Device for determining the instant of reception of an acoustic wave

In a method of marine seismic prospecting comprising transmitting an acoustic wave from a seismic source and detecting the time at which the directly transmitted seismic wave is received at a predetermined first sensor, with the echoes of the acoustic wave being detected by a predetermined arrangement of second sensors whereby the time of reception of the directly transmitted wave at the first sensor is used in a comparison system to determine the propagation time of the echoes, the improvement comprising a method, in a system wherein the first sensor is intermittently connected to a processing and recording system for transmitting data thereto indicating a receipt of the direct acoustic wave, of determining the time of reception of the directly transmitted acoustic wave which comprises the steps of:

• generating a voltage varying over time in a predetermined manner upon receipt of the directly transmitted wave at the predetermined first sensor;
• detecting at least two discrete values of the voltage generated in the predetermined manner, at successive time instants separated by an interval of time .DELTA.T greater than the intervals of time separating two successive transmission of data from the predetermined first sensor to the recording and processing system;
• and
• calculating from the discrete voltage values detected, and from the interval of time .DELTA.T, the time of receipt of the acoustic wave at the first sensor.

A device for determining the time of reception of an acoustic signal at a sensor, comprising:

• sensing means associated with sequential data transmission means for being intermittently connected for transmitting data to a recording and processing system;
• voltage generating means for generating a voltage varying over time in a predetermined manner;
• trigger means associated with said sensing means and with said voltage generating means for triggering the operation of said voltage generating means at the time of receipt of the acoustic signal at said sensing means;
• selecting means associated with said voltage generating means for detecting at least two discrete values of the voltage generated by said voltage generating means, at successive time instants separated by an interval of time .DELTA.T greater than the intervals of time separating two successive transmissions of data from said sensing means to said recording and processing system;
• and
• determining means associated with said selecting means for calculating, from said transmitted discrete values of said voltage and said interval of time .DELTA.T, the time of reception of the acoustic signal at said sensing means.