Applications

Predicted seafloor facies. Red is rock, orange is coarse sand, yellow is sand, and green is mud.

A main objective of the Seafloor Mapping Project is to generate geological and biological meaningful information from the multibeam data. Multibeam backscatter strength is dependent on a number of factors, such as the composition of the seafloor, seafloor roughness, sediment properties (grain-size, water content, bulk density), and volume reverberation within the sediment. Remote Sensing and GIS analytical techniques are used to predict the distribution of geologic facies on a pixel-by-pixel basis in Central Santa Monica Bay, California, USA using multibeam backscatter and bathymetry data. Traditionally, geoscientists interpret seafloor facies by intuition, whereas this project uses decision-based algorithms that can distinguish small-scale features.

Original (top) and processed (bottom) backscatter data.

Co-registered, georeferenced multibeam backscatter is key information for any seafloor characterization procedure aimed at identifying underlying geological facies. However, before any quantitative interpretations of the backscatter image can be made, the data must be normalized and corrected for uneven gain normalizations and artifacts generated by the sounder (uncompensated beam patterns, etc.). Post-processing correction algorithms are being developed to minimize data collection artifacts.

Shaded relief bathymetry image with colored isobaths at intervals used to calculate material volumes.

Three shallow, rocky pinnacles in Central San Francisco Bay, California, USA are shipping hazards to large cargo and oil ships entering and leaving the Bay. The Pacific Seafloor Mapping Project working with the US Army Corps of Engineers used high resolution multibeam data to calculate the volume of material needed to be excavated for large ships to pass safely overhead.

Seafloor stability map offshore Eureka, CA. Blues are more stable and yellows are less stable.

A seafloor stability map was generated for the region offshore Eureka, California, USA. This is a very tectonically active region with faults and underwater landslides. USGS scientists needed to locate areas of the seafloor that are susceptible to failure during an earthquake, possibly generating a tsunami. Multibeam bathymetry and backscatter data were used with sediment density and potential seismic acceleration data to predict areas at high risk of failure.

Historical seafloor change. Reds indicate erosion, blues indicate deposition.

A study in Central San Francisco Bay, California, USA shows the bottom morphology changed both by natural and human impacts. The study calculated the difference between single-beam bathymetric surveys conducted in 1957 and 1970 and a multibeam survey conducted in 1997.

3-D view of a ROV with multibeam bathymetry as ground control.

Traditionally, remotely operated vehicles (ROVs) were navigated on a backdrop of a rough bathymetric map. Multibeam bathymetry and backscatter data is now used as real-time ground control for ROVs, allowing the operator and scientists to view the ROV relative to a large area of the ocean floor. To date, the PSFMP has been involved in two such ROV cruises in the Gulf of Mexico.

Perspective view of the ocean floor off Oahu, Hawaii. The orange and yellows show dredge disposal deposits.

Many coastal cities have offshore dredge disposal sites. Multibeam bathymetry and backscatter data collected off Hawaii and California, USA have been used to accurately map the distribution of material on the seafloor and how it has moved over the years.