Spectral ringing suppression and optimal windowing for attenuation and Q measurements

Geophysics ◽  
1998 ◽  
Vol 63 (2) ◽  
pp. 632-636 ◽  
Author(s):  
Cheh Pan
Keyword(s):  
Fourier Transform ◽  
Acoustic Waves ◽  
Gibbs Phenomenon ◽  
Window Length ◽  
Spectral Ratios ◽  
Paper Briefly ◽  
Velocity Change ◽  
Zero Line ◽  
First Arrival ◽  
Ringing Effect

In the first part of this paper, briefly the appearance of the Gibbs phenomenon in a discrete Fourier transform and its removal is discussed. The data‐flipping method is then applied to suppress the ringing effect in the spectral ratios for a more accurate measurement of attenuation and Q from seismic or acoustic waves. Such a measurement is invariant to velocity change. The second part concerns optimal windowing of wave modes. Data flipping makes measurement less sensitive to window length. A floating‐length window designed to pick up first arrivals cycle by cycle improves the result. A pickup of the first arrival up to the trough of the second cycle, instead of only to the zero‐line before the trough of the second cycle, gives much better attenuation and Q estimates.

A Novel Approach to Photoacoustic FT-IR Spectroscopy: Rheo-Photoacoustic Measurements

1989 ◽  
Vol 43 (8) ◽  
pp. 1387-1393 ◽  
Author(s):  
William F. McDonald ◽  
Hans Goeitler ◽  
Marek W. Urban
Keyword(s):  
Molecular Structure ◽  
Thin Films ◽  
Fourier Transform ◽  
Acoustic Waves ◽  
Polymeric Materials ◽  
Photoacoustic Signal ◽  
Novel Approach ◽  
Ft Ir ◽  
Property Changes ◽  
Ft Ir Spectroscopy

A new rheo-photoacoustic Fourier transform infrared cell has been developed to perform stress-strain studies on polymeric materials. The rheo-photoacoustic measurements lead to the enhancement of the photoacoustic signal and allow one to monitor the effect of elongational forces on the molecular structure of polymers. Propagating acoustic waves are detected as a result of the deformational changes and thermal property changes upon the applied stress. Applications of this technique to fibers, films, and adhesion of thin films are presented.

Field trials of a seismoelectric method for detecting massive sulfides

Geophysics ◽  
1995 ◽  
Vol 60 (2) ◽  
pp. 365-373 ◽  
Author(s):  
Anton W. Kepic ◽  
Michael Maxwell ◽  
R. Don Russell
Keyword(s):  
Electromagnetic Radiation ◽  
Acoustic Waves ◽  
Seismic Energy ◽  
Field Trials ◽  
P Wave ◽  
Massive Sulfides ◽  
P Wave Velocity ◽  
Electromagnetic Emissions ◽  
First Arrival ◽  
Exploration Tool

An underground test of a seismoelectric prospecting method for massive sulfides was performed at the Mobrun Mine (Rouyn‐Noranda, Quebec) in June 1991. The method is based upon the conversion of seismic energy to high‐frequency pulses of electromagnetic radiation by sulfide minerals. The delay between shot detonation and detection of the electromagnetic radiation gives a one‐way traveltime for the acoustic wave to reach the zone of seismoelectric conversion, which when combined with P‐wave velocity allows the shot‐to‐ore zone distance to be calculated. A 0.22-kg explosive charge located within 50 m of the orebody provided the seismic excitation, and the resulting electromagnetic emissions were received by electric dipole and induction‐coil antennas. First‐arrival information from a 35‐shot survey above an orebody, the 1100 lens, provides firm evidence that short duration pulses of electromagnetic radiation are produced by the passage of acoustic waves through the orebody. The survey also demonstrated that seismoelectric conversions could be induced at shot‐to‐orebody distances of 50 m and detected at distances of up to 150 m from the orebody. Areas of seismoelectric conversion are highlighted in sections produced by plotting the position of seismic wavefronts during signal reception. The sections show anomalies that correlate with the known structure and location of the orebody and demonstrate the potential of using this seismoelectric phenomenon as an exploration tool.

