oa Study on the Navigation Problems of Deep Tow Seismic

A high frequency deep-tow seismic survey was carried out in the Nankai Trough area in 1996. The objective of the survey was to obtain high resolution seismic sections and velocity profiles of the methane hydrate zone, inferred from the strong BSR events seen on conventional seismic data. A special feature of the survey is that both the source and the streamer cable are towed close to the seabed. This special acquisition geometry requires special data processing to handle the varying source and receiver depths. A CMP floating datum processing sequence was designed which led to high quality sections of the shallow geology. The processing sequence was applied to a number of lines, totaling 200 km. The quality of the final stack sections was highly variable. It was found during the processing that the positions of source and receiver caused problems to harm the quality of the final sections. We classify the positioning problems as (1) streamer cable feathering, (2) source and cable depths, (3) relative shotpoint position and (4) absolute shotpoint position. The floating datum processing with static corrections could fix the problems (1) and (2). Post stack correction techniques are applied to fix (3) and (4) using 3D marine seismic. We are planning to use deep-tow seismic survey for hydrothermal deposits. Hydrothermal deposit is specially limited and higher resolution is necessary than methane hydrates. The very high frequency of the data is considered to make the data processing much more sensitive to errors or approximations. In this paper the navigation problems are reviewed to design the new deep-tow seismic system.