Narasimman Sundararajan - Academia.edu (original) (raw)

Papers by Narasimman Sundararajan

Ridge-regression algorithm for gravity inversion of fault structures with variable density

Journal of Applied Geophysics, 2019

Abstract In general, a quantitative interpretation of geophysical data yields information on the ... more Abstract In general, a quantitative interpretation of geophysical data yields information on the nature of subsurface structures of geologic interest besides depth of the source and the associated physical property contrast. However, all geophysical interpretation invariably incurs an inherent ambiguity including VLF-EM method. Techniques such as Karous-Hjelt (K H) current density, Hilbert transform etc. are in vogue to estimate the depth to the source that are either qualitative or semi quantitative. Here, we present a comparative analysis of the depth derived from VLF-EM signals by different methods over a uranium rich basement fractures of Raigarh District, Chhattisgarh, India. The obtained results are based on techniques that are not very common in VLF-EM data interpretation such as Euler deconvolution (ED), Hartley spectral analysis and analytical signal approach of denoised in-phase component realized by Empirical Ensemble Mode Decomposition (EEMD). The estimated depth from ED and Hartley spectral analysis range 10–62 m and 12–40 m respectively are compared with K H pseudo section, Hilbert transform and drilling depth. Overall, the results of the aforesaid techniques have shown satisfactory comparison wherein the Hilbert transform of EEMD de-noised in-phase component of traverse T1 (35 m), Hartely power spectrum of the principal profile PPQ (40 m) and the radially averaged power spectrum (38.8 m and 40 m) are close to the drilling depth. Therefore, the results obtained by methods presented emphasize that these techniques are equally applicable to VLF-EM signals for estimation of depth to subsurface conductors.

Natural Hazards, 2013

Site characterization was carried out for Muscat region using the ambient noise measurements appl... more Site characterization was carried out for Muscat region using the ambient noise measurements applying the horizontal-to-vertical spectral ratio (HVSR) technique and using active seismic survey utilizing the multichannel analysis of surface waves (MASW) of survey data. Microtremors measurements were carried out at 459 sites using shortperiod sensors. This extensive survey allowed the fundamental resonance frequency of the soft soil to be mapped and areas prone to site amplification to be identified. The results indicate a progressive decrease in the fundamental resonance frequencies from the southern and eastern parts, where the bedrock outcrops, toward the northern coast where a thickness of sedimentary cover is present. Shear wave velocity (Vs) was evaluated using the 2-D MASW at carefully selected 99 representative sites in Muscat. These 99 sites were investigated with survey lines of 52 m length. 1-D and interpolated 2-D profiles were generated up to a depth range 20-40 m. The vertical Vs soundings were used in the SHAKE91 software in combination with suitable seismic input strong motion records to obtain the soil effect. Most of the study area has amplification values less than 2.0 for all

Computers & Geosciences, 2008

A code, TODGINV, to determine the parameters of 2D anticlinal and synclinal structures besides es... more A code, TODGINV, to determine the parameters of 2D anticlinal and synclinal structures besides estimating linear regional gravity background is presented wherein the density contrast varies with depth based on a parabolic equation. The main program, TODGINV, is supported by five subroutines namely GANTCLINE, GSYNCLINE, PDSANT, PDSSYN and NOREQS. Forward modeling is realized through the subroutine GANTCLINE in case of an anticlinal structure while GSYNCLINE in case of a synclinal structure. PDSANT and PDSSYN compute the partial derivatives of anticlinal and synclinal structures, respectively, whereas NOREQS solves the system of normal equations. The efficiency of the code is illustrated with a set of synthetic gravity anomalies over an anticlinal and a synclinal structure both with and without regional background. Further, the code is exemplified with the gravity anomalies of the Pays De Bray anticline, France, and the results are found to be more consistent with borehole information rather than with those of Alessandrello et al. (1983, Automatic three-layer, three-dimensional deconvolution of the Pays De Bray anticline. Geophysical Prospecting 31, 608-626).

