signal is reconstructed. Then, the corresponding THz-SAR imaging algorithm is proposed to estimate and compensate the phase error caused by the high-frequency vibration error of the motion platform and realize high-frequency vibration error estimation and compensation for THz-SAR imaging. Finally, the effectiveness of the novel algorithm proposed in this paper is demonstrated by simulation results.

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“…According to (9), the phase error of an echo signal caused by high-frequency vibration error in each range gate can be regarded as the SFM signal, which can be expressed as…”

Section: Lfrft-based High-frequency Vibration Error Estimation Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A Novel High-Frequency Vibration Error Estimation and Compensation Algorithm for THz-SAR Imaging Based on Local FrFT

Ding

Zheng

et al. 2020

Sensors

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“…Using the time-domain signal, the image of the object under test can be reconstructed using the migration-based radar imaging method known as the backprojection algorithm [18], [22] due to its simple implementation and robustness of the geometry of the synthetic aperture antenna. Additionally, the algorithm lacks data dependencies and inherits a high degree of parallelism [23], which is used in this paper to reduce the computational time. In the following, the principle of the backprojection algorithm is described for 2-D and 3-D imaging.…”

Section: A Raw Datamentioning

confidence: 99%

Short-Range SAR Imaging From GHz to THz Waves

et al. 2021

Self Cite

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Synthetic aperture radar (SAR) is a well-known imaging technique and most commonly used up to the microwave frequency spectrum (below 30 GHz) which provides spatial resolution in the sub-m range. To enhance the resolution, higher frequency spectra such as millimeter-wave (mmWave) and terahertz (THz) regions are being investigated. The mmWave and THz spectral ranges extend the SAR applications to nondestructive testing (NDT), material characterization, and sub-mm resolution imaging. However, the higher frequency spectrum suffers from higher path loss and potentially higher atmospheric absorption that limits the propagation distance. Nevertheless, the mmWave/THz spectrum is suitable for short-range applications such as indoor room profiling. From theoretical analysis, it can be summarized that the higher frequency spectrum provides better resolution but a comparative study on the impact on the image quality of the frequency spectrum ranging from GHz to THz has not been presented. Besides, as of the hardware complexity of the THz devices, the optimum range of the spectrum is always under investigation. The optimum range is defined where no strong improvements in the image quality are achievable with further increases in the frequency spectrum. Therefore, this paper presents an overview of electronics-based imaging using the SAR technique for the frequency spectrum ranging from GHz to THz with the focus on NDT and high-resolution imaging. Seven frequency bands: 5-10 GHz, 68-92 GHz, 75-110 GHz, 0.122-0.168 THz, 0.22-0.33 THz, 0.325-0.5 THz, and 0.85-1.1 THz are selected for a comparative analysis. The results are presented for 2D and 3D imaging using the backprojection algorithm. Additionally, state-of-the-art imaging based on SAR technique with electronics transceiver modules has only been demonstrated up to the sub-0.75 THz, whereas in this paper the spectrum up to 1.1 THz has been addressed.INDEX TERMS GHz and THz comparison, high-resolution imaging, non-destructive testing, synthetic aperture radar, terahertz imaging, radar imaging.This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination.

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“…Different from low-frequency motion error, highfrequency vibration error does not affect the track of THz-SAR due to its small vibration amplitude. However, it influences the phase of radar echo signal and produces paired echo in SAR imaging, which seriously affects the image quality [13], [14]. Currently, various paired echo suppression methods have been presented.…”

Section: Introductionmentioning

confidence: 99%

Estimation of High-Frequency Vibration Parameters for Terahertz SAR Imaging Based on FrFT With Combination of QML and RANSAC

et al. 2021

IEEE Access

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High-frequency vibration of motion platform leads to paired echo for synthetic aperture radar (SAR) imaging, especially in terahertz band due to its shorter wave length. Different from most existing parameters estimation methods only considering single component high-frequency vibration, in this paper a novel method considering multi-components vibration model is proposed based on fractional Fourier transform (FrFT) with combination of quasi-maximum likelihood (QML) and random sample consensus (RANSAC). Based on the model establishment of high-frequency vibration error in the echo, its instantaneous chirp rate (ICR) is firstly estimated by FrFT in sliding sub-aperture, followed which the vibration parameters are coarsely obtained through spectrum analysis and least square (LS) regression. To further refine the parameters estimates, QML is developed for compensating the deviation both caused by the frequency spectrum leakage and the error propagation effects by one-dimensional search over the vibration frequency. Meanwhile, RANSAC is adopted for avoiding the outlier of the ICR estimates in LS regression, especially at low signal-to-noise ratio (SNR). Thus, the refinement strategy based on the combination of QML and RANSAC is developed, whose utilization improves the estimation accuracy of vibration parameters. Finally, the paired echo in terahertz SAR (THz-SAR) imaging is effectively suppressed by the proposed method, and the high-quality THz-SAR imaging results are achieved. Both simulations of single component and multi-components high-frequency vibration are used to verify the validity of the proposed method. The simulation results show that the proposed method has higher estimation accuracy even at low SNR.INDEX TERMS Fractional Fourier transform (FrFT), high-frequency vibration, quasi-maximum likelihood (QML), random sample consensus (RANSAC), terahertz synthetic aperture radar (THz-SAR).

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SAR Signal Processing Architecture and Effects of Motion Errors for mmWave and THz Frequencies

Cited by 8 publications

References 6 publications

A Novel High-Frequency Vibration Error Estimation and Compensation Algorithm for THz-SAR Imaging Based on Local FrFT

A Novel High-Frequency Vibration Error Estimation and Compensation Algorithm for THz-SAR Imaging Based on Local FrFT

Short-Range SAR Imaging From GHz to THz Waves

Estimation of High-Frequency Vibration Parameters for Terahertz SAR Imaging Based on FrFT With Combination of QML and RANSAC

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