PZ Calibration in Shallow Waters - The Britannia OBS Example

In marine multi-component data processing, the vertical component of particle velocity Z is calibrated against the pressure component P to correct for coupling discrepancies and sensitivity differences between hydrophone and geophone. The PZ calibration processing step is crucial to the success of wavefield decomposition into up- and down-going waves, as well as into compressional and shear waves. In this paper, we present a new application of the conventional cross-ghosting technique. Our PZ calibration approach is implemented in the x-t domain and considers far offset reflected or refracted energy and their water layer reverberations. These events are commonly and easily identified in shallow water data as they arrive earlier than the direct arrival. Compared to other published techniques, our method is less sensitive to near-offset noise, source bubbles and irregular or sparse offset sampling. We successfully apply the proposed approach to an OBS data set acquired at 150 m water depth over the Britannia field in the North Sea.