Journal of The Geological Society of India, Oct 22, 2015

Geochemical analysis of ground water samples in the vicinity of lakes and drainage network were c... more Geochemical analysis of ground water samples in the vicinity of lakes and drainage network were carried out in and around a selected set of polluted lakes in the city of Hyderabad, India for possible restoration of the polluted lakes from the state of eutrophication. The results reveal, in general the concentration of TDS and major ions higher in the down stream areas due to shallow water table as well as seepage from lakes and nalas. Further, the concentration of trace elements in ground water was found to be within the permissible limits. The Piper and Wilcox diagrams indicate that the ground water in the study area has low sodium and high salinity hazard.

Abstract An integrated geophysical strategy employing magnetic, electrical and refraction seismic... more Abstract An integrated geophysical strategy employing magnetic, electrical and refraction seismic methods was used to delineate geological contacts associated with an outlier in biotite gneiss and sandstones located near Tiruvuru, Andhra Pradesh, India. Generally these contacts are favorable for ground water occurrence and exploration. In this study, magnetic method used as a reconnaissance tool was found to be highly effective for delineating contacts and estimating the depths to the basement based on Hilbert transform analysis, Fourier spectral method followed by Geosoft modeling. Also the width of the outlier was established using the amplitude of the analytic signal of the magnetic anomalies. Refraction seismic studies proved to be useful in determining accurately the thickness of various layers. Certain low velocity pockets which are favorable to groundwater accumulation were also identified. Location of contacts was supported by vertical electrical soundings (VES) through pseudo sections; the depth to subsurface contact within the outlier was derived from geoelectrical sections. Reliability of interpretation is substantiated by correlating the signal with known geology and bore well data.

Geophysics, 1982

Procedures are formulated using the Hilbert transform for interpreting vertical magnetic anomalie... more Procedures are formulated using the Hilbert transform for interpreting vertical magnetic anomalies of (I) the sheets (finite and infinite depth extent) (2) the dike, and (3) the horizontal circular cylinder. The applicability of the method is tested on theoretical models. The method is also applied on the well-known Kursk field anomaly of a sheet (infinite-depth extent) and the field anomaly of a dike of Karimnagar, Andhra Pradesh. India.

On a Sustainable Future of the Earth's Natural Resources

ABSTRACT Geophysical methods are known to play an indispensable role in mineral exploration. Over... more ABSTRACT Geophysical methods are known to play an indispensable role in mineral exploration. Over the years, they have undergone a phenomenal improvement in the design and development of equipment, methods and precision of data acquisition, processing and interpretation. Every geophysical method is directly or implicitly related to one or other physical property contrasts of the subsurface rock(s) and the target to be explored. Due to the fact that each geophysical method is specifically more suitable for a particular type or nature of mineral deposit with limited depth of exploration, many a time single geophysical method seldom yields highly reliable/desired results. This may be attributed to several factors including the quality of data, various noise factors, geophysical field parameters, choice of interpretation tools and techniques and above all, the inherent limitations of the method itself. Therefore, success of any geophysical survey may be enhanced by combining two or more geophysical methods for a particular investigation followed by right choice of processing and interpretation tools. This approach is called integrated geophysical strategy which ensures greater accuracy and highly reliable results. It is to be emphasized that geophysical modeling provides a generalized non-unique solution in terms of geometry (shape and size etc.) of subsurface sources. The spatial location of subsurface sources and their depth of burial can also be accurately be estimated by mathematical tools. This chapter presents the salient features of various geophysical methods and their applications and few case studies.

Journal of the Geological Society of India

It is well known that the potential hazard during an earthquake is mainly in alluvium or alluvium... more It is well known that the potential hazard during an earthquake is mainly in alluvium or alluvium filled basins; shear wave velocity plays a significant role in estimating the possible hazard during an earth quake in such an area. This paper presents shear wave velocity profile from Jabalpur, Central India mainly dominated by alluvial soil that was moderately affected by an earthquake of magnitude 6.5 in May, 1997. The acquired shear wave velocity by Multichannel Analysis of Surface Wave (MASW) in as many as 36 sites over alluvial soil ranges from 200 m/sec to 400 m/sec and in a few sites marginally less than 200 m/sec corresponding to a sub-surface depth of 30–35 m. Further, the computed N values vary as low as near zero to less than 25. The study is substantiated by the estimation of P-wave velocity by refraction seismic method at the same locations of MASW which ranges from 350 m/sec to 2200 m/sec. The results suggest that the damage during an earth quake appears to be highly unlikely in view of the marginally high Vs up to depth of 30 m. This study on seismic hazard is substantiated by the estimation of frequency of the ground as well as amplification which is found to be a maximum of about 2.5 in the frequency band of 2–6 Hz in west and north western portion of the study area.

