ALBERT

Notes: The 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.

Notes: “Remote sensing” techniques have been used for many years as an exploration tool; broadly speaking, any method using sensors not directly connected to the earth's surface falls into this group.It is preferable, however, to use the term solely with reference to a number of new sensors which have recently become available to earth scientists for the detection of various radiations of the electromagnetic spectrum in the wave length range from 0.1 micron (UV) to some centimeters including the visible and infrared regions.Radiations artificially induced in the earth (active sensing) or spontaneous radiations (passive sensing) can be detected. Some of the bands investigated seem promising for application to geological surveys, especially using sensors on aircraft and satellites, which allow synoptic and large scale investigations.A brief account is given of the results already achieved and of future developments such as the ERTS and manned satellite (post Apollo) “earth observation” programmes.The potential role of Europe in the field is discussed.Details are given of some applications of thermal I.R. imagery to geological and vulcanological problems, with special emphasis on the research carried out in Italy.

Notes: When the fixed-source electromagnetic method is applied the quantities measured are influenced by the resistivity of the whole environment. This occurs mostly in the cases of measurements in areas with prevailing high resistivities, and if a weathered layer with considerably lower resistivity than that of the original rock has been formed near the surface. For this reason it is important to be acquainted with the properties of the two-layer ground with an overlying conductive layer.In the present paper attention will be drawn to theoretical calculations connected with the field of the homogeneous ground and that of the two-layer ground.

Notes: In mathematical statistical filtering the deconvolution problem can be solved by two different methods:〈list xml:id="l1" style="custom"〉1by inverse filtering2by 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.

Notes: The use of the electrical image method in calculating the potential of a source in the presence of a buried conductive sphere proves to be difficult because of the great number of terms making up the potential formula. The disadvantages contained by this method are avoided here by resorting to the theory of graphs. In view of this aim the “propagation” of the electrical images due to the sphere has been represented by an infinite graph to which an infinite matrix has been attached.Taking this as a basis several FORTRAN IV programs for the computation of resistivity pseudo-sections for various electrode configurations have been coded, and a great deal of such pseudo-sections have already been calculated with an IBM-360 computer. Using these results, recommendations regarding both the methodology of the geoelectrical prospecting of spherical shaped conductors and the most suitable way of building resistivity pseudo-sections are developed.

Notes: An account is given of the use of the square array technique in investigating the surface effects of rotational anisotropy when the axes of anisotropy are inclined to the surface. It is shown that, as with other arrays, two anisotropy parameters 〈inlineGraphic alt="inline image" href="urn:x-wiley:00168025:GPR249:GPR_249_mu1" location="equation/GPR_249_mu1.gif"/〉 and n can be derived by varying the array orientation.On the basis of these considerations, the effects of such anisotropy on the values of the mean apparent resistivity and azimuthal inhomogeneity ratio normally obtained in square array measurements is reviewed.Particular attention is paid to the variation of resistivity with orientation and it is noted that, in areas of moderate anisotropy, this variation is lower for the square than for the Schlumberger array.In addition to this advantage, the azimuthal inhomogeneity ratio obtained from square array measurements may be used to indicate the severity of anisotropy in an area and two field examples of this use are given.Where anisotropy is severe, gross variations of apparent resistivity with orientation are obtained with either square or collinear arrays. In these circumstances, the use of crossed measurements is considered and the particular stability of the crossed square array demonstrated.

Notes: Electrical resistivity sounding was attempted with success in 1960 on the surface of the Nile water in Khor Kundi El-Bahari, the starting place for the construction of the offset channel of the High Dam. The method was applied to determine the depth to the upper surface of the granite below the alluvium and Nile water. The success of the method conducted at two stations in the Khor is attributed to the favourable geological conditions of the section which consists of nearly homogeneous layers besides the good earthing conditions of electrodes dipped in water. The high resistivity contrast between water and granite facilitates interpretation of sounding curves. Factors interfering with the results of interpretation are mentioned.

Notes: This 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.

Notes: By applying dynamic corrections a seismic trace recorded at a distance x from the energy source should be varied in such a way as to obtain a trace which would be recorded at zero-distance, i.e. at the source itself. Only such a zero-offset-trace contains the correct sequence of reflection coefficients (reflectivity function), whilst all other traces contain a distorted reflectivity function. In the simplest case, the reflectivity function is compressed over a shorter time whereas in more complicated cases a partial inversion of the reflectivity function results. This happens when some of the reflection hyperbolae intersect one another.The reconstruction of the true zero-offset reflectivity function by the application of dynamic corrections can only be an approximative process. In the first case mentioned we must expect a decrease in accuracy of the corrected trace in comparison with a zero-offset-trace. In the second case, where intersections of the hyperbolae occur, accurate reconstruction is clearly impossible.The problems are discussed with the help of theoretical and practical examples.

Notes: Fourier 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.

Notes: In this paper it is shown how one may obtain a generalized Ohm's law which relates the induced polarization electric field to the steady-state current density through the introduction of a fictitious resistivity defined as the product of the chargeability and the resistivity of a given medium.The potential generated by the induced polarization is calculated at any point in a layered earth by the same procedure as used for calculating the potential due to a point source of direct current.On the basis of the definition of the apparent chargeability ma, the expressions of ma for different stratigraphie situations are obtained, provided the IP measurements are carried out on surface with an appropriate AMNB array. These expressions may be used to plot master curves for IP vertical soundings.Finally some field experiments over sedimentary formations and the quantitative interpretation procedure are reported.

Notes: In the linear filter method of interpreting resistivity sounding data, as developed by Ghosh (1971), it appears that the filter function in the x-domain approaches an oscillating function for both large positive and large negative abscissa values. In the present note the reason for this oscillating behaviour is derived, and a possible practical application is indicated.

Notes: Amplitude spectra of input FM signals used in the vibratory source method of seismic exploration often show undesirable oscillations near the initial and terminal frequencies. These oscillations have an effect on the correlation background and distort the output signal. Considerable improvement in reducing the amplitude of these oscillations is obtained using a proper taper fuction. Attention is given to the relation between the tapering time and bandwidth of the spectrum.Analyses of the spectra of the received data from vibratory sources show considerable attenuation in comparison with the original field sweep. Since the matched filtering process will result in a series of waveforms which have the shape of the autocorrelation of the input signal, consideration is given to the autocorrelation function and its zero-lag coefficient of the FM signal in the presence of attenuation. A method has been developed which compensates for the attenuation and recovers the distortion of waveforms when the received data is correlated.The design of a waveform shaping filter for vibratory source data is given to reduce the influence of phase distortion on the received waveforms as well as to increase S/N ratio resolution. Parameters used for this filter are based on the properties of the FM signal and its autocorrelation function.Several examples from field data are presented to illustrate the methods. The results indicate that the use of the above techniques yields sections with good frequency resolution and improved S/N ratio.

Notes: Results of rock magnetic investigations and magnetic field measurements in the Logar Valley, Afghanistan, are presented. Rock magnetic investigations on samples of the ore and the country rock have demonstrated that the chromite is strongly magnetic, whereas the country rock has proved predominantly non-magnetic, partly weakly magnetic. The isanomalic maps show strong anomalies of some 1000 γ above the known chromite occurrences. Anomalies of the country rock amounting to some 100 γ have been observed only above basic dikes. The measured anomalies have been interpreted quantitatively by 2- and 3-dimensional models. This interpretation is demonstrated and the question of chromite detection discussed. Model graphs are used to investigate in detail whether the extension in depth of ore bodies can be estimated.

