In June of 2011, the U.S. Geological Survey conducted a geophysical survey offshore of the Chandeleur Islands, LA to investigate the geologic controls on barrier island framework. This report serves as an archive of unprocessed digital chirp subbottom data, trackline maps, navigation files, GIS information, and formal FGDC metadata. Gained digital images of the seismic profiles are also provided. The archived trace data are in standard Society of Exploration Geophysicists (SEG) SEG Y revision 0 format (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 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>).
Purpose:
To archive all digital chirp subbottom profile data and associated files collected during cruise 11BIM01.
Supplemental_Information:
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, 11BIM01 tells us the data were collected in 2011 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 subbottom 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, c for 424 chirp), '##' 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.
All Chirp systems use a signal of continuously varying frequency; the system used during this survey produces high-resolution, shallow-penetration (typically less than 50-ms) profile images of sub-seafloor stratrigraphy. The towfish contains a transducer that transmits and receives acoustic energy and is typically towed 1 - 2 m below the sea surface. As transmitted acoustic energy intersects density boundaries, such as the seafloor or sub-surface sediment layers, some energy is reflected back toward the transducer, received, and recorded by a PC-based seismic acquisition system. This process is repeated at regular time intervals (for example, 0.125 s) and returned energy is recorded for a specific duration (for example, 50 ms). In this way, a two-dimensional (2-D) vertical image of the shallow geologic structure beneath the towfish is produced.
The seismic source utilized during 11BIM01 consisted of an EdgeTech SB-424 towfish running DISCOVER v. 3.51 acquisition software and towed about 2 m behind the GPS antenna. The data were acquired using a frequency sweep that varied between 4 - 24 kHz; 4 - 20 kHz and 4 - 16 kHz, a 43 kHz sample frequency, and approximately 75 ms record length. Based on survey speeds of 3.5 knots, the shot spacing was about 0.450 m.
The binary portion of the unprocessed seismic data are stored in SEG Y rev. 0 (Barry and others, 1975), IBM float format, which is a standard digital format that can be read and manipulated by most seismic processing software packages; the first 3,200 bytes of the file header are in ASCII format instead of EBCDIC format. The SEG Y formatted trace files have a .sgy extension. The SEG Y files may be downloaded and processed with commercial or public domain software such as Seismic Unix (SU) (Cohen and Stockwell, 2010). 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 1,000 shots, and produce a printable, gained GIF image of each profile. The printable profiles provided here are GIF images that were gained using SU software. Refer to the Software page of this report for links to example SU processing scripts and USGS software for viewing the SEG Y files (Zihlman, 1992).
Time_Period_of_Content:
Time_Period_Information:
Range_of_Dates/Times:
Beginning_Date: 20110603
Ending_Date: 20110613
Currentness_Reference: Data collection interval
Status:
Progress: Complete
Maintenance_and_Update_Frequency: None planned
Spatial_Domain:
Bounding_Coordinates:
West_Bounding_Coordinate: -88.920242
East_Bounding_Coordinate: -88.788672
North_Bounding_Coordinate: 30.101264
South_Bounding_Coordinate: 29.871811
Keywords:
Theme:
Theme_Keyword_Thesaurus: ISO 19115 Topic Category
Theme_Keyword: geoscientificinformation
Theme_Keyword: oceans
Theme:
Theme_Keyword_Thesaurus: None
Theme_Keyword: Geology
Theme_Keyword: Coastal information
Theme_Keyword: Marine
Theme_Keyword: Subbottom profile
Theme_Keyword: Seismic reflection
Theme_Keyword: Chirp
Theme_Keyword: Society of Exploration Geophysicists
Theme_Keyword: SEG Y
Theme_Keyword: Barrier Island Mapping
Theme_Keyword: 11BIM01
Place:
Place_Keyword_Thesaurus: Geographic Names Information System (GNIS) Content
Place_Keyword: United States of America
Place_Keyword: Louisiana
Place_Keyword: Gulf of Mexico
Place_Keyword: Chandeleur Islands
Access_Constraints: None. These data are held in the public domain.
Use_Constraints:
The U.S. Geological Survey requests to be acknowledged as originator of the data in future products or derivative research.
Figure 3. Area 1 detailed trackline map of digital chirp subbottom data collected during USGS Field Activity 11BIM01. This map was created at a scale of 1:31,865.
