Sea floor maps showing topography, sun-illuminated topographic imagery, and backscatter intensity of the Stellwagen Bank National Marine Sanctuary Region off Boston, Massachusetts

Online link https://geo-nsdi.er.usgs.gov/metadata/open-file/00-410/metadata.faq.html
Description This data set contains the sea floor topographic contours, sun-illuminated topographic imagery, and backscatter intensity generated from a multibeam sonar survey of the Stellwagen Bank National Marine Sanctuary region off Boston, Massachusetts, an area of
Originators Valentine, Page C.; Middleton, Tammie J.; and Fuller, Sarah J.
Publication U.S. Geological Survey Open-File Report 00-410

Related topics

States or counties

Overview of attributes

Sun-illuminated topographic imagery
This map combines contoured topography and sun-illuminated topographic
imagery. The image shown here uses a sun elevation angle of 45 degrees
above the horizon from an azimuth of 350 degrees and a vertical
exaggeration of four times. In effect, topographic relief is enhanced by
having the sun illuminate the sea floor from a position 10 degrees west
of north so that shadows are cast on the southern flanks of seabed
features. Unnatural-looking stripes and patterns oriented parallel or
perpendicular to survey track lines are artifacts of data collection.
Blank areas represent places where no data exists. The topographic
imagery is identical to that shown on Sheet 3 of this report.
Backscatter Imagery
This map combines the sun-illuminated topography with the backscatter
intensity (shown here in color) of the sea floor. Backscatter intensity
is a measure of the hardness and roughness of the sea floor as determined
from the strength of sound waves reflected from the seabed during the
survey. High-backscatter materials (red and orange) are coarse sand,
gravel (including piles and ridges of boulders), and rock outcrops.
Moderate backscatter (green) represents sand or muddy sand. Low
backscatter (blue) represents sandy mud and mud. These interpretations
apply best in regions of low regional topography, because steep slopes
can divert the paths of some of the reflected sound waves away from the
survey vessel. Thus, seabed that slopes steeply away from the survey
track can produce a lower backscatter intensity than if it were level.
Unnatural-looking stripes and patterns oriented parallel or perpendicular
to survey track lines are artifacts of data collection. Blank areas
represent places where no data exists.

http://pubs.usgs.gov/of/2000/of00-410/methods.htm

Bathymetric contour line

polyline within coverage bathymer

Label Definition
CONTOUR Depth of the bathymetric contour. Values are in meters above sea level, so all values given are negative. Double of width 13, but values are integer. Another attribute "INTERVAL" contains the same data stored as an integer.