Notes: This work deals with a theoretical investigation of the magnetotelluric sounding where the horizontal layers of a geological section do not have a sharp but a transitional boundary. The ratio of the horizontal electric to the horizontal magnetic components gives a measure of “Cagniard impedance”, which together with the phase relationship between them, enables one to determine the subsurface geometry and the true resistivities.Utilising the principle of similitude a set of Resistivity Master Curves and the corresponding phase relationships are presented here for the case where the lower half-space is infinitely resistive. The relation between the relative transition thickness and the cut-off period is illustrated.

Notes: A point source or a dipole source of electric current, placed on a randomly layered semi-infinite medium, produces an inhomogeneous random potential field on the surface. The variance of the random potential, normalized with reference to the normal field (that is, a field due to a point source or a dipole source on a homogeneous medium), falls off inversely as the distance from the source. The conductivity of the layers is assumed to vary randomly about a mean value (unity) such that the variations can be represented by a zero mean homogeneous random function. Further the variations are assumed to be small compared to the mean so that the first order perturbation is adequate. The analysis shows that the dipole field is more sensitive than the single pole field to the conductivity variations.

Notes: Book reviewed in this article:F. Link, Eclipse Phenomena in AstronomyMarine Geophysical Researches–an International Journal for the Study of the Earth Beneath the SeaM. K. Polshkov (editor): Exploration Geophysics, Vol. 48

Notes: The relationship between porosity and formation factor in unconsolidated homogeneous and anisotropic sediments without granule-liquid interaction is investigated by introducing a parametric model that simulates a variable cellular structure.In this hypothesis, porosity φ and F-factor are calculated for some fixed values of the parameter, solving numerically two integral expressions.From these calculations the form of the function φ=f(F), corresponding to the proposed model, has been deduced. This relation is in very good agreement with Archie's empirical law for unconsolidated sands which requires that F=φ--1,3. Therefore it seems that the validity of Archie's law is theoretically confirmed for the unconsolidated sediments considered in this paper.

Notes: In a previous publication (Koefoed 1968) a function called the “raised kernel function” has been introduced as an intermediate function in the interpretation of resistivity sounding data, and methods have been described both for the determination of the raised kernel function from the apparent resistivity function, and for the determination of the layer distribution from the raised kernel function.In the present paper a procedure is described by which the second step in this interpretation method–i.e. the determination of the layer distribution from the raised kernel function–is considerably accelerated. This gain in interpretation speed is attained by the use of a standard graph for a function which defines the reduction of the raised kernel function to a lower boundary plane.

Notes: Despite the use of CDP and digital methods the Zechstein base is still the deepest horizon in the vast salt-dome basin of Central Europe for which continuous information can be obtained by reflection seismics. Thus in North-western Germany, in addition to reflection seismics, the refraction seismic method has been increasingly used for a reliable survey of deeper horizons.The first part of the paper deals with the investigation of the various possibilities and limitations of refraction seismics with regard to the investigation of Pre-Zechstein layers in a basin with a tectonically very complicated overburden. The recording techniques specially developed for continuous profiling of the desired refraction seismic arrivals and the data processing methods are described.The main problems of interpretation are then discussed, in particular with regard to depth representation. The advantages and disadvantages of the various methods, e.g. Gardner's, Hales' and Wyrobek's, and of the wave-front method, are compared. On account of the tectonically complicated overburden Thornburgh's wave-front method proved to be the most useful.In a further section the various possibilities for velocity determinations are mentioned, e.g. Wyrobek's determination of the overburden velocity, for which the wave-front method automatically furnishes the necessary corrections to a deep datum.Finally, some examples are given for the results obtained, including some incidental information on the deeper crust.

Notes: Two alternative types of diagrams are shown which allow the direct conversion of readings taken by certain types of proton magnetometers into magnetic field strength. The accuracy of these diagrams is discussed and found to satisfy the requirements.

Notes: In order to locate relatively optimum sites for drilling exploratory holes for fresh water, an electrical resistivity survey was conducted along the new Mahukona-Kawaihae Road on the west flank of the Kohala Mountain. Two resistivity soundings made at the same stations, using the Schlumberger electrode configuration, determined an a spacing of 275 feet for horizontal profiling with the Wenner array.The correlation coefficient of the elevation to profile data was 0.41. A procedure for removing elevation effect from observed apparent resistivity was developed. Based on the reduced resistivity profile, four relatively optimum sites for additional exploration, such as by drilling, are specified. There is no specific interpretation of the data that can definitely indicate the occurrence of large underground reservoirs of fresh water anywhere along the profile. This is because the interpretation of horizontal profiling data is essentially relative and not absolute.

Notes: The problem of a plane wave incident on a non-isotropic dipping layer lying over an isotropic conducting substratum has been studied and some numerical results are presented to show the effects of〈list xml:id="l1" style="custom"〉1) degree of anisotropy m,2) conductivity contrast between the substratum to the upper layer b,3) angle of inclination of the axis of anisotropy α,on the variation of amplitude and phase difference of the wave impedance with the normalized skin-depth (d/δ1).

Notes: Consideration of the spectral representation of gravity and magnetic fields shows the field to be the result of the convolution of factors depending on the parameters of the field. Wiener filters, calculated using model transformations, provide an optimum method for altering these factors and hence effecting field transformations.

Notes: The seismic velocity of sedimentary rocks is determined by the porosity, the velocity in the matrix and that in the fluid. The last two are known experimentally. The velocity can be measured from the surface. By applying the time average equation we can find the porosity. If the only difference at two points is the nature of the fluid in one layer, the ratio of the reflectivities of the layer at these points determines the nature of the fluid; this ratio is equal to the ratio of the amplitudes at these points. The size of the reservoir can then be found.The method can be applied to both oil exploration and production. It is more accurate in the latter case because more information is available than in the former case. The method is also more effective in developing discovered fields than the conventional method of relying only on the geological structural configurations.

Notes: A discussion is given of the requirements, the advantages and the methods to be considered in attempting the quantitative interpretation of gravity or magnetic fields from computed maps of the vertically derived field.The transform which is used here is the first vertical derivative (or vertical gradient) with or without downward continuation, but the computed maps are in fact obtained by a controllable Fourier method in which two kinds of operations can be simultaneously performed in complete independance: on one hand the separation of any part of the data by frequency cut-off, and on the other hand the transformation by vertical derivation or continuation of the part which is retained.Taking as raw data either actual surveys or artificially constructed maps, it is first shown how separated and transformed maps of this type can be efficiently obtained under quite flexible conditions, using a special computer program. It is further seen that for correctly controlled filterings the accuracy of the computed maps actually permits to take them as the basis for quantitative interpretation.To effect this, any one of the conventional methods which make use of equivalent model computations may in the first place be adapted to the interpretation of gradients, with the benefits, however, of an enhanced lateral separation of the anomalies and of a large attenuation of the regional effects.Particularly, the delineation of horizontal contours for even fairly complex models can often be made directly in a sufficiently safe way on the anomalies as they show on the vertical gradient maps. This greatly accelerates the process of determining equivalent model bodies.More special methods of interpretation can also be designed by taking into account first the fact that the vertical derivation of the field amounts to an operation of separation on the field's sources themselves, and in addition the availability of the frequency form of the information as a result of using a Fourier method of transform computation.Trial utilisations of various such interpretation processes of either the conventional or the less conventional type, are presented especially in connection with an interpretation study on transformed maps of parts of an offshore aeromagnetic survey (English Channel).

Notes: Generation of electrical power through the use of natural steam obtained from the Earth has the potential to be a significant source of pollution-free power. Successful future exploitation of geothermal power depends upon the development of cost-effective exploration techniques. A field experiment in the Imperial Valley of California indicates that there is a close empirical relationship between hot water deposits at depth and an anomalously high seismic background level at the surface. If this relationship proves to be a general one, it will serve as the basis of a simple and inexpensive method of geothermal exploration.