Figure 4. Area 2 detailed trackline map of digital chirp subbottom data collected during USGS Field Activity 11BIM01. This map was created at a scale of 1:29,145.
Figure 5. Area 3 detailed trackline map of digital chirp subbottom data collected during USGS Field Activity 11BIM01. This map was created at a scale of 1:41,370.
Figure 6. Area 4 detailed trackline map of digital chirp subbottom data collected during USGS Field Activity 11BIM01. This map was created at a scale of 1:30,000.
Figure 7. Area 5 detailed trackline map of digital chirp subbottom data collected during USGS Field Activity 11BIM01. This map was created at a scale of 1:39,700.
Figure 8. Area 6 detailed trackline map of digital chirp subbottom data collected during USGS Field Activity 11BIM01. This map was created at a scale of 1:50,200.
Directory containing printable images of all subbottom profiles.
Browse_Graphic_File_Type: GIF
Data_Set_Credit:
Funding and (or) support for this study was provided by the USGS Coastal and Marine Geology Program. We thank R/V Survey Cat captain Nancy DeWitt (SPCMSC) for her assistance in data collection and Will Pfeiffer and Noreen Buster for their assistance with swath data processing. This document was improved by the reviews Paul Knorr and Kyle Kelso of the USGS - St. Petersburg, FL. Disc Image Credit: Schmaltz, Jeff, MODIS Rapid Response Team at the NASA Goddard Space Flight Center, 2004, UnitedStates.A2004106.1855.500m.jpg. Also available on-line at <http://eoimages.gsfc.nasa.gov/ve/6886/UnitedStates.A2004106.1855.500m.jpg>
Cross_Reference:
Citation_Information:
Originator: Cohen, J.K., and Stockwell, J.W., Jr., CWP/SU
Publication_Date: 2010
Title:
Seismic Unix Release 41: A free package for seismic research and processing, Center for Wave Phenomena, Colorado School of Mines
The validity or accuracy of marine subbottom profiles is highly qualitative and depends on equipment and operating condition variables. Visual inspection of the images rendered from the data did not show any major anomalies.
Logical_Consistency_Report:
This dataset is from one field activity with consistent instrument calibrations.
Completeness_Report:
These data are collected along tracklines (2-D) and are therefore inherently incomplete. Geologic details between lines must be inferred. No data were collected for lines 11c49, 11c74, 11c75, 11c76, and 11c131. While attempting to collect data for line 11c49, it was determined that the chirp cable was malfunctioning. A temporary splint was placed on the cable for line 11c50; however, a generator failure also occurred at this time resulting in the system being restarted for the subsequent line. Line 11c51 lost navigation data between shots 3032-3510. No navigation fixes were recoreded for line 11c128_b from shots 3281-3523, this too was most likely caused by a temporary loss of power (please see the operation log for additional information).
Positional_Accuracy:
Horizontal_Positional_Accuracy:
Horizontal_Positional_Accuracy_Report:
As the subbottom data were acquired, the position of the vessel was continuously determined by a CodaOctopus F190 DGPS and subsequently sent to Hypack 2010 navigation software to ensure a consistent grid spacing during data collection. Positions were recorded and written to the trace headers in latitude and longitude coordinates about every 1 s using navigation from the CodaOctopus F190 receiver with OmniSTAR High Performance (HP) correction (accurate to within 20 cm). The approximately 2-m offset between the chirp shot and ship's GPS was not accounted for during acquisition nor have the ASCII navigation files and trackline maps been corrected to reflect the offset.
Vertical_Positional_Accuracy:
Vertical_Positional_Accuracy_Report:
These data are not to be used for bathymetry. Two-way travel (TWT) times shown on the printable profile images are relative to the chirp towfish position, not to the sea surface.
Lineage:
Process_Step:
Process_Description:
Chirp processing: The acquisition system was set to only record up to 200 MB of data for each file. Any line exceeding this limitation was divided into two trace files or more (for example, 11c10 and 11c10_a). The SEG Y data were processed with Seismic Unix to produce gained GIF images of the subbottom profiles included in this report. A representative chirp data processing sequence consisted of (1) stripping off navigation data for each shot and converting to SU format, (2) applying automatic gain control, (3) generating a PostScript image of the traces, and (4) converting the PostScript image to a GIF image. For additional SU processing and script details, please refer to <https://pubs.usgs.gov/ds/772/software/su/readme.txt>.
