Abstract: A method for underwater exploration which makes use of a parabolic transmitter (1) and a parabolic receiver (3), the transmitter (1) and the receiver (3) being both open at their lower side and immersed below the seawater surface. The electric breakdown discharge occurring between both electrodes (15) of the transmitter (1) generates a primary signal and a pulse which is called “cavitation bubble pulse.” The method consists in enhancing the signal (23) produced by the implosion of the cavitation bubble, to the detriment of the primary signal (13?), by appropriately adjusting the value of the “spark gap” (distance d between the electrodes) so as to optimize the delay time (t) and consequently the acoustic efficiency of the transmitter, by transferring the electrostatic energy to the bubble implosion signal.

Abstract: A method of and an apparatus for the high-resolution sea bottom prospecting, in which an electroacoustic paraboloidal transducer is placed into water, the electrodes of which are near the focus of the paraboloid and are connected both to a capacitor bank the capacitance of which may be varied at will and to a supply circuit for the generation of an electroacoustic discharge between said electrodes. As the capacitance varies the delay time between the primary pulse or underwater prospecting pulse and the cavitation pulse is recorded at any discharge, and at the same time dominant frequency of the prospecting signal spectrum is determined. Afterwards capacitance values are set so as to provide both cavitation pulses the contribution of which to the resulting pulse is minimum and a dominant frequency spectrum as broad as possible.

Abstract: This invention relates to a method and a microprocessor-based apparatus for directly measuring the noise using a nuisance index (L.sub.DI) bound to two physical parameters of the noise: the average energy level (L.sub.E) and the fluctuation level of the noise.The apparatus is comprised of a microphone (M) connected to a pre-amplifier (1) and a detecting unit (2) controlling an analogical-to-digital converter (3) associated to a time (4) feeding a signal to a digital filter (5) and at the same time to one input of a comparator (6). The filter (5) feeds the filtered signal to an integrator (7) supplying the parameter (L.sub.E) and simultaneously to the second input of comparator (6) which supplies the parameter (L.sub..phi.) through counter (8) associated to a trimmer (10). Parameters (L.sub.E) and (L.sub..phi.) are indicated in block (9) of the display.

Abstract: A seismic source consists of an electroacoustic transducer having a metallic structure, shaped like an empty round paraboloid (1) closed at the base by means of an elastic diaphragm and filled with a proper liquid. Around the focus of the paraboloid two main electrodes (5) are set and an auxiliary electrode (6) is put between the first ones. The main electrodes (5) are connected to a set of capacitors (C.sub.o) supplied by a high-voltage power supply (HT). One of the main electrodes (5b) and the auxiliary electrode (6) are connected to a trigger pulse generator (EHT) driven by a remote control (4) via a synchronization pulse generator (3). The discharge between the main electrodes (5) primed by a preliminary spark, generates an acoustic pulse through the liquid medium of the transducer on the ground where the paraboloid (1) is engaged. So the transducer generates seismic waves utilized for shallow prospecting both on land and underwater.