scholarly journals Multi-mode analysis of Rayleigh-type Lg. Part 1. Theory and applicability of the method

1981 ◽  
Vol 71 (4) ◽  
pp. 973-984 ◽  
Author(s):  
Michel Cara ◽  
J. Bernard Minster
Keyword(s):  
Linear Array ◽  
Random Phase ◽  
Mode Analysis ◽  
Phase Fluctuations ◽  
Time Frequency ◽  
Analysis Technique ◽  
Crustal Structures ◽  
Velocity Changes ◽  
Multi Mode ◽  
Lateral Heterogeneities

abstract Rayleigh-type Lg propagating in a laterally homogeneous continental crust can be synthesized by adding only a few overtones at periods greater than 2 sec. Under minimal assumptions, we show that wavenumber analysis of Lg recorded on a several hundred kilometers long linear array of 10 stations allow us to isolate the different overtones, providing a tool to study crustal structures and excitation of the overtones at the source. In this first paper, we use synthetic Lg seismograms to investigate the applicability of a time-frequency-wavenumber analysis technique (UC diagram algorithm) to realistic arrays of stations. The behavior of the algorithm in the presence of lateral heterogeneities is studied numerically by introducing either random or coherent phase perturbations. We find that (1) the method is tractable if random phase fluctuations from station to station are spread over less than half a cycle, and (2) coherent velocity changes between two halves of a profile are spatially averaged if they are too small to be resolved by the array.

scholarly journals Multi-mode analysis of Rayleigh-type Lg. Part 2. Application to southern California and the northwestern Sierra Nevada

1981 ◽  
Vol 71 (4) ◽  
pp. 985-1002
Author(s):  
Michel Cara ◽  
J. Bernard Minster ◽  
Ronan Le Bras
Keyword(s):  
Sierra Nevada ◽  
Southern California ◽  
Mode Conversion ◽  
Wave Train ◽  
Companion Paper ◽  
Mode Analysis ◽  
Time Frequency ◽  
Short Period ◽  
Multi Mode ◽  
Group Velocities

abstract The UC diagram technique described in the companion paper (Part 1), is applied to nine sets of Lg phases recorded through the CEDAR system in southern California, and two sets of Lg phases recorded along the northwestern margin of the Sierra Nevada. A clear image of the signal is obtained in time-frequency-wavenumber space, and we discuss in particular observations at 2.5-sec period, for events 200 to 300 km outside the profiles. From the gross features of UC diagrams we conclude that a representation of Lg as a single coherent multi-mode wave train is oversimplified in the case of southern California but is more appropriate for the Sierra block. In southern California, peaks observed at group velocities smaller than 3.2 km/sec are not predicted by realistic crustal models of the area, and are probably due to lateral heterogeneities effects such as mode conversion and multipathing. On the other hand, for group velocities between 3.2 and 3.6 km/sec, peaks observed in either area can generally be interpreted in terms of overtones excited at the source and propagating through spatially averaged structures, although care must be taken to monitor the stability of the algorithm on actual short-period records.

Time-Frequency Channel Parameterization with Application to Multi-Mode Receivers

2009 ◽  
Vol E92-B (12) ◽  
pp. 3717-3725
Author(s):  
Thomas HUNZIKER ◽  
Ziyang JU ◽  
Dirk DAHLHAUS
Keyword(s):  
Frequency Channel ◽  
Time Frequency ◽  
Multi Mode

Image encryption based on Fractional wavelet transform, Arnold transform with the double random phases in HSV color domain

2020 ◽  
Vol 13 ◽  
Author(s):  
Aarushi Shrivastava ◽  
Janki Ballabh Sharma ◽  
Sunil Dutt Purohit
Keyword(s):  
Wavelet Transform ◽  
Image Encryption ◽  
Fractional Fourier Transform ◽  
Color Image ◽  
Random Phase ◽  
Arnold Transform ◽  
Time Frequency ◽  
Key Space ◽  
Secret Keys ◽  
Fractional Wavelet Transform