Notes: In massive rocks ground waters mainly flow in fracture zones whose permeability greatly changes depending on their filling. When studying ground-water flow in fissures, the results of observations of the electric fields of filtrational origin—which, in this case, considerably differ from those in porous media—can be used. Therefore the authors have made experiments on fissured media models. The measurements have been made in a special filtration tube with the fissured media simulated by a system of quartz glass plates. The spacings between plates were regarded as fissure widths. The observations have been made in fully open “fissures” and in those partially filled with sand or sandy-clay material.These experiments have resulted in establishing a dependence between the values of streaming potentials and pressure drops. The SP values have particularly been found to decrease with the opening of “fissures”. The most intensive electro-filtrational fields were observed at 40 per cent filling with medium grained sand. Additions of argillaceous material to the sand filler brought about sharp reductions in the intensity of electro-filtrational potentials.

Notes: During the last few years the airpulser, or air gun, has become very common as an energy source for marine seismic surveys. This paper describes the physical processes which take place during the operation of the pulser and develops theoretical results concerning the energy and frequency of the radiated signal and the amplitude decay of the secondary bubble pulses. The theory takes into account the presence of the airpulser itself which is assumed to be a rigid sphere within the bubble of released air. The theoretical results are combined and compared with measurements made of the pressure within the airpulser, the acceleration of the body of the pulser, and the amplitude and frequency of the signal radiated into the surrounding water. A formula for calculating the bubble frequency is given and a diagram made of the energy partition between mechanical losses, radiated energy, etc. Finally, a comparison is made of the energy release from the airpulser with that from TNT.

Notes: An equivalent stratum model is used to provide an explanation for the power spectrum characteristics of potential fields.The power spectrum of observed magnetic fields is found to consist of effects due to sources which can be represented by apparent monopoles and dipoles. Similarly, the power spectrum of observed gravity fields is found to consist of two groups of effects. A matched filter is proposed whereby the effects due to the two components in the potential field can be separated. As a consequence of the established theoretical expressions a scheme is suggested whereby the aliasing power of sampled data can be estimated. Also, the concepts of downward continuation, reduction to the pole, and reduction to pseudo-gravity of magnetic fields are re-examined in light of the theoretical expressions due to the equivalent stratum model.

Notes: The oscillatory character of the solution obtained by Qureshi and Mula's method for the direct determination of two-dimensional mass distributions from gravity anomalies is examined.

Notes: A number of resistivity profiles over dolerite and metadolerite dykes have been taken using Wenner and Schlumberger configurations around Dhanbad in order to find the potential of these for water accumulation. These dykes give rise to both resistivity highs and lows as compared to the background. The results are discussed in the light of known theories. Some suitable sites for water accumulation have been delineated.

Notes: Differential and difference soundings of resistivity for real, imaginary and complex values of the newly introduced parameters ν and μ are considered. The transverse and longitudinal differential soundings, known up to the present, correspond with the values ν= 1 and ν=— 1.The point of departure is the generalization of the concept of Dar Zarrouk parameters and the dimensional analogy between D.Z. resistivity and transverse and longitudinal differential resistivities. Properties of generalized D.Z. curves as well as the method of their construction are given. The examples of differential and difference curves are presented and the properties of these curves are discussed; particulary the effective spacings are determined. The problems of the realization of differential and difference soundings are considered; the bisymmetrical and asymmetrical arrays are proposed as a practical ones.

Notes: It is pointed out that after identifying reflection events from the same horizon on two records obtained on the same spread from two different shotpoints, one can simultaneously estimate parameters of reflection events and relative static corrections. The parameters of reflection events are treated as quantities to compute whereas relative static corrections are treated as quantities to minimize by the least squares method. Static corrections obtained from different horizons for the same point on the spread are averaged.The case of more than one pair of records for the same spread (or part of the spread), vital for multiple coverage, is also discussed.

Notes: Après avoir essayé?analyser, par voie optique, ľeffet de la réflexion fantôme sur des enregistrements sismiques, on montre ľapplication de deux méthodes de filtrage de ce fantôme sur des exemples réels.La première méthode utilise là mise à feu séquentielle de charges situées à différentes profondeurs dans un même trou; il s'agit ?un filtrage réalisé sur le terrain. Le deuxième procédé consiste à filtrer, au central, des enregistrements réalisés à des profondeurs de tir différentes avant de les sommer.

Notes: A high sensitivity thermometer using a thermistor sensing element was designed for practical measurements in the field.The most suitable procedures for the elimination of diurnal and seasonal variation of temperature, the influence of vegetation cover and of other effects were investigated.Positive results of geothermic measurements have been acquired on sulfide deposits. By far the most important results of geothermic measurements have been obtained in hydrogeological problems, e.g. the investigation of circulation of underground water. In the case of prospection for cold mineral waters the combination of geothermic measurements with gasometric analyses is very useful. As the classical domain for geothermic investigation, prospection for hot water is to be mentioned.

Notes: The conditions for creating and recording converted waves in the area of the Panonien basin are considered. Comparison between the characteristics of converted waves recorded in the field and characteristics of converted waves calculated for the model which approximately corresponds to lithophysical conditions of the area is made.The comparative interpretation of the crustal structure along the profile, using different types of waves, is given.

Notes: Direct interpretation methods of resistivity curves are discussed, which use the kernel function of the apparent resistivity. This function results from the consideration of the problem of diverse electrodes configurations.Several expressions for the determination of the kernel function of the potential from the kernel function of the apparent resistivity are given.

Notes: A method to analyse aeromagnetic profiles is proposed: several horizontal (width-) and vertical (amplitude-) parameters are deduced from the anomalies. These parameters are then compared with diagrams drawn on a logarithmic scale. The comparison yields depth and magnetization of the causative bodies.The method lends itself equally well to a quick estimate and to a thorough interpretation, depending on the number of parameters deduced and on the number of diagrams. It can be applied also to the anomalies of the total field and its vertical gradient.

Notes: Book review in this Article:H. Wöhlbier, R. H. Wöhlbier, F. H. Wöhlbier, H. Baston, Worldwide Directory of Mineral Industries Education and Research.

Notes: Water seepage from reservoirs causes appreciable anomalies of natural electric fields. The possibility of mapping leakage places by means of the SP method has been discussed by the authors in an earlier report. Further work has shown that detailed measurements of the natural electric field allow to determine the seepage rates from individual areas of a water reservoir in relative units. If data on the total discharge from a water reservoir are available, the conventional seepage units can be converted into absolute ones. Using this technique on a water reservoir in Armenia has permitted to control the change of the leakage rate as hydroinsulation operations were in progress. It has been established that as a result of shielding the bottom with clay material leakage from the central part of the reservoir has stopped. On the other hand, construction of cement seepage-proof protection has had so far no appreciable positive effect.

Notes: The seismometer-ground system is represented by a damped oscillatory system. Relatively simple approximation formulas are derived to express the coupling between ground and seismometer. These expressions are applicable in seismic exploration. The coupling is that of a mass, suspended by a spring, to the surface that the ground would have in absence of the seismometer. It results in a low-pass filtering of the ground motion, which is due to the presence of the seismometer. This effect is expressed in a unit-impulse response. It appears that, over a sufficiently homogeneous ground and for low frequencies, one has a true coupling between ground and seismometer. To obtain a sufficiently large pass-band, a low seismometer housing-mass together with a not too small housing radius are necessary.