Sultan Qaboos University Journal for Science [SQUJS]

The Proterozoic basement of the Dhofar region of the Sultanate of Oman might be considered as a p... more The Proterozoic basement of the Dhofar region of the Sultanate of Oman might be considered as a potential source of Uranium mineralization like other Proterozoic basins of the world, which collectively contribute 30%-40% to the global production. Uranium exploration assumes great importance in this part of the world and therefore geochemical and geophysical exploration for Uranium was initiated. Initial, random sampling of the study area with Gamma ray spectrometry as well as in situ XRF (Xray Florescence) analysis indicated the presence of around 30-40 ppm of Uranium. Since Gamma ray spectrometry results in the calculation of the heat produced during radioactive decay of Potassium (K), Uranium (U) and Thorium (Th) within the rocks in the study area, measurements were acquired along eleven traverses of varying length from 100-250 m at a traverse interval of 20 m and sampling interval of 10 m. Individual plots of the concentrations of radioelements such as U, K and Th have shown...

Journal of the Geological Society of India

A detailed hydrogeological investigations comprising well inventory, water level monitoring, lake... more A detailed hydrogeological investigations comprising well inventory, water level monitoring, lake bathymetry, infiltration and pump tests were carried out in a few selected observation wells in order to estimate transmissivity (T) and storativity (S) in all major lakes which are highly polluted by the discharge of sewage and other chemical effluents in greater Hyderabad. The salient features of results are presented lake wise which would be of immense use in restoration of all lakes. Also, the outcome of this study along with infiltration rates may be used for modeling in future to simulate the surface water-ground water interaction.

IETE Technical Review

ABSTRACT The Hartley transform is an efficient and economical alternative to the Fourier transfor... more ABSTRACT The Hartley transform is an efficient and economical alternative to the Fourier transform in its applications to the field of digital signal processing. The characteristics of the Hartley transform are almost the same as that of its progenitor, with a conspicuous exception that the Hartley transform is purely a real valued function unlike the Fourier transform. Despite the fact that the Fourier transform and the Hartley transform are similar, with varying kernels, some of the properties associated with them differ marginally. The direct and inverse Hartley transforms posses the same kernal and hence the Hartley transform has the twin distinction of being both self reciprocal and having the neat property shared both by nature and computers of occupying the real domain. Basically being a real valued function, it is efficient and economical in its applications. A brief comparative analysis of the properties of these twin transforms is incorporated.

Sultan Qaboos University Journal for Science [SQUJS]

The Hartley transform, as in the case of the Fourier transform, is not suitably applicable to non... more The Hartley transform, as in the case of the Fourier transform, is not suitably applicable to non-stationary representations of signals whose statistical properties change as a function of time. Hence, different versions of 2-D short time Hartley transforms (STHT) are given in comparison with the short time Fourier transform (STFT). Although the two different versions of STHT defined here with their inverses are equally applicable, one of them is mathematically incorrect/incompatible due to the incorrect definition of the 2-D Hartley transform in literature. These definitions of STHTs can easily be extended to multi-dimensions. Computations of the STFT and the two versions of STHTs are illustrated based on 32 channels (traces) of synthetic seismic data consisting of 256 samples in each trace. Salient features of STHTs are incorporated.

ICTACT Journal on Image and Video Processing

The Wavelet transform has emerged over recent years as a key time frequency analysis and coding t... more The Wavelet transform has emerged over recent years as a key time frequency analysis and coding tool for the Electrocardiogram (ECG). Its ability to separate out pertinent signal components has led to a number of wavelet based techniques which supersede those based on traditional Fourier methods. It is interesting to note that researchers in the field of Wavelet transform tend to take an approach to their study by either concentrating on the discrete Wavelet transform or the continuous Wavelet transform but relatively a few explore both in depth. Efficacy of Wavelet transform in highlighting small perturbations in an ECG which are not visible to the naked eye is presented in this paper using both CWT and DWT. On the other hand a new mother wavelet is presented for exclusive ECG analysis.

