Bathymetry from 2013 interferometric swath bathymetry systems survey of Columbia River Mouth, Oregon and Washington

The USGS R/V Parke Snavely was equipped with an Applanix Position and Orientation System for Marine Vessels (POS/MV) inertial motion unit (IMU) for the duration of the survey. The POS/MV received Differentially Corrected Global Positioning System (DGPS) aided positional navigation from dual Trimble model 4000 DGPS receivers, and commercial C-Nav satellite differential stations. The DGPS data were combined with the inertial vessel motion measurements (pitch, roll, and heading) directly within the POS/MV hardware so that high-precision position and attitude corrections were fed in real time to the sonar acquisition equipment. Sound velocity measurements were collected continuously with an Applied Micro Systems Micro sound velocimeter (SV) deployed on the transducer frame for real-time sound velocity adjustments at the transducer-water interface. Additionally, water column sound velocity profiles (SVP) were collected approximately every 2 hours throughout each survey day with an Applied Micro Systems, SvPlus 3472. DGPS data and measurements of vessel motion were combined in the POS/MV hardware to produce a high-precision vessel attitude packet. This packet was transmitted to the Swath Processor 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 the previously measured sound-velocity profiles in SEA Swath Processor. A series of statistical filters were applied to the raw samples that isolated the seafloor returns from other spurious targets in the water column. Finally, the processed data were stored line-by-line in both raw (.sxr) and processed (.sxp) trackline files. Applanix POS/MV records raw inertial and GNSS data while surveying that is later refined through post processing to incorporate publicly available GPS data from nearby base stations. During post processing the POS M/V data is run through POSPac software to produce a Smoothed Best Estimate of Trajectory (SBET) file, which is then used to create new .sxp line files using the Swath Processor software. CARIS HIPS and SIPS bathymetry processing software was used to further clean and bin the raw bathymetry data. Processed .sxp files were imported to CARIS and were filtered to remove obvious erroneous soundings and soundings towards the noisier out beams and then gridded into base surfaces. Base surfaces were exported to ASCIIRaster files and imported into ESRI GIS software. The bathymetry grid was projected horizontally to North American Datum of 1983 (NAD83). The grid was also transformed vertically to the North American Vertical Datum of 1988 (NAVD88) using the GEOID12A model. Note that the USGS collects bathymetric data for scientific purposes only. The USGS does not guarantee that full bottom search has been achieved and the data have not been inspected for dangers to navigation.

Extraneous text removed from Semi-Major Axis tag. Point of Contact and Metadata Contact were updated to PCMSC static contact information, and Data Processing Contact information was added. No data or data information were changed. This updated metadata file was also slipped inside the zip file containing the data.

Data and metadata files were moved to a different location on ScienceBase, resulting in a change of ID number in the Online_Linkage and Network_Resources URLs of the metadata. In addition, edits were made as needed to bring the metadata up to current PCMSC standards including adding disclaimers, and refining keywords. No data were changed, however the metadata file is now only found at the top level download and not tucked inside the data zip (to allow easier updates in the future). Users are advised to compare the metadata date of this file to any similar file to ensure they are using the most recent version.

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