New developments in deep-towed seismic acquisition

A unique multichannel seismic system, built and operated by the Naval Research Laboratory, allows broad band, high resolution investigations in the upper several hundred metres of deep-water sediment. The deep-towed, acoustic/geophysics system (DTAGS) described here eliminates these problems, making the system ideal for performing detailed geophysical investigations in shallow sediments of deep water. The DTAGS source is a Helmholtz resonator, and operates at a sound level of 200 dB (re 1 μPa at 1 m) over a frequency range of 220 to 1000 Hz, with a response that is largely independent of depth of operation, (0 to 6000 metres water depth). Each omni-directional hydrophone is very sensitive, exhibiting a self noise level of only 0.07 μbar RMS, and a total harmonic distortion of less than -90 dB. The received signal is locally digitized before telemetered to the topside acquisition computer, where it is monitored in real time and recorded in industry-standard SEGY format. In summary, the DTAGS is a scaled down multichannel seismic system that exhibits about an order of magnitude better resolution, both vertically and laterally, than a conventional surface-towed, airgun, multichannel seismic system.