U.S. Geological Survey Open-File Report 00-019

Gulf of Mexico GLORIA Sidescan Sonar Geologic Interpretation:
ArcView data coverages


This CD-ROM contains copies of the 250 m resolution GLORIA sidescan sonar mosaic for the Gulf of Mexico and it's geologic interpretation.  The imagery and interpretation have been archived here to preserve this legacy data set.  The data are intended to be GIS-ready in as much as the data do not require any additional cleanup, formatting, renaming of fields or other "data work" to use the data in the GIS of choice.  This project used Environmental Systems Research Institute's (ESRI) ARC/INFO and associated products.  This does not mean that the user will not wish to do additional processing, especially if they are utilizing a different GIS software package or spheroid, but that it is not necessary to do additional processing simply to utilize the data in its minimum archive format.


In March 1983, President Reagan signed a proclamation establishing an Exclusive Economic Zone (EEZ) extending 200 nautical miles from the coasts of the United States, Puerto Rico, the Northern Mariana Islands, and the U.S. territories and possessions. In 1984, the U.S. Geological Survey (USGS) began a program to map these areas of the EEZ. To accomplish the mapping of the deep water portion of these areas (depths greater than 400 m), the USGS selected the long-range sidescan sonar system GLORIA (Geological LOng-Range Inclined Asdic), owned and operated by British colleagues at the United Kingdom's Institute of Oceanographic Sciences (IOS), now the Southampton Oceanography Centre, Challenger Division. The GLORIA system was developed specifically to map the morphology and texture of seafloor features in the deep ocean (Somers, 1978).

In July 1982, prior to the EEZ declaration, the USGS conducted a GLORIA survey along the Continental Slope in the northern Gulf of Mexico.  Three additional cruises were conducted from 7 August to 22 October, 1985 as an integral part of the EEZ mapping program.  Data sets from these cruises were digitally processed (Chavez, 1986) and, for the first time, digitally mosaicked to create maps of the seafloor in the deepwater portion of the Gulf of Mexico (EEZ Scientific Staff, 1985).  A total of 16 digital mosaics of a 2 degree by 2 degree (or smaller) area with a 50 meter pixel resolution were completed for the Gulf of Mexico. These individual mosaics were later combined to produce the 250 m overview of the Gulf of Mexico available on this CD-ROM.

Creating the Interpretations

From the digital mosaics, researchers created interpretive maps.  These interpretive maps were included as part of the USGS Atlas of the U. S. Exclusive Economic Zone, Gulf of Mexico and eastern Caribbean areas (EEZ Scientific Staff, 1985).  Later, the interpretive overlays were digitized and ARC/INFO data coverages created.  The coverages were combined to create an overview image showing the geology of the Gulf of Mexico GLORIA composite mosaic that was made available on USGS DDS-15.  Unfortunately, the original ARC coverages were subsequently misplaced.

Rather than totally re-digitize the interpretation from the 16 digital mosaics, the decision was made to utilize the interpretation image found on USGS Publication DDS-15.  The unprojected image was registered to a 250 m Gulf of Mexico composite GLORIA mosaic.  The newly registered and projected interpretation was next rasterized creating a file of vector segments of the geologic boundaries.  However, due to the stepping nature of the image at geologic boundaries, the vector information also showed stepping.  The stepping was more obvious as the user zoomed in to get a closer look at the data set.  To smooth the vector information, the boundaries were interactively edited using the vector editing capabilities of the PCI Remote Sensing software package Imageworks.  The final vector information was overlayed on the registered GLORIA image for verification and the final vector segments were output in the ARC/INFO export format.

The ARC exported dataset was then imported into ARC/INFO where the ARC polygons were built.  No additional editing was done in ARC.  The polygon information was then exported as an ArcView shapefile.  The shapefile was then processed within ArcView to add the necessary table information for color coding and identification of the various geologic provinces.

An additional ArcView shapefile highlighting Gulf of Mexico features names is also made available on this CD-ROM.  The GIS data coverage was created from a Microsoft Excel spread sheet found at the National Oceanic and Atmospheric's National Geophysical Data Center's (NGDC) Marine Geology & Geophysics website. The information contained in the spread sheet was edited to include only those features that would pertain to the planned Gulf of Mexico Internet Map Server for the USGS, Woods Hole Field center.
Therefore, this is not a complete listing as would be found from NOAA-NGDC.

Reference List

Viewing the Data Coverages

The data coverages, imagery and shapefiles, archived on this disk have been prepared for use with the ESRI software package ArcView version 3.0b or greater.  To support viewing the shapefiles, ArcView and ArcExplorer project files have been compiled and included on this CD-ROM.  When these files are opened by their respective programs, the user may view and interact with the different data layers.  These files were included to allow the user a quick way of viewing the datasets as a complete product.  Depending on the available software, the user may select the appropriate files from the following table to quickly open the project file.
Filename Description
arcvieww.apr ArcView project file to be used within Netscape for Windows
arcviewu.apr ArcView project file to be used within Netscape for Unix.  This project file assumes the CD-ROM has been mounted to the directory /cdrom.
arcexplr.aep ArcExplorer project file to be used within Internet Explorer

To open the project files, the user must have the appropriate software installed and running on their computer system.  For further details on the software requirements, the user may check "What's needed!" page. [an error occurred while processing this directive]