bluuebunny/crossref_metadata_2025_split huggingface dataset:
APPLICATION OF GEOPHYSICAL METHODS FOR STUDYING THE TECHNICAL STATUS OF EARTH DAMS*
Authors: BOGOSLOVSKY V. A. , OGILVY A. A. 
Published: April 2006

AbstractEarth dams are constructed on a wide scale for hydrotechnical and reclamative purposes. However, the great water permeability of soils and their bad gradation are frequently responsible for the development of mechanical suffusion and other phenomena resulting in dam destruction.Geophysical observations allow under certain conditions to forecast the development of adverse factors. They thus are, as practice shows, an important tool to observe the technical status of dams.The difference in propagation velocities of elastic waves in the zone of aeration and full saturation determines the applicability of the reflected wave method for determining the depth of seepage flow in the dam supporting mass. This can be also achieved by electrical sounding and induced polarization methods since the resistivity and polarizability of air‐dry and water‐saturated grounds differ considerably.Maps of equal potentials measured on the dam slope reflect the configuration of the contours of water table of the water flow passing through the dam. This makes it possible to obtain data on the direction and intensity of flow as well as on the presence of heterogeneous grounds filling the dam supporting mass. Besides, regime observations conducted according to the SP method allow to forecast the development of suffusion and observe the redeposition of grounds. If the SP anomalies do not increase with time, the suffusion processes can be regarded as fading out. Enhanced amplitude and increasing areas of anomalies show the intensification of these processes.Combined application of some of the above mentioned methods allowed to obtain many practical results on a number of dams in Transcaucasia and Central Asia. The true position of the depression surface determined in the dam of one of the high‐mountain water reservoirs, for instance, considerably differed from the designed one. The configuration of the seepage flow surface and its fluctuation caused by the rise and drop of the water level in the reservoir have been studied in detail on another dam situated on a plain. The sites of the most intensive outwash of fine material have also been located and the processes of soil redeposition in the dam supporting mass characterized. The data of the geophysical investigations were used to plan hydroinsulation and repair work.
VELOCITY DISPERSION OF SEISMIC WAVES*
Authors: O'BRIEN P. N. S. , LUCAS A. L. 
Published: April 2006

SummaryIn well velocity surveys made to calibrate Sonic (CV) Logs the calibration survey uses frequencies around 50 Hz whereas the Sonic Logging tool uses frequencies around 20 kHz. There thus exists the possibility of making a direct measure of velocity dispersion. In any one survey the disturbing factors, both instrumental and operational, will often mask any dispersive effect that might exist. Consequently this paper reports on a statistical analysis of the velocity differences resulting from calibration surveys and Sonic logs. Only Borehole Compensated Sonic Logs were used. Four areas were investigated: the North Sea, Abu Dhabi, Libya and Alaska. After rejecting logs and calibration records which were obviously in error there remained 424000 feet (about 130 km) of usable log distributed throughout 66 wells. The four areas were analysed separately and in no case was the estimated dispersion significantly different from zero. However, the mean values did correlate with lithology from (− 0.17 ± 0.18)% for the essentially carbonate section in Abu Dhabi to (+ 0.45 ± 0.25)% for the sand‐shale section in Alaska, a positive sign meaning that the higher frequencies travelled faster. Except for Alaska the calibration surveys were made with a wall‐clamp geophone, and for these areas amplitude measurements were made. After suitable corrections estimates of the absorption parameter Q were obtained. These varied from 20 to 200 with mean values of 63 for Libya, 70 for Abu Dhabi and 88 for the North Sea (excluding the Tertiary). If, as is usually assumed, the absorption mechanism is linear and is described by a Q which is independent of frequency, then these values would necessarily imply dispersion of several percent. As instanced above no such dispersion was observed. It is possible that the expected dispersion was compensated for by invasion of the mud filtrate into the borehole walls, but it is more likely that the absorption mechanism was substantially non‐linear.
THE APPLICATION OF LINEAR FILTER THEORY TO THE DIRECT INTERPRETATION OF GEOELECTRICAL RESISTIVITY SOUNDING MEASUREMENTS*
Authors: GHOSH D. P. 
Published: April 2006

