Wavelet Analysis of Geophysical Well-log Data of Bombay Offshore Basin, India     

E. Chandrasekhar  V. Eswara Rao 《Mathematical Geosciences》2012,44(8):901-928

Geophysical well-log (bore-hole) data facilitate understanding of the physical properties of the subsurface formations as a function of depth measured in a well. In the present study, the wavelet transformation technique was applied to the well-log data of three wells in the Bombay High oil field, India, in order to identify depths to the tops of oil and/or gas formation zones (pay zones). Continuous wavelet transformation (CWT) was performed on gamma-ray, resistivity, neutron porosity and velocity log data sets in order to determine the space-localization of the oil and/or gas formation zones. The choice of a mother wavelet is important and largely depends on the data under investigation. We have applied a variety of wavelets to the different log data sets to not only identify the depths to the tops of formation zones, but also to determine the optimum wavelet that best characterizes the pay zones. On examination of scalogram plots of each log corresponding to each wavelet for their better resolution in identifying the formation boundaries, we have found that the scalograms corresponding to the Gaus1 wavelet appeared to give the best resolution in identifying the depths of pay zones in all the well-log data sets of all three wells. To further validate the above observation, a histogram analysis of CWT coefficients is made. This showed that, of all the wavelets considered for the present study, Gaus1 wavelet is the most appropriate and optimum for determining the space-localization of pay zones in all the well-log data sets considered in the present study. The depths of pay zones estimated from scalogram plots of logs agree well with those provided by the Oil and Natural Gas Corporation Ltd., India.  相似文献   

Noise reduction methods in the analysis of near infrared lunar occultation light curves for high angular resolution measurements     

Tapas Baug  Thyagarajan Chandrasekhar 《天文和天体物理学研究(英文版)》2013,(11):1363-1380

A lunar occultation （LO） technique in the near-infrared （NIR） provides angular resolution down to milliarcseconds for an occulted source, even with ground- based 1 m class telescopes. LO observations are limited to brighter objects because they require a high signal-to-noise ratio （S/N ~40） for proper extraction of angular diameter values. Hence, methods to improve the S/N ratio by reducing noise using Fourier and wavelet transforms have been explored in this study. A sample of 54 NIR LO light curves observed with the IR camera at Mt Abu Observatory has been used. It is seen that both Fourier and wavelet methods have shown an improvement in S/N compared to the original data. However, the application of wavelet transforms causes a slight smoothing of the fringes and results in a higher value for angular diameter. Fourier transforms which reduce discrete noise frequencies do not distort the fringe. The Fourier transform method seems to be effective in improving the S/N, as well as improving the model fit, particularly in the fainter regime of our sample. These methods also provide a better model fit for brighter sources in some cases, though there may not be a significant imorovement in S/N.  相似文献   

Overview of the legal aspects of remote sensing     

B L Deekshatulu  V Raghu  M G Chandrasekhar 《Journal of the Indian Society of Remote Sensing》1995,23(3):125-138

When remote sensing images became available from satellites, several countries began to voice their concerns about the legality of such observations of their territory by another country. These apprehensions were primarily prompted on account of the fact that remote sensing capability was available only with the highly-developed superpowers and it had economic and security-related implications. Over the years, these concerns were raised in international fora and the interpretation of various provisions of International Law and Multilateral Treaties on Space as applicable to remote sensing were extensively debated. In 1986, a broad consensus was reached at the United Nations on the principles related to activities of States in Remote Sensing of countries by satellites. These aimed at the growth of these activities in a manner that encouraged cooperation among states in the use of this technology and at the same time attempted to mitigate the concerns of many State regarding their sovereign rights. It had become evident with the passage of time that many of the apprehensions about remote sensing were becoming less relevant in the face of the potential benefits available to all countries due to rapid technological advancements. The current paper examines various aspects related to the development of the international legal framework for remote sensing activities from space and their applications.  相似文献   

Quantification of Agricultural Water Productivity at Field Scale and Its Implication in On-Farm Water Management     

Rangaswamy Madugundu  Khalid A. Al-Gaadi  ElKamil Tola  Virupakshagouda C. Patil  Chandrasekhar M. Biradar 《Journal of the Indian Society of Remote Sensing》2017,45(4):643-656

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Search for the near infrared counterparts to the IRAS sources     

H. C. Bhatt  T. Chandrasekhar  N. M. Ashok 《Astrophysics and Space Science》1984,103(2):405-407

As part of a program to search for the near infrared counterparts to the far infrared sources discovered by the Infrared Astronomical Satellite (IRAS) we have scanned two areas including the IRAS error boxes for the sources IRAS 0453+444 and IRAS 1717-087 at 2.2 m down to the flux density limit of 1 Jy. Results on the IRAS sources and the detection of two new bright near infrared sources are reported and discussed.  相似文献   

The role of general relativity in astronomy: Retrospect and prospect     

S. Chandrasekhar 《Journal of Astrophysics and Astronomy》1980,1(1):33-45

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On the anomalous features of the geomagnetic quiet-day field variations at Nagpur, India     

E. Chandrasekhar  S. Alex 《Geophysical Journal International》1996,127(3):703-707

The quiet-day geomagnetic field variation data from the recently commissioned Nagpur geomagnetic observatory, which has augmented the currently active latitudinal chain of Indian magnetic observatories, are analysed for the year 1993- The variations for diurnal frequencies (Sq) recorded at Nagpur do not follow the expected trend with latitude. This is most conspicuous in the northward horizontal ( X ) component. The anomalous behaviour at Nagpur is also seen in the diurnal harmonic amplitudes when compared with those of the neighbouring stations Alibag (south of Nagpur) and Ujjain (north of Nagpur). This behaviour is attributed to the presence of electrically conducting anomalous sources in the vicinity of Nagpur. The anomalous internal source is inferred to be located at relatively shallower depths and is highly localized.  相似文献   

An integrated approach for resource development using remote sensing — A case study specific to hill areas     

A K Gupta  P P Nageswara Rao  K Ganesha Raj  C B S Dutt  M G Chandrasekhar 《Journal of the Indian Society of Remote Sensing》1993,21(2):99-108

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Some aspects of the diurnal and semidiurnal tidal wind field in meteor zone     

P.C.S. Devar  G. Chandrasekhar  M.I. Ahmed 《大气科学进展》1989,6(3):357-364

The diurnal and semidiurnal tidal wind field variations in the altitudes between 80 and 100 km of the earth’s atmosphere over a mid-latitude station are studied by means of the phases of the zonal and meridional wind measurements made at Atlanta (34oN, 84oW). The rotation of diurnal tidal wind vector is seen to be clockwise at lower heights (80-86 km), swinging between clockwise and unti-clockwise at intermediate heights (88-96 km) and anti-clockwise at higher-heights (96- 100 km). The senses of rotation of diurnal and semidiurnal tidal wind vectors are compared between the stations located in the same and opposite hemispheres. The results are consistent with the tidal theory in the case of Atlanta and Adelaide (35oS, 139oE) whereas in the case of other stations considered in the present study, they showed marked variations.  相似文献   

Some remarks on the state of matter in the interior of stars     

S. Chandrasekhar 《Journal of Astrophysics and Astronomy》1994,15(2):119-125

It is shown that forall stars for which the radiation-pressure is greater than a tenth of the total pressure, an appeal to theFebmi-Dirac statistics to avoid the central singularity which arises in the discussions of the centrally condensed and the collapsed stars cannot be made. The bearing of this result on the possible state of matter in the interior of stars is indicated.  相似文献