Elimination of source‐generated noise from correlated vibroseis data (the ‘ghost‐sweep’ problem)[Link]

The most common noise‐reduction methods employed in the vibroseis technique (e.g. spike and burst reduction, vertical stacking) are applied in the field to reduce noise at a very early stage. In addition, vibrator phase control systems prevent signal distortions produced by non‐linearity of the source itself. However, the success of these automatic correction methods depends on parameter justification by the operator and the actual characteristics of the distorting noise. More specific noise‐reduction methods (e.g. Combisweep (Trade mark of Geco‐Prakla), elimination of harmonics) increase production costs or need uncorrelated data for the correction process. Because the field data are usually correlated and vertically stacked in the field to minimize logistical and processing costs, it is not possible to make subsequent parameter corrections to optimize the noise reduction after correlation and vertical stacking of a production record.

The noise‐reduction method described here uses the final recorded, correlated and stacked vibroseis field data. This method eliminates signal artifacts caused e.g. by incorrect vibroseis source signals being used in parameter estimation when a frequency–time analysis is combined with a standard convolution process. Depending on the nature of the distortions, a synthetically generated, nearly recursive noise‐separation operator compresses the noise artifact in time using a trace‐by‐trace filter. After elimination of this compressed noise, re‐application of the separation operator leads to a noise‐corrected replacement of the input data. The method is applied to a synthetic data set and to a real vibroseis field record from deep seismic sounding, with good results.