Predicted Seafloor Facies of Central Santa Monica Bay, California

Mapping surficial seafloor facies (sand, silt, muddy sand, rock, etc.) should
be the first step in marine geological studies and is crucial when modeling
sediment processes, pollution transport, deciphering tectonics, and defining
benthic habitats. This report outlines an empirical technique that predicts the
distribution of seafloor facies for a large area offshore Los Angeles, CA using
high-resolution bathymetry and co-registered, calibrated backscatter from
multibeam echosounders (MBES) correlated to ground-truth sediment samples. The
technique uses a series of procedures that involve supervised classification
and a hierarchical decision tree classification that are now available in
advanced image-analysis software packages. Derivative variance images of both
bathymetry and acoustic backscatter are calculated from the MBES data and then
used in a hierarchical decision-tree framework to classify the MBES data into
areas of rock, gravelly muddy sand, muddy sand, and mud. A quantitative
accuracy assessment on the classification results is performed using
ground-truth sediment samples. The predicted facies map is also ground-truthed
using seafloor photographs and high-resolution sub-bottom seismic-reflection
profiles.

This Open-File Report contains the predicted seafloor facies map as a
georeferenced TIFF image along with the multibeam bathymetry and acoustic
backscatter data used in the study as well as an explanation of the empirical
classification process.

[Summary provided by the USGS.]