One other important process is the vibroseis correlation. This involves crosscorrelation of a sweep signal with the recorded vibroseis trace. The sweep is a frequency-modulated vibroseis source signal input to the ground. The convolutional model for vibroseis data is described in field data examples.
Figure 1.1-20 shows a vibroseis sweep signal, a recorded common-source gather, and the correlated gather. The sweep length is 10 s with a frequency band of 6 to 60 Hz. The 15-s uncorrelated vibroseis record yields a 5-s correlated record. Note that the early part of the uncorrelated record contains low-frequency energy with increasingly higher frequencies at late times. This is because an upsweep (frequency increasing with time) signal was used in this data example.
- Analog versus digital signal
- Frequency aliasing
- Phase considerations
- Time-domain operations
- Crosscorrelation and autocorrelation
- Frequency filtering
- Practical aspects of frequency filtering
- Bandwidth and vertical resolution
- Time-variant filtering