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. For more information about the trackline naming convention used, refer to the metadata.

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.

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 displays acquisition geometries for this field activity. For more information about the acquisition geometry, refer to the science logbook and handwritten FACS logs. Table 1 is a summary of acquisition parameters. See the digital FACS equipment log for details about the acquisition equipment used. Table 2 lists trackline statistics.

The unprocessed seismic data are stored in SEG-Y format (Barry and others, 1975). For a detailed description of the data format, refer to the SEG-Y Format page. See the How To Download SEG-Y Data page for download instructions. The printable profiles provided here are GIF images that were filtered and gained using Seismic Unix software. Refer to the Software page for details about the processing and examples of the processing scripts. 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. Caution–other browsers may result in spurious or no information given in the status window. The printable profile images and interactive profiles can be viewed from the Profiles page or from links on the trackline maps.

A summary of the navigation system used can be found in table 1, and a more detailed description is given in the digital FACS equipment log. To view the trackline maps and navigation files, and for more information about these items, see the Navigation page.

The original trace files for lines 04b04, 04b10, 04b16, 04b20, and 04b27 were divided into two trace files each (e.g., 04b04 became 04b04a and 04b04b) because the original total number of traces exceeded the maximum allowed by the processing software. No digital data were collected for line 04b29. Navigation is missing for shots 15,896-16,014 of line 04b11, the first 159 shots of line 04b16a, and the first 838 shots of line 04b22. On the trackline maps, the location of missing navigation data within a line is inferred by linear interpolation of first and last known data points. All data were collected from UTM Zone 17; however, the navigation equipment was incorrectly set to UTM Zone 18 for lines 04b01-04b19 during data collection. Consequently, each data set was processed with respect to the UTM reference zone it was created in.