1. A method of geophysical prospecting to obtain a figurative representation for geophysical interpretation, comprising: (a) positioning a first transmitter dipole and a first receiver dipole in cooperation with subsoil; (b) supplying an impulsive excitation current to said first transmitter dipole, said current comprising a group of excitation pulses of alternate polarity, each followed by a zero current; (c) detecting transient signals, produced at the output of said first receiver dipole; (d) defining predetermined time intervals consecutive to said excitation pulses and simultaneous to said zero current and which include substantially all useful parts of said transient phenomenon, wherein said detecting occurs as a function of time, at least during said time intervals; (e) preprocessing said signals including sampling, digitalizing, recording and temporally marking said signals during said time interval to produce digitally recorded samples which correspond temporarily to said time intervals; (f) processing said digitally recorded samples, wherein said step of processing comprises: (i) statistically evaluating said digitally recorded samples of said transient phenomenons as a function of time; (ii) after said evaluating step, smoothing said digitally recorded samples by digital filtering to produce a smoother digital representation of said transient phenomenon free of a substantial portion of surrounding noise.