Geophysical Transactions, 1993

The Wavelet transform has emerged over recent years as a key time frequency analysis and coding t... more The Wavelet transform has emerged over recent years as a key time frequency analysis and coding tool for the Electrocardiogram (ECG). Its ability to separate out pertinent signal components has led to a number of wavelet based techniques which supersede those based on traditional Fourier methods. It is interesting to note that researchers in the field of Wavelet transform tend to take an approach to their study by either concentrating on the discrete Wavelet transform or the continuous Wavelet transform but relatively a few explore both in depth. Efficacy of Wavelet transform in highlighting small perturbations in an ECG which are not visible to the naked eye is presented in this paper using both CWT and DWT. On the other hand a new mother wavelet is presented for exclusive ECG analysis.

Procedia Materials Science, 2015

T wave alternans (TWA) is an acute and serious problem associated with the heart and mostly they ... more T wave alternans (TWA) is an acute and serious problem associated with the heart and mostly they are reflected in Electrocardiogram (ECG). It is identified as an alteration of the amplitude and morphology of the T wave that occurs in every other beat indicating electrical instability in acute ischemia, where it may precede ventricular tachyarrhythmia. The analysis of TWA is introduced recently as a new diagnostic tool for identification of patients with an increased risk of ventricular tachyarrhythmia or sudden cardiac death. ECGs recorded by sophisticated equipment with specific software can only diagnose TWA. The hard and software are exorbitantly costlier and therefore not available everywhere. In the present study, the TWA is brought out very well from the amplitude of continuous Wavelet transform (CWT) which is not only cheap and simple but also highly reliable and may be considered as an alternate tool for such investigations. This study is also substantiated by the exclusively proposed new mother wavelet namely ECG wavelet. The results are presented highlighting the salient features.

Ridge-regression algorithm for gravity inversion of fault structures with variable density

Journal of Applied Geophysics, 2019

Abstract In general, a quantitative interpretation of geophysical data yields information on the ... more Abstract In general, a quantitative interpretation of geophysical data yields information on the nature of subsurface structures of geologic interest besides depth of the source and the associated physical property contrast. However, all geophysical interpretation invariably incurs an inherent ambiguity including VLF-EM method. Techniques such as Karous-Hjelt (K H) current density, Hilbert transform etc. are in vogue to estimate the depth to the source that are either qualitative or semi quantitative. Here, we present a comparative analysis of the depth derived from VLF-EM signals by different methods over a uranium rich basement fractures of Raigarh District, Chhattisgarh, India. The obtained results are based on techniques that are not very common in VLF-EM data interpretation such as Euler deconvolution (ED), Hartley spectral analysis and analytical signal approach of denoised in-phase component realized by Empirical Ensemble Mode Decomposition (EEMD). The estimated depth from ED and Hartley spectral analysis range 10–62 m and 12–40 m respectively are compared with K H pseudo section, Hilbert transform and drilling depth. Overall, the results of the aforesaid techniques have shown satisfactory comparison wherein the Hilbert transform of EEMD de-noised in-phase component of traverse T1 (35 m), Hartely power spectrum of the principal profile PPQ (40 m) and the radially averaged power spectrum (38.8 m and 40 m) are close to the drilling depth. Therefore, the results obtained by methods presented emphasize that these techniques are equally applicable to VLF-EM signals for estimation of depth to subsurface conductors.