Navigation processing: Shotpoint navigation, start of line, and 1,000-shot-interval location files were extracted using Seismic Unix software and output as ASCII text files; they were then processed with PROJ.4.7.0 (<http://trac.osgeo.org/proj/>) to generate UTM coordinates (WGS84, Zone 16, meters) from latitude and longitude coordinates. Text files for each seismic line were concatenated into comma-delimited text files (for use with ESRI software); one containing unique shotpoint positions (11bim01.txt), another containing the 1,000-shot-interval locations (s11bim01.txt) and the last containing start of line locations (11bim01_s), which can be viewed within the nav folder.
All concatenated, comma-delimited text files were imported into ArcGIS and saved as either a point or polyline file in the ESRI shapefile format.
Trackline map creation: The trackline maps was created using ESRI ArcGIS 10 software. The processed navigation file, 11bim01.txt, was imported into ArcMap 10 and processed using the Points to Lines ArcScript to create a line shapefile of the cruise tracklines (11bim01_trkln). The 1,000-shot-interval file, s11bim01.txt, and the start of line file, 11bim01_s.txt, were imported into ArcMap as point shapefiles 11bim01_shots and 11bim01_sol. Please refer to the shapefile metadata included in the ArcGIS map document located under the Software section of this archive for additional details. All maps were exported to Adobe Illustrator v. 14 for further editing then later converted into JPEG format by Adobe Dreamweaver v. 10 Build 4117. The maps are unprojected (geographic coordinates, WGS84). The USGS is the originator of all layers used. Please see the ArcGIS readme file for detailed information about the GIS files used in this report.
Data Series preparation: In addition to the process steps described above, the following steps were taken to produce this Data Series report: the handwritten cruise logs were scanned and saved as a PDF file, digital logs were created by A. Forde using the cruise logs and personal accounts of the crew members and saved as PDF files, and an HTML-based format was used to present the various parts of this archive.
Horizontal X and Y locations (latitude and longitude and Zone 16 UTM coordinates) for each shot are provided as ASCII text files, along with the date and time (UTC) the shot was recorded.
Sequential unique whole numbers that are automatically generated.
Attribute:
Attribute_Label: Shape*
Attribute_Definition: Feature geometry.
Attribute_Definition_Source: ESRI
Attribute_Domain_Values:
Unrepresentable_Domain: Coordinates defining the features.
Attribute:
Attribute_Label: UTMX
Attribute_Definition: UTM-X coordinate (Zone 16)
Attribute_Definition_Source: Universal Transverse Mercator Geographic Coordinate System
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 315130
Range_Domain_Maximum: 326898
Attribute_Units_of_Measure: meters
Attribute:
Attribute_Label: UTMY
Attribute_Definition: UTM-Y coordinate (Zone 16)
Attribute_Definition_Source: Universal Transverse Mercator Geographic Coordinate System
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 3308709
Range_Domain_Maximum: 3331466
Attribute_Units_of_Measure: meters
Attribute:
Attribute_Label: Line
Attribute_Definition: Trackline number
Attribute_Definition_Source: U.S. Geological Survey
Attribute_Domain_Values:
Unrepresentable_Domain:
The naming convention used for each subbottom 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, c for Chirp), '##' 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.
Attribute:
Attribute_Label: Shot
Attribute_Definition: Shotpoint number
Attribute_Definition_Source: U.S. Geological Survey
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 1
Range_Domain_Maximum: 11354
Attribute:
Attribute_Label: Lon
Attribute_Definition: Longitude (decimal degrees)
Attribute_Definition_Source: World Geodetic System 1984 Geographic Coordinate System
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: -88.917917
Range_Domain_Maximum: -88.793833
Attribute_Units_of_Measure: decimal degrees
Attribute:
Attribute_Label: Lat
Attribute_Definition: Latitude (decimal degrees)
Attribute_Definition_Source: World Geodetic System 1984 Geographic Coordinate System
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 29.896167
Range_Domain_Maximum: 30.101153
Attribute_Units_of_Measure: decimal degrees
Attribute:
Attribute_Label: YEAR
Attribute_Definition: Year
Attribute_Definition_Source: U.S. Geological Survey
Attribute_Domain_Values:
Range_Domain:
Range_Domain_Minimum: 2011
Range_Domain_Maximum: 2011
Attribute:
Attribute_Label: DOY:HR:MIN:SEC
Attribute_Definition: Day of year:hour:minute:second
Attribute_Definition_Source: U.S. Geological Survey
Attribute_Domain_Values:
Unrepresentable_Domain: Day of year, hour, minute and second of data acquisition
Overview_Description:
Entity_and_Attribute_Overview:
Binary data file: Trace data are available as binary files in SEG Y format. These files have a .sgy extension and range in size from 6.1 to 200.3 MB. These data can be found by going to <http://cmgds.marine.usgs.gov>.
