In July of 2005, the U.S. Geological Survey (USGS), in cooperation with the Florida Geological Survey (FGS), conducted a geophysical survey of the Atlantic Ocean offshore of Florida's east coast from Flagler Beach to Daytona Beach. This report serves as an archive of unprocessed digital boomer subbottom data, trackline maps, navigation files, GIS information, and formal FGDC metadata. Filtered and gained digital images of the seismic profiles are also provided. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG Y revision 0 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.
These data are also available for viewing using GeoMapApp (<
http://www.geomapapp.org/>) and Virtual Ocean (<
http://www.virtualocean.org/>) multi-platform open source software. In addition, the SEG Y files can also be downloaded from the USGS Coastal and Marine Geoscience Data System (<
http://cmgds.marine.usgs.gov>)
The data archived here were collected under a cooperative agreement between the Florida Geological Survey and the USGS.
The USGS Saint Petersburg Coastal and Marine Science Center (SPCMSC) - St. Petersburg, FL, assigns a unique identifier to each cruise or field activity. For example, 05FGS01 tells us the data were collected in 2005 for the Florida Geological Survey (FGS) cooperative agreement 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 cruise ID. The naming convention used for each subbottom line is as follows: yye##a, where 'yy' are the last two digits of the year in which the data were collected, 'e' is a 1-letter abbreviation for the equipment type (for example, b for boomer), '##' 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 subbottom processing system consists of an acoustic energy source that is made up of capacitors charged to a high voltage and discharged through a transducer in the water. The transducer is towed on a sled floating on the water surface and when discharged emits a short acoustic pulse, or shot, that propagates through the water column and shallow stratigraphy below. The acoustic energy is reflected at density boundaries (such as the seafloor or sediment layers beneath the seafloor), detected by the receiver (hydrophone streamer), 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.An Applied Acoustic Engineering CSP 300 provided 100 Joules of energy per shot. Reflected energy was received by a Benthos Mesh 15-m-long streamer and recorded by Triton Elics International, Inc. (TEI) Delph Seismic v. 2.7 acquisition software. The streamer contains 10 hydrophones evenly spaced every 0.305 m. The streamer was positioned directly behind the research vessel (parallel to the boomer sled), with a lateral separation of approximately 7 m. Refer to figure 1 included with this archive for a diagram of the acquisition geometry. The sample frequency of the data was 24 kHz, and record length was 100 ms. The shot spacing was highly variable; however, based on survey speeds of 3 knots and a shot rate of every 0.5 s, shot spacing was about 0.514 m.The unprocessed seismic data are stored in SEG Y rev. 0, 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.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 Chesapeake Technology, Inc. (CTI) SonarWeb software to produce a geospatially interactive version of the profile that allows the user to obtain a geographic location and depth from the profile for a given cursor position on the profile; this information is displayed in the status bar of the browser. Please note that clicking on the profile image switches it to "Expanded View" (a compressed image of the entire line) and cursor tracking is not available in this mode. 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 3.6 or greater for all platforms. PC Instructions: For both browsers, the status bar and JavaScript must be enabled. If using Internet Explorer 6 or greater, you must disable scripts/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>. Macintosh Instructions (Firefox Only): From the Menu Bar go to Preferences > Content (tab) > Checkmark "Enable JavaScript"> Click Advanced... > Checkmark "Change Status Bar Text". Verify that the status bar is enabled by selecting View from the Menu Bar and looking for a checkmark next to "Status Bar"; if the check is missing, highlight and select the text to activate the bar.
