Archive of Digital Boomer Sub-bottom Data Collected During USGS Field Activities 97LCA01, 97LCA02, and 97LCA03, West-Central and East Coast Florida, February through July 1997

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, 97LCA01 tells us the data were collected in 1997 for the Lakes and Coastal Aquifers (LCA) 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 cruise ID. The naming convention used for each seismic line is as follows: xx#a, where xx is an abbreviation of the survey area the data were collected in, # is a 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 sub-bottom 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 and sediment column. The acoustic energy is reflected at density boundaries (such as the seafloor or sediment layers beneath the lake bottom), 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 ORE GeoPulse power supply provided 105 Joules of energy per shot for field activity 97LCA01 and varied between 280/455 Joules for 97LCA03; 97LCA02 used a Huntec ESU-PSU power supply, which provided 480 Joules per shot. Reflected energy, for all three activities, was received by an Innovative Transducers, Inc. (ITI) ST-5 streamer and recorded by Delph Seismic or Delph Win acquisition software. The streamer contains 10 hydrophones evenly spaced every 0.610 m. Phones 4 - 8 (97LCA01); 4 - 9 (97LCA02); and 3 - 8 (97LCA03) were used for all lines, with the exception of 97LCA03, which used phones 3 - 6 on July 15. The streamer was positioned either directly behind the boomer sled, or directly behind the research vessel (parallel to the boomer sled), with a lateral separation of approximately 4 m. Refer to figure 1 included with this archive for a diagram of the acquisition geometries. The sample frequency of the data varied between 12 and 16 kHz, and record lengths between 50 and 100 ms. The shot spacing was highly variable, however, based on survey speeds of 2 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, 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 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. NOTE: Navigation data were recorded to two different sections of the SEG-Y trace headers, creating two navigation datasets. For details, see the Horizontal Positional Accuracy Report under the Data Quality Information section below.The printable profiles provided here are GIF images that were filtered and gained using Seismic Unix software.