Broadband Signal Processing for Shallow-water OBN Data

In recent decades, ocean-bottom acquisition has been considered useful due to its wide-azimuth and broadband character. However, advances in marine technology have considerably broadened the bandwidth of towed-streamer images and revealed power in airgun sources at lower frequency than historically expected. Ocean-bottom data suddenly look less impressive in their bandwidth than previously. This may be due to problems of noise attenuation and signal protection at low frequency, which is an issue for ocean-bottom data that are dominated by surface-wave energy below 5 Hz. Revisiting this problem with a tailored ocean-bottom processing strategy and carefully separating signal and noise, ocean-bottom data from 45 m of water in the North Sea show useable power below 3 Hz. Although broadband streamer technology is catching up, it seems that ocean-bottom data are still relatively rich in low-frequency signal if processed appropriately. Combined with the full azimuth range and long offsets, ocean-bottom data are still an attractive choice for reservoir characterization.