Sun-illuminated Sea Floor Topographic Maps and Perspective View Imagery; Quadrangle 4

Multibeam data were processed using SwathEd, a suite of multibeam software editing and display tools developed by Dr. John Hughes Clarke of the Ocean Mapping Group, University of New Brunswick (UNB). The navigation and topographic data were both edited using this software. Tidal corrections were obtained from NOAA's Boston Tide Gauge (Station 8443970) and merged into the data set using UNB's tidal routines. The topographic information was converted into an ascii textfile containing lat, long, and depth fields, using a script created by Bill Danforth at the U.S. Geological Survey. The ascii file was brought into Arc/Info, and a grid was generated and processed using ESRIs Arc/Info version 7.0.4 software. A point coverage containing depth values was created using the routine point-generate. The grid was created based on the depth values for each of the points using the command pointgrid. The grid was filtered with a 9 by 9 focalmedian filter. Contours were generated using latticecontour. All editing and edgematching was done by hand using arcedit. The shaded relief images shown here were created using a light source that is 45 degrees above the horizon from an azimuth of 350 degrees. The vertical exaggeration in the images is four times. In effect, topographic relief is enhanced by illuminating the sea floor from a position 10 degrees west of north so that shadows are cast on the southern flanks of seabed features. Some features in the images are artifacts of data collection. They are especially noticeable where the seabed is smooth and include small highs and lows and unnatural-looking features and patterns that are oriented parallel or perpendicular to survey tracklines. For a depiction of the topographic contours alone, and for an explanation of survey and topographic data processing methods, see the companion maps by Valentine and others (1997a-r). Topographic contour maps of all 18 quadrangles of the map series are available on a CD-ROM in EPS, PS, Arc export, and PDF file formats (Valentine and others, 1998). Blank areas represent places where no data exists.

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