Defining the Bandwidth of Vibroseis Sweep Data at the Target, not at the Source

Hydraulic seismic vibrators are the preferred source for land vertical seismic profile (VSP) surveys. The introduction of new, more powerful vibrators wogether with the use of Maximum Displacement (MD) sweeps has resulted in the extension of the bandwidth from less than three octaves to nearly seven. One of the advantages of the design procedure for MD sweeps is that the spectrum of the resulting sweep is an input to, rather than a result of, the design process. This enables the design of sweeps where the spectrum contains sections of the bandwidth that have been enhanced. The data presented in this paper shows that the bandwidth of the data received downhole can be successfully adjusted by varying the power spectrum of the transmitted sweep. Even in highly attenuated terrains this enables us to transmit high frequency energy to significant depth.