An approximation technique for determining optimal Combisweep parameters
S. M. Dougherty, James H. Justice · Geophysics · 1988
Abstract The autocorrelation of a linear FM (frequency modulated) signal consists of a main peak, a primary side lobe, and far side lobes (Figure 1), the side lobes often being referred to as correlation noise (Werner and Krey, 1979; Edelmann and Werner, 1982). One of the aims of Vibroseis signal design is to find and input sweep signal whose autocorrelation has a narrow main peak (high temporal resolution) and low correlation noise as defined by the main peak to primary side lobe amplitude ratio Am/Ap (Figure 1) (Werner and Krey, 1979). A simple and easily implemented method of reducing correlation noise is amplitude tapering (Edelmann, 1966), but unfortunately tapering induces an increase in main peak width (Berkhout, 1984), an undesirable effect. A technique of linearly combining individual autocorrelations, called Combisweep, was shown to increase Am/Ap (Werner and Krey, 1979). However, Werner and Krey made no attempt to optimize parameter selection.