Notes: The effect of a conducting overburden on the electromagnetic response of sulphide ore-bodies has been studied with the help of quantitative electromagnetic model experiments. These experiments were conducted at a fixed, crystal controlled, frequency of 100 kHz using a number of transmitter-receiver configurations, though the results discussed here mostly pertain to a horizontal coplanar system. An analysis of the anomaly profiles—after accounting for the regional anomaly—indicates a general enhancement of the response. This is attributed (a) to the concentration of the current lines in the host-rock effected by the embedded target and (b) to the change in the phase and space orientation of the field vectors, brought about by the conducting overburden. The enhancement is most pronounced in the case of non-symmetrical bodies such as veins and ribbon-like structures represented by sheet models, but is also observed to a lesser degree for isometric structures. These results are expected to pave the way for a more accurate interpretation of the induction prospecting data.

Notes: Mit der vorliegenden Arbeit wird das Echo-Log als ein geophysikalisches Meßverfahren zur Bestimmung von Form und Volumensverteilung von Aussolungshohlräumen im Salzgebirge vorgestellt. Hierzu werden neue terminologische Begriffe wie Echo, Echostrahl, Echostrahler, Echozeit, Echogramm usw. erläutert. Weiter wird über die Meßausrüstung, Durchführung der Vermessung sowie die Ergebnisdarstellung berichtet.In einem letzten Abschnitt wird zwischen Echos, die auf einem direkten Weg von der Hohlraumfläche zurückgeworfen werden und anderen bei der Registrierung erfaßten Empfangssignalen unterschieden.In this paper the Echo-Log is presented as geophysical measuring method for determining form and volume spread of leached cavities in salt formations. Therefore, new terminological definitions like Echo, Echo Beam, Echo Transducer, Echo Time, Echogram etc. will be explained. Furthermore, also the measuring equipment, execution of a survey and the presentation of the results will be described.In the last paragraph the difference between Echo directly reflected from cavity walls and other in the cavities registered signals will be discussed.

Notes: The 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.

Notes: The 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”.

Notes: In the interpretation of magnetic anomalies and in paleomagnetism, the anisotropy of magnetic susceptibility is commonly neglected. Nevertheless, this property has basic significance, because, owing to susceptibility anisotropy, the directions of the vectors of induced and remanent magnetization are deflected from the direction of the Earth's magnetic field. Almost all rock types investigated possess higher or lower degree of the susceptibility anisotropy. Effusive and sedimentary rocks have the lowest degree of anisotropy. For the latter, the “masking effect” of the paramagnetic mineral components has some influence on the anisotropy degree due to the low mean susceptibility of sedimentary rocks. Metamorphic and plutonic rocks usually exhibit a considerable degree of anisotropy. The highest degree of anisotropy has been found in the rocks containing ferromagnetic minerals with mimetic fabric.The dependence of the degree of the susceptibility anisotropy on the degree of metamorphism proved to be very complicated; of the rock sequence from slates to gneisses, the transient rocks (roofing slates and mica-schist-gneisses) showed the highest degree of anisotropy. This result can be used in geology for reliable determination of these rock types.

Notes: A technique utilizing the convolution theorem is developed to obtain the time-domain electromagnetic response for a number of input pulses from the given step-function response. For illustration an idealized model of a homogeneously conducting non-permeable sphere placed in a uniform field is considered. The nature of the responses due to different types of pulses and their usefulness in estimating the constitution parameter of the sphere are discussed. To show the applicability of the suggested technique to generalized systems, calculations for a conducting permeable sphere are presented in the appendix.

Notes: One of the most important aspects in interpretation of gravity and magnetic anomalies, which generally represent the sum of many effects from the subsoil, is that these effects cannot be adequately separated into individual effective anomalies by means of known procedures. Moreover, the concept itself of anomaly separation must be expanded in a certain sense, because the addition of these effects in the mapped anomalies can arise from many structures situated in the subsoil in different relative positions to one another. A combined procedure is proposed, based on Fourier analysis utilising both periodic complex functions and nonperiodic ones, by use of which the number of individual effective anomalies cumulated in the mapped anomalies is obtained. In order to illustrate the use of this procedure and the advantages of obtaining more valuable informations on geological causes of anomalies, one example from Romania is given.

Notes: A number of electrical resistivity arrays are available to the exploration geophysicist in the conduct of vertical or horizontal profiling. The advantage of using central-type arrays which produce large potential drops, such as the Wenner or the Schlumberger, must be weighed against the ease of acentral arrays such as the polar and equatorial arrays.A series of nomograms has been designed to provide a means of rapid calculation of the potential drop to be obtained by any of the various central and acentral arrays, as a function of apparent resistivity, electrode spacings and available transmitter power. The same nomograms may also be used for approximate computation of the apparent resistivities in routine surveys. However, the accuracy of resistivity calculation is directly related to the accuracy of drawing lines between the scales and hence is rather limited in reduced-size nomograms in this paper.

Notes: De préférence, les sismographes seront disposés dans un lieu sans bruit, oú il n'y aurait pas besoin de patternes. Par contre, si les bruits sont tels qu'une patterne est nécessaire, l'objectif de la patterne est d'améliorer le rapport signal/bruit et donc de rendre le signal le plus utile possible. La patterne sera dessinée en fonction des charactéristiques du signal, des charactéristiques du bruit, et de la géologie du site.Il a été démontré que, dans le sens pratique, l'opération optimum sur les données d'une patterne est représentée par le proces “delai et somme”. L'augmentation du nombre N de senseurs sur une surface donnée diminue les espacements entre les senseurs et peut augmenter la coherence entre les bruits enrigistrés aux senseurs voisins, donnant donc moins d'amélioration au rapport signal/bruit que la √N anticipée. L'augmentation du nombre de senseurs par l'augmentation proportionnelle de la surface de la patterne peut resulter en la détérioration du signal, et peut également donner moins d'amélioration que la √N Ces deux effets, ainsi que l'élément économique, combinent à limiter le nombre de senseurs qui peuvent être employés.Bien que les données sur lesquelles l'on a basé ces conclusions soient tirées de la sismologie conventionnelle, ces principes sont également valables pour l'exploration sismique et pour d'autres mesures géophysiques qui emploient des dispositifs dans lesquelles plusieurs senseurs sont requis.

Notes: Recent improvements in instrumentation and field techniques have made time domain electromagnetic methods more acceptable. This acceptance has prompted further theoretical work for use in the interpretation of field data.The asymptotic solutions for the transient electromagnetic field components in the vicinity of a fault zone separating two media of high resistivity contrast are obtained for low frequency or late time. Excitation is by normally incident plane waves at the earth's surface. Because of the slow convergence of the asymptotic time series expansions, a numerical polygonal inversion is performed on the real part, or in-phase term, of the time-harmonic surface expressions for the electric and magnetic field components.For both impulsive and step excitation the transient electric field normal to the contact is more sensitive to changes in the structural attitude of the fault plane than the transient electric field parallel to the contact. The transient anomalous vertical magnetic field for either impulsive or step excitation appears to be most diagnostic of dip angle, although waveform shape does not seem to be significantly dependent on the slope of the fault. For dip angles greater than 90 degrees, as measured on the poorly conducting side of the contact, all field components become more insensitive as indicators of the structural attitude. The results presented here should be useful in obtaining several geologic parameters descriptive of a fault zone or lateral resistivity inhomogeneity from transient electromagnetic soundings; they should also provide an aid to differentiating with available geological information between layering effects on transient electromagnetic responses and effects largely due to lateral changes in resistivity.

Notes: Velekin 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.

