The signature of an air gun array: Computation from near‐field measurements including interactions—Practical considerations

We have refined our system for calculating the signature of an interacting air gun array from near‐field measurements of its pressure field. We use an iterative technique to calculate a notional array of noninteracting sources from the near‐field hydrophone measurements. The notional signatures form the basis for calculating the array signature in any direction. The success of our iterative technique depends upon prudent positioning of the hydrophones, one close to each air gun. In normal operation the forward motion of the hydrophones and upward motion of the air gun bubbles are important effects which must be included in the equations. A linear model for this motion is adequate and improves the method significantly. The vertically traveling “far‐field” signature calculated by our extended method matches an equivalent “far‐field” measurement very closely. We present array signatures obtained in very bad weather conditions (force 8). In this extreme test the signatures are very stable from shot to shot. Therefore it is not necessary to calculate the array signature every shot; however, continuous recording of near‐fields should still be carried out as a check on signature stability.