A fast, modified parabolic Radon transform

Geophysics ◽  
2011 ◽  
Vol 76 (1) ◽  
pp. V11-V24 ◽  
Author(s):  
Brahim Abbad ◽  
Bjørn Ursin ◽  
Milton J. Porsani
Keyword(s):  
Frequency Domain ◽  
Radon Transform ◽  
Low Frequency ◽  
Small Time ◽  
Time Interval ◽  
Seismic Line ◽  
Frequency Domain Methods ◽  
Multiple Paths ◽  
Value Decomposition ◽  
Parabolic Radon Transform

We propose a fast and efficient frequency-domain implementation of a modified parabolic Radon transform (modified PRT) based on a singular value decomposition (SVD) with applications to multiple removal. The problem is transformed into a complex linear system involving a single operator after merging the curvature-frequency parameters into a new variable. A complex SVD is applied to this operator and the forward transform is computed by means of a complex back-substitution that is frequency independent. The new transform offers a wider curvature range at signal frequencies than the other PRT implementations, allowing the mapping in the transform domain of low-frequency events with important residual moveouts (long period multiples). The method is capable of resolving multiple energy from primaries when they interfere in a small time interval, a situation where most frequency-domain methods fail to discriminate the different wave types. Additionally, the method resists better to amplitude variations with offset (AVO) effects in the data than does the iteratively reweighted least-squares (IRLS) method. The proposed method was successfully applied to a deep-water seismic line in the Gulf of Mexico to attenuate water-bottom multiples and subsequent peg-legs originating from multiple paths in the water column. Combining the suggested method with the surface-related multiple elimination (SRME) has led to the best attenuation results in removing residual multiple energy in the stack.

EFFECT OF PHYSICAL ACTIVITIES ON HEART RATE VARIABILITY AND SKIN CONDUCTANCE

2021 ◽  
pp. 2150038
Author(s):  
Ankita Soni ◽  
Kirti Rawal
Keyword(s):  
Heart Rate ◽  
Heart Rate Variability ◽  
Frequency Domain ◽  
Skin Conductance ◽  
Time Domain ◽  
Low Frequency ◽  
Physical Activities ◽  
Rr Intervals ◽  
Warm Up ◽  
Frequency Domain Methods

The sympathetic and parasympathetic function of the Autonomic Nervous System[Formula: see text]ANS[Formula: see text] is the primary cause of the variations in Heart Rate and Skin Conductance[Formula: see text]SC[Formula: see text] during different physical activities. This paper aims to analyze the effect of different physical activities i.e. (a) Supine (b) Standing and (c) Warm-up, on Heart Rate Variability (HRV) and SC. The standard dataset of 18 subjects has been used to analyze the effect of physical activities on the HRV and SC. In the used dataset, the subjects are in supine, standing, and warm-up positions. The linear methods (time domain & frequency domain) of HRV are implemented on the standard dataset for analyzing the effect of physical activities. It has been observed with the analysis of the HRV that the mean value of time domain methods i.e. the NN interval’s standard deviation (SDNN), the successive RR interval’s root mean square (RMSSD), RR intervals with more than 50 ms differences in between them (NN50), percentage of successive RR intervals that have the difference of more than 50 ms (pNN50) are decreased and the value of Heart rate (HR) increased when the activity has been changed from supine to standing and standing to the warm-up positions. The value of frequency domain methods, such as low frequency (LF) and the ratio of low and high frequency (LF/HF) increased, while the value of HF decreases as activity changes from supine to standing and from supine to warm-up position. Further, the increment is also observed in the value of SC when activity is switched from supine to standing and from standing to the warm-up position. It is concluded from the results that there is a significant decrement that is observed in the value of HRV, while the increment is observed in the value of SC and HR. Decrement of HRV reflects that the sympathetic activity is increased as activity changed from supine to standing and further from standing to warm-up positions.

scholarly journals A Fish Chorus on the Margin of New Jersey Atlantic Continental Shelf

2021 ◽  
Vol 8 ◽  
Author(s):  
Qianchu Zhang ◽  
Boris Katsnelson
Keyword(s):  
New Jersey ◽  
Continental Shelf ◽  
Frequency Domain ◽  
Acoustic Signal ◽  
Background Noise ◽  
Low Frequency ◽  
Maximum Intensity ◽  
Single Type ◽  
Time Interval ◽  
Fish Sounds