Natural Hazards, 2013

Site characterization was carried out for Muscat region using the ambient noise measurements appl... more Site characterization was carried out for Muscat region using the ambient noise measurements applying the horizontal-to-vertical spectral ratio (HVSR) technique and using active seismic survey utilizing the multichannel analysis of surface waves (MASW) of survey data. Microtremors measurements were carried out at 459 sites using shortperiod sensors. This extensive survey allowed the fundamental resonance frequency of the soft soil to be mapped and areas prone to site amplification to be identified. The results indicate a progressive decrease in the fundamental resonance frequencies from the southern and eastern parts, where the bedrock outcrops, toward the northern coast where a thickness of sedimentary cover is present. Shear wave velocity (Vs) was evaluated using the 2-D MASW at carefully selected 99 representative sites in Muscat. These 99 sites were investigated with survey lines of 52 m length. 1-D and interpolated 2-D profiles were generated up to a depth range 20-40 m. The vertical Vs soundings were used in the SHAKE91 software in combination with suitable seismic input strong motion records to obtain the soil effect. Most of the study area has amplification values less than 2.0 for all

Computers & Geosciences, 2008

A code, TODGINV, to determine the parameters of 2D anticlinal and synclinal structures besides es... more A code, TODGINV, to determine the parameters of 2D anticlinal and synclinal structures besides estimating linear regional gravity background is presented wherein the density contrast varies with depth based on a parabolic equation. The main program, TODGINV, is supported by five subroutines namely GANTCLINE, GSYNCLINE, PDSANT, PDSSYN and NOREQS. Forward modeling is realized through the subroutine GANTCLINE in case of an anticlinal structure while GSYNCLINE in case of a synclinal structure. PDSANT and PDSSYN compute the partial derivatives of anticlinal and synclinal structures, respectively, whereas NOREQS solves the system of normal equations. The efficiency of the code is illustrated with a set of synthetic gravity anomalies over an anticlinal and a synclinal structure both with and without regional background. Further, the code is exemplified with the gravity anomalies of the Pays De Bray anticline, France, and the results are found to be more consistent with borehole information rather than with those of Alessandrello et al. (1983, Automatic three-layer, three-dimensional deconvolution of the Pays De Bray anticline. Geophysical Prospecting 31, 608-626).

Journal of The Geological Society of India, Oct 22, 2015

Geochemical analysis of ground water samples in the vicinity of lakes and drainage network were c... more Geochemical analysis of ground water samples in the vicinity of lakes and drainage network were carried out in and around a selected set of polluted lakes in the city of Hyderabad, India for possible restoration of the polluted lakes from the state of eutrophication. The results reveal, in general the concentration of TDS and major ions higher in the down stream areas due to shallow water table as well as seepage from lakes and nalas. Further, the concentration of trace elements in ground water was found to be within the permissible limits. The Piper and Wilcox diagrams indicate that the ground water in the study area has low sodium and high salinity hazard.

Abstract An integrated geophysical strategy employing magnetic, electrical and refraction seismic... more Abstract An integrated geophysical strategy employing magnetic, electrical and refraction seismic methods was used to delineate geological contacts associated with an outlier in biotite gneiss and sandstones located near Tiruvuru, Andhra Pradesh, India. Generally these contacts are favorable for ground water occurrence and exploration. In this study, magnetic method used as a reconnaissance tool was found to be highly effective for delineating contacts and estimating the depths to the basement based on Hilbert transform analysis, Fourier spectral method followed by Geosoft modeling. Also the width of the outlier was established using the amplitude of the analytic signal of the magnetic anomalies. Refraction seismic studies proved to be useful in determining accurately the thickness of various layers. Certain low velocity pockets which are favorable to groundwater accumulation were also identified. Location of contacts was supported by vertical electrical soundings (VES) through pseudo sections; the depth to subsurface contact within the outlier was derived from geoelectrical sections. Reliability of interpretation is substantiated by correlating the signal with known geology and bore well data.

Geophysics, 1982

Procedures are formulated using the Hilbert transform for interpreting vertical magnetic anomalie... more Procedures are formulated using the Hilbert transform for interpreting vertical magnetic anomalies of (I) the sheets (finite and infinite depth extent) (2) the dike, and (3) the horizontal circular cylinder. The applicability of the method is tested on theoretical models. The method is also applied on the well-known Kursk field anomaly of a sheet (infinite-depth extent) and the field anomaly of a dike of Karimnagar, Andhra Pradesh. India.

