Apparatus for real time correlation in seismic prospection

• US 4,549,285 A
• Filed: 07/07/1982
• Issued: 10/22/1985
• Est. Priority Date: 07/08/1981
• Status: Expired due to Fees

• Current Assignee: Société D'Etudes Recherches Et Constructions Electroniques Sercel
• Original Assignee: Societe D'Etudes Recherches et Constructions
• Inventors: Naudot, Jean-Claude, Fleurance, Claude
• Primary Examiner(s): Cangialosi, Salvatore
• Assistant Examiner(s): Lobo, Ian J.
• Application Number:
  US06/396,008
• Time in Patent Office: 1,203 Days
• Field of Search: 367/59, 367/60, 367/63, 367/38, 367/39, 367/40, 367/42, 367/41, 364/421, 346/33 C
• US Class Current: 367/60
• CPC Class Codes: G01V 1/375 Correlating received seismic signals with the emitted source signal

Abstract

The invention provides an apparatus for seismic prospecting which is to effect a correlation in real time between a pilot signal and a picked-up seismic signal. With N being the number of samples corresponding to the desired thoroughness of investigation, the apparatus comprises the following: a buffer of N samples of the pilot signal; at least one buffer for a sample of the picked-up signal; at least one calculation circuit, in which the correlation operations are carried out; at least one result memory, which is to contain the N points of the correlation function; and a circuit for addressing the memories.

Claims

1. In a system for seismic prospecting of subsoil by vibration, comprising:

a source of controlled vibrations;

at least one seismic channel comprising a seismic pick-up for receiving reflecting signals from the subsoil, and means for sampling and digitizing the signal received by the pick-up into successive picked-up samples;

means for exciting the source by a pilot signal;

means for sampling and digitizing the pilot signal into successive pilot samples; and

digital recording means for recording signals derived from the pilot samples and picked-up samples,

an apparatus for providing real time correlations for said seismic channel comprising;

a buffer for storing N samples of the pilot signal, N being a number of samples associated with a time T corresponding to the predetermined degree of investigation;

at least one buffer for storing one sample of the received signal;

at least one calculation circuit comprising a multiplication circuit for producing the products of each picked-up sample multiplied by N consecutive samples of the pilot signal;

at least one result memory, into which are cumulatively introduced N product sums respectively corresponding to correlations of the picked-up signal with the pilot signal, each of said correlations being determined as a function of a respective, variable time lag;

a circuit for addressing the pilot signal buffer, the result memory, and also cooperating with said calculation circuits.

2. An apparatus according to claim 1, wherein each calculation circuit comprises a floating point circuit.

3. An apparatus according to claim 1 wherein each calculation circuit is common to two seismic channels.

4. An apparatus according to claim 1 wherein each calculation circuit is common to four seismic channels.

5. An apparatus according to claim 1 wherein said calculation circuit further comprises an addition circuit for adding the products produced in said multiplication circuit to corresponding memory locations in said result memory.

6. A method of seismic prospecting comprising:

emitting controlled vibrations into subsoil to be studied in response to a pilot signal;

sampling and digitizing the pilot signal into successive pilot samples;

receiving a reflected signal from the subsoil;

sampling and digitizing the received signal into successive picked up samples; and

cross correlating the pilot and received signals in real time comprising;

storing N samples of the pilot signal N in a pilot signal buffer having N locations, where N is a number of samples representing time T corresponding to the predetermined degree of investigation;

individually storing one sample at a time of the received signal;

multiplying the stored sample of the received signal by each of the N stored samples of the pilot signal to produce N products; and

adding the N products to memory locations of a result memory to form N product sums respectively corresponding to correlations of the received signal with the pilot signal in accordance with the formula;

##EQU4## wherein I(t) represents the correlation function stored in a result memory location t, and t=1 . . . N, and p represents the number of samples corresponding to the complete duration of the pilot signal, each of said correlations being determined as a function of a respective variable time lag;

wherein said pilot samples are stored sequentially in said pilot signal buffer and locations in said pilot signal buffer are written over with new samples, and wherein said pilot signal buffer and said result memory are addressed by a circuit in order to carry out said cross-correlation.