We report herein an underwater biological chorus coming from the margin of the New Jersey Atlantic continental shelf that we tentatively attribute to a species of fish. The chorus occurred every night for over a month during the Shallow Water 2006 experiment and covers the frequency band 150–4,800 Hz, with maximum intensity in the band from 1450 to 2,000 Hz. Remarkable intensity peaks occurred at 500, 725, 960, 1,215, 1,465, 1,700, and 1,920 Hz, rising to as much as 20 dB above the background noise without the chorus. The chorus begins at sunset and reaches its maximum intensity within an hour, following which it weakens slightly and then gradually climbs again to a peak before sunrise, at which point it quickly weakens and disappears. Its frequency-domain characteristics and the nocturnal timing are reminiscent of sound produced by underwater animals. The intensity of the chorus weakens along the across-shelf path going shoreward, which indicates that the chorus originates from the margin of the continental shelf rather than from the coastal zone, as is generally considered. The chorus contains a single type of acoustic signal that takes the form of double-pulse bursts that last about 8.7 ms, with each pulse containing several acoustic cycles. The time interval between successive bursts varies from 1.5 to 1.9 s. Signals containing a number of bursts vary in length from tens to hundreds of seconds. Although it is impossible to determine the fish species responsible for the chorus, its characteristics, including its low frequency and intensity, its single type of short-duration sound signal, and its multiple peaks in the frequency domain, are all consistent with the general characteristics of fish sounds.

A Kind of DWT Domain Image Digital Watermarking Algorithm Research

2014 ◽  
Vol 1044-1045 ◽  
pp. 991-994
Author(s):  
Tao Liu
Keyword(s):  
Image Processing ◽  
Wavelet Transform ◽  
Frequency Domain ◽  
Digital Watermarking ◽  
Wavelet Decomposition ◽  
Low Frequency ◽  
Discrete Wavelet ◽  
Original Image ◽  
Adaptive Watermarking ◽  
Frequency Domain Methods

An image-adaptive watermarking algorithm based on wavelet transform was proposed. At first, A digital image used as watermarking was scrambled. Next, the original image was decomposed by discrete wavelet transform,and in accordance with the characteristics of human visual system, wavelet decomposition in the low-frequency domain, Methods which average of adjacent domain instead of single wavelet decomposition coefficients was used to estimate and quantitative, watermarking was adaptively embedded in wavelet coefficients of low-frequency domain. At last, the simulation experimental results show that the algorithm for a variety of conventional image processing has good robustness.

Extreme Response Analysis of Floating Structures Using Coupled Frequency Domain Analysis

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
Ying Min Low ◽  
Andrew J. Grime
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Low Frequency ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Coupled Analysis ◽  
Statistical Techniques ◽  
Frequency Domain Methods ◽  
Extreme Response ◽  
The Mean

In the dynamic analysis of a floating structure, coupled analysis refers to a procedure in which the vessel, moorings, and risers are modeled as a whole system, thus allowing for interactions between various system components. Because coupled analysis in the time domain is impractical owing to prohibitive computational costs, a highly efficient frequency domain approach was developed in a previous work, wherein the drag forces are linearized. The study showed that provided the geometric nonlinearity of the moorings/risers is insignificant, which often holds for ultradeepwater systems, the mean-squared responses yielded by the time and frequency domain methods are in close agreement. Practical design is concerned with the extreme response, for which the mean upcrossing rate is a key parameter. Crossing rate analysis based on statistical techniques is complicated as the total response occurs at two timescales, with the low frequency contribution being notably non-Gaussian. Many studies have been devoted to this problem, mainly relying on a technique originating from Kac and Siegert; however, these studies have mostly been confined to a single-degree-of-freedom system. The aim of this work is to apply statistical techniques in conjunction with frequency domain analysis to predict the extreme responses of the coupled system, in particular the modes with a prominent low frequency component. It is found that the crossing rates for surge, sway and yaw thus obtained agree well with those extracted from time domain simulation, whereas the result for roll is less favorable, and the reasons are discussed.

