Bathymetry Hillshade--Offshore of Refugio Beach Area, California

During the USGS mapping mission, Real Time Kinematic (RTK) GPS data and measurements of vessel motion (heave, pitch, and roll) were combined in a CodaOctopus F190 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 the raw samples that discriminate the seafloor returns (soundings) from other unintended targets in the water column. During the survey, the WGS84 (G1150) reference frame was used for both horizontal and vertical measurements. The soundings were post-processed to NAVD 1988. Finally, the soundings were converted into 2-m-resolution bathymetric-surface-model grids. During the Fugro Pelagos mapping mission that was completed as part of the National Coastal Mapping Program of USACE, the Leica ALS60 topographic-lidar and the SHOALS-1000T bathymetric-lidar systems were mounted on an aircraft that flew survey lines at an altitude of 300 to 400 m (bathymetry) and 300 to 1,200 m (topography), at speeds of between 135 and 185 knots. The ALS60 system collected data at a maximum pulse rate of 200 kHz, and the SHOALS system collected data at 1 kHz. Information on aircraft position, velocity, and acceleration were collected using the Novatel and POS A/V 410 systems (SHOALS) and the onboard GPS/IMU system (ALS60). Aircraft-position data were processed using POSPac software, and the results were combined with the lidar data to produce 3-D positions for each lidar shot. Various commercial and proprietary software packages were used to clean the data, to convert all valid data from ellipsoid to orthometric heights, and to export the data as a series of first-return topography and bathymetry ASCII files.

USGS 2-m-resolution bathymetry data from mapping cruise S-8-08-SC were downloaded from USGS archives.

Topographic - Bathymetric lidar data were provided to the USGS, PCMSC by USACE.

Transform all bathymetry data to common projection, datum, and UTM zone. Merge all 2-m bathymetry data into 2-m-resolution bathymetry grid and clip to the Offshore of Refugio Beach, California, map area boundary. An illumination having an azimuth of 300 degrees and 45 degrees above the horizon was applied to the 2-m bathymetry grid to create shaded relief imagery.

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.

Performed minor edits to the metadata to correct typos. 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.