Electrode Sparker
 The schematic above (derived from Trabant, 1984) illustrates the basic components of the electrode sparker system |
The sparker is a relatively high powered sound source, dependent on an electrical arc that momentarily vaporizes water between positive and negative leads. The collapsing bubbles produce a broad band (50 Hz - 4 kHz) omnidirectional pulse which can penetrate several hundred meters into the subsurface. Hydrophone arrays towed nearby receive the return signals. It can operate only in salt water in order to meet the conductivity needs of the system.
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| Sparker readied to deploy |
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System Operation
The sparker system (operated at 50-4000Hz); generally yields greater penetration than the boomer or chirp systems, with resolution on the order of a few meters. Sparker systems have a simple design and are versatile in that the resolution and penetration can be varied by changing the capacitance and/or the voltage of the system. It is cost effective to operate and has a high energy output. However, the long generated pulse length, limited directivity and repeatability, and creation of a bubble pulse limit its efficacy in many settings. It requires a high-voltage power supply on board the ship to generate the electrical energy imparted to the point electrodes. It is easily deployed off the stern, or may be towed along-side the ship. Currently, it is not used widely because of the high maintenance (the system must be pulled periodically to trim or replace the electrodes) and limitations of fresh and brackish water environments (the electrodes must discharge into a conducting fluid, i.e. salt water).
System Usage
The sparker works well in continental shelf regions where hard sand and semi-consolidated sediments are common bottom types. It also can be used in deeper-water environments.
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| Sparker profile collected off Washington Shelf. Vertical scale is sec. two-way travel time. Channels are cut into surrounding sediments (Foster et al., 2000). |
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| Sparker profile collected offshore southern Long Island, N.Y. Vertical scale is sec. two-way travel time. Channels, filled with muddy sediments are cut into more sandy sedimentary layers (Foster et al, 1999). |
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References
Foster, D.S., McKinney, B.A., and Schwab, W.C., 1999, Stratigraphic Framework Maps of the Nearshore Area of Southern Long Island from Fire Island to Montauk Point, New York: U.S. Geological Survey Open File Report 99-559.
Foster, D.S., P. A. McCrory, W. W. Danforth, and T. F. O'Brien, 2000, Archive of Boomer/Sparker Data Collected During USGS Cruise MCAR 98008 (M3-98-WO)
Washington Shelf, 24 June - 5 July, 1998, U.S.G.S. Open File Report 99-592, 3 CD-ROM’s.
Trabant, P.K., 1984, Applied High-Resolution Geophysical Methods: Boston, Ma., International Human Resources Development Corporation, p.103.
