Investigation of flow and flow noise around a seismic streamer cable

In marine seismic explorations, flow noise from the turbulent boundary layer that forms around a streamer cable due to its relative motion through water significantly affects the quality of collected data. Understanding this noise generation mechanism is valuable for the development of future seismic streamer cables. We qualitatively characterize the area of turbulent flow surrounding a seismic streamer cable, and relate this characteristic to the statistics of the measured noise signal. The main finding is that the boundary layer thickness around a seismic streamer appears to be about 25 cm in an ocean environment. This is significantly larger than the thickness of 2.5 to 5 cm that has been reported in the literature from laboratory experiments. We attribute this discrepancy to the unsteadiness of the ocean environment. Estimations of the spatial extent of the recorded boundary layer noise indicate that the "optimal" hydrophone separation needs to be about 0.5 m for the noise to be uncorrelated. The signal-to-noise ratio on streamer cables would therefore be improved if hydrophones were placed more densely than the current industry practice of about 1 m.