After more than twenty years of field practice, the most widely used signal in the Vibroseis technique remains the original so–called linear sweep. To many, it seems that substantial improvement should be expected from taking advantage of more sophisticated signal design techniques.
The purpose of this paper is to present a tutorial survey of the basic concepts involved in signal design, tying together the known features of the linear sweep with those of the more general type. Several particular types of nonlinear sweeps are analyzed and the results of a field test seem to confirm the conclusions drawn from the conceptual analysis.
After a brief consideration of still another type of nonlinear signals, a particular variety of pseudorandom sweeps, the author concludes by giving his views of what might be the role of nonlinear signal design in the future development of the Vibroseis technique.