Notes: It has been necessary to resort to the use of “long-line” refraction marine operations in certain areas where it proved impossible to eliminate singing from reflection records despite the number and variety of programs at our disposal for this purpose.Experience has shown that manual processing of offshore refraction records takes a disproportionate length of time in comparison with the surveys themselves, and this is incompatible with the requirements for choosing the site of an exploration well. It thus became necessary to find an “industrial approach” to the solution of this processing problem.It was apparent that automatic picking could also facilitate the interpretation of land refraction data, and that in the case of both marine and land work the interpretations would be more accurate when factors were taken into account which could not be considered when working without the aid of a digital computer.For these reasons a set of programs was developed for automatic picking and interpretation of refracted arrivals.The picking itself consists in searching for the maximum values of the normalized cross-correlation functions of the traces with a “model” trace. The first results thus supplied are: “picked” times, intercept times, maximum values of the correlations, and the values of the tie constants between overlapping spreads.Next, the construction of the relative intercept time curves is performed; a statistical analysis of these curves then allows the determination of the offset distance.From these elements,⊙ either the delay time curve is produced, after ensuring correct reciprocal times by means of additional minor corrections.Such work is carried out in order to enable the geophysicist to gain a sound idea of the quality of the interpretation. To assist in this aim, part of the trace on both sides of the pick is plotted on the final documents. Valid groupings of several traces involving the same amount of refraction data are thus possible.⊙ or the refractor depth is constructed with the wavefront method, making use of the relative intercept times.Such a procedure, which is normally applied to first breaks, can also be used for later arrivals exhibiting slight interference and should represent an important step towards processing secondary arrivals with high interference.The development of this package, in response to a need which is shared by both SNPA and CGG, is the result of the joint efforts of the Geophysical Group of SNPA's Pau Research Center and CGG's Technical and Scientific Departments.

Notes: This 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.

Notes: The expression for the potential due to a point source of current, placed on the surface of a horizontal three-layer earth, has been derived when conductivity in the second layer varies linearly with depth and changes abruptly at the boundaries. Master curves for Wenner and Schlumberger configurations have been presented for an insulating basement and for one value of conductivity gradient in the second layer.

Notes: Using a method and definition given earlier (Roy and Apparao, 1971), this paper computes the depths of investigation in homogeneous ground for (a) the Wenner α, β and γ configurations, (b) the three electrode system and (c) the dipole-dipole arrangements when the dipole lengths are not infinitesimally small. The results for (a) and (b) have been summarised in a table, while those for (c) are shown as contour diagrams. In all the dipolar arrangements examined in this paper, except the equatorial, the depth of investigation decreases (and the vertical resolution increases) with increase in any or both of the dipole lengths. For the equatorial set up, this decrease (or increase) is very small.

Notes: The unsuitability of a particular method of computation of second derivative to varying types of field problems evinces the need of a method by which it may be possible to obtain a wide range of filters. This requirement is achieved by incorporating a mathematical smoothing operator, e-λρ2, λ and ρ being the smoothing parameter and radial frequency respectively, in the theoretical frequency response of second derivative operation. A few sets of weights for various smoothing parameters, are presented. The analysis of Bouguer gravity anomaly map of Los Angeles Basin, California, U.S.A., is carried out by Elkins's (1951) and Rosenbach's (1953) methods and the sets of weights given in this paper which clearly establishes their filtering equivalence.

Notes: The 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.

Notes: Design procedures and characteristics of three stacking filters are discussed which may find application in various three-dimensional velocity filtering problems. These filters are derived in the time-domain as optimum multichannel Wiener filters. Random stationary functions are assumed as stochastic models for the seismic traces. All power and crosspower spectra which are the basic elements of the multichannel normal equations are statistically averaged according to specific three-dimensional considerations. Various properties of the input traces may be incorporated in the design of the optimum filters. With fairly general assumptions about the input these filters are deterministic in the sense that they are applicable to a broad class of input traces with similar statistics in amplitudes and arrival times of signals.

Notes: An 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.

Notes: The interpretation of the gravity anomaly on a horizontal plane over a causative body having circular symmetry about a vertical axis is considered from a rather unconventional approach. As the analytical expression for the gravity effect of a circular body assumes a closed form only on the axis of symmetry, the interpretation in this approach is carried out with the anomaly profile along the axis—which leads to simpler and faster computation.A numerical method is developed for computation of the anomaly profile along the vertical axis from the horizontal radial profile of the symmetric anomaly by upward continuation. Provision is also made for an end correction when the radial profile has only a limited extension.Some simple geometrical shapes are assumed for the causative body. Its parameters are then determined from least squares fitting of its gravity effects to the observed (upward continued) vertical profile (i) by the steepest descent method and (ii) by the Newton-Raphson method.Some applications of these methods are demonstrated.

Notes: In comparing the similarity between time, frequency, and phase measurements as used in the induced polarization method of geophysical prospecting, parameters must first be defined and the basis for comparison established. The conditions for mathematical equivalence then follow in a natural sequence. Laboratory measurements are made on a variety of rock samples to indicate the type of comparison and correlation expected from field measurements.Results indicate that frequency domain and phase measurements are equivalent, but two frequency domain measurements are needed to produce the same amount of polarization information as a single phase measurement. Frequency and time domain measurements will be similar but never equivalent due to the basic differences in their respective parameter definitions.

Notes: From 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.

Notes: A 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.

Notes: In this paper an idealized valley of a semi-elliptic cross-section is considered. For a Schlumberger configuration on the axis, sets of master curves are calculated for the ratio of semi-axis a/b= 1, 2, 3, 4, 5 in corresponding to various resistivity ratios of surrounding rocks and valley sediments. For small resistivity ratios, these model curves have the shape of three-layer curves for horizontal bedding and are often equivalent to them within the accuracy of measurements. The axial ratio a/b considerably affects the depth determination of valley sediments. In the special case of a circular cross-section (a/b= 1) the influence of the position of the electrodes on the sounding curve is studied in more detail.The application of the master curves in practice shows that the influence of the specific shape of the valley on soundings should not be neglected. In general, the valleys have a greater “true” depth than can be seen from the interpretation of a sounding by master curves corresponding to the horizontal bedding.

Notes: In the theoretical part of the present paper, formulas have been analyzed for a magnetic dipole in a homogeneous and unbounded medium. The magnetic field is elliptically polarized in the region between the quasistatic zone and the far field. Since the position and the shape of the polarization ellipses depend on the complex wave number, k, it is possible to determine k by measuring the polarization ellipses. From k, the conductivity and the dielectric constant of the medium are easily calculated. The functions required for the measuring method have been computed and plotted in graphs.In the experimental part it was examined how far the theory may be applied to measurements of propagation through rock at frequencies ranging from 100-1000 kHz. These measurements showed that reasonably defined mean values of rock parameters can be given only if the deviations of the field from the theoretically expected field are not too high. These deviations have been named field distortions and have been examined by means of statistical methods (variance ratio tests). Gallery cavity and inhomogeneity or anisotropy of the medium account for these distortions.

Notes: Non dynamite seismic energy sources have shown only limited success in difficult shallow-water or marsh prospect areas, and none have applicability to both environments. Recently, a method has been devised to adapt a marine pneumatic source for operation in abrasive surroundings. A system composed of four of these modified sources together with associated emplacement and retrieval mechanisms has been developed and has proven to be a reliable and efficient seismic energy source for both shallow-water and marsh applications.

Notes: On présente des profils de sismique réflexion obtenus dans la partie Sud-Est du Golfe de Gascogne en eau profonde avec raccordement au plateau continental.La technique employée était celle du Flexotir à un ou deux canons en couverture triple. La charge totale par tir était égale à 50 ou 100 grammes suivant les cas. La vitesse du navire était ?environ 6,5 nœuds, ce qui a permis de couvrir 1000 kilomètres de profil en 9 jours de travail. La distance entre traces sur les coupes est de 60 mètres, ce qui per-met une étude assez détaillée.De bons résultats ont été obtenus par des fonds allant jusqu à 4000 mètres. La pénétration sous le fond atteint souvent 5 secondes (temps double).Le Flexotir constitue une méthode de prospection sismique bien adaptèe àľocéano-graphie de grande reconnaissance.