Extreme Response Analysis of Floating Structures Using Coupled Frequency Domain Analysis

2010 ◽  
Author(s):  
Ying Min Low ◽  
Andrew J. Grime
Keyword(s):  
Frequency Domain ◽  
Time Domain ◽  
Low Frequency ◽  
Domain Analysis ◽  
Frequency Domain Analysis ◽  
Coupled Analysis ◽  
Statistical Techniques ◽  
Frequency Domain Methods ◽  
Extreme Response ◽  
The Mean

In the dynamic analysis of a floating structure, coupled analysis refers to a procedure in which the vessel, moorings and risers are modeled as a whole system, thus allowing for the interactions between the various system components. Because coupled analysis in the time domain is impractical owing to prohibitive computational costs, a highly efficient frequency domain approach was developed in a previous work, wherein the drag forces are linearized. The study showed that provided the geometric nonlinearity of the moorings/risers is insignificant, which often holds for ultra-deepwater systems, the mean-squared responses yielded by the time and frequency domain methods are in close agreement. Practical design is concerned with the extreme response, for which the mean upcrossing rate is a key parameter. Crossing rate analysis based on statistical techniques is complicated as the total response occurs at two timescales, with the low frequency contribution being notably non-Gaussian. Many studies have been devoted to this problem, mainly relying on a technique originating from Kac and Siegert; however, these studies have mostly been confined to a single-degree-of-freedom system. The aim of this work is to apply statistical techniques in conjunction with frequency domain analysis to predict the extreme responses of the coupled system, in particular the modes with a prominent low frequency component. It is found that the crossing rates for surge, sway and yaw thus obtained agree well with those extracted from time domain simulation, whereas the result for roll is less favorable, and the reasons are discussed.

scholarly journals ATTENUATION OF MULTIPLE REFLECTIONS ASSOCIATED WITH DIABASE SILLS FROM SOLIMÕES BASIN THROUGH THE PARABOLIC RADON TRANSFORM AND MULTICHANNEL PREDICTIVE DECONVOLUTION

2019 ◽  
Vol 37 (2) ◽  
Author(s):  
Misael Possidonio de Souza ◽  
Michelangelo Gomes da Silva ◽  
Milton J. Porsani
Keyword(s):  
Radon Transform ◽  
Oil And Gas ◽  
Synthetic Data ◽  
Low Frequency ◽  
Real Data ◽  
Multiple Reflections ◽  
Predictive Deconvolution ◽  
Fortran 90 ◽  
Parabolic Radon Transform

ABSTRACT. The Solimões Basin Brazil will still be the subject of many discussions in the future due to the success of oil exploration in the 1970s with the discovery of oil and gas fields. The geology of this basin is characterized by significant thick igneous rocks layers, the diabase sills, which can be seen in any stacked section as reflectors with strong amplitude but low frequency. The high contrast of seismic impedance between the sedimentary rock layers and the diabase sills generate multiple reflection and reverberations that can lead to wrong seismic interpretation of stacked sections. In this work, to improve the quality of the stacked sections, we propose a seismic process flow that includes multiple filtering steps in land data, throughout the Multichannel Predictive Deconvolution and the Parabolic Radon Transform. This study was first performed on synthetic data to test the methodology, and then in real data provided by Agência Nacional de Petróleo, Gás Natural e Biocombustíveis (ANP). The conventional processing flowchart was applied using commercial processing software such as SeisSpace/ProMAX, and Fortran 90 codes available in the Centro de Pesquisa em Geofísica e Geologia, Universidade Federal da Bahia (CPGG/UFBA). The results obtained were satisfactory with the methodology used, besides visible improvements in the quality of the stacked seismic sections after attenuation of unwanted noises. Keywords: multiple attenuation, seismic processing, seismic reflection.RESUMO. A Bacia do Solimões será ainda tema de muitas discussões no futuro, devido ao sucesso da exploração de petróleo nas décadas de 1970 com a descoberta de campos de oléo e gás. A geologia desta bacia é caracterizada por espessas camadas de rochas ígneas, as soleiras de diabásio, que podem ser vistas em toda seção empilhada como refletores com forte amplitude e baixa frequência. O alto contraste de impedância sísmica entre as rochas sedimentares e as soleiras de diabásio gera reflexões múltiplas e reverberações que podem levar a uma interpretação sísmica errada das seções empilhadas. Neste trabalho, para melhorar a qualidade das seções empilhadas, propomos um fluxograma de processamento que adicione etapas de filtragem de múltiplas, através da Deconvolução Preditiva Multicanal e da Transformada Radon parabólica. Este estudo foi realizado primeiramente em dados sintéticos para testar a metodologia, e depois em dados reais cedidos pela Agência Nacional de Petróleo, Gás Natural e Biocombustíveis (ANP). O fluxograma de processamento convencional foi aplicado utilizando software comercial de processamento, como o SeisSpace/ProMAX, códigos implementados em Fortran 90 disponíveis no Centro de Pesquisa em Geofísica e Geologia, Universidade Federal da Bahia (CPGG/UFBA). Os resultados obtidos foram satisfatórios com a metodologia utilizada, além de visíveis melhorias na qualidade das seções sísmicas empilhadas após atenuação dos ruídos indesejados.Palavras-chave: atenuação de múltiplas, processamento sísmico, sísmica de reflexão.

