scholarly journals Application of an Automatic Noise or Signal Removal Algorithm Based on Synchrosqueezed Continuous Wavelet Transform of Passive Surface Wave Imaging: A Case Study in Sichuan, China

2021 ◽  
Vol 11 (24) ◽  
pp. 11718
Author(s):  
Jie Fang ◽  
Guofeng Liu ◽  
Yu Liu
Keyword(s):  
Wavelet Transform ◽  
Surface Wave ◽  
Surface Waves ◽  
Continuous Wavelet Transform ◽  
Cross Correlation ◽  
Underground Structure ◽  
Inversion Method ◽  
Continuous Wavelet ◽  
Dispersion Measurement ◽  
Wave Imaging

Passive surface wave imaging based on noise cross-correlation has been a research hotspot in recent years. However, because randomness of noise is difficult to achieve in reality, prominent noise sources will inevitably affect the dispersion measurement. Additionally, in order to recover high-fidelity surface waves, the time series input during cross-correlation calculation is usually very long, which greatly limits the efficiency of passive surface wave imaging. With an automatic noise or signal removal algorithm based on synchrosqueezed continuous wavelet transform (SS-CWT), these problems can be alleviated. We applied this method to 1-h passive datasets acquired in Sichuan province, China; separated the prominent noise events in the raw field data, and enhanced the cross-correlation reconstructed surface waves, effectively improving the accuracy of the dispersion measurement. Then, using the conventional surface wave inversion method, the shear wave velocity profile of the underground structure in this area was obtained.

scholarly journals Inversion of Nearshore X-Band Radar Images to Sea Surface Elevation Maps

2018 ◽  
Vol 10 (12) ◽  
pp. 1919 ◽  
Author(s):  
Pavel Chernyshov ◽  
Teodor Vrecica ◽  
Yaron Toledo
Keyword(s):  
Wavelet Transform ◽  
Continuous Wavelet Transform ◽  
High Efficiency ◽  
Surface Elevation ◽  
Wave Number ◽  
Inversion Method ◽  
Continuous Wavelet ◽  
Modulation Transfer ◽  
Radar Images ◽  
X Band

A new method to invert X-band radar images for linear shoaling conditions is proposed. The commonly used approach for this type of inverse problems is the Fourier transform. Unlike in deep water conditions, in the shoaling region, waves are modulated both in terms of wavelength and amplitude. However, Fourier analysis assumes spacial and temporal periodicity, and homogeneity limiting its applicability to this region. In order to overcome these limitations, a wavelet based technique is developed. The proposed technique treats every spatial radar image within the time sequence individually, so no information on the dispersion relation is required. For validation purposes, surface elevation range-time shoaling realizations based on the mild slope equation are prepared. A radar imaging model including tilt and shadowing modulations, speckle noise, and the radar equation is applied to these realizations to provide modeled grazing incidence radar images. The inversion process starts with the application of the continuous wavelet transform independently for each spacial image. The procedure continues with employing a successive range independent modulation transfer function to the wavelet spectra in the wavenumber domain. Then, after a phase shift correction, an inverse continuous wavelet transform is applied. The procedure is finalized by a calibration of the retrieved maps. After the calibration, a thorough comparison between the original and the reconstructed surface elevations is performed. It shows high efficiency of the proposed method in treating wave number and amplitude modulated signals, as well as in addressing local phase shifts due to tilt modulation and noise contamination. The new inversion method is proven to have high accuracy in inhomogeneous conditions. It shows high potential to be implemented for individual wave reconstruction using real aperture radars.

IDENTIFICATION OF ROTATING PRESSURE WAVES IN A CENTRIFUGAL COMPRESSOR DIFFUSER BY MEANS OF THE WAVELET CROSS-CORRELATION

2006 ◽  
Vol 04 (02) ◽  
pp. 373-382 ◽  
Author(s):  
LONGIN HORODKO
Keyword(s):  
Correlation Function ◽  
Wavelet Transform ◽  
Centrifugal Compressor ◽  
Continuous Wavelet Transform ◽  
Signal Analysis ◽  
Cross Correlation ◽  
Rotating Stall ◽  
Pressure Waves ◽  
Continuous Wavelet ◽  
Compressor Impeller

Rotating stall is usually the first symptom of approaching compressor instability. It consists of zones of a turbulent flow, which rotate slower than the compressor impeller. The wavelet cross-correlation function was applied to detect rotating objects, whereas the continuous wavelet transform was used to identify different phases of the compressor operation. These methods of signal analysis enabled the identification of rotating pressure waves that appear during all phases of operation. Some of them have several times shorter wavelength than these manifested by the rotating stall. What is more, rotating pressure waves, though very weak, appear also during the stable compressor operation.

Determination of the Slip-Up Time for Slip Form System Using Surface Wave Velocity

2013 ◽  
Author(s):  
H. S. Kim ◽  
Y. J. Kim ◽  
W. J. Chin ◽  
H. Yoon
Keyword(s):  
Compressive Strength ◽  
Wavelet Transform ◽  
Surface Wave ◽  
Wave Velocity ◽  
Continuous Wavelet Transform ◽  
Setting Time ◽  
Continuous Wavelet ◽  
Surface Wave Velocity ◽  
Form System

When applying the slip form system, the early setting time of concrete corresponds to the hardening time of early-age concrete indicating that cast-in-place concrete has developed sufficient strength to be safely stripped off the form. This hardening time is thus an important indicator for the determination of the slip-up velocity of the slip form system. Therefore, need is for a technique enabling to evaluate the early hardening time of concrete in order to secure the safety of the slip form system and the quality of the constructed concrete. Among the methods using ultrasonic waves, this paper applies the surface wave velocity to evaluate the degree of hardening of concrete so as to estimate the early setting time and decide the slip-up time of the slip form system. To that goal, penetration resistance test, compressive strength test and surface wave velocity measurement test are performed concurrently with respect to the mix materials and curing temperature of concrete. The test results are used to derive the relationship between the compressive strength and surface wave velocity according to the early hardening time of concrete. Continuous wavelet transform is applied for the measurement of the surface wave velocity. The validity of the application of the continuous wavelet transform is verified through numerical analysis. Finally, the surface wave velocity required for the slip-up of the slip form system is proposed and the applicability of the proposed surface wave velocity for the determination of the climbing time of the slip form system is verified by means of tests on a reduced-scale slip form system prototype.

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