U.S. Geological Survey Data Series 428
1U.S. Geological Survey, St. Petersburg, FL 33701.
2Jacobs Technology Inc., St. Petersburg, FL 33701.
U.S. Department of the Interior
U.S. Geological Survey
Florida Integrated Science Center - St. Petersburg
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In April and July of 1981, the U.S. Geological Survey (USGS) conducted geophysical surveys to investigate the shallow geologic framework of the Alabama-Mississippi-Louisiana Shelf in the northern
A standardized naming convention was established to allow for better management of scanned trackline images within the MASH data rescue project. Each cruise received a unique field activity identification (ID) based on the year the data were collected, the first two digits of the survey vessel name, and the number of cruises made (to date) by that vessel that year (for example, 81CA1 represents the first cruise made by the R/V Carancahua in 1981.) The new field activity IDs 81CA1 and 81GY6 presented in this report were originally referred to as Carancahua 81-1 and Gyre 81-6 at the USGS in St. Petersburg, FL, and 81021, and 81007, and 81008 at the USGS in Woods Hole, MA. A table showing the naming convention lineage for cruise IDs in the MASH data rescue series is included as a Portable Document Format (PDF) file. This report serves as an archive of high-resolution scanned Tagged Image File Format (TIFF) and Graphics Interchange Format (GIF) images of the original boomer and minisparker paper records, navigation files, trackline maps, Geographic Information System (GIS) files, cruise logs, and formal Federal Geographic Data Committee (FGDC) metadata for cruises 81CA1 and 81GY6.
The minisparker from the 81GY6 survey was a caged acoustic energy source generated by a high voltage electrical discharge between multiple electrodes in saltwater. The minisparker cage is usually towed 5 to 10 meters (m) behind the survey vessel and just beneath the sea surface. The heat generated by the electrical discharge rapidly vaporizes the water, resulting in a small explosion which propagates through the water and sediment column. The boomer system from the 81CA1 survey uses an acoustic energy source called a plate, which consists of capacitors charged to a high-voltage and discharged through a transducer in the water. The source is towed on a sled, at sea level and when discharged emits a short acoustic pulse, or shot, which propagates through the water and sediment column.
The acoustic energy discharged by both the boomer and the minisparker systems was reflected at density boundaries (such as the seafloor or sediment layers beneath the seafloor), detected by the hydrophone receiver, and the amplitude of the reflected energy recorded by an Edward P. Curley Lab (EPC) thermal plotter. This process was repeated at timed intervals (for example, 0.5 seconds (s)) and recorded for specific intervals of time (for example, 100 milliseconds (ms)). The timed intervals are also referred to as the shot interval or fire rate. On both minisparker and boomer analog records the recorded interval is referred to as the sweep, which is the amount of time the recorder stylus takes to travel from the top of the record to the bottom of the record, therefore recording the amplitude of the reflected energy of a single shot. In this way consecutive recorded shots produce a two-dimensional (2-D) vertical image of the shallow geologic structure beneath the ship track.
Much of the geophysical data collected by the USGS prior to the late 1990s was recorded in analog format and stored as paper copies. Scientists onboard made hand-written annotations onto these records to note latitude and longitude, time, line number, course heading, and geographic points of reference. Each paper roll typically contained numerous survey lines and could reach more than 90 feet (ft) in length. All rolls are stored at the USGS Florida Integrated Science Center (FISC)-St. Petersburg, FL. To preserve the integrity of these records and improve accessibility, analog holdings were converted to digital files.
Paper records were scanned at 200 dots per inch (dpi) using an IDEAL/Contex Crystal TX 40-inch (1394) large-format scanner and converted to TIFF format using WIDEimage software (version 2.8.1) in the black and white adaptive mode. Whole roll TIFF images of multiple lines were manually cropped into individual survey lines using WIDEimage. Line images longer than 30,000 pixels were separated into smaller segments for editing with Adobe Photoshop Creative Suite 2 (CS2), where a metadata header file was appended to each survey line or line segment. Images of individual survey lines were named by combining the MASH cruise ID with the survey line (or trackline) number using an underscore, for example, 81CA1_2. If survey lines were longer than 30,000 pixels, the split segments were identified by appending a letter in alphabetical order to the line name, for example, 81CA1_5(a). The metadata header file appended to each line or line segment was created in Adobe Illustrator CS2. These header-merged images were then converted to grayscale, flattened, and saved as TIFFs with lossless (LZW) image compression. To facilitate easy viewing or printing of the scanned profiles on any computing platform using Web browser software, TIFF images were scaled to 25% (with constrained proportions and bicubic resampling) in Photoshop and saved as GIF images.
The uncompressed TIFF image files of the whole survey line or line segment (if greater than 30,000 pixels) are stored in the ORIGINALS folder as .tif files. Compressed line images with headers attached are stored in the PRINTABLE folder in both TIFF and GIF formats. Header files, in Adobe Illustrator format, can be found in the HEADERS folder.
Trackline maps and navigation files can be accessed from the Navigation page. The navigation fixes from the LOng Range Navigation (LORAN)-C system are numbered by trackline and correspond to identical hand-numbered vertical event marks on the scanned profiles. Scanned images of the available handwritten cruise logbooks are provided as PDF files. Refer to the Acronyms page for expansions of acronyms and abbreviations used in this report. Formal FGDC metadata are also included and can be viewed on the Metadata page. The GIS page contains links to the documents and shapefiles used to create the trackline maps provided in this report.
Site locations for selected CI-87 (Chandeleur Islands, 1987) vibracores are included on the survey and trackline maps. More information on these cores, including scanned PDF versions of the description sheets, text files of the interpreted classification profiles, and formal FGDC metadata can be found in the CI-87 vibracores folder.
This disc contains a readme (26-KB .doc file) document, which provides a brief description of the report; GIS files, and all the Hypertext Markup Language (HTML) files, folders, and images used to produce the Web pages included in this report. The Contents page is a diagram of the location of all files and folders contained on this disc and provides links to these files and folders.
To access the information contained on this disc, use a Web browser to open the file index.html. This report is divided into seven sections: Acronyms, Contents, Navigation Data and Maps, Seismic Profiles, Field Activity Logs, Metadata, and GIS. Links at the top and bottom of each page provide access to these sections. This report contains links to the USGS and collaborators or other resources that are accessible only if access to the Internet is available while viewing these documents.
Funding and (or) support for this study were provided by the USGS Coastal and Marine Geology Program. Funding for the data rescue effort was also provided by the Minerals Management Service (MMS). Original survey personnel included Ron Miller, Jack Kindinger, Arnold Buoma, Neal Lillard, Bob Woolsey, Dan Cooper, Ron Boyd, Linda Massingill, Ronnie Wells, Betty Reed, John West, Rusty Tirey, Bob Bowles, Barry Irwin, Jim Dodd, Dave Mason, Ken Parolski, Dave Nichols, Larry Handley, Chuck Stelting, and Doug Owens. This document was improved by the reviews of Chandra Dreher (Jacobs Technology Inc.) and Shawn Dadisman (USGS) at the FISC-St. Petersburg, FL.
Any additional data or information relevant to the 81CA1 or 81GY6 surveys would be appreciated. Please refer to the Metadata page for contact information.
Kindinger, J.L., Miller, R.J., Stelting, C.E., and Bouma, A.H., 1982, Depositional history of Louisiana-Mississippi outer continental shelf: U.S. Geological Survey USGS Open-file Report 82-1077, 59 p.