APPLICATION OF THE EMPIRICAL MODE DECOMPOSITION METHOD TO GROUND-ROLL NOISE ATTENUATION IN SEISMIC DATA

2013 ◽  
Vol 31 (4) ◽  
pp. 619 ◽  
Author(s):  
Luiz Eduardo Soares Ferreira ◽  
Milton José Porsani ◽  
Michelângelo G. Da Silva ◽  
Giovani Lopes Vasconcelos
Keyword(s):  
Empirical Mode Decomposition ◽  
Seismic Data ◽  
Low Frequency ◽  
High Amplitude ◽  
Seismic Line ◽  
Seismic Processing ◽  
Mode Decomposition ◽  
Ground Roll ◽  
Fortran 90 ◽  
Emd Method

ABSTRACT. Seismic processing aims to provide an adequate image of the subsurface geology. During seismic processing, the filtering of signals considered noise is of utmost importance. Among these signals is the surface rolling noise, better known as ground-roll. Ground-roll occurs mainly in land seismic data, masking reflections, and this roll has the following main features: high amplitude, low frequency and low speed. The attenuation of this noise is generally performed through so-called conventional methods using 1-D or 2-D frequency filters in the fk domain. This study uses the empirical mode decomposition (EMD) method for ground-roll attenuation. The EMD method was implemented in the programming language FORTRAN 90 and applied in the time and frequency domains. The application of this method to the processing of land seismic line 204-RL-247 in Tacutu Basin resulted in stacked seismic sections that were of similar or sometimes better quality compared with those obtained using the fk and high-pass filtering methods.Keywords: seismic processing, empirical mode decomposition, seismic data filtering, ground-roll. RESUMO. O processamento sísmico tem como principal objetivo fornecer uma imagem adequada da geologia da subsuperfície. Nas etapas do processamento sísmico a filtragem de sinais considerados como ruídos é de fundamental importância. Dentre esses ruídos encontramos o ruído de rolamento superficial, mais conhecido como ground-roll . O ground-roll ocorre principalmente em dados sísmicos terrestres, mascarando as reflexões e possui como principais características: alta amplitude, baixa frequência e baixa velocidade. A atenuação desse ruído é geralmente realizada através de métodos de filtragem ditos convencionais, que utilizam filtros de frequência 1D ou filtro 2D no domínio fk. Este trabalho utiliza o método de Decomposição em Modos Empíricos (DME) para a atenuação do ground-roll. O método DME foi implementado em linguagem de programação FORTRAN 90, e foi aplicado no domínio do tempo e da frequência. Sua aplicação no processamento da linha sísmica terrestre 204-RL-247 da Bacia do Tacutu gerou como resultados, seções sísmicas empilhadas de qualidade semelhante e por vezes melhor, quando comparadas as obtidas com os métodos de filtragem fk e passa-alta.Palavras-chave: processamento sísmico, decomposição em modos empíricos, filtragem dados sísmicos, atenuação do ground-roll.

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