Archive of Digital Boomer Seismic Reflection Data Collected Offshore Northeast Florida during USGS Cruise 02FGS01 in October 2002
In October of 2002, the U.S. Geological Survey (USGS), in cooperation with the Florida Geological Survey (FGS), conducted a geophysical survey of the Atlantic Ocean offshore Nassau and Duval Counties in northeast Florida, from the northern tip of Amelia Island to Jacksonville Beach. This report serves as an archive of unprocessed digital boomer seismic reflection data, trackline maps, navigation files, GIS files, and formal Federal Geographic Data Committee (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 Y format (rev. 0) (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 USGS St. Petersburg Coastal & Marine Science Center (SPCMSC) in Florida assigns a unique identifier to each cruise or field activity. For example, 02FGS01 tells us the data were collected in 2002 as part of cooperative work with the Florida Geological Survey 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 or 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 one-letter abbreviation for the equipment type (for example, b for boomer), '##' is a two-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 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 the receiver, 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 image of the shallow geologic structure beneath the ship track is produced.
An EG&G GeoPulse power supply provided 175 joules per shot. Reflected energy was received by an Innovative Transducers, Inc. (ITI) ST-5 10-channel streamer and recorded by Triton Elics International, Inc. (TEI) Delph Seismic acquisition software. The streamer contains 10 hydrophones evenly spaced every 2 feet. However, only phones 3-8 were used. The streamer was positioned parallel to the boomer sled and laterally separated from it by 7 meters. Please refer to figure 1 (
http://pubs.usgs.gov/ds/653/html/fig1.html) for a diagram of the acquisition geometry. The sample frequency of the data is 24 kilohertz, the record length is 100-120 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 is 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), with the exception of the first 3,200 bytes of the card image header, which is stored in comma delimited 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 only needed 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 SEG Y files (Zihlman, 1992).
