GIS Data Catalog
Multibeam bathymetry and backscatter data were
acquired using the SeaBeam 2112 multibeam echo sounder. The
12KHz system uses up to 150 beams covering approximately 150 degrees
swath width at depths less than 1,000 meters, and 120 degrees swath width
for depths up to 5,000 meters. The swath width decreases to
approximately 90 degrees for depths greater than 5,000 meters.
The operation of
the SeaBeam system is dependent upon the depth of the water, i.e.
the deeper the water, the longer the pulse width, the slower
the ping rate, and the narrower the swath width.
The multibeam swath width in the deeper regions was between
10,000 meters and 12,000 meters ( 5.3 nautical miles to 6.5
This multibeam swath coverage allowed the survey line spacing
to be established at 6
nautical mile intervals with an east - west azimuth.
The pulse width ranged between 7 ms and 20 ms, with ping
intervals varying between 8 seconds to 20 seconds.The SeaBeam system recorded the raw data files to a Silicon
Graphics Incorporated (SGI) Origin 2 computer.The data files were automatically opened and closed with a 6
Mb limit.This enabled
adequate and efficient data management procedures.The total file size for the processed 2003 SeaBeam bathymetric data was approximately 557
corrections were required by the SeaBeam acquisition system to
account for water column temperature and salinity variations.The cast data were derived from three separate sources.A deep water Conductivity Temperature and Density (CTD) cast
was obtained prior to the start of SeaBeam data collection.A Seabird Electronic Model 9/11 Conductivity Temperature and
Density probe was used for obtaining CTD cast data.The maximum depth obtained with this instrument was 3,000
Tables were used to supplement the cast data with velocity values
for water depths between 3,000 meters and 9,000 meters. Levitus Tables represent the annual average water velocity structure
for a one degree by one degree area centered at -66.5 degrees
longitude and 19.5 degrees latitude. This water velocity
profile is in the form of discrete (depth, velocity) points where
the depth is in meters and the velocity in meters per second.
For additional information on how the profile was used see
the Excel spreadsheet SVP_2003
in the data\svp directory.Additional speed of sound data
were recorded using the Sippican
Expendable Bathythermograph (XBT).XBT c ast data were limited to range of 760 meters to 1365 meters
Electronic Model SBE-21 Thermosalinograph (TSG) was constantly
monitored for surface sound velocity values.Monitoring the TSG values enabled the scientific crew to
determine when additional sound velocity data were required.
were entered in the acquisition system for real time application
with beam forming and beam steering capabilities.Variations in sound speed due to temperature and salinity differences
within the water column affect the ray path and two way travel time of each
formed beam from the SeaBeam transducer to the sea floor. The correct
sound velocity variations are thus required to account for any "bending" of the
ray path, since this will affect the final depth measurement of each formed
beam.No evidence of multibeam swath cupping or frowning was
evident during data acquisition and processing.
Data processing was performed by NOAA hydrographers.The data pipeline included transferring the SeaBeam MB41 raw
data files from the SGI computer to a processing laptop via file
transfer protocol (ftp).Once
the transfer was complete, the raw file was converted using CARIS
5.3 Hips Sips software.The
processing crew (NOAA hydrographers) maintained the same processing
procedures as employed byNOAA
hydrographic field units.
Once the data were converted, a Digital Terrain Model (DTM) or
DTM (has not been
cleaned for noisy data) was generated for visual detection of artifacts and missed depths.The next step entailedreviewing
and editing the data with CARIS Swath Edit, followed with CARIS Sub
Set mode editing.Both editing processes allowed the hydrographer to
eliminate data artifacts or outliers.
editing, the weighted mean grid (or DTM) was re-generated with a grid
resolution of 150 and 200 meters.A colorized by depth and grey toned surface model was
exported as a TIF image and submitted to USGS team members. The
150 meter weighted grid was also exported as an ASCII XYZ data set
that was converted to a gridded UTM (prt03final.gutm) file which can be read by GeoZui3D.
is a highly interactive 3D Visualization system developed in the Data
Visualization Research Lab at the Center
for Coastal and Ocean Mapping at the University of New Hampshire.
It is designed to support research by providing support for
innovative data visualization. It is also intended to be a practical
and useful tool for fusing multiple sources of georeferenced Data.
GeoZui3D, CARIS 3D Viewer, and IVS
Fledermaus were used for
visual data interpretation by USGS geologists.The exported ASCII XYZ data set was also converted into a
MapInfo Vertical Mapper Grid that was used to generate a 150 meter contour
products submitted to USGS team members included the 150 meter
resolution, weighted grid image files, both colorized by depth with
sun illumination and gray tone surface model; 500 meter interval
contour file; backscatter mosaics with 25 and 75 meter resolution;
GeoZui3D ASCII gutm grid file with 150 meter grid interval.The image files were used in a project poster that described
the results and interpretations of the geologic/bathymetric survey
and are included in the ArcView GIS project file.