Originator: Peter Dartnell
Originator: Rikk G. Kvitek
Title: Backscatter A --Offshore of Tomales Point, California
Originator: Nadine E. Golden
Title: California State Waters Map Series Data Catalog
Series_Name: Data Series
Issue_Identification: DS 781
Publication_Place: Reston, VA
Publisher: U.S. Geological Survey
This part of DS 781 presents data for the acoustic-backscatter map of the Offshore of Tomales Point map area, California. Backscatter data are provided as separate grids depending on mapping system or processing method. The raster data file is included in "BackscatterA_8101_ OffshoreTomalesPoint.zip", which is accessible from http://pubs.usgs.gov/ds/781/OffshoreTomalesPoint/data_catalog_OffshoreTomalesPoint.html
The acoustic-backscatter map of the Offshore of Tomales Point map area, California, was generated from backscatter data collected by California State University, Monterey Bay (CSUMB), by Fugro Pelagos, and by the U.S. Geological Survey. Mapping was completed between 2004 and 2010, using a combination of 200-kHz and 400-kHz Reson 7125, and 244-kHz Reson 8101 multibeam echosounders, as well as 234-kHz and 468-kHz SEA SWATHPlus phase-differencing sidescan sonars. 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.
To expand geologic mapping to the seafloor within the California's State
Waters, to update coastal geologic mapping, and to contribute to a uniform regional geologic database, which can be used geographic information systems. Additionally, to provide a geologic map for the public and geoscience community to aid in assessments and mitigation of geologic hazards in the Point Reyes coastal region and to provide sufficient geologic information for land-use and land-management decisions both onshore and offshore. This information is not intended for navigational purposes.
Currentness_Reference: ground condition
Maintenance_and_Update_Frequency: As needed
Theme_Keyword_Thesaurus: USGS Metadata Identifier
Theme_Keyword_Thesaurus: Global Change Master Directory (GCMD)
Theme_Keyword: Oceans > Bathymetry/SeafloorTopography > Bathymetry
Theme_Keyword: Oceans > Bathymetry/SeafloorTopography > Seafloor Topography
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: sidescan sonar
Theme_Keyword: marine geophysics
Theme_Keyword_Thesaurus: USGS Thesaurus
Theme_Keyword: sidescan sonar
Theme_Keyword: image mosaics
Theme_Keyword: marine geophysics
Theme_Keyword: sea-floor characteristics
Theme_Keyword: sea-floor acoustic reflectivity
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: Tomales Bay
Place_Keyword: Tomales Point
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)
This database has been approved for release and publication by the Director of the USGS. Although this database has been subjected to rigorous review and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, it is released on condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use.
USGS-authored or produced data and information are in the public domain. Acknowledge the U.S. Geological Survey and California State University, Monterey Bay, Seafloor Mapping Lab in products derived from these data. Share data products developed using these data with the U.S. Geological Survey.
This information is not intended for navigational purposes. Read and fully comprehend the metadata prior to data use. Uses of these data should not violate the spatial resolution of the data. Where these data are used in combination with other data of different resolution, the resolution of the combined output will be limited by the lowest resolution of all the data.
Although this Federal Geographic Data Committee-compliant metadata file is intended to document these data in nonproprietary form, as well as in ArcInfo format, this metadata file may include some ArcInfo-specific terminology.
Contact_Person: Peter Dartnell
Contact_Position: Physical Scientist
U.S. Geological Survey,
Pacific Coastal and Marine Science Center
Address_Type: mailing and physical address
Contact_Voice_Telephone: (831) 460-7415
Contact_Facsimile_Telephone: (831) 427-4709
Address: 400 Natural Bridges Dr.
City: Santa Cruz
Acoustic backscatter imagery of the Offshore of Tomales Point map area.