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Backscatter D: Offshore of Tomales Point, California, 2010

Identification Information

Citation
Title
Backscatter D: Offshore of Tomales Point, California, 2010
Originator
Kvitek, Rikk G.
Originator
Dartnell, Peter
Originator
Pacific Coastal and Marine Science Center
Originator
Seafloor Mapping Lab
Originator
Golden, Nadine E.
Publisher
Geological Survey (U.S.)
Place of Publication
Santa Cruz , California , US
Publication Date
2015-01-01
Edition
1.0
Identifier
http://purl.stanford.edu/bj819cr5980
Geospatial Data Presentation Form
mapDigital
Collection Title
California State Waters Map Series (USGS Data Series 781)
Other Citation Details
These data were downloaded from http://pubs.usgs.gov/ds/781 on July 15, 2015
Series
Series Title
USGS Data Series
Issue
781
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.
Supplemental Information
None
Temporal Extent
Currentness Reference
ground condition
Time Period
Begin
2004-01-01T00:00:00
End
2010-12-31T00:00:00
Bounding Box
West
-123.097508
East
-122.894724
North
38.25538
South
38.095521
ISO Topic Category
oceans
imageryBaseMapsEarthCover
Place Keyword
California
Marin County (Calif.)
Pacific Ocean
Tomales Bay (Calif.)
Place Keyword Thesaurus
geonames
Temporal Keyword
2004-2010
Theme Keyword
Coasts
Digital elevation models
Remote sensing
Bathymetric maps
Multibeam mapping
Submarine topography
Submarine geology
Sediments (Geology)
Marine sediments
Ocean bottom
Seismic reflection method
Theme Keyword Thesaurus
lcsh
Legal Constraints
Other Restrictions
This item is in the public domain. There are no restrictions on access or use.
Legal Constraints
Other Restrictions
This item is in the public domain. There are no restrictions on access or use.
Status
completed
Maintenance and Update Frequency
asNeeded
Collection
Collection Title
California State Waters Map Series (USGS Data Series 781)
URL
http://purl.stanford.edu/ng324gh5570
Publication Date
2013-01-01
Language
eng
Credit
Dartnell, P., Erdey, M.D., Kvitek, R.G., and Bretz, C.K. (2014). Backscatter D: 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/bj819cr5980.
Point of Contact
Contact
Dartnell, Peter
Position Name
Physical Scientist
Email
PDartnell@usgs.gov
Phone
831-460-7415

Spatial Reference Information

Reference System Identifier
Code
32610
Code Space
EPSG
Version
2.1(3.0.1)

Data Quality Information

Quantitative Attribute Accuracy Report
Absolute External Positional Accuracy
Absolute External Positional Accuracy
Lineage
Process Step
Description
During the Fugro Pelagos and CSUMB mapping missions, an Applanix Position and Motion Compensation System for Marine Vessels (POS/MV, 320, v4) was used to accurately position the vessels during data collection, and it also accounted for vessel's motion such as heave, pitch, and roll (position accuracy, +/-2 m; pitch, roll, and heading accuracy, +/-0.02; heave accuracy, +/-5%, or 5 cm). KGPS altitude data (Fugro Pelagos, StarFix HP XP units; CSUMB, NavCom 2050) were used to account for tide cycle fluctuations and sound velocity profiles were collected with an Applied Microsystems SVPlus sound velocimeter. Soundings were corrected for vessel motion using the Applanix POS/MV data, for variations in water-column sound velocity using the AM SVPlus data, and for variations in water height (tides) using vertical-position data from the KGPS receivers. The multibeam backscatter data then were processed using Geocoder (Fugro Pelagos Modified Test Release 16) or Geocoder within Caris HIPS and SIPS. Within Geocoder, the backscatter intensities were radiometrically corrected (including despeckling and angle-varying gain adjustments), and the position of each acoustic sample was geometrically corrected for slant range. This processed imagery was stored as Georeferenced, Backscatter Rasters (GeoBARs). After GeoBARs were created for each line, they were mosaicked into 1-m or 2-m resolution images. Overlap between parallel lines was resolved using a priority table based on the distance of each sample from the ship track, with samples closest to- and furthest from- the ship track given the lowest priority. An anti-aliasing algorithm was also applied. The SWATHPlus backscatter data were processed using SXPTools v 2.0 (David Finlayson, USGS) and SEA Grid Processor v 3.02.19.0. The SXPTools sxpegn command was used to equalize the backscatter amplitude, and the sxpmagic command was used to help fill gaps and remove artifacts near nadir. After processing with SXPTools, lines were imported into Grid Processor and mosaicked into 1-m or 2-m resolution images. The mosaic images for each survey block was exported as a GeoJpeg from Grid Processor and converted to GeoTiff using Adobe Photoshop or GIMP. In some cases memory limitations in Grid Processor required tiling a block mosaic into 2 or more sub-mosaics.
Process Date
2010-01-01T00:00:00
Process Step
Description
California Seafloor Mapping Project 1- or 2-m resolution backscatter imagery within this map were downloaded from California State University, Monterey Bay, Seafloor Mapping Lab (http://seafloor.csumb.edu/SFMLwebDATA.htm) and converted to grids. Backscatter grids of similar mapping systems were merged in a GIS and clipped to the boundary of the map area. Grids from different mapping systems were not merged together due to different mapping frequencies and processing techniques. Grids were projected horizontally to WGS-84 using ESRI ArcTools.
Process Date
2012-01-01T00:00:00
Process Step
Description
During the USGS mapping within Tomales Bay (Anima and others, 2008), DGPS data and measurements of vessel motion (heave, pitch, and roll) were combined in a CodaOctopus F180 attitude and position system to produce a high-precision vessel attitude packet. This packet was transmitted to the acquisition software in real time and combined with instantaneous sound-velocity measurements at the transducer head before each ping. The returned samples were projected to the seafloor using a ray-tracing algorithm working with previously measured sound-velocity profiles. Statistical filters were applied to discriminate seafloor returns (soundings and backscatter intensity) from other unintended targets in the water column. Backscatter data were processed using USGS software SXPTools (David Finlayson, USGS) and mosaiced into 2-m resolution images.
Process Date
2012-01-01T00:00:00

Distribution Information

Format Name
Raster Dataset
Distributor
Stanford Geospatial Center
Online Access
http://purl.stanford.edu/bj819cr5980
Protocol
http
Name
BackscatterD_USGS_OffshoreTomalesPoint.tif
Function
download

Content Information

Content Type
image

Spatial Representation Information

Raster
Number of Dimensions
2
Row Count
8866
Column Count
8871
Cell Geometry Type
area
Corner Points
Point
491468.834992 4216418.552623
Point
491468.834992 4234150.552623
Point
509210.834992 4234150.552623
Point
509210.834992 4216418.552623
Center Point
500339.834992 4225284.552623

Metadata Reference Information

Hierarchy Level
dataset
Metadata File Identifier
edu.stanford.purl:bj819cr5980
Parent Identifier
http://purl.stanford.edu/ng324gh5570.mods
Dataset URI
http://purl.stanford.edu/bj819cr5980
Metadata Date Stamp
2017-11-21
Metadata Standard Name
ISO 19139 Geographic Information - Metadata - Implementation Specification
Metadata Standard Version
2007
Character Set
utf8
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