Notes: A second deep Schlumberger sounding has been carried out in South Africa, this time using a newly completed power transmission line, not yet in sevice, as emission line. The maximum current electrode separation attained was 600 km. The sounding was situated on a shield area with a thin cover of sedimentary rocks (Karroo System) overlying the archaean granite. The center was chosen near to the village of Dealesville.It is shown that lateral effects at large AB spacings are unlikely, but due to numerous dolerite intrusions in the sediments surface electrode effects must be guarded against; thus AB positions were chosen by geologists. Because of a low signal/noise ratio at large AB spacings the measurements were treated statistically; in particular, the elimination of non-random events improved the measuring accuracy.Although a thin conducting layer at the base of the sedimentary succession decreased the resolution of the sounding curve, the results, which were interpreted with the aid of a computer, show positively that〈list xml:id="l1" style="custom"〉(a). the crust is multi-layered with a highly resistant portion having a minimum resistivity of 15000 ohm.m and(b). a good, thick conductor appears as the final layer.The Dealesville results are in complete agreement with those obtained from the first deep Schlumberger sounding at Pofadder (Van Zijl 1969) except that the transverse resistance of the lowermost resistant crust is about 100% larger at Pofadder due probably to a second period of metamorphism. Both electrical studies support the view of a dehydrated lower crust (granulite facies).

Notes: A two-coil induction logging system in an infinite homogeneous medium has been theoretically analysed for the relative contributions of various ground elements to the total signal at the receiver. Unlike an earlier approximate treatment by Doll (1949), the present analysis takes skin effect into account (while neglecting displacement currents). Contour diagrams depicting relative contributions from every ground point and diagrams for vertical and radial/lateral investigation characteristics are presented. The results differ significantly from Doll's in the following points:〈list xml:id="l1" style="custom"〉1The relative contribution is frequency and conductivity dependent;2It does not show symmetry with respect to the center of coil system;3It alternates between positive and negative values with distance;4Real and imaginary contributions for a given conductivity and frequency are different from each other.The possibilities of a horizontal-horizontal sonde is briefly examined and found to be inferior to the usual sonde because of its higher sensitivity to the mud column and the invaded zone.

Notes: The paper deals with the early stages of development of a convenient form of electromagnetic induction method of sounding referred to as ‘Central Frequency Sounding’ and abbreviated as CFS. The method is introduced as a rapid and useful technique for investigation of shallow engineering and hydro-geological problems. Sets of theoretical two-layer master curves, suitable for interpretation of field data involving measurement of the vertical magnetic component of the field induced at the center of a loop placed on a two-layer earth, have been presented.The approximate but reasonably accurate solutions for a two-layer earth of any arbitrary resistivity contrast have been considered for the purpose and expressed in a form suitable for computation. The computed results have been presented in sets of curves useful for interpretation of field data.

Notes: Book reviewed in this article:J. A. Jacobs, Geomagnetic Micropulsations.G. Kunetz, Principles of direct current resistivity prospecting.T. Rikitake, Electromagnetism and the Earth's Interior.E. Orellana and H. M. Mooney, Master Tables and Curves for Vertical Electrical Sounding.

Notes: La polarisation provoquée (P.P.) est un phénomène particulièrement complexe non seulement du point de vue des mécanismes physiques qu'elle met en jeu, mais aussi du point de vue mathématique. A cause de ľanalogie que présentent les techniques expérimentales de sondage électrique classique de résistivité?une: part, et de sondage P.P. ?autre part, on éprouve une certaine tendance à interpréter les données du second à la manière du premier. C'est pourquoi il nous a semblé utile de calculer un modèle mathématique idéalisé et schématisé qui permette tout au moins de se rendre compte de ľallure générale du phénomène auquel on peut s'attendre. On s'est placé dans le cas le plus simple, celui ?une couche mince polarisable qui présenterait la même conductibilitéélectrique que le milieu dans lequel elle est intercalée. On se propose de fournir le résultat de ce calcul pour le cas simple ?une seule électrode ?injection et ?une seule électrode de mesure et, à partir de ces données, de calculer ľallure ?un sondage P.P. de type classique avec quadripôle Wenner.On compare ensuite le diagramme calculé avec une courbe expérimentale obtenue sur un modèle figurant une couche mince de minerai disséminé II s'avère, en fin de compte, que ľallure générale du phénoméne fournit une base de contrôle solide àľexpérimentation sur modèles réduits.

Notes: In seismic studies being carried out to elucidate the structure at depth of the Midland Valley rift and the Tertiary igneous province in the West of Scotland, a lack of deep boreholes makes the collection of velocity data imperative for identification of seismic events and for determinations of depth. Three methods are used to investigate the correlation of seismic velocities and geological formations. The results show as strong a dependence of velocity on method of measurement as on lithology and the wide spread of values within a given formation makes the attribution of discrete velocity ranges to specific formations impossible. Changes of velocity are more significant than absolute values. The variations in both are discussed.

Notes: Measurement of the depth to water in wells can be accomplished by timing the fall of a marble or BB. Depth to water can also be determined in terms of the frequency of the reverberations heard in a well. These two methods are called the rock and the bong techniques respectively. Their theoretical basis, their proper execution, and their usefulness are discussed.

Notes: The feasibility of determining the ground-water contribution to stream flow during periods of storm runoff by continuous monitoring of a stream's electrical conductance was investigated. Methods involving graphical techniques or ground-water stage versus base flow rating curves are generally used to determine the ground-water contribution, but the ground-water contribution can also be estimated if stream flow and the conductance of surface water and of ground water are known. The conductance method was tested on a 95-square-mile basin in north-central Illinois. Continuous records of stream flow, stream-flow conductance, and ground-water stage within the basin were collected. A rating curve of base flow versus mean ground-water stage was constructed, and ground-water discharges determined from the rating curve were compared with those computed from conductance data. The conductance method normally gave a lower estimate of the ground-water contribution than did the rating-curve method. However, analyses of storms which were preceded by extended dry periods resulted in much lower estimates of ground-water discharge by the rating-curve method than by the conductance method. The conductance method offers a simple alternative for use in areas where observation wells are unavailable or where rating curves are difficult to construct.

Notes: Observation wells and access holes for neutron probe use were drilled by a jet-percussion drill rig in coarse alluvial material near Tucson, Arizona. The method combines the jetting action which effectively removes loose materials with the percussion necessary to break up tighter formations and large particles. A unique feature of the equipment is the provision for simultaneous drilling and driving the casing to keep the hole open in loose formations. Washed samples of the material being drilled can be obtained from the recirculating water system. Drilling rates were from seven to ten feet per hour, and costs including casing were less than $1.50 per foot. Maximum depth is about 100 feet.Hydrologic study of a ground-water reservoir requires access to the aquifer. Observations are made where the water table intersects the land surface, such as at springs or seeps, or through existing wells. However, wells are not always found in desired locations or are pumped so heavily that their usefulness as observation wells is impaired. Measurements are also made in the unsaturated zone with neutron moisture measuring equipment, which requires a small diameter cased access hole for the neutron probe.An observation well needs a diameter only large enough for access by measuring devices and must be immediately responsive to changes in aquifer water level. For neutron probe use, the required diameter is about two inches, and the well must have no significant effect on moisture movement in the unsaturated zone. To meet these requirements the drilling process should have no lasting effect on the formation surrounding the well. Finally, since the wells have no economic utility, construction cost must be low.A network of observation wells and neutron probe access holes was drilled as part of a project to evaluate the natural recharge from Rillito Creek near Tucson, Arizona. The formation along the creek bed is a coarse alluvial outwash containing almost no clay, considerable running sand, and some large gravel and boulders. Commercial churn (percussion) and hydraulic rotary drills, commonly used for drilling in this area, were first tried but encountered much difficulty in the loose materials.Previous investigators used jetting equipment drill small diameter holes in a variety of alluvi formations (Cederstrom and Tibbitts, 1961; Bowma: 1911; and Pillsbury and Christiansen, 1947). Howeve in most cases, either open hole drilling was used because the fine material content and the limited numb. of boulders or large gravel particles made this methc possible, or drilling mud was used to maintain th hole. The jetting method uses water pumped unde pressure through hollow rods and a drill bit to loose the material and carry it to the surface. The jettin water receives little aid from the drill in loosenin the material to be removed. Usually the drill cutting are settled out in a tank or basin, and the water i recirculated.

