ON THE TRANSFORMATION OF DIPOLE TO SCHLUMBERGER SOUNDING CURVES * BY D. PATELLA** ABSTRACT PATELLA, D., 1974, On the Transformation of Dipole to Schlumberger Sounding Curves, Geophysical Prospecting 22, 315-329. A method is described to transform a dipole sounding curve, obtained with any one of the common dipole arrays over a horizontally layered earth, to the form of a Schlum- berger sounding curve. Starting from the general expression which relates the dipole apparent resistivity to the Schlumberger apparent resistivity and its derivative with respect to the spacing, it is possible with some approximations to derive an easy numerical computation procedure in order to perform the transformation. The applicability of the method is discussed briefly. Dipole arrays are at present used mainly in deep geo-electrical explorations. Their practical advantages with respect to the classical configurations of Schlumberger and Wenner are: (i) the relatively short spreads with consequently, short cable length, and (ii) the minimization of the problems of inductive coupling and associated errors, since the cables for the current and measuring circuits are separated. Fig. I shows the four possibilities of arranging dipoles: azimuthal, parallel, radial and perpendicular. For I3 = o the parallel as well as the radial arrays are transformed into the polar array, and for 0 = x/z the azimuthal as well as the parallel arrays are transformed into the equatorial array. Alpin (1950) showed the relations between dipole and Schlumberger ap- parent resistivities, in and FQ respectively, in the case of a layered earth. In particular there exist the following expressions : * Paper read at the 35th meeting of the European Association of Exploration Geophys- icists at Brighton, June 1973. ** Osservatorio di Geofisica e Fisica Cosmica, University of Bari, Italy. Geophysical Prospecting, Vol. zz 21