AbstractKoefoed has given practical procedures of obtaining the layer parameters directly from the apparent resistivity sounding measurements by using the raised kernel function H(λ) as the intermediate step. However, it is felt that the first step of his method—namely the derivation of the H curve from the apparent resistivity curve—is relatively lengthy.In this paper a method is proposed of determining the resistivity transform T(λ), a function directly related to H(λ), from the resistivity field curve. It is shown that the apparent resistivity and the resistivity transform functions are linearily related to each other such that the principle of linear electric filter theory could be applied to obtain the latter from the former. Separate sets of filter coefficients have been worked out for the Schlumberger and the Wenner form of field procedures. The practical process of deriving the T curve simply amounts to running a weighted average of the sampled apparent resistivity field data with the pre‐determined coefficients. The whole process could be graphically performed within an quarter of an hour with an accuracy of about 2%.
MAPPING OF TECTONICS OF SEDIMENTS BY AIRBORNE MAGNETICS*
Authors: LINSSER H. 
Published: April 2006

AbstractThe considerable increase of sensitivity of new magnetometers allows the elaboration of magnetometric maps with contour intervals of fractions of one gamma. On these maps, small anomalies appear which had never been visible before. They are caused by susceptibility contrasts within the sediments.The areal distribution of these small undulations of the magnetic field depends on tectonics, therefore their analysis can give useful information about the tectonic pattern of the sediments. This paper discusses the automatic transformation of these small anomalies into tectonic units. The problem is solved by a method called Digital Template Analysis which has already yielded very useful results in gravity interpretation.The application of the method described is restricted to surveys executed by high sensitivity magnetometers. Therefore it is supposed that in most oil exploration problems these magnetometers will replace instruments with lower sensitivity. The improved magnetometer surveys in combination with the interpretation method described represent a most efficient, fast and unexpensive reconnaissance method.
A SOLUTION OF THE DIPPING INTERFACE PROBLEM USING THE SQUARE ARRAY RESISTIVITY TECHNIQUE*
Authors: BROADBENT M. , HABBERJAM G. M. 
Published: April 2006

AbstractApparent resistivity measurements with the square array technique in the vicinity of a dipping interface have the advantage over collinear array methods that they are less dependent on orientation of the array.In order to exploit this, existing potential solutions for the dipping interface problem have been adapted for the computation of apparent resistivities over such a feature using a square array.Comprehensive interpretation techniques covering this problem are given and the limitations imposed by residual array orientation effects are discussed.
COMPARISON OF “AQUAFLEX” WITH CONVENTIONAL EXPLOSIVE FOR SEISMIC REFRACTION MEASUREMENTS AT SEA*
Authors: BLUNDELL D. J. , HANDLEY R. L. 
Published: April 2006

AbstractA seismic refraction line fired using conventional explosive charges was repeated using a seismic cord, “Aquaflex”. It was found that travel times and frequencies were the same for both kinds of source and that amplitudes from “Aquaflex” were comparable with those produced using conventional explosives more than ten times the weight. This advantage carries with it gains in cost and efficiency and reduces damage to fishing.
POSITIONING OF MARINE SURVEYS WITH AN INTEGRATED SATELLITE NAVIGATION SYSTEM*
Authors: KRONBERGER F. P. , FRYE D. W. 
Published: April 2006

AbstractFor almost two years, satellite navigation has been used in reconnaissance exploration. However, only in the last six months has it been demonstrated that an “integrated” system provides navigational accuracy for all geophysical prospecting. This paper describes the accuracy of the integrated system and illustrates its merits.The primary objective of the integrated system is to provide continuous, accurate, geodetic position information. This is accomplished by integrating instantaneous position, velocity and heading from outputs of the Doppler sonar, gyrocompass, velocimeter, vertical references with periodic updates obtained from the Navy Navigation Satellite System. Each of the subsystems, their operations and functions will be discussed.Satellite navigation offers many advantages for marine surveys. Features for point‐to‐point automatic steering, onboard plotting of shotpoint data, firing of seismic energy source as a function of exact distance and real‐time data logging onto digital tape have been implemented. With the onboard computer all navigation, gravity and magnetic information is recorded on tape and some preprocessing and filtering of gravity and magnetic data may be accomplished.
DIURNAL CORRECTIONS TO MAGNETIC SURVEYS—AN ASSESSMENT OF ERRORS*
Authors: RIDDIHOUGH R. P. 
Published: April 2006

