This part of DS 781 presents data for the acoustic-backscatter map of Drakes bay and Vicinity map area, California. Backscatter data are provided as separate grids depending on mapping system or processing method. The raster data file is included in "BackscatterC_7125_DrakesBay.zip", which is accessible from https://pubs.usgs.gov/ds/781/DrakesBay/data_catalog_DrakesBay.html
The acoustic-backscatter map of Drakes Bay and Vicinity map area, California, was generated from backscatter collected by California State University, Monterey Bay (CSUMB), and by Fugro Pelagos. Mapping was completed between 2007 and 2010, using a combination of 200-kHz and 400-kHz Reson 7125, and 244-kHz Reson 8101 multibeam echosounders, as well as 468-kHz SEA SWATHPlus interferometric system. These mapping missions combined to collect backscatter data from about the 10-m isobath to beyond the 3-nautical-mile limit of California's State Waters. Within the acoustic-backscatter imagery, brighter tones indicate higher backscatter intensity, and darker tones indicate lower backscatter intensity. The intensity represents a complex interaction between the acoustic pulse and the seafloor, as well as characteristics within the shallow subsurface, providing a general indication of seafloor texture and composition. Backscatter intensity depends on the acoustic source level; the frequency used to image the seafloor; the grazing angle; the composition and character of the seafloor, including grain size, water content, bulk density, and seafloor roughness; and some biological cover. Harder and rougher bottom types such as rocky outcrops or coarse sediment typically return stronger intensities (high backscatter, lighter tones), whereas softer bottom types such as fine sediment return weaker intensities (low backscatter, darker tones). These data are not intended for navigational purposes.
These data are intended for science researchers, students, policy makers, and the general public. These data can be used with geographic information systems or other software to identify seafloor features.
Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Although this Federal Geographic Data Committee-compliant metadata file is intended to document the data set in nonproprietary form, as well as in Esri format, this metadata file may include some Esri-specific terminology.
Theme_Keyword_Thesaurus: USGS Metadata Identifier
Theme_Keyword_Thesaurus: Global Change Master Directory (GCMD)
Theme_Keyword: Acoustic Reflectivity
Theme_Keyword_Thesaurus: ISO 19115 Topic Category
Theme_Keyword_Thesaurus: Data Categories for Marine Planning
Theme_Keyword: physical habitats and geomorphology
Theme_Keyword_Thesaurus: Marine Realms Information Bank (MRIB) keywords
Theme_Keyword: multibeam echo sounder
Theme_Keyword_Thesaurus: USGS Thesaurus
Theme_Keyword: sonar methods
Theme_Keyword: image mosaics
Theme_Keyword: interferometric sonar
Theme_Keyword: marine geophysics
Theme_Keyword: sea-floor characteristics
Theme_Keyword: sea-floor acoustic reflectivity
Theme_Keyword: maps and atlases
Theme_Keyword: geospatial datasets
Theme_Keyword_Thesaurus: Coastal and Marine Ecological Classification Standard (CMECS)
Theme_Keyword: Marine Nearshore Subtidal
Theme_Keyword: Marine Offshore Subtidal
Theme_Keyword: Transform Continental Margin
Theme_Keyword: Continental/Island Shelf
Theme_Keyword: Rock Substrate
Theme_Keyword: Unconsolidated Mineral Substrate
Place_Keyword_Thesaurus: Geographic Names Information System (GNIS)
Place_Keyword: Pacific Ocean
Place_Keyword: State of California
Place_Keyword: Drakes Bay
Place_Keyword: Marin County
Place_Keyword_Thesaurus: Coastal and Marine Ecological Classification Standard (CMECS)
Place_Keyword: Northern California Ecoregion
Stratum_Keyword_Thesaurus: Coastal and Marine Ecological Classification Standard (CMECS)
USGS-authored or produced data and information are in the public domain from the U.S. Government and are freely redistributable with proper metadata and source attribution. Please recognize and acknowledge the U.S. Geological Survey as the originator(s) of the dataset and in products derived from these data. This information is not intended for navigation purposes.