SWATHplus acquisition software (version 3.05.19) was used to digitally log the bathymetric data at a rate of 30 pings/second and 3,072 samples per swath (ping) in the SWATHplus SXR format. Data collection parameters are saved into a SWATHplus session file in SEA's SXS format. These files that can be later used for data replay.
An Octopus F180R Attitude and Positioning system (see: <http://www.codaoctopus.com/motion/f180/index.asp>) recorded ship motion (heave, pitch, roll, and yaw). These data were transmitted via network connection to the SWATHplus data collection software. The Octopus F180R Inertial Measurement Unit (IMU) was mounted directly above the SWATHplus transducers, to minimize lever arm offsets that can lead to positioning errors. The F180R uses two L1 antennas for position and heading accuracy. The antennas are mounted on a rigid horizontal pole, 3 meters above the F180R IMU, with a horizontal separation of 1 meter and are offset from the IMU in a forward/aft configuration. The forward offset of the primary antenna from the IMU is 0.5 meters, with no port/starboard offset.
Eight sound-velocity profiles were acquired during survey operations at roughly 4-hr intervals using an Applied Microsystems SV Plus V2 Velocimeter (Applied Microsystems, 2008).
Video and digital photographs were collected at 37 stations using the USGS Mini SEABOSS (Blackwood and Parolski, 2001). Mini SEABOSS stations were selected based on preliminary acoustic-backscatter mosaics, with the objective of characterizing broad areas of different backscatter intensity. With the Mini SEABOSS deployed, the research vessel was allowed to drift with occasional power from the vessel to control drift direction. Continuous video was collected over a total of 11.5 km of lake and riverbed. Video drift position was derived from the HYPACK® navigation files based on the start and end times of the drift. For some portions of the drift, there was no navigation, so the position was derived from the time and position stamp in the video at 30-s intervals.
Grab samples of the surficial sediment were collected at 15 stations, typically at the end of a drift. The upper 2 cm of sediment was scraped from the surface of the sample for texture analysis. Sediment samples were collected at locations with relatively fine-grained sediment (sand or mud). Samples were not collected in gravel or cobble areas where gravel prevented full closure of the sampler and resulted in a washed-out sample.
A total of 13 bottom samples were submitted for grain-size analysis. Two partially recovered, washed-out samples were not submitted. Grain-size analysis was performed at the USGS Sediment Laboratory at WHCMSC using methods described by Poppe and others (2005).
The seismic reflection profiling system utilized a Boomer energy source operated with a power output of 175 joules. The Boomer source was fired at 0.5 s intervals. A single-channel Benthos AQ4 streamer received the seismic reflection signal. The analog signal was band-pass filtered between 100 and 3000 Hz. A 23-db gain was applied. The analog signal was digitized and recorded in SEG-Y format using SonarWiz.MAP +SBP software version 4.03.0089. DGPS coordinates were recorded in the SEG-Y file trace headers in arc seconds. The layback distance from the DGPS antenna to the source and receiver was estimated and applied to the position during acquisition. A total of 200 ms of data were acquired for each trace. A total of 58.5 km of Boomer profiles were collected.
Chirp sub-bottom profiles were collected using a dual-frequency (3.5 and 200 kHz) Knudsen Engineering Limited (KEL) Chirp 3200 system. Chirp sub-bottom data with a peak frequency of 3.5 kHz were recorded in SEG-Y format with DGPS navigation logged to the SEG-Y file trace headers. The Chirp system was fired at a rate of 0.25 or 0.5 s. The trace length was set to 67 ms. A total of 80 km of Chirp sub-bottom data were collected.
The aerial extent of six unique units was hand drawn within ArcGIS 9.2 using ArcGIS EDITOR tools. Polygon shapefiles were generated for each of the six interpreted units: muddy sand, sand, sand and gravel, gravel and cobbles, and two units of silty clay (Qu (Quaternary undifferentiated deposits) and Qd (Quaternary glacial drift). The projection for each polygon shapefile was defined as UTM, zone 17N, WGS84, meters.
Four of the six shapefiles defining the surficial geologic units contained multiple polygons (sand, sand and gravel, gravel and cobbles and siltyclay). To ensure that each shapefile contained only one polygon of a specific bottom unit, the DISSOVLE command was used within Arc Toolbox - Data Management Tools - Generalization; aggregating polygons within each shapefile. Once each shapefile contained only one polygon, the EDITOR was used within ArcGIS to copy the individual polygons (i.e. surficial geologic units) into one master shapefile, saved as surficial_geology.shp.
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