The limitations in conventional marine seismic surveys such as imaging of complicated geology in deep water motivate a quest for new and alternative technologies such as OBNs (ocean-bottom nodes). High-quality data from the sea floor can be acquired with ocean-bottom node acquisition techniques which can provide wide-azimuth data set with sparse receiver interval and dense source interval. The main challenge with the ocean-bottom nodes is now processing and imaging of the data. The mirror migration technique is an effective solution for this challenge by separation of the seabed hydrophone and geophone data into up-going and down-going waves. In this study we apply the mirror migration method on a real OBN dataset and demonstrate that using multiples to image the shallow sea bottom improves the continuity and image quality, which is very important for subsurface depth/velocity model derivation. We also demonstrate the challenges associated with such datasets.
Water-bottom reverberations in marine acquisition are a well-known problem and many researchers have worked on suppressing them. The assumption that multiples are noise is the main reason for the attempts to suppress these reverberations. However, the only difference between primaries and multiples is that multiples travel along different paths (Dash, 2009). The water layer multiples (down-going wavefield) can be used to improve the image quality and illumination at shallow subsurface. Imaging with the down-going wavefield is called the mirror imaging method.
A main challenge with the ocean-bottom nodes is now processing and imaging of the data. Acquiring the data on the sea floor from deep water, with a large distance between nodes makes the conventional processing steps difficult to apply for OBN datasets. Another disadvantage of the OBN survey with sparse receiver intervals is that shallow subsurface is poor illuminated (Alerini, 2009). The mirror migration technique is an effective solution for this challenge by separation of the seabed hydrophone and geophone data into up-going and down-going waves.