Source and receiver geometry corrections for deep towed multichannel seismic data

High resolution seismic data were collected using a Deep-Tow Acoustics/Geop hysics System (DTAGS) near ODP site 889/890, offshore Vancouver Island for deep sea gas hydrate study. The near bottom configuration and wide high-fre quency bandwidth allow much better resolution of the structures in the uppe r similar to 400 m. However, the short 2-6 m wavelengths imply accurate pos itioning of the source and receivers to properly determine moveout velociti es and to stack the data. Consequently, a method of estimating the depths o f the source and hydrophones using sea-surface reflection times was develop ed. Travel time corrections based on these sea surface measurements were ap plied to the data by marching a time window along the seismic trace to acco unt for the angular dependency of the reflected raypath. The need for these corrections is clearly illustrated by the results, which show non-linear d epth variations of up to 50-100 m for both the source and the hydrophone ar ray.