U.S. Geological Survey Data Series 445
The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG-Y format (Barry and others, 1975) and may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU). Example SU processing scripts and USGS software for viewing the SEG-Y files (Zihlman, 1992) are also provided.
The boomer plate is an acoustic energy source that consists of capacitors charged to a high voltage and discharged through a transducer in the water. The transducer is towed on a sled at the lake surface and when discharged emits a short acoustic pulse, or shot, that propagates through the water, sediment column, or rock beneath. The acoustic energy is reflected at density boundaries (such as the lake bottom, sediment, or rock layers beneath the lake bottom), detected by the receiver, and recorded by a PC-based seismic acquisition system. This process is repeated at timed intervals (for example, 0.5 s) and recorded for specific intervals of time (for example, 100 ms). In this way, a 2-D vertical image of the shallow geologic structure beneath the ship track is produced.
The power supply was a C-Products C-Boom Low Voltage Boomer (LVB) System, which provided 100 Joules per shot. Reflected energy was received by a 1.8-m-long Teledyne Instruments SDS-55 hydrophone array streamer and recorded by Triton Imaging, Inc. SB-Logger (FSSB) v. 1.6.500.90 and Chesapeake Technology, Inc. (CTI) SonarWiz.SBP acquisition software. The streamer contained 10 hydrophones evenly spaced every 0.2 m. All phones were turned on during data acquisition. Please refer to figure 1 included with this archive (Data Series 445) for a diagram of the acquisition geometry. The sample frequency of the data was 24 kHz, and the record length was 100 ms. Based on survey speeds of approximately 2.5 knots and a shot rate of every 0.500 s, the shot spacing was about 0.6425 m.
The unprocessed seismic data are stored in SEG-Y, integer, IBM format, which is a standard digital format that can be read and manipulated by most seismic processing software packages (Barry and others, 1975). The SEG-Y formatted trace files have a .sgy extension. Also provided are example Seismic Unix scripts that allow the user to strip off navigation fixes from the SEG-Y headers, along with a fix for every 500 shots, and produce a filtered and gained GIF image of each profile.
The printable profiles provided here are GIF images that were filtered and gained using Seismic Unix software. The processed SEG-Y data were exported to CTI SonarWeb software to produce geospatial versions of the profiles, which allow the user to obtain a geographic location and depth from the profile for a cursor position. This information is displayed in the status bar of the browser. NOTE: The only supported Web browsers that properly display all features of the geospatial profiles are Internet Explorer 6 or greater for Windows and Firefox 1.5 or greater for all platforms. For all browsers, the status bar and JavaScript must be enabled. Firefox also requires "Change status bar text" to be checked under Advanced JavaScript Options. If using Internet Explorer 7, you must disable Active Content/Active X controls. To do this, right click the information bar (found at the top of the page), left click "Allow Blocked Content...", and then select "Yes". Use of other browsers may result in spurious or no information given in the status window. Firefox may be downloaded at http://www.mozilla.org/products/firefox.
All the processed SEG-Y data were then exported to CTI SonarWeb software to produce a geospatial version of each profile that allows the user to obtain a geographic location and depth for a cursor position on the profile. Refer to the Supplemental Information section above for details on how to use the geospatial profiles.
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U.S. Geological Survey
URL: pubsdata.usgs.gov/pubs/ds/445/html/metadata.html
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