Archive of Digital Boomer Seismic Reflection Data Collected During USGS Field Activity 04SGI01 in the Withlacoochee River of West-Central Florida, March 2004

The USGS Florida Integrated Science Center (FISC) - St. Petersburg assigns a unique identifier to each cruise or field activity. For example, 04SGI01 tells us the data were collected in 2004 for the Surface Groundwater Interactions (SGI) Project and the data were collected during the first field activity for that project in that calendar year. Refer to <http://walrus.wr.usgs.gov/infobank/programs/html/definition/activity.html> for a detailed description of the method used to assign the field activity ID. The naming convention used for each seismic line is as follows: yye##a, where yy is the last two digits of the year in which the data were collected, e is a 1-letter abbreviation for the equipment type (i.e., b for boomer and c for chirp), ## is a 2-digit number representing a specific track, and a is a letter representing the section of a line if recording was prematurely terminated or rerun for quality or acquisition problems. The boomer 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 water 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 the receiver, and recorded by a PC-based seismic acquisition system. This process is repeated at timed intervals (e.g., 0.25 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. A C-Products C-Boom power supply provided 100 joules per shot. Reflected energy was received by a Benthos MESH streamer and recorded by Triton Elics International, Inc. (TEI) Delph Seismic acquisition software. The streamer contains ten hydrophones evenly spaced about every 30.5 cm (every 12 inches). The sample frequency of the data is 24 kHz. Record length for all tracklines is 100 ms, and the shot rate was every 0.25 s. Shot spacing varied and should be calculated for each line of interest. Coherent noise was detected on most of the profiles. Attempts to mitigate the noise had varying degrees of success and included frequent changes in the acquisition geometry and grounding of the power supply. The source of the noise remains uncertain, but a new generator or the engine propeller might be the origin. Figure 1 included with this archive (Data Series 119) displays acquisition geometries for this field activity. For more information about the acquisition geometry, refer to the science logbook and handwritten FACS logs also included with this archive. 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 TEI 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. Cautionother browsers may result in spurious or no information given in the status window. Firefox may be downloaded at http://www.mozilla.org/products/firefox.