Seafloor character, 2-m-resolution grid--Offshore of Monterey, California

The seafloor-character map was produced using video-supervised maximum likelihood classification of the bathymetry and intensity of return from sonar systems. The classification was supervised using signatures defined by hand-drawn polygons located through sediment samples and video-observation ground truthing applying methodology described in Cochrane (2008), available at http://doc.nprb.org/web/research/research%20pubs/615_habitat_mapping_workshop/Individual%20Chapters%20High-Res/Ch13%20Cochrane.pdf.
The two variants used in this classification were backscatter intensity and derivative rugosity. Rugosity measures terrain ruggedness as the variation in three-dimensional orientation of grid cells within a neighborhood. Vector analysis is used to calculate the dispersion of vectors normal (orthogonal) to grid cells within the specified neighborhood. This method effectively captures variability in slope and aspect into a single measure. Ruggedness values in the output raster map can range from 0 (no terrain variation) to 1 (complete terrain variation). The calculation was performed using the Terrain Ruggedness (VRM) tool. Bathymetry data were collected at two different resolutions: at 2-m resolution, down to approximately 90-m water depth (1998-2012 CSUMB and MBARI data); and at 5-m resolution, in the deeper areas (1998-2012 MBARI data). The final resolution of the seafloor-character map is determined by the resolution of both the backscatter and bathymetry datasets; therefore, separate seafloor-character maps were generated to retain the maximum resolution of the source data.
Classes I, II and III values were delineated using multivariate analysis. Class IV values were determined on the basis of visual characteristics using both bathymetry and backscatter (slight depression in the seafloor, very high backscatter return). The resulting map (gridded at 2 m) was cleaned by hand to remove data-collection artifacts (for example trackline nadir). Editing was performed in Photoshop, with which individual pixels were selected and values adjusted to remove noise. Selection occurred without antialiasing, and the resulting grid was identical but for the edited pixels. The four seafloor classes were then colored to indicate which of the five California MLPA depth zones they are located in: Depth Zone 2 (intertidal to 30 m), Depth Zone 3 (30 to 100 m), Depth Zone 4 (100 to 200 m), or Depth Zone 5 (deeper than 200 m). These were further subdivided into one of the following slope classes: Slope Class 1 (0 degrees - 5 degrees; flat), or Slope Class 2 (5 degrees - 30 degrees; sloping). Depth Zone 1 (intertidal), Slope Class 3 (30 degrees to 60 degrees; steeply sloping), Slope Class 4 (60 degrees - 90 degrees; vertical), or Slope Class 5 (greater than 90 degrees; overhang) are not present in the region covered by the 2-m-resolution grid for the Offshore of Monterey map area.

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