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

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

IEEE Access ◽

10.1109/access.2020.3047856 ◽

2020 ◽

pp. 1-1

Author(s):

Yinwei Li ◽

Qi Wu ◽

Jiawei Wu ◽

Ping Li ◽

Qibin Zheng ◽

...

Keyword(s):

High Frequency ◽

High Frequency Vibration ◽

Sar Imaging ◽

Vibration Parameters

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Compensation for High-Frequency Vibration of Platform in SAR Imaging Based on Adaptive Chirplet Decomposition

IEEE Geoscience and Remote Sensing Letters ◽

10.1109/lgrs.2016.2544945 ◽

2016 ◽

Vol 13 (6) ◽

pp. 792-795 ◽

Cited By ~ 17

Author(s):

Yong Wang ◽

Zhaofa Wang ◽

Bin Zhao ◽

Liang Xu

Keyword(s):

High Frequency ◽

High Frequency Vibration ◽

Sar Imaging

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Analysis on vibration for a high-frequency electro-hydraulic cleaning system controlled by improved two-dimensional rotary valve

Advances in Mechanical Engineering ◽

10.1177/1687814018811412 ◽

2018 ◽

Vol 10 (12) ◽

pp. 168781401881141

Author(s):

Xiancheng Ji ◽

Yan Ren ◽

Hesheng Tang

Keyword(s):

Vibration Frequency ◽

High Frequency ◽

Functional Materials ◽

Pressure Amplitude ◽

Two Dimensional ◽

Rotary Valve ◽

Sinusoidal Vibration ◽

High Frequency Vibration ◽

Cleaning System ◽

Sinusoidal Waveform

Conventional high-frequency cleaners utilize functional materials (e.g. piezoelectric ceramics, magnetostrictive materials) excited by electrical signals to realize high-frequency vibration, even ultrasonic vibration. However, it is difficult to produce a large force without sacrificing bandwidth because of the physical characteristics of materials themselves. Therefore, a high-frequency high-power cleaner driven by electro-hydraulic excitation is proposed. Only a few studies are performed on electro-hydraulic cleaners, owing to the limitation of frequency bandwidth of the electro-hydraulic system. Thus, a rotary valve named two-dimensional valve is improved and adopted to improve high-frequency performances of the electro-hydraulic cleaner. In this article, a two-dimensional rotary valve with a linear variable differential transformer is designed, and the vibration characteristics of the electro-hydraulic cleaner controlled by this valve are discussed in detail, especially vibration acceleration, vibration frequency, and pressure amplitude. A prototype of the electro-hydraulic cleaner is modeled and both a theoretical analysis and experimental investigation are carried out. Theoretical and experimental results indicate that the electro-hydraulic cleaning system outputs sinusoidal vibration waveforms, especially in a high-frequency domain, which could realize the vibration frequency of 2669 Hz. The measured waves at different frequencies (below the resonant frequency) demonstrate different distortions compared with the sinusoidal waveform. These distortions can be associated with the hydraulic resonance. At hydraulic resonance (1903 Hz), the amplitude is increased significantly and the vibration waveform becomes more pronounced. Nevertheless, the study does provide an access to the electro-hydraulic high-frequency vibration applied in cleaning or other engineering cases.

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A High-Frequency Vibration Error Compensation Method for Terahertz SAR Imaging Based on Short-Time Fourier Transform

Applied Sciences ◽

10.3390/app112210862 ◽

2021 ◽

Vol 11 (22) ◽

pp. 10862

Author(s):

Yinwei Li ◽

Qi Wu ◽

Jiawei Jiang ◽

Xia Ding ◽

Qibin Zheng ◽

...

Keyword(s):

High Frequency ◽

Singular Values ◽

Sar Image ◽

Short Time Fourier Transform ◽

High Frequency Vibration ◽

Window Width ◽

Vibration Parameters ◽

Short Time ◽

Vibration Error ◽

Optimal Window

High-frequency vibration error of a moving radar platform easily introduces a non-negligible phase of periodic modulation in radar echoes and greatly degrades terahertz synthetic aperture radar (THz-SAR) image quality. For solving the problem of THz-SAR image-quality degradation, the paper proposes a multi-component high-frequency vibration error estimation and compensation approach based on the short-time Fourier transform (STFT). To improve the robustness of the method against noise effects, STFT is used to extract the instantaneous frequency (IF) of a high-frequency vibration error signal, and the vibration parameters are coarsely obtained by the least square (LS) method. To reduce the influence of the STFT window widths, a method based on the maximum likelihood function (MLF) is developed for determining the optimal window width by a one-dimensional search of the window widths. In the case of high noise, many IF estimation values seriously deviate from the true ones. To avoid the singular values of IF estimation in the LS regression, the random sample consensus (RANSAC) is introduced to improve estimation accuracy. Then, performing the STFT with the optimal window width, the accurate vibration parameters are estimated by LS regression, where the singular values of IF estimation are excluded. Finally, the vibration error is reconstructed to compensate for the non-negligible phase of the platform-induced periodic modulation. The simulation results prove that the error compensation method can meet THz-SAR imaging requirements, even at a low signal-to-noise ratio (SNR).

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ESTIMATION OF DYNAMIC EFFECTS FROM VIBRATION DIPPING OF SHEET PILES ON ENVIRONMENTAL BUILDINGS IN CONDITIONS OF WEAK WATER-SATURATED SOILS

Construction and Geotechnics ◽

10.15593/2224-9826/2020.3.09 ◽

2020 ◽

Vol 11 (3) ◽

pp. 102-116

Author(s):

R. A Mangushev ◽

A. V Gurskiy ◽

V. M Polunin

Keyword(s):

High Frequency ◽

Soil Mass ◽

Vibration Velocity ◽

Sheet Pile ◽

Significant Excess ◽

Vibration Acceleration ◽

Dynamic Impact ◽

High Frequency Vibration ◽

Soil Foundation ◽

Water Saturated

In weak, structurally unstable soils, the use of the technology of high-frequency vibration immersion of sheet piles, in some cases, is obviously dangerous, and the issue of assessing the limits of applicability of this technology in certain conditions is relevant. The assessment of the dynamic impact on the soil foundation can be made by the level of vibrations. Regulatory documents impose requirements on the level of vibrations of the surrounding soil mass and buildings, however, it is not entirely correct to assess the influence of the technology of high-frequency vibration driving of sheet piles only by the values of vibration acceleration and vibration velocity. The object of the study is the values of deformations of foundations reinforced with piles. At the experimental construction site, we were carried out for the level of vibrations of foundations reinforced with piles 18 m length, from high-frequency vibration immersion of a pipe sheet pile with a diameter of 1200 mm and a length of 18 m. In the process of driving the sheet piles, we were making constant geodesic control over the deformations of adjoining buildings was carried out. The main results are: the example given in the article shows that when the foundations are strengthened, the deformations of the foundation (settlement) remain within the permissible values, despite the significant excess of the permissible level of vibrations of the building foundations. The proposed methodology for the numerical prediction of base deformations from vibration immersion of sheet piles gives satisfactory convergence with the results of field observations and makes it possible to assess qualitatively and quantitatively the settlements of buildings in the surrounding development from vibration immersion / extraction of sheet piles at the preliminary stages of construction.

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