摘要:

ABSTRACTIn the first part, the author, recalling the principle ofd/ccurrent measurements, shows by means of some examples, different experimental results relative to the induced polarization phenomenon. He presents the case of the negative induced polarization which can be explained by geometric effects. He gives some examples of saturation curves and discusses the problem of the linearity of the I.P. phenomenon. Then he shows some aspects which demonstrate that I.P. decay curves do not always conform to the general law. He concludes by showing the influence of the current electrodes, the position of which, relative to the polarizable bodies, may alter the shape of the I.P. anomalies.In the second part, the author presents different case histories of I.P. mineral surveys where I.P. is compared to other geophysical methods and drilling results.

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1968.tb01811.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

ABSTRACTAn interpretation method is suggested for apparent resistivity profiles over a medium of continuously varying resistivity. The medium is replaced by an equivalent laminated system of constant resistivity in each layer and evaluated by superposition. The approximation facilitates detailed subsurface profiling as required for underground storage projects or water infiltration schemes.

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1968.tb01812.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

ABSTRACTA theoretical solution is obtained for the problem of a two‐layer earth with transitional boundary. In practice, the transition layer can stand for the weathered zone in hard rock areas where the degree of weathering diminishes with depth. Master curves and tables of data are presented for the case when the lower half‐space is infinitely resist

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1968.tb01813.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

ABSTRACTWhen, in a two‐layer earth, the substratum is insulating or infinitely conducting, the thickness of the top layer can be determined from surface potential measurements along a radius from a single point power electrode. The observed potential needs to be numerically integrated in a direction perpendicular to the said radius, and Figure 4 can then be used to find the thickness. A field example is include

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1968.tb01814.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

ABSTRACTMagneto‐telluric measurements were carried out at a group of eight sites, from Braunschweig to Lübeck, to determine the resistivity values associated with the North German conductivity anomaly. The data were analyzed for scalar and tensor apparent resistivities over the period range 5–2000 seconds. The results in general indicate very conductive (˜I Ω‐m) sediments overlying a resistive basement which is strongly lineated.Interpreted basement depth (˜6 km) is compatible with published seismic refraction data. Principal conductivity axes in the basement appear to be directly related to trends of salt domes and major troughs. A major change in axis direction occurs near the center of the North Germa

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1968.tb01815.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

ABSTRACTIn order to increase the seismic efficiency of the Sparker‐system developments were made in 1966/67. Results illustrating the main steps of this development are discussed. A new type of electrode called Transploder electrode was field‐tested and proved to be promis

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1968.tb01816.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY

摘要:

ABSTRACTIt was found in Part I of this paper that approximating the sharp cut‐off frequency characteristic best in a mean square sense by an impulse response of finite lengthMproduced a characteristic whose slope on a linear frequency scale was proportional to the length of impulse response, but whose maximum overshoot of ±9% was independent of this length (Gibbs' phenomenon). Weighting functions, based on frequency tapering or arbitrarily chosen, were used in Part II to modify the truncated impulse response of the sharp cut‐off frequency characteristic, and thereby obtain a trade‐off between the value of maximum overshoot and the sharpness of the resulting characteristic. These weighting functions, known as apodising functions, were dependent on the time‐bandwidth productMξ, where2ξ, corresponded to the tapering range of frequencies.Part III now deals with digital filters where the number2N–1 of coefficients is directly related to the finite lengthMof the continuous impulse response. The values of the filter coefficients are taken from the continuous impulse response at the sampling instants, and the resulting characteristic is approximately the same as that derived in Part II for the continuous finite length impulse response. Corresponding to known types of frequency tapering, we now specify a filter characteristic which is undefined in the tapering range, and determine the filter coefficients according to a mean square criterion over the rest of the frequency spectrum. The resulting characteristic is dependent on the time bandwidth productMξ= (N–1/2)ξ up to a maximum value of 2, beyond which undesirable effects occur. This optimum partially specified characteristic is an improvement on the previous digital filters in terms of the trade‐off ratio for values of maximum overshoot less than 1%. Similar to the previous optimum characteristic is the optimum partially specified weighted digital filter, where greater “emphasis is placed on reducing the value of maximum overshoot than of maximum undershoot”. Such characteristics are capable of providing better trade‐off ratios than the other filters for maximum overshoots greater than 1/2%. However these filters have critical maximum numbers2.NC–1 of coefficients, beyond which the resulting characteristics have unsuitable shapes. This type of characteristic differs from the others in not being a biassed odd function a

ISSN:0016-8025    

DOI:10.1111/j.1365-2478.1968.tb01817.x

出版商:Blackwell Publishing Ltd    

年代:1968

数据来源: WILEY