Objective: In the recent multimedia technology images play an integral role in communication. Here in this paper, we propose a new color image encryption method using FWT (Fractional Wavelet transform), double random phases and Arnold transform in HSV color domain. Methods: Firstly the image is changed into the HSV domain and the encoding is done using the FWT which is the combination of the fractional Fourier transform with wavelet transform and the two random phase masks are used in the double random phase encoding. In this one inverse DWT is taken at the end in order to obtain the encrypted image. To scramble the matrices the Arnold transform is used with different iterative values. The fractional order of FRFT, the wavelet family and the iterative numbers of Arnold transform are used as various secret keys in order to enhance the level of security of the proposed method. Results: The performance of the scheme is analyzed through its PSNR and SSIM values, key space, entropy, statistical analysis which demonstrates its effectiveness and feasibility of the proposed technique. Stimulation result verifies its robustness in comparison to nearby schemes. Conclusion: This method develops the better security, enlarged and sensitive key space with improved PSNR and SSIM. FWT reflecting time frequency information adds on to its flexibility with additional variables and making it more suitable for secure transmission.

The Applicated Comparation of Three Signal Analytical Methods for Ocean CSEM Signature

2013 ◽  
Vol 798-799 ◽  
pp. 561-564
Author(s):  
Ji Yu Zhou ◽  
Feng Dao Zhou
Keyword(s):  
Frequency Analysis ◽  
Oil And Gas ◽  
Time Frequency Analysis ◽  
Hilbert Huang Transform ◽  
Time Frequency ◽  
Analysis Technique ◽  
Oil And Gas Resources ◽  
Concentration Degree ◽  
Short Time ◽  
Better Than

Sea is rich in oil and gas resources, the marine controlled source electromagnetic method (CSEM) is a kind of method seabed oil gas geophysical technology rising in recent years. Because of the problem of CSEM about the air wave in the shallow water, the research of time-frequnecy analysis technique is used to suppress the air wave in this paper. The basic idea is: because of the CSEM signals speed are different in the air and submarine, so the time which received by the receiving points are also different through these two kinds of ways. Using the time-frequency analysis technique and theoretical calculation, we can determine which part of the signal is spread over the ocean, so as to suppress the air wave effectively. This paper lists several methods of time-frequency analysis, such as Short-time Fourier transform, W-V distribution, Wavelet transform, Hilbert Huang transform. Through the time-frequency graph,we get the conclusion that HHT is better than others in concentration degree,and W-V distribution is better than STFT.Compared with the original signal, the time-frequency graph is the best in using Smooth Puseudo W-V Distribution.I have a detailed analysis about real case in using SPWVD at last.

scholarly journals Dispersion estimation from linear array data in the time-frequency plane

2005 ◽  
Vol 53 (10) ◽  
pp. 3738-3748 ◽  
Author(s):  
A. Roueff ◽  
J.I. Mars ◽  
J. Chanussot ◽  
H. Pedersen
Keyword(s):  
Linear Array ◽  
Array Data ◽  
Time Frequency

Effect of initial stress and rotation on magneto-thermoelastic material with voids and energy dissipation

2017 ◽  
Vol 13 (2) ◽  
pp. 331-346 ◽  
Author(s):  
Mohamed Ibrahim A. Othman ◽  
Mohamed Ibrahim M. Hilal
Keyword(s):  
Laser Pulse ◽  
Initial Stress ◽  
Pulse Heating ◽  
Normal Mode Analysis ◽  
Mode Analysis ◽  
Content Type ◽  
Thermoelastic Material ◽  
Analysis Technique ◽  
Laser Pulse Heating ◽  
Physical Quantities

Purpose The purpose of this paper is to study the effect of rotation and initial stress on magneto-thermoelastic material with voids heated by a laser pulse heating. Design/methodology/approach The analytical method used was the normal mode analysis technique. Findings Numerical results for the physical quantities were presented graphically and analyzed. The graphical results indicate that the effect of rotation, initial stress and magnetic fields are observable physical effects on the thermoelastic material with voids heated by a laser pulse. Comparisons are made with the results in the absence and the presence of the physical operators, also at various times. Originality/value In the present work, the authors shall investigate the effect of the rotation, initial stress, magnetic field and laser pulse on thermoelastic material with voids subjected to a laser pulse heating acting as a thermal shock. A comparison is also made between the two types (types II and III) of Green-Naghdi theory in the absence and the presence of the physical operators. Such problems are very important in many dynamical systems.

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