Entity_and_Attribute_Overview:
Graphic image file: Printable versions of the subbottom profiles are available as GIF images, links to these images can be found on the Profiles page of this report or by going to <https://pubs.usgs.gov/ds/772/profiles/printable/>.
Entity_and_Attribute_Overview:
Navigation file: Navigation files are available as ASCII text files. Provided are raw (unprocessed) shotpoint navigation files (11c**.txt), processed shotpoint navigation (11bim01.txt), processed 1,000-shot-interval location (s11bim01.txt), and a start of line file (11bim01_s.txt). Fields/Attributes [FID, Shape] marked above with an asterisk (*) were created by ESRI ArcGIS and are used exclusively by the shapefiles created from the three aforementioned .txt files; these fields are not included in the original navigation files. All remaining attributes listed above in the Entity_and_Attribute_Information: section that do not have an accompanying asterisk are found in 11bim01.txt, s11bim01.txt, and11bim01_s.txt. Raw and processed navigation data files can be found by going to <https://pubs.usgs.gov/ds/772/nav/>.
Entity_and_Attribute_Overview:
GIS file: The GIS project used to create the trackline maps is provided as a .zip file composed of ESRI map documents, shapefiles, and metadata.
Entity_and_Attribute_Detail_Citation: Information is derived from SEG Y headers.
All of this report is available online. The SEG Y files are downloadable from the Coastal and Marine Geoscience Data System (<http://cmgds.marine.usgs.gov>).
Resource_Description: U.S. Geological Survey Data Series 772
Distribution_Liability:
This DVD publication was prepared by an agency of the United States Government. Although these data have been processed successfully on a computer system at the U.S. Geological Survey, no warranty expressed or implied is made regarding the display or utility of the data on any other system, nor shall the act of distribution imply any such warranty. The U.S. Geological Survey shall not be held liable for improper or incorrect use of the data described and (or) contained herein. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof.
Standard_Order_Process:
Digital_Form:
Digital_Transfer_Information:
Format_Name: SEG Y rev. 0
Format_Information_Content:
The SEG Y rev. 0 format (Barry and others, 1975) presented here consists of the following: a 3,600-byte reel identification header, with the first 3,200 bytes consisting of an ASCII header block followed by a 400-byte binary header block, both of which include information specific to line and reel number; a trace data block that follows the reel identification header, with the first 240 bytes of each trace block consisting of the binary trace identification header; and seismic data samples that follow the trace identification header.
File_Decompression_Technique: None
Transfer_Size: 29.41 GB
Digital_Transfer_Option:
Offline_Option:
Offline_Media: DVD
Recording_Format: ISO 9660
Compatibility_Information: Unix, Linux, DOS, Macintosh
Digital_Form:
Digital_Transfer_Information:
Format_Name: map document, shapefile, metadata
Format_Information_Content:
The GIS project used to create the trackline maps is composed of map documents, shapefiles, and metadata. Map documents were created with ESRI ArcGIS 10 software. The shapefiles provided may also be viewed using other versions of ESRI desktop software including their free software or ArcGIS Explorer (<http://www.esri.com/software/arcgis/explorer/>).
Fees: None, if obtained online; otherwise, prices vary.
Ordering_Instructions:
Publications are available from USGS Information Services, Box 25286, Federal Center, Denver, CO 80225-0046 (telephone: 1-888-ASK-USGS, e-mail: infoservices@usgs.gov).
Technical_Prerequisites:
Use of SEG Y data requires specialized seismic processing software, such as public domain software Seismic Unix (<http://www.cwp.mines.edu/cwpcodes/>).
