 |
|
|
||||
| 95LCA03 and 96LCA02 Data Archive |
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 sea surface and when discharged emits a short acoustic pulse, or shot, that propagates through the water and sediment column. The acoustic energy is reflected at density boundaries (such as the seafloor or sediment layers beneath the seafloor), detected by a receiver, and recorded by a PC-based seismic acquisition system. This process is repeated at timed intervals (e.g., 0.5 s) and recorded for specific intervals of time (e.g., 100 ms). In this way, a two-dimensional vertical image of the shallow geologic structure beneath the ship track is produced.
For both field activities, an ORE GeoPulse power supply provided 105 joules per shot. Reflected energy was received by an Innovative Transducers, Inc. (ITI) ST-5 streamer and recorded by Delph acquisition software. The streamer contains ten hydrophones evenly spaced over a length of 6 m (every 2 feet). Acquisition geometry and phones used varied throughout the field activites. Refer to figure 1 and the operations logbooks included with this archive (Data Series 217) for more detail. The sample frequency of the data is 12 kHz. Record length is 100 ms for 95LCA03 and 125 ms for 96LCA02. The shot rate for both field activities was every 0.5 s, and shot spacing is approximately every 2 m.
The unprocessed seismic data are stored in SEG-Y, integer, Motorola 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 .TRA extension. Additional recording parameters for each trace file can also be found in the .PAR file associated with each .TRA file. However, the .PAR and .PLN files included here are only needed to process or display the data with Delph Seismic software. 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 then exported to Chesapeake Technology, Inc. (CTI) SonarWeb software to produce an interactive version of the profile that allows the user to obtain a geographic location and depth from the profile for a curser position. This information is displayed in the status bar of the browser. Warning! The only supported web browsers that properly display all features of the interactive profiles are Internet Explorer 6 for Windows and Firefox 1.5 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. Caution–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.
Although all data and software published on this disc have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and related materials and (or) the functioning of the software. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data, software, or related materials.
U.S. Department of the Interior |
U.S. Geological Survey
URL:
Page Contact Information: Publishing Services
Page Last Modified: