|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|
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.
polyline within coverage bathymer
|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.|