AbstractThe comparison of a group of continuous total field stations in Ireland with the record of the total field from Valentia Observatory enables the errors which would be involved in using the Observatory as a diurnal correction base to be examined. For the most part, for a single correction, these errors lie between ± 2 and ± 6 gammas. However, they have three notable characteristics: (i) they are not closely dependent on the magnetic ‘noisiness’ of the day, (ii) they are only marginally reduced by the application of station‐base time differences and (iii), they are strongly related to differences between the amplitude of the daily magnetic variation at the station and at the base. A permanent geographical basis for the latter differences enables a system for the estimation of the errors to be proposed.
GOSSES BLUFF AIRBORNE MAGNETIC SURVEY*
Authors: YOUNG G. A. 
Published: April 2006

AbstractAn airborne magnetic survey of an area of 580 km2 centred on Gosses Bluff was flown in 1968. This survey formed part of a joint project by the Australian Bureau of Mineral Resources and the United States Geological Survey to evaluate the hypothesis that Gosses Bluff is of impact origin.Analyses of the magnetic data show that shallow sources of magnetic disturbance flank the Bluff on its southern side. Interpretation of the magnetic anomalies indicates their source to be shock‐melted breccias of possible Jurassic age.
POTENTIAL FIELD CONTINUATION BETWEEN GENERAL SURFACES*
Authors: SYBERG F. J. R. 
Published: April 2006

AbstractThe theory of potential field continuation is studied with a view of extending it to include continuation between non‐linear surfaces. This theoretical extension is regarded as useful in reducing observed potential fields along one general surface to another general surface.It is demonstrated that the continuation operators considered in past geophysical literature are special cases of the generalized operators. In view of the tremendous growth in the art of high‐speed computing it is possible to consider applications of the generalized operators. In worked examples upward continuation between a general surface and a datum is considered for the gravity field due to geometrically simple sources; this in order to test the accuracy of the digital applications. It is indicated that for observations on an undulating surface it is possible to account for considerable errors when, during interpretation, the observation locations are taken to be along a datum. For aids to profile interpretation in areas of considerable topographic relief some simple convolution operators for continuation between linear, non‐parallel surfaces are proposed.
CONDUCTING SPHERE IN ELECTROMAGNETIC INPUT FIELD*
Authors: MALLICK K. 
Published: April 2006

AbstractA frequency‐domain analysis is outlined for a conducting sphere in a uniform Input field: inequispaced alternating half‐sine wave pulses. The Barringer Input air‐borne electromagnetic exploration system uses such source fields. Theoretical profiles of Hρ(t), the horizontal magnetic component over the sphere from different elevations and for various conductivity and geometrical factors are presented. Based on these results some useful features such as penetration and detectibility are discussed.
GEOPHYSICAL CATEGORIZATION OF THE PRECAMBRIAN IN SOUTH INDIA*
Authors: VOGELSANG D. 
Published: April 2006

AbstractThe ground follow‐up of a magnetic and radiometric air survey had to cope with the usual dilemma to check a great number of anomalies within a short time. A limited aggregate of magnetic anomalies, expected to correspond to magnetite quartzites was statistically selected for ground identification by this method: the ratios length/width times amplitude were listed for all coherent contours and the calculation of the standard deviation per unit area resulted in different key‐numbers for a new lithological “Salem Unit” and for the charnockitic or gneissic environment. The ground work thus directed and reduced by 85% yielded a substantial potential of iron ore. This was supported by by abundant determinations of the magnetic susceptibilities, confirming the sources of anomalies and revealing the amenabilities of iron ores for the magnetic separation process.The lines of truncation of anomalies were found to represent a system of local and regional faults and shear zones, which segregated the area into different tectonic blocks. These sutures have also provided the ways of intrusion for alkaline and basic magmae in the style of a “Rift” structure, housing several carbonatites and impregnations of metal sulphides.The airborne radiometrics obtained many uranium indications by gamma ray spectrometry. However, they led only to disseminated uranium‐silicates, associated with syenites, granites and pegmatites, each emanating a characteristic photon energy spectrum. But in general the radiation of thorium prevails, marking northern Madras as a “Thorium Province”.
A TWO‐AND THREE‐DIMENSIONAL GRAVITY DOT CHART*
Authors: MORGAN N. A. , FAESSLER C. W. 
Published: April 2006

