DTAGS

This multichannel seismic system, known as the Deep Towed Acoustics/Geophysics System (DTAGS), is towed from a ship to obtain high-resolution seismic data sampling the ocean bottom and subbottom. Both the source and receivers are towed approximately 300 m above the seafloor in water depths up to 6 km to achieve the geometry required to resolve the fine scale structure (~5 m vertical resolution, with ~15 m horizontal sampling) of the upper 1 km of marine sediments. The source frequency bandwidth is 250Hz  to 1kHz with a raw source level of ~197dB re 1 mPa @ 1 m.

Either a horizontal or a vertical multichannel receiving array can be used with the system. The horizontal array has  48-channels with a nominal hydrophone spacing of 15m; this array provides the length required to resolve the compressional velocities within the upper 1km of sediments. The vertical array has 24 hydrophone channels with an overall array length of 104 m.  The vertical array is designed to study low grazing-angle acoustic backscatter in deep water.  All channels are telemetered to the tow ship via an armored coaxial cable. Thus, both geoacoustic backscatter and seismic data can be monitored in "real time".  Seismic processing computer systems are used to provide preliminary seismic interpretations while at sea.

Other applications of the system:
bulletGeotechnical studies for placing deep ocean drill rigs and towers
bulletSeabed waste disposal
bulletNatural hazard studies
bulletDetailed investigations of natural gas hydrates.
This technology is available for Cooperative Research and Development Agreements (CRADA) between industry and N.R.L  A detailed description of the features of the new deep-tow seismic system is available (right click to download)  DeepTow.pdf

 

 

This cartoon demonstrates the advantage of the deep-tow geometry and higher source-frequencies available with DTAGS as compared with conventional surface-tow multichannel systems.  Note the the first Fresnel zone is substantially reduced with  DTAGS relative to that for the surface-tow system.  The geometry obtained by deep-towing the source and receivers allows one to sample equivalent wavenumber space with a much smaller array. The combination of features available with DTAGS makes it ideal for high-resolution studies of the upper 1km of marine sediments in water depths to 6 km.

The following link will take you to comparative seismic sections (DTAGS vs. high-resolution surface-tow multichannel seismic data).