Scope of Work
Sonar, 3.5kHz 1,
Apx 1: Statistics 1
Apx 1: Statistics 2
Apx 2: Equipment 1
Apx 2: Equipment 2
Bathymetric data was collected with a Raytheon DSF-6000, 12-kHz profiling system.
Occasionally the 3.5-kHz system was used when the 12-kHz system was not operational.
Data were automatically logged and merged with the sidescan sonar and navigation data.
Following the survey, the bathymetric data were merged with depths from existing NOAA
National Ocean Survey navigation charts numbers 19362 and 19364, USGS bathymetric data
collected during previous survey; and data taken from the National Geophysical Data Center
(NGDC, Boulder, CO) to produce the bathymetric map shown in figure 5, plate 1, and Chase
and others (1994).
GEOPHYSICAL PROFILING SYSTEMS
High-resolution 3.5-kHz Seismic Reflection Profiling System
High-resolution 3.5-kHz subbottom profiles were collected concurrently with sidescan
sonar imagery, to determine the acoustic signature and thickness of both the dredged material
and natural sedimentary layers (figures 3 and 4). The profiling system comprises an Ocean
Data Equipment Corporation Bathy 2000 signal correlator, and a Raytheon PTR transceiver,
both driving a 3.5-kHz subbottom profiler housed in a towfish. Pulse repetition rates were
0.25, 0.5 and 1.0 sec. Real-time 3.5 kHz-return signals were displayed on a 16-bit format
color monitor and on analog ink-jet color paper records. All data are digital, merged with
navigation and archived on optical disc.
Chirp Sonar High-Resolution Profiling System
A Datasonics CAP-6000A chirp sonar subbottom profiling system was also used in an
effort to map the thickness and extent of any surficial sedimentary layers associated with
dredged material disposal. Operational and theoretical details of the chirp sonar are explained
in Appendix 2 and references cited therein. The acoustical data were displayed real time on a
super VGA graphics monitor and paper copies were produced on a color-jet printer. All data
were archived on Sony digital audio tapes. The monitor and paper copies displayed color
acoustic profiles and a variety of system settings. The chirp sonar proved unsuccessful owing
to a combination of system noise and possibly the carbonate substrate. The poor quality of the
chirp data precludes any detailed description of the profiles and subsequent interpretation. The
chirp sonar data are not discussed in the remainder of the report.