Notes: Under steady state conditions of flow, the seepage toward a single gravity well is governed by the Laplace Equation which may be written in terms of either the hydraulic head, the pressure head or the velocity potential. Although this equation is linear, the principle of superposition cannot be applied to sum up the individual effects in the case of a multiple gravity well system due to the variation of the flow domain under the effect of one or several wells. A method is presented allowing the use of the superposition principle in a restricted form. The superposition of the decrements of the base pressure heads than the initial heads before pumping is valid. Also the decrements in the areas of the pressure head diagrams across specific vertical sections than the original areas can be summed up together.The limitations of Dupuit's well formula are explained. The validity of that formula has been proven on the basis of the analysis of the hydraulic forces within the flow medium, an approach which is different than that given by Hantush and Charney. Furthermore, the derived equation is written in terms of the areas of the pressure head diagrams across vertical sections and termed as the Unified Well Formula because it has been proven that the same formula is also valid for artesian wells.The analysis of the hydraulic forces leads to the development of an equation for the free surface. This equation is then solved numerically in one iterative cycle. Due to the lack of simple available solutions, only one case, previously solved by the relaxation techniques, is compared with the presented method. The maximum percent difference in the depth of saturation within 82% of the flow region does not exceed 3.2% whereas in the remainder 18% of the flow region around the well, the percent difference varies between 2.63% to 4.67%. Even these differences do not really indicate actual errors due to the approximation implied in the relaxation method itself using a coarser grid.This distribution of the hydraulic head across a vertical section is assumed parabolic. Although Polubarinova-Kochina presented a mathematical proof which leads to the same conclusion, yet for the reasons explained in the text, the writer preferred to use this type of distribution as a valid physical assumption.The results of the analysis of each single well are applied to determine the pattern of the interference between several gravity wells. By means of the presented approach, the resultant values of the depths of saturation can be obtained on the basis of the explained restricted procedure, of superposition. The hydraulic potential distribution within the flow medium of a multiple gravity well system can also be obtained. The assumption of the parabolic hydraulic head distribution is maintained in analyzing a group of wells. It is recommended to establish a proper computer program covering a grid system that encompasses all the wells and their individual influence regions in a certain well field.In the entire analysis, Dupuit's assumptions are eliminated. However, the two main assumptions in the given analysis are: (a) the parabolic distribution of the hydraulic head across a vertical section within the flow medium, and (b) the elimination of the circumferential velocities. These two introduced assumptions are -i in the writer's opinion – practically valid.

Notes: Carbonate aquifers with highly developed anisotropic permeabilities and other fractured rocks under water-table or semiwater-table conditions present complex hydrologic settings in which to predict the sustained yield of individual wells or groups of wells. Yields of wells in these settings are particularly responsive to the position of the water level and its relationship to one or more producing zones. Often a well's total capacity may be accounted for by one or more openings encountered in drilling which are separated by varying thicknesses of essentially nonproductive rock. A well s yield is determined more by the position of the water table with respect to these openings than to the proportion of saturated rock penetrated by the well bore.A permeability profile must be defined for. these wells along with their available drawdown, and the inclination of water-yielding openings. Permeability profiles may be roughly estimated from detailed driller's logs and caliper logs, and more precisely determined from flow meter surveys; packer tests and by pumping wells after successive increments of drilling or by a combination of increasing casing lengths and extended drilling. Available drawdown is dependent upon the inclination and position of significant water-yielding openings exposed within the bore hole and seasonal variations in the water-table position. In gently dipping carbonate rocks openings may follow bedding planes or selected beds favoring conduit development. Where this is known to be the case, pumping levels may be allowed to approach the top o.f one or another of these zones depending upon which is most productive.Where openings‘are inclined, pumping levels should be kept well above the depth at which the opening was penetrated to minimize the risk of dewatering conduits where they occur higher in elevation adjacent to the well bore compared to where they were penetrated by the well bore, Test holes may be drilled immediately adjacent to the potential production well to define the inclination of individual conduits or wells test pumped when possible at rates sufficient to draw the pumping level to the top of the opening in question. The latter is preferable because reductions in yield can be observed directly as a function of drawdown. To determine available drawdowns in fractured rocks, a permeability or yield profile, the inclination of openings adjacent to the well and seasonal variations in water levels must be known.

Notes: A field experiment has been installed near Firebaugh in the San Joaquin Valley of California to test submergence of drains as a means of denitrification of ground water. Laboratory and field experiments have shown that denitrification occurs in saturated soil where there is ample organic carbon available for bacterial metabolism. Denitrification and dilution of high nitrate ground water were accomplished in the field.

Notes: As round-water research is accelerated and basic data on aquifer parameters become more abundant, a statistical approach to evaluation of the ground-water regimen becomes increasingly useful. One such statistical technique is the fitting of polynomial trend-surfaces to ground-water levels. Barcholomew County, Indiana was chosen as a test site to derive techniques which could give additional guidance in the selection of areas suitable for the development of future ground-water resources.Trend-surface maps and maps of the deviations from the trend-surfaces were prepared from water-level data and evaluated to establish their relationships with the hydrogeologic regimen. A field-testing program was carried out to evaluate aquifer parameters.On the basis of the results obtained from these studies, the following conclusions were drawn:〈list xml:id="l1" style="custom"〉1A mathematically fitted surface may be considered to approximate the water-table or piezomecric surface, and will be sensitive to fluctuations in the ground-water reservoir.2The anomalous areas of the trend-surface represent local effects superimposed on the regional base and may be explained by a particular set of geologic, hydrologie or man-made conditions.From these conclusions, it appears that trend-surface analysis provides a rapid, inexpensive method of delineating attractive areas for detailed ground-water investigations.

Notes: Accurate measurement of static water levels in wells tapping deeply buried aquifers and aquitards at the Nevada Test Site requires evaluation of and correction for several factors exclusive of instrumentation. Both the drilling method used and the depth of the hole at the time of measurement significantly affect determination of the static water level for the aquitards, and frequently these factors preclude head determination in an economically justifiable time. Density of fluid in the drill stem and hole deviation affect the determination of accurate static water levels for the aquifers. In the principal aquifers, in which hydraulic gradients are as low as 0.5 foot per mile, direct measurement of depth to water is preferable to pressure-gage measurements at the aquifer face. Case histories and graphs are presented to illustrate the magnitude of errors that can result when these factors are disregarded.

