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

Dates

Start Date: 2013-05-13
End Date: 2013-05-25
Publication Date: 2015-12-30

Citation

Gelfenbaum, G.R., Finlayson, D.P., Dartnell, P., Carlson, E., Stevens, A.W., 2015, Bathymetry and backscatter from 2013 interferometric swath bathymetry systems survey of Columbia River Mouth, Oregon and Washington: U.S. Geological Survey data release, https://doi.org/10.5066/F7T72FHB.

Summary

Introduction High-resolution swath bathymetry and backscatter were collected in the mouth of the Columbia River (MCR) as part of the Office of Naval Research (ONR) funded River and Inlet Dynamics Experiment in 2013. The goal of the U.S. Geological Survey’s component of the research was to evaluate the various hydrodynamic and sediment transport processes in the Columbia River estuary entrance using a combination of field observations coupled with Delft3D model simulations. The MCR is a dynamic estuary inlet with large waves, large tidal currents, and a significant river discharge, resulting in strong estuarine circulation. The field component of the study consisted of an intensive in-situ experiment including bottom-mounted instrument [...]

Summary

Introduction

High-resolution swath bathymetry and backscatter were collected in the mouth of the Columbia River (MCR) as part of the Office of Naval Research (ONR) funded River and Inlet Dynamics Experiment in 2013. The goal of the U.S. Geological Survey’s component of the research was to evaluate the various hydrodynamic and sediment transport processes in the Columbia River estuary entrance using a combination of field observations coupled with Delft3D model simulations. The MCR is a dynamic estuary inlet with large waves, large tidal currents, and a significant river discharge, resulting in strong estuarine circulation. The field component of the study consisted of an intensive in-situ experiment including bottom-mounted instrument tripods, mobile instrument platforms, GPS-equipped drifters, and collection of maps of bed sediment grain-size and swath surveys of bathymetry and backscatter. The swath bathymetric surveys revealed ubiquitous seafloor bed forms throughout the estuary entrance. The bathymetric data are used to set bottom boundary conditions for the numerical models of hydrodynamics and to explore the characteristics of the seafloor roughness. Bottom roughness is an important boundary condition in hydrodynamic models of shallow environments and bed form size and roughness are poorly predicted. The purpose of this data release is to make available the methods, the metadata, and the processed bathymetry and backscatter data from the May 13 – 25, 2013 interferometric swath survey of the mouth of the Columbia River.

Mapping Mission

Mapping took place daily over 13 days from May 13, 2013 through May 25, 2013 (U.S. Geological Survey field activity S-03-13-WO) using a 234.5 kHz SEA (Systems Engineering and Assessment Ltd.) SWATHplus-M phase-differencing sidescan sonar. The sonar was pole mounted on the side of the 34-ft USGS mapping vessel R/V Parke Snavely and affixed to a hull brace. The R/V Parke Snavely was outfitted with three networked workstations and a navigation computer for use by the captain and survey crew for data collection and initial processing.

Data Processing

Vessel Position and Attitude

The 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 accounted for during post-processing.

Sound Velocity Measurements

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.

Sonar Sounding Processing

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. As many as 20 pings per second were transmitted with each ping consisting of 2,048 samples per side (port and starboard). 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. During data collection, soundings were referenced to a tidal datum using predicted tide data from the Astoria Station.

Post-Processed Navigation

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.

Digital Terrain Model Production

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 outer beams and then gridded into Bathymetric with Associated Statistical Error (BASE) surfaces. BASE surfaces were exported to ASCIIRaster files and imported into ESRI GIS software (Fig 1). Note that the USGS collects bathymetric data for scientific purposes only. The USGS does not guarantee that a full bottom search has been achieved and the data have not been inspected for dangers to navigation.

Figure 1. Shaded-relief bathymetry, Columbia River Mouth OR-WA. 2013 U.S. Geological Survey S-03-13-WO.

Backscatter Image Production

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. The raw 16-bit backscatter data recorded simultaneously with bathymetry by the SWATHplus system was georeferenced and gain-normalized by the program SXPEGN written by the USGS to enhance the backscatter imagery. The program normalizes for time-varying signal loss and beam directivity differences. The resulting normalized amplitude values are re-scaled to 16 bit, and gridded into a GeoJPEG using GRID Processor Software supplied by SEA. The image was imported into ESRI GIS software and projected to North American Datum of 1983. The image was then converted to a GeoTIFF file using ESRI GIS software (Fig. 2). Backscatter values range from -11.12 to 65546 and are the output of the SXPEGN process.

Figure 2. Acoustic backscatter, Columbia River Mouth OR-WA. 2013 U.S. Geological Survey S-03-13-WO.

Estimates of Bathymetric Uncertainty

Although the USGS collects bathymetry and acoustic backscatter data for research purposes only (not for navigational charts) it is useful to access the accuracy of the data. Standard deviation of soundings in areas of lower relief is a good measure of the precision of the sonar measurements. These absolute numbers are a good indication of the distribution of uncertainty in bathymetric soundings, however bathymetric errors increase with range from the system (depth) and natural variability of the seafloor. Also, by comparing calculated Total Vertical Uncertainty (TVU) with standardized IHO TVU survey order thresholds, which are based on a combination of coverage, depth, and accuracy (International Hydrographic Organization, 2008), we can access the accuracy of the bathymetry data in this report. TVU is defined as

TVU (x,y) = 1.96 * σ (x,y) (equation 1)

where σ (x,y) is the standard deviation of a cell located at coordinate (x, y). Standard deviation values for a subset of the bathymetry data over lower relief seafloor were exported from the CARIS BASE surface as an ASCII XYZ file. These files were gridded in Fledermaus (QPS) software and converted to ESRI GRIDs. TVU was calculated using GIS raster math with equation 1.

The mean standard deviation for the lower relief sub-area is 0.28 m with a maximum of 0.96 m. The mean TVU is 0.54 m, this falls slightly outside the IHO standard for first-order surveys of 0.5 m for areas shallower than 100 m, however there are outlier cells that exceed both first- and even second-order standard thresholds.

References

International Hydrographic Organization (IHO), 2008, IHO standards for hydrographic surveys (5th ed.): Monaco, International Hydrographic Bureau Special Publication 44, 28 p.

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Contacts

Point of Contact :: PCMSC Science Data Coordinator
Originator :: Peter Dartnell, Guy R Gelfenbaum, David P Finlayson, Emily Carlson, Andrew Stevens
Metadata Contact :: PCMSC Science Data Coordinator
Publisher :: U.S. Geological Survey
USGS Mission Area :: Natural Hazards
SDC Data Owner :: Pacific Coastal and Marine Science Center
Distributor :: U.S. Geological Survey - ScienceBase

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USGS_CR_swath_sampleImage.png “A) Swath map of data; B-E) sample detail pull-outs”	5.37 MB	image/png
USGS_CR_bathymetry.png “Figure 1”	7.21 MB	image/png
USGS_CR_acousticBackscatter.png “Figure 2”	5.27 MB	image/png

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

Dates

Citation

Summary

Summary

Introduction

Mapping Mission