Spectral decomposition of seismic data with continuous-wavelet transform

Geophysics ◽  
2005 ◽  
Vol 70 (6) ◽  
pp. P19-P25 ◽  
Author(s):  
Satish Sinha ◽  
Partha S. Routh ◽  
Phil D. Anno ◽  
John P. Castagna
Keyword(s):  
Fourier Transform ◽  
Wavelet Transform ◽  
Continuous Wavelet Transform ◽  
Time Scale ◽  
Fixed Time ◽  
Frequency Resolution ◽  
Continuous Wavelet ◽  
Window Length ◽  
Time Frequency ◽  
Frequency Map

This paper presents a new methodology for computing a time-frequency map for nonstationary signals using the continuous-wavelet transform (CWT). The conventional method of producing a time-frequency map using the short time Fourier transform (STFT) limits time-frequency resolution by a predefined window length. In contrast, the CWT method does not require preselecting a window length and does not have a fixed time-frequency resolution over the time-frequency space. CWT uses dilation and translation of a wavelet to produce a time-scale map. A single scale encompasses a frequency band and is inversely proportional to the time support of the dilated wavelet. Previous workers have converted a time-scale map into a time-frequency map by taking the center frequencies of each scale. We transform the time-scale map by taking the Fourier transform of the inverse CWT to produce a time-frequency map. Thus, a time-scale map is converted into a time-frequency map in which the amplitudes of individual frequencies rather than frequency bands are represented. We refer to such a map as the time-frequency CWT (TFCWT). We validate our approach with a nonstationary synthetic example and compare the results with the STFT and a typical CWT spectrum. Two field examples illustrate that the TFCWT potentially can be used to detect frequency shadows caused by hydrocarbons and to identify subtle stratigraphic features for reservoir characterization.

Removal of the Gibbs phenomenon and its application to fast-Fourier-transform-based mode solvers

2007 ◽  
Vol 24 (12) ◽  
pp. 3772 ◽  
Author(s):  
J. G. Wangüemert-Pérez ◽  
R. Godoy-Rubio ◽  
A. Ortega-Moñux ◽  
I. Molina-Fernández
Keyword(s):  
Fourier Transform ◽  
Fast Fourier Transform ◽  
Gibbs Phenomenon

scholarly journals A study of acoustic characteristics of voluntary expiratory sounds produced before and immediately after swallowing

2022 ◽  
Vol 12 (1) ◽  
Author(s):  
Shoma Hattori ◽  
Shinji Nozue ◽  
Yoshiaki Ihara ◽  
Koji Takahashi
Keyword(s):  
Fourier Transform ◽  
Fast Fourier Transform ◽  
Time Window ◽  
Maximum Amplitude ◽  
Comparison Method ◽  
Window Length ◽  
Acoustic Characteristics ◽  
The Mean ◽  
Time Waveform ◽  
The Relationship

AbstractTo evaluate the expiratory sounds produced during swallowing recorded simultaneously with videofluorographic examination of swallowing (VF) using fast Fourier transform (FFT), and to examine the relationship between dysphagia and its acoustic characteristics. A total of 348 samples of expiratory sounds were collected from 61 patients with dysphagia whose expiratory sounds were recorded during VF. The VF results were evaluated by one dentist and categorized into three groups: safe group (SG), penetration group (PG), and aspiration group (AG). The duration and maximum amplitude of expiratory sounds produced were measured as the domain characteristics on the time waveform of these sounds and compared among the groups. Time window-length appropriate for FFT and acoustic discriminate values (AD values) of SG, PG, and AG were also investigated. The groups were analyzed using analysis of variance and Scheffé's multiple comparison method. The maximum amplitude of SG was significantly smaller than those of PG and AG. The mean duration in SG (2.05 s) was significantly longer than those in PG (0.84 s) and AG (0.96 s). The AD value in SG was significantly lower than those in PG and AG. AD value detects penetration or aspiration, and can be useful in screening for dysphagia.

A first arrival picking method of microseismic data based on single time window with window length independent

2018 ◽  
Vol 22 (6) ◽  
pp. 1613-1627
Author(s):  
Tong Shen ◽  
Xianguo Tuo ◽  
Huailiang Li ◽  
Yong Liu ◽  
Wenzheng Rong
Keyword(s):  
Time Window ◽  
Window Length ◽  
Single Time ◽  
Microseismic Data ◽  
First Arrival
Sign in / Sign up

Export Citation Format

Share Document