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Pacific Coastal & Marine Science Center

This is an abstract from the 1993 Eastern Pacific Ocean Conference at Stanford Sierra Camp, Fallen Leaf Lake, California.

Computer generated shaded relief and perspective view images of the seafloor offshore Central California

Norman M. Maher, Jere A. Swanson, Herman A. Karl, and John L. Chin

The U.S. Geological Survey (USGS) began a major geologic and oceanographic study of the Farallon continental margin in 1989. This investigation, the first of several planned adjacent to major population centers, was designed to establish a good scientific data base on a segment of continental shelf and slope adjacent to the San Francisco Bay area in order to evaluate and monitor human impact on the marine environment. As part of this study a series of shaded relief and perspective view images of the seafloor were created to aid in the interpretation of the offshore geology and for use in report figures, educational aids, and public displays.

A shaded relief image (542 kb) encompassing the newly designated Monterey Bay National Marine Sanctuary (MBNMS), and the southern two thirds of the Cordell Bank and Gulf of the Farallones National Marine Sanctuaries was created from National Oceanic and Atmospheric Administration (NOAA) multibeam bathymetric data gridded to a 250 meter spacing, digitized contours from NOAA 1:250,000 nautical charts, and Defense Mapping Agency (DMA) Digital Elevation Model (DEM) data with a grid spacing of 30 arc seconds. The merged data was re-gridded and transformed to a shaded relief image using Arc/Info software running on a Sun SparcStation 2. Color and annotations were added to the image with Adobe Photoshop and Adobe Illustrator on a Macintosh IIfx. Higher resolution shaded relief images covering a much smaller area west of the Farallon Islands were generated from raw high resolution swath bathymetry supplied by NOAA. The raw data was gridded to a 30 meter cell spacing and processed with software developed by the USGS to produce gray scale and color shaded relief and perspective view images. The color images grade from blue in the deep areas to yellow in the shallow areas.

The images produced to date have proven useful as aids for visualizing the offshore topography of the Farallon slope. The shaded relief images derived from the 30 meter gridded data show considerably more detail of fine features than conventional isobath maps. The images have been particularly useful for helping administrators, policy makers, and the general public quickly understand the topography of the continental slope offshore Central California. Work in progress includes draping processed sidescan sonar mosaics over bathymetry to produce images that show both topography and geology and the production of animated "fly-by" videos.

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