Archive of digitized analog boomer seismic reflection data collected during U.S. Geological S cruises Erda 90-1_HC, Erda 90-1_PBP, and Erda 91-3 in Mississippi Sound, June 1990 and September 1991

The USGS Saint Petersburg Coastal and Marine Science Center (SPCMSC) currently holds 13 major geophysical surveys from the northern Gulf of Mexico in its paper repository. A conservative estimate of 2,000 line-kilometers (km) of data is available. Paper copies of data are difficult and expensive to duplicate and share with other facilities, and cannot be analyzed using standard GIS and interpretative software. Conversion of this data into a usable digital format is necessary to archive the geologic information that otherwise might be lost, requiring additional redundant and very expensive marine-geophysical surveys. The USGS National Geological and Geophysical Data Preservation Program (NGGDPP, http://datapreservation.usgs.gov) addresses the need to preserve, catalog, and provide access to geological and geophysical data for scientific research and economic development. In addition to the current efforts under the NGGDPP, four geophysical investigations from the 1980s and 1990s were previously archived through a preservation project in collaboration with the Bureau of Ocean Energy Management (Harrison and others, 2007; Sanford and others, 2009a, b, c). The USGS-SPCMSC scans its analog HRSP holdings using a large-format continuous scanner. The analog to digital conversion process used for this report is similar to the processes used previously in Harrison and others, (2007) and Sanford and others, (2009a, b, c). The digital files are converted into Tagged Image File Format (TIFF) for standard accessibility by raster image processors. The TIFF images are also converted to the Society of Exploration Geophysicists Y format (SEG-Y) files. This standard non-proprietary format is the accepted industry standard for seismic data, and can be accessed by all major seismic data processing and interpretation systems. To accompany the HRSP, navigation and metadata files are generated for use in GIS, database and Internet Message Access Protocol (IMAP) services, and included in USGS data archives. The northern Gulf of Mexico is a passive continental margin, where minimal structural change to the shallow stratigraphy has occurred during the last few thousand years (Anderson and others, 2004). Therefore, subsurface data collected from this environment for the purposes of geologic assessment can be considered useful in perpetuity. The geologic information collected by the USGS in the northern Gulf of Mexico remains a valuable resource for sea floor and stratigraphic investigations, and is continuously revisited by researchers interested in Holocene and recent earth processes. For example, decades-old geologic data is commonly used in sediment resource studies in coastal Louisiana (for example, Kindinger and others, 2001; Kulp and others, 2002; Rogers and others, 2009) and previously collected datasets across the Mississippi-Alabama shelf have been used in recent geologic-framework assessments (Roberts and others, 2004; Greene and others, 2007; Flocks and others, 2011). This publication describes data collection and processing methods for seismic profiles created from analog boomer seismic-reflection data collected during three surveys (Erda 90-1_HC, Erda 90-1_PBP and Erda 91-3) in 1990 and 1991. The seismic data were collected using a single-channel Huntec boomer/benthos hydrophone system with Ocean Research Equipment (ORE) Geopulse power supply. The system consists of an electromagnetic sound source mounted on a catamaran sled towed behind the vessel at the water surface. The signal emitted from the sound source is received by a 5 m-long hydrophone streamer towed alongside the sled. The received signal is processed into response amplitudes via a topside computer running the acquisition software; the settings varied by cruise. The seismic data were printed onto paper rolls as two-dimensional profiles representing track length and depth (time). Geographic positioning of the system was collected using a long range navigation (LORAN) system and annotated onto the paper copies.