Bathymetry--Offshore of Ventura, California

The bathymetry and shaded-relief maps of the Offshore of Ventura map area in southern California were generated from data collected by California State University, Monterey Bay, Seafloor Mapping Lab (CSUMB) and by the U.S. Geological Survey (USGS). All these mapping missions combined to collect bathymetry from about the 10-m isobath to beyond the 3-nautical-mile limit of California's State Waters. During the CSUMB mapping missions, an Applanix position and motion compensation system (POS/MV) was used to accurately position the vessel during data collection, and it also accounted for vessel motion such as heave, pitch, and roll (position accuracy, +/-2 m; pitch, roll, and heading accuracy, +/-.02 degrees; heave accuracy, +/-5 percent, or 5 cm). NavCom 2050 GPS receiver (CNAV) data were used to account for tidal-cycle fluctuations, and sound-velocity profiles were collected with an Applied Microsystems (AM) 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 CNAV receiver. Final XYZ soundings and bathymetric-surface models were referenced to the World Geodetic System of 1984 (WGS 1984) relative to the North American Vertical Datum of 1988 (NAVD 1988). During the USGS mapping missions, differential GPS data (2006) and GPS with real-time kinematic corrections (2010) were combined with measurements of vessel motion (heave, pitch, and roll) 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 that works with previously measured sound-velocity profiles. Statistical filters were applied to the raw samples that discriminate the seafloor returns (soundings) from unintended targets in the water column. The original 2006 soundings were referenced to the WGS 1984 relative to the MLLW (Mean Lower Low Water) tidal datum, but, through postprocessing using National Oceanic and Atmospheric Administration?s (NOAA's) VDatum tool, the soundings were transformed to NAVD 1988. The original 2010 soundings were referenced to the WGS 1984 datum using real-time kinematics GPS and then transformed through postprocessing to the NAVD 1988. Finally, the soundings were converted into 2-m-resolution bathymetric-surface-model grids. In 2009, Fugro Pelagos collected bathymetric- and topographic-lidar data along the Ventura and Santa Barbara County coastlines for the U.S. Army Corps of Engineers Joint Lidar Bathymetry Technical Center of Expertise. Although bathymetric coverage was good northwest and southeast of the map area, the coverage within the Offshore of Ventura map area was very sparse; therefore, these data are not included in this map.

California State University, Monterey Bay, Seafloor Mapping Lab 2-m-resolution bathymetry data (CSMP survey blocks D - F) were downloaded from http://seafloor.csumb.edu/SFMLwebDATA.htm

Merge all bathymetry data into 2-m-resolution bathymetry grid and clip to the Offshore of Ventura map area boundary.

Added Distribution_Information section to metadata to facilitate data download.

Keywords section of metadata optimized for discovery in USGS Coastal and Marine Geology Data Catalog.

Added keywords from Coastal and Marine Ecological Classification Standard (CMECS) to metadata.

Edited metadata to add keywords section with USGS persistent identifier as theme keyword. No data were changed.

Metadata was modified to bring up to current USGS PCMSC standards. USGS Thesaurus and keywords were added, information for accompanying Open-File Report added to Abstract and Cross Reference sections, Point of Contact and Metadata Contact information was updated, and Process Steps were refined. Information about the data available for download and different Network Resource Name links and details were given in the Standard Order Process section. Minor typos were corrected. No data information was changed. The metadata available from a harvester may supersede metadata bundled within a download file. Users are advised to compare the metadata dates to determine which metadata file is most recent.