On a Sustainable Future of the Earth's Natural Resources

ABSTRACT Geophysical methods are known to play an indispensable role in mineral exploration. Over... more ABSTRACT Geophysical methods are known to play an indispensable role in mineral exploration. Over the years, they have undergone a phenomenal improvement in the design and development of equipment, methods and precision of data acquisition, processing and interpretation. Every geophysical method is directly or implicitly related to one or other physical property contrasts of the subsurface rock(s) and the target to be explored. Due to the fact that each geophysical method is specifically more suitable for a particular type or nature of mineral deposit with limited depth of exploration, many a time single geophysical method seldom yields highly reliable/desired results. This may be attributed to several factors including the quality of data, various noise factors, geophysical field parameters, choice of interpretation tools and techniques and above all, the inherent limitations of the method itself. Therefore, success of any geophysical survey may be enhanced by combining two or more geophysical methods for a particular investigation followed by right choice of processing and interpretation tools. This approach is called integrated geophysical strategy which ensures greater accuracy and highly reliable results. It is to be emphasized that geophysical modeling provides a generalized non-unique solution in terms of geometry (shape and size etc.) of subsurface sources. The spatial location of subsurface sources and their depth of burial can also be accurately be estimated by mathematical tools. This chapter presents the salient features of various geophysical methods and their applications and few case studies.

Journal of the Geological Society of India

It is well known that the potential hazard during an earthquake is mainly in alluvium or alluvium... more It is well known that the potential hazard during an earthquake is mainly in alluvium or alluvium filled basins; shear wave velocity plays a significant role in estimating the possible hazard during an earth quake in such an area. This paper presents shear wave velocity profile from Jabalpur, Central India mainly dominated by alluvial soil that was moderately affected by an earthquake of magnitude 6.5 in May, 1997. The acquired shear wave velocity by Multichannel Analysis of Surface Wave (MASW) in as many as 36 sites over alluvial soil ranges from 200 m/sec to 400 m/sec and in a few sites marginally less than 200 m/sec corresponding to a sub-surface depth of 30–35 m. Further, the computed N values vary as low as near zero to less than 25. The study is substantiated by the estimation of P-wave velocity by refraction seismic method at the same locations of MASW which ranges from 350 m/sec to 2200 m/sec. The results suggest that the damage during an earth quake appears to be highly unlikely in view of the marginally high Vs up to depth of 30 m. This study on seismic hazard is substantiated by the estimation of frequency of the ground as well as amplification which is found to be a maximum of about 2.5 in the frequency band of 2–6 Hz in west and north western portion of the study area.

Sultan Qaboos University Journal for Science [SQUJS]

The Proterozoic basement of the Dhofar region of the Sultanate of Oman might be considered as a p... more The Proterozoic basement of the Dhofar region of the Sultanate of Oman might be considered as a potential source of Uranium mineralization like other Proterozoic basins of the world, which collectively contribute 30%-40% to the global production. Uranium exploration assumes great importance in this part of the world and therefore geochemical and geophysical exploration for Uranium was initiated. Initial, random sampling of the study area with Gamma ray spectrometry as well as in situ XRF (Xray Florescence) analysis indicated the presence of around 30-40 ppm of Uranium. Since Gamma ray spectrometry results in the calculation of the heat produced during radioactive decay of Potassium (K), Uranium (U) and Thorium (Th) within the rocks in the study area, measurements were acquired along eleven traverses of varying length from 100-250 m at a traverse interval of 20 m and sampling interval of 10 m. Individual plots of the concentrations of radioelements such as U, K and Th have shown...

Journal of the Geological Society of India

A detailed hydrogeological investigations comprising well inventory, water level monitoring, lake... more A detailed hydrogeological investigations comprising well inventory, water level monitoring, lake bathymetry, infiltration and pump tests were carried out in a few selected observation wells in order to estimate transmissivity (T) and storativity (S) in all major lakes which are highly polluted by the discharge of sewage and other chemical effluents in greater Hyderabad. The salient features of results are presented lake wise which would be of immense use in restoration of all lakes. Also, the outcome of this study along with infiltration rates may be used for modeling in future to simulate the surface water-ground water interaction.

