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High-resolution MCS in deepwater

Naval Research Laboratory, Stennis Space Center, Mississippi, U.S.

S. E. Spychalski

High Tech, Inc., Gulfport, Mississippi, U.S.

Corresponding author: gettrust@nrlssc.navy.mil

The first 20% of the full text of this article appears below.

In the early 1980s, the Navy developed instrumentation to quantify the geoacoustic properties of the upper 500 m to 1 km of marine sediments in water depths to 6000 m. To obtain this information with the resolution required to support Navy systems (several meters in depth and a few tens of meters along track), a system operating from the sea surface could not be used. Thus, a new system was needed that operated below the surface.

The initial development of such a system (now known as the deep towed acoustics/geophysics system, or DTAGS) was carried out at the Naval Ocean Research and Development Activity (NORDA), which is now part of the Naval Research Laboratory (NRL). Here we overview the development of DTAGS, discuss technical and scientific results obtained with this system, and present plans for enhancing the capabilities of the system.

	Review of the DTAGS

 
The design concept for DTAGS was to adapt proven multichannel seismic (MCS) techniques to obtain high-resolution information about marine sediments in the deep ocean environment. As towed hydrophone arrays that could operate at full ocean depths existed at that time, the most difficult task was the development of a seismic source. After a review of impulsive sources and transducer sources, NRL was selected to construct an acoustic source based on a transducer with a Helmholtz cavity driven by five piezoelectric ceramic rings (Figure 1). This source covered the frequency band of interest (250-650 Hz) with a sound pressure level (SPL) of (197 dB//1 µPascal @ 1 m) sufficient to sample the upper marine sediments. The original system was replaced 18 months ago by an upgraded Helmholtz resonator that has improved source SPL (200 dB//1 µPascal @ 1 m) and increased bandwidth (220 Hz–1 kHz). The new system (Figure 2) has a simplified instrument . . . [Full Text of this Article]