Backscatter B (7125): Offshore of Tomales Point, California, 2010

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Abstract/Contents

Abstract
This layer is a georeferenced raster image containing acoustic-backscatter data for the offshore area of Tomales Point, California. The acoustic-backscatter map of the area was generated from data collected by California State University, Monterey Bay (CSUMB), Fugro Pelagos and by the U.S. Geological Survey (USGS). 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). A map that shows these data is published in Open-File Report 2015-1088, "California State Waters Map Series--Offshore of Tomales Point, California." This layer is part of USGS Data Series 781.
Purpose
In 2007, the California Ocean Protection Council initiated the California Seafloor Mapping Program (CSMP) to create a comprehensive seafloor map of high-resolution bathymetry, marine benthic habitats and geology within the 3-nautical-mile limit of California's State Waters. CSMP has divided coastal California into 110 map blocks, each to be published individually as United States Geological Survey Open-File Reports (OFRs) or Scientific Investigations Maps (SIMs) at a scale of 1:24,000. Maps display seafloor morphology and character, identify potential marine benthic habitats and illustrate both the seafloor geology and shallow (to about 100 m) subsurface geology. Data layers for bathymetry, bathymetric contours, acoustic backscatter, seafloor character, potential benthic habitat and offshore geology were created for each map block, as well as regional-scale data layers for sediment thickness, depth to transition, transgressive contours, isopachs, predicted distributions of benthic macro-invertebrates and visual observations of benthic habitat from video cruises over the entire state. This coverage can be used to to aid in assessments and mitigation of geologic hazards in the coastal region and to provide sufficient geologic information for land-use and land-management decisions both onshore and offshore. These data are intended for science researchers, students, policy makers, and the general public. This information is not intended for navigational purposes.The data can be used with geographic information systems (GIS) software to display geologic and oceanographic information.

Description

Type of resource cartographic, software, multimedia
Form Raster Dataset
Place Santa Cruz, California, US
Publisher Geological Survey (U.S.)
Date valid 2004 - 2010
Publication date 2015
Edition 1.0
Language English
Digital origin born digital
Map data Scale not given. ; Custom projection W 123°5ʹ51ʺ--W 122°53ʹ41ʺ/N 38°15ʹ19ʺ--N 38°5ʹ44ʺ, Scale not given ; EPSG::4326

Creators/Contributors

Creator Kvitek, Rikk G.
Creator Dartnell, Peter
Creator Pacific Coastal and Marine Science Center
Creator Seafloor Mapping Lab
Creator Golden, Nadine E.

Subjects

Subject Coasts
Subject Submarine topography
Subject Submarine geology
Subject Ocean bottom
Subject Seismic reflection method
Subject California
Subject Marin County (Calif.)
Subject Pacific Ocean
Subject Tomales Bay (Calif.)
Subject 2004-2010
Subject Oceans
Subject Imagery and Base Maps
Subject Environment
Subject Geoscientific Information
Genre Geospatial data
Genre Cartographic dataset

Bibliographic information

Supplemental information None
WGS84 Cartographics This layer is presented in the WGS84 coordinate system for web display purposes. Downloadable data are provided in native coordinate system or projection.
Location https://purl.stanford.edu/sb976wc2810

Access conditions

Use and reproduction
This item is in the public domain. There are no restrictions on use.
Copyright
This work is in the Public Domain, meaning that it is not subject to copyright.

Preferred citation

Dartnell, P., Erdey, M.D., Kvitek, R.G., and Bretz, C.K. (2014). Backscatter B (7125): Offshore of Tomales Point, California, 2010. California State Waters Map Series Data Catalog: U.S. Geological Survey Data Series 781. Available at: http://purl.stanford.edu/sb976wc2810.

Collection

California State Waters Map Series Data Catalog

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