On the usage of direct measurements of water velocity in deep water OBN surveys

Abstract

The speed of sound in the ocean has spatial and temporal variations that, if not taken into account, affect the quality of images obtained from seismic data, particularly in deep waters. Pressure Inverted Echo Sounders (PIES) and Sound Velocity Profiles (SVPs) are two types of sensor-logging devices that are used for the direct measurements of the speed of sound in the ocean. PIES measure the average sound velocity through a column of water from the seabed to the sea surface. SVPs measure the sound velocity as a function of the water depth at a limited number of locations. We have developed a method to visualize and analyze these two classes of measurements to estimate quantities that can be directly used for processing seismic data acquired in ocean bottom node (OBN) surveys. The application of this method to a deep water OBN survey gives water velocity variations that are in good agreement with the results obtained with a completely different approach based on the inversion of traveltimes extracted from seismic data.