In September and October of 2003, the U.S. Geological Survey (USGS), in cooperation with the Florida Geological Survey, conducted geophysical surveys of the Atlantic Ocean offshore northeast Florida from St. Augustine, Florida, to the Florida-Georgia border. This report serves as an archive of unprocessed digital boomer subbottom profile data, trackline maps, navigation files, Geographic Information System (GIS) files, Field Activity Collection System (FACS) logs, and formal Federal Geographic Data Committee (FGDC) metadata. Filtered and gained (a relative increase in signal amplitude) digital images of the seismic profiles are also provided.
To archive all digital boomer subbottom profile data collected during cruises 03FGS01 and 03FGS02 and associated files.
The USGS St. Petersburg Coastal and Marine Science Center (SPCMSC) in Florida assigns a unique identifier to each cruise or field activity. For example, 03FGS01 tells us the data were collected in 2003 as part of cooperative work with the Florida Geological Survey (FGS) and that 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' 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 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 floating on the water 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 seafloor, sediment, or rock layers beneath the seafloor), detected by the hydrophones, and recorded by a PC-based seismic acquisition system. This process is repeated at timed intervals (for example, 0.5 seconds) and recorded for specific intervals of time (for example, 100 milliseconds). In this way, a two-dimensional (2-D) vertical profile of the shallow geologic structure beneath the ship track is produced.
For both cruises, a C-Products C-Boom power supply provided 100 -110 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 10 hydrophones evenly spaced every 12 inches. Refer to the handwritten FACS operation log included with this archive for diagrams and descriptions of acquisition geometry, which varied throughout the cruises. The sample frequency of the data is 20-24 kilohertz, the record length is 100 milliseconds, and the shot rate was every 0.5 seconds. Shot spacing was approximately every 1 meter.
The binary portion of 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 all seismic processing software packages (Barry and others, 1975), with the exception of the first 3,200 bytes of the card image header, which are stored in ASCII format instead of the standard EBCDIC format. 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 needed only to process or display the data with TEI Delph Seismic software. The SEG Y files may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU) (Cohen and Stockwell, 2005). Also provided are example SU 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 printable, gained GIF image of each profile. The printable profiles provided here are GIF images that were filtered and gained using SU software. Refer to the Software page for links to example SU processing scripts and USGS software for viewing the SEGY files (Zihlman, 1992).
The SEG Y files are available on the DVD version of this report or on the Web, downloadable via the USGS Coastal and Marine Geoscience Data System (
http://cmgds.marine.usgs.gov). The data is also available for viewing using GeoMapApp (
http://www.geomapapp.org) and Virtual Ocean (
http://www.virtualocean.org) multi-platform open source software.
