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Method of source coding and harmonic cancellation for vibrational geophysical survey sources

  • US 4,982,374 A
  • Filed: 10/23/1989
  • Issued: 01/01/1991
  • Est. Priority Date: 10/23/1989
  • Status: Expired due to Term
First Claim
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1. In a seismic survey using multiple vibrational seismic energy sources which are activated concurrently in sweeps of constantly changing frequency within a seismic frequency range to generate seismic signals, a method of reducing harmonic distortion and crossfeed, comprising:

  • (a) selecting the highest order harmonic which has sufficient signal strength to cause significant harmonic distortion of the sweep signals;

    (b) selecting the number of seismic energy sources to be used in the survey;

    (c) selecting a number of sweeps for each seismic energy source in excess of the number of seismic energy sources used;

    (d) selecting initial phase angles for each sweep of each seismic energy source so that substantially all harmonics up to and including said highest order harmonic are suppressed, wherein the step of selecting initial phase angles comprises;

    (i) constructing a table with N rows and N columns, where N is the number of sweeps, each entry eH,M being calculated from the formula
    
    
    space="preserve" listing-type="equation">e.sub.H,M =H(M) modulo N,where H is the row number and M is the column number;

    (ii) selecting a number of columns equal to the number of sources such that the number in the first row of each selected column does not appear again in any selected column before the row H=F+1, where F is the highest order harmonic determined to cause significant crossfeed;

    (iii) assigning a selected column to each seismic energy source, the initial phase angle for the nth sweep of that seismic energy source being represented by the number in the nth row of that column multiplied by 2π

    /N.

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