IETE Technical Review

ABSTRACT The Hartley transform is an efficient and economical alternative to the Fourier transfor... more ABSTRACT The Hartley transform is an efficient and economical alternative to the Fourier transform in its applications to the field of digital signal processing. The characteristics of the Hartley transform are almost the same as that of its progenitor, with a conspicuous exception that the Hartley transform is purely a real valued function unlike the Fourier transform. Despite the fact that the Fourier transform and the Hartley transform are similar, with varying kernels, some of the properties associated with them differ marginally. The direct and inverse Hartley transforms posses the same kernal and hence the Hartley transform has the twin distinction of being both self reciprocal and having the neat property shared both by nature and computers of occupying the real domain. Basically being a real valued function, it is efficient and economical in its applications. A brief comparative analysis of the properties of these twin transforms is incorporated.

Sultan Qaboos University Journal for Science [SQUJS]

The Hartley transform, as in the case of the Fourier transform, is not suitably applicable to non... more The Hartley transform, as in the case of the Fourier transform, is not suitably applicable to non-stationary representations of signals whose statistical properties change as a function of time. Hence, different versions of 2-D short time Hartley transforms (STHT) are given in comparison with the short time Fourier transform (STFT). Although the two different versions of STHT defined here with their inverses are equally applicable, one of them is mathematically incorrect/incompatible due to the incorrect definition of the 2-D Hartley transform in literature. These definitions of STHTs can easily be extended to multi-dimensions. Computations of the STFT and the two versions of STHTs are illustrated based on 32 channels (traces) of synthetic seismic data consisting of 256 samples in each trace. Salient features of STHTs are incorporated.

ICTACT Journal on Image and Video Processing

The Wavelet transform has emerged over recent years as a key time frequency analysis and coding t... more The Wavelet transform has emerged over recent years as a key time frequency analysis and coding tool for the Electrocardiogram (ECG). Its ability to separate out pertinent signal components has led to a number of wavelet based techniques which supersede those based on traditional Fourier methods. It is interesting to note that researchers in the field of Wavelet transform tend to take an approach to their study by either concentrating on the discrete Wavelet transform or the continuous Wavelet transform but relatively a few explore both in depth. Efficacy of Wavelet transform in highlighting small perturbations in an ECG which are not visible to the naked eye is presented in this paper using both CWT and DWT. On the other hand a new mother wavelet is presented for exclusive ECG analysis.

Geophysical Transactions, 1993

The Wavelet transform has emerged over recent years as a key time frequency analysis and coding t... more The Wavelet transform has emerged over recent years as a key time frequency analysis and coding tool for the Electrocardiogram (ECG). Its ability to separate out pertinent signal components has led to a number of wavelet based techniques which supersede those based on traditional Fourier methods. It is interesting to note that researchers in the field of Wavelet transform tend to take an approach to their study by either concentrating on the discrete Wavelet transform or the continuous Wavelet transform but relatively a few explore both in depth. Efficacy of Wavelet transform in highlighting small perturbations in an ECG which are not visible to the naked eye is presented in this paper using both CWT and DWT. On the other hand a new mother wavelet is presented for exclusive ECG analysis.

Procedia Materials Science, 2015

T wave alternans (TWA) is an acute and serious problem associated with the heart and mostly they ... more T wave alternans (TWA) is an acute and serious problem associated with the heart and mostly they are reflected in Electrocardiogram (ECG). It is identified as an alteration of the amplitude and morphology of the T wave that occurs in every other beat indicating electrical instability in acute ischemia, where it may precede ventricular tachyarrhythmia. The analysis of TWA is introduced recently as a new diagnostic tool for identification of patients with an increased risk of ventricular tachyarrhythmia or sudden cardiac death. ECGs recorded by sophisticated equipment with specific software can only diagnose TWA. The hard and software are exorbitantly costlier and therefore not available everywhere. In the present study, the TWA is brought out very well from the amplitude of continuous Wavelet transform (CWT) which is not only cheap and simple but also highly reliable and may be considered as an alternate tool for such investigations. This study is also substantiated by the exclusively proposed new mother wavelet namely ECG wavelet. The results are presented highlighting the salient features.