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. 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. Array signatures obtained in very bad weather conditions (force 8) are presented. In this extreme test the signatures are very stable from shot to shot.--Modified journal abstract.