Sea Surface Wave Height Estimation from Dual-Sensor Towed Streamer

Abstract

This thesis adresses the problem of how to image the time-varying sea surface based on dual sensor marine seismic data. Although flat and stationary sea surface assumptions may suffice during the processing of marine seismic data acquired under calm weather conditions, this idealistic sea surface condition is seldom encountered in practice. Thus, such assumptions may lead to miss-interpretation and miss-location of events. In this work a sea surface imaging tool based on dual-sensor data has been developed. These data are decomposed into upgoing and downgoing wavefields and extrapolated to the sea surface where an adequate imaging condition is applied in order to obtain the sea surface image. Time varying changes of the sea surface is obtained by applying the imaging technique in a sliding window. The imaging tool was tested employing scattered data computed from the Helmholtz-Kirchhoff integral with time varying boundaries (representing realistic time-varying sea conditions using the Pierson-Moskowitz spectrum with directivity included). Thus we could model marine seismic experiments efficiently including such effects as streamer depth variation and moving receivers. In the case of a 3D data acquisition set-up, the effect of sparse streamer spacing was shown to give a reduced resolution but with the low-frequency characteristics of the sea surface still preserved. Spectral analyses of the imaged sea surfaces were also carried out and feasible speeds and directions of the moving sea surfaces were recovered. Finally, the technique was applied to field data (both 2D and 3D) acquired from different locations under different sea surface conditions. Realistic sea surface variations both with respect to wave heights, prevailing wind directions and speeds were obtained demonstrating the potential of the proposed technique.