Archive of Datasonics SIS-1000 Chirp Subbottom Data Collected During USGS Cruise SEAX 95007 New York Bight, 7-25 May, 1995
This DVD-ROM contains copies of the navigation and field chirp subbottom
data collected aboard the R/V Seaward Explorer, from 7-25 May, 1995. The
coverage is in the New York Bight area. This DVD-ROM (Digital Versatile
Disc-Read Only Memory) has been produced in accordance with the UDF
(Universal Disc Format) DVD-ROM Standard (ISO 9660 equivalent) and is
therefore capable of being read on any computing platform that has
appropriate DVD-ROM driver software installed. Access to the data and
information contained on this DVD-ROM was developed using the HyperText
Markup Language (HTML) utilized by the World Wide Web (WWW) project.
Development of the DVD-ROM documentation and user interface in HTML allows
a user to access the information by using a variety of WWW information
browsers (i.e. NCSA Mosaic, Netscape) to facilitate browsing and locating
information and data. To access the information contained on this disk
with a WWW client browser, open the file 'index.htm' at the top level
directory of this DVD-ROM with your selected browser. The HTML documentation is written utilizing some HTML 4.0 enhancements. The disk
should be viewable by all WWW browsers but may not properly format on some
older WWW browsers. Also, some links to USGS collaborators and other
agencies are available on this DVD-ROM. These links are only accessible if
access to the Internet is available during browsing of the DVD-ROM.
The archived Chirp subbottom data are in standard Society of Exploration
Geologists (SEG) SEG-Y format (Barry and others, 1975) and may be
downloaded for processing with software such as Seismic Unix or SIOSEIS.
The subbottom data were recorded on the ISIS data acquisition system in
QMIPS format. Chirp subbottom channel extracted from raw QMIPS format
sonar files and converted to 16-bit Int. SEG-Y format using the program
QMIPSTOSEGY. Even though the data are in SEG-Y format, it is not the
conventional time series data (e.g. voltages or pressures), but rather
instantaneous amplitude or envelope detected and therefore all of the
amplitudes are positive (though not simply rectified). DOS and Microsoft
Windows compatible software for plotting SEG-Y files (PLOTSEIS) and
viewing SEG-Y headers (DUMPSEGY) is located in the PLOTSEIS directory.
Processed chirp profiles (GIF images) may be viewed on this DVD-ROM with
your WWW browser.
For more information on the seismic surveys see
https://cmgds.marine.usgs.gov/fan_info.php?fan=1995-007-FA
These data are also available via GeoMapApp (
http://www.geomapapp.org/) and Virtual Ocean (
http://www.virtualocean.org/) earth science exploration and visualization applications.
Seismic reflection profiles are acquired by means of an acoustic source (usually generated electromagnetically or with compressed air), and a hydrophone or hydrophone array. Both elements are typically towed in the water behind a survey vessel, or some cases, mounted on side of the hull. The sound source emits a short acoustic pulse, which propagates through the water and sediment columns. The acoustic energy is reflected at density boundaries (such as the seafloor or sediment layers beneath the seafloor), and detected at the hydrophone. As the vessel moves, this process is repeated at intervals ranging between 0.5 and 20 meters depending on the source type. In this way, a two-dimensional image of the geologic structure beneath the ship track is constructed. For more information concerning seismic reflection profiling at the USGS Woods Hole Field Center, see
https://woodshole.er.usgs.gov/operations/sfmapping/