AbstractThis paper presents a dot chart for calculating gravity effects from two‐dimensional bodies with the addition of a supplementary set of curves which can be used to determine the “end corrections” to modify the calculated effects when the length of the body is not relatively long with respect to the horizontal dimensions of the cross‐section. The use of the chart is demonstrated by different examples. The results of theoretical cases amenable to mathematical treatment and computer results both compare favorably to those computed using the present chart.A fundamental incentive of constructing this chart, in a final form ready to use, is to make it available to gravity interpreters for utilization. Future effort in chart construction is thereby avoided.
COMPUTATION OF TYPE CURVES FOR ELECTROMAGNETIC DEPTH SOUNDING WITH A HORIZONTAL TRANSMITTING COIL BY MEANS OF A DIGITAL LINEAR FILTER*
Authors: KOEFOED O. , GHOSH D. P. , POLMAN G. J. 
Published: April 2006

AbstractThe computation method described in this paper is based on the existence of a linear relationship between the mutual coupling ratio and the kernel function in the integral expression for it. Accordingly, the mutual coupling ratio can be determined by first computing sample values of the kernel function and then subjecting these to a digital linear filter. In the present paper the appropriate sampling distance is determined and the values of the digital filter coefficients are computed, both for electromagnetic sounding with horizontal coils and for electromagnetic sounding with perpendicular coils.
CALCULATION OF THE VERTICAL GRADIENT OF THE GRAVITY FIELD USING THE FOURIER TRANSFORM*
Authors: AGARWAL B. N. P. , LAL T. 
Published: April 2006

AbstractFourier transform techniques have been used to calculate the theoretical filter (amplitude) response function of Nth order vertical derivative continuation operation. The amplitude response functions of the vertical gradient and its continuation follow from the same. These response functions are subsequently used to calculate the weighting coefficients suitable for two dimensional equispaced data. A shortening operator has been incorporated to limit the extent of the operator. For comparative study, some of the developed coefficient sets and the one presented in this paper are analysed in the frequency domain and their merits and demerits are discussed.
TURAM INTERPRETATION BY CURVE MATCHING USING A LINE CURRENT APPROXIMATION*
Authors: DUCKWORTH K. 
Published: April 2006

AbstractThe interpretation of Turam data is treated by means of a development of the conventional approach to this type of data. The development consists of a curve matching technique based upon a line current approximation to the true induced current pattern.The technique requires computation facilities which are readily available in modern programmable calculators.Practical examples of the use of the method illustrate that it can reveal information concerning the geometry of a conducting body which would not be gained by the conventional approach.
THE KALMAN FILTER AS A PREDICTION ERROR FILTER*
Authors: OTT N. , MEDER H. G. 
Published: April 2006

AbstractIn mathematical statistical filtering the deconvolution problem can be solved by two different methods:

by inverse filtering
by calculating the prediction error.

Both methods are well known in the theory of Wiener filters.If, however, the generating process of the signal is known and can be described by a set of linear first order differential equations, then the Kalman filter can also be used to solve the deconvolution problem. In the case of the inverse filtering method this was shown by Bayless and Brigham (1970). But, while their method can only be used if the original signal is a colored random process, this paper shows that in the case of a white process the prediction error filtering method is a more appropriate approach. The method is extremely efficient and simple. This can be demonstrated by an example which maybe of special interest for seismic exploration.
APPLICATION DU FILTRE DE KALMAN A LA NAVIGATION*
Authors: FAIL J. P. 
Published: April 2006