Notes: The purpose of well screens and gravel packs is to maintain open access within the aquifer ensuring that thorough development of the well is not impeded by sand. Where a well draws on unconsolidated sands and gravels, or other friable materials, the installation of a screen and pack is essential.The use of correctly designed equipment is important and this paper represents a review of the diverse types available, but does not set out to make any recommendations.Well screen designs should incorporate the following features:〈list xml:id="l1" style="custom"〉1Minimum entrance velocity.2Maximum open area of screen.3Correct design of slots to minimize blockages.4Slot size should match aquifer or gravel pack medium.5Screen material should be corrosion resistant.6Screen should allow for periodic maintenance.Commercial well screens fall into various categories according to their slot designs. A slot shape, offering the maximum open area consistent with strength, is a priority and the material used in screen manufacture has an important bearing on this. Blockage of screens may be caused by chemical deposition formed by precipitation or corrosion products, and coated screens have been introduced seeking to inhibit this.Gravel packs should include the following design features:〈list xml:id="l2" style="custom"〉1Sand free operation after development.2Give lowest possible resistance to permeation.3Offer low entrance velocities.4Be resistant to chemical attack and have an efficient service life.The gravel pack should ensure that the completed well operates free of sand; thus the particle size of the pack depends upon the particle size of the aquifer. Gravel pack design should be guided by standard sieve analysis.It is evident from the variety of claims made for well screens and gravel packs that further research is necessary. It is suggested that the following points need further investigation:〈list xml:id="l3" style="custom"〉•. Improved design of nonblocking opening.•. Design consideration of screen resistance to chemical attack.•. Best type of gravel and optimum thickness of the pack.•. Head loss through the screen and pack.

Notes: Theoretical analyses predicted and experimental observations—confirmed a mechanism by which strong capilary forces hindered instead of helped promote infiltration into soils. Infiltration into an unsaturated soil overlying an impermeable barrier displaces the air from the soil interstices. Unable to escape downward, the air may escape upward in bubbles travelling through large pores, or, if the pores are small and the capillary forces are large, the air is compressed between the wetting front and the barrier. This reduces the infiltration rate and may result in an almost stable wetting front. Under certain calculable conditions the air pressure build-up is sufficient to cause sudden localized horizontal rupturing of the soil at the wetting front and to lift it along with the infiltrating water, forming a cavity. The air-filled cavity breaks the flow passages and percolation ceases through pores terminating in the cavity. Observations with soil columns have shown that when provision was made fot the displaced air to escape less than one minute was required for the wetting front to move three inches; when the air was not free to escape and the soil raptured, two weeks were required for the wetting front to move this distance. Grain size and packing play a role by limiting the capillary pressure build-up and the bubbling pressure. This phenomenon should emphasize precautions to be followed in applying laboratory infiltration results to engineering predictions of field conditions.

Notes: Ground-water irrigation has developed rapidly in the High Plains region of the United States, especially in Texas since the 1930's and more recently in western Kansas. Although most land sales transactions do not show the water value separate from the dry land value, the availability of ground water has greatly affected land values. This study measures this effect by two methods for an area of southwestern Kansas where ground-water irrigation has become important.The purchasers of all farm land sold in the selected area between 1962-67 were surveyed to obtain information on sale price and numerous factors which it was thought might have a bearing on the land value. One method of measuring the effect of ground water on land value involved matching a number of tracts not known to have available ground water for irrigation with an equal number having ground water. Since other factors were matched as closely as possible, the differences in land value were attributed to water. The second method was multiple regression in which total tract land value and land value per acre for some 160 tracts were related to several factors–soil and topographic conditions, tract size, availability of ground water for irrigation, nearness to elevator, mineral rights, and wheat allotment. Both methods produced approximately the same results–for the period studied the availability of ground water for irrigation contributed $95 to $100 per acre to the value of the land.

Notes: In the Rothschild area, Wisconsin, most water wells are completed in glacial deposits. When glacial deposits are unsaturated or thin, wells are completed in fractured crystalline rocks of Pre-Cambrian age. Specific capacity data from 56 wells tapping these fractured rocks reveal:〈list xml:id="l1" style="custom"〉1Yields and specific capacity are generally small, with a median specific capacity of log 0.17 gpm/ft and a mean value of log 0.10 gpm/ft.2Wells which are close together may have substantially different specific capacities.3The occurrence of saturated sand and gravel above the crystalline rocks has no obvious influence on yield or specific capacity.4Specific capacities of wells seem to be inversely proportional to (a) thickness of rocks penetrated below the water table, (b) depth of the wells below the water table, and (c) depth of the wells below the land surface.Assuming that specific capacities of wells are related to the number of contributing fractures penetrated and that the number of fractures diminishes linearly with depth, the following relation is derived: 〈displayedItem type="mathematics" xml:id="mu1" numbered="no"〉〈mediaResource alt="image" href="urn:x-wiley:0017467X:GWAT37:GWAT_37_mu1"/〉 where Sc= specific capacity, Q = discharge, s = drawdown, B = a constant, b = fracture frequency at the land surface, z = depth, and E = maximum depth of fracturing. In the Rothschild area, E = 100 feet.In exploring for ground water in a fractured rock, the problem is to find the area of maximum b. If sound scientific methods are not available, then exploration will consist of drilling wells at random until a satisfactory well is completed. However, because wells achieve 60 to 80 percent of their yield in the first 20 feet below the water table, test wells should be pump tested when they have reached a depth of about 20 feet below the water table. Unsuccessful wells need not be drilled to completion.

Notes: Despite rainfalls which commonly exceed 200 inches per year in the mountainous portions of many of the islands in the Hawaiian chain, most streams in the islands are very flashy, and only a few carry water throughout the year. This is owing to the extremely permeable nature of the volcanic rocks and soils which make up the Hawaiian islands, and, in fact, the permeability of some of the younger volcanic rocks is so great that virtually no runoff occurs. As a result, development of reliable year-round sources of surface water is difficult especially on the leeward portions of the islands. Furthermore, surface storage is difficult because of the high infiltration capacities of the rock and soil cover. Consequently, development of ground water provides the most abundant and the most reliable source of water supply for these islands. Three modes of fresh ground-water occurrence may be distinguished: perched, dike-confined, and basal. Although perched and dike-confined ground water are of considerable local importance, the basal ground-water body is by far the most widely developed and most important source of fresh ground water for these islands.

Notes: This is the second part of a two-part series (Kent and Sendlein, 1972) in which an approximation of the quantity of bedrock recharge is made. Procedures used for the definition of the ground-water system were described in Part I. In Part II, a subsurface ground-water budget equates subsurface recharge from the bedrock aquifer to discharge through sand and gravel and to discharge by pumping. The Darcy equation is used to compute recharge and discharge volume flow rates. Estimates of permeability were obtained from existing pump-test data and the hydraulic gradients were determined from the piezometric map. Two conceptual models are proposed to account for the maximum and minimum cross sectional areas of the bedrock aquifer through which ground water could flow into the sands and gravel and thus are used to represent the maximum and minimum limits of recharge. Upper, lower and average values of bedrock recharge are determined for each model and compared with the average natural discharge for the entire ground-water basin (“total basin” approach). Comparisons are also made for portions of the basin (“partial basin” approach). Upper and lower limits of recharge are chosen from recharge values which are nearest to the average discharge estimate. This determination is based on the assumption that recharge is equal to discharge. Results of this study indicate a quantity of bedrock recharge between a lower limit of 0.23 mgpd and an upper limit of 2.5 mgpd is possible for an 800-square mile basin.The purpose of this approach is to provide an approximation of ground-water recharge from bedrock into an unconfined unconsolidated ground-water basin, and to provide an estimate of its importance to urban ground-water use.

Notes: Book Reviewed in this article:WATER PUBLICATIONS OF STATE AGENCIES complied by Gerald J. Giefer.