AbstractThis paper is concerned with an application of the Kalman filter to integrated navigation systems. It is shown that this filter is well adapted to resetting the dead‐reckoning position by means of a radio‐hyperbolic system or of a Doppler sonar. The algorithm can also be used for resetting the dead‐reckoning position by means of a satellite navigation system.The first part is briefly concerned with stochastic processes and system theory. The canonical equations for navigation problems are written. The second part is devoted to the Kalman filter. The third part discusses the application of the algorithm to navigation problems and presents some simulation results.
PARAMETER OPTIMIZATION OF VELOCITY DEPTH FUNCTIONS OF GIVEN FORM BY USE OF ROOT‐MEAN‐SQUARE VELOCITIES*
Authors: MARSCHALL R. 
Published: April 2006

AbstractFrom seismic surveys zero offset reflection times and root‐mean‐square velocities are obtained. By use of Dix‐Krey's formula, the interval velocities can be calculated.If no well velocity survey exists, the interval velocities and T(o) times are the only available information. The suggested way to get a regionally valid velocity distribution is to select N“leading horizons”, where a major change in the velocity parameters occurs and to compute the parameters of the selected velocity depth function (in most cases linear increase with depth) by a special approximation for the interval between two adjacent “leading horizons”.Herewith all reflection horizons within the interval are taken into account.
A Ge(Li) BORE HOLE PROBE FOR IN SITU GAMMA RAY SPECTROMETRY*
Authors: LAUBER A. , LANDSTRÖM O. 
Published: April 2006

AbstractThis report describes the construction and properties of a Ge(Li) bore hole probe for in situ gamma ray spectrometry. The probe has the form of a cylinder 8.9 cm in diameter and 160 cm long. It contains a 22 cm3 coaxial Ge(Li) detector, cooled by liquid nitrogen. Holding time of the assembled probe is in excess of ten hours, energy resolution is 2.3 keV for 122 keV photons and 2.6 keV for 1333 keV photons.The probe has been used in field experiments in the Ranstad uranium mine and for the study of neutron activation spectra obtained in bore hole models. Results from these experiments are presented and discussed. It is stressed that the Ge(Li) probe gives promise to become a powerful tool in bore hole activation analysis.
ANALYSIS OF LEAST SQUARES SMOOTHING OPERATORS IN THE FREQUENCY DOMAIN*
Authors: CHAN S. H. , LEONG L. S. 
Published: April 2006

AbstractThe process of data smoothing by least squares operators with real and symmetric coefficients is shown to be equivalent to linear digital filtering. Study of the frequency response functions of the least squares operators shows that these operators are essentially low‐pass filters. The frequency response functions are characterized by the presence of a main lobe centered about the zero frequency together with a number of minor lobes of smaller amplitudes at higher frequencies. The predominant band of frequencies which is passed by a least squares operator occurs within the main lobe of the frequency response function. The filtering characteristics of a least squares operator are dependent on the degree of the polynomial and the number of data points. Generally speaking, the higher the degree of the polynomial the broader the pass band of the filter will be. But the effect of the number of data points on the pass band is exactly opposite.Several figures showing the plots of the half‐power frequency, the quarter‐power frequency, and the half‐width of the main lobe for a large number of least squares operators with different combinations of the degree of the polynomial and the number of data points are presented in this paper. These figures will be helpful to those people who wish to make a selection of least squares operators suitable for their purposes.
TIME DOMAIN ELECTROMAGNETIC RESPONSE OF A SHIELDED CONDUCTOR*
Authors: NEGI J. G. , VERMA S. K. 
Published: April 2006

AbstractVelekin and Bulgakov (1967) in an interesting model experiment while studying the transient electromagnetic response of a conductive sphere placed below a thin conductive sheet found that at the earlier stages of the transience, the composite system response corresponded to the response due to the overlying sheet alone and at the later stages, it corresponded to that of the sphere alone. To examine whether such a separation of responses due to individual components can be analytically studied and applied to other source configurations, we have analyzed an idealized model consisting of two spherical shells. We find that in corroboration with the above results, the general nature of the curve consists of two humps representing the responses dominated by the outer shell and the inner shell respectively. In addition, however, we find that the two humps gradually disappear to yield a smooth decay curve for increasing values of the ratio σd1b/σ2d2a (where σ1, σ2 are the conductivities, d1, d2 are the thicknesses of the outer and inner shells respectively, and b and a are their respective distances from the centre) and the effect of inner shell on the composite system response is considerably reduced.