# Nearshore Benthic Mapping in the Great Lakes:
## 2 Materials and Methods
### Field Data Collection  
As part of on-going shoreline mapping in the region, ISGS collected initial ground truth data at 24 random points within the study area from 11 to 12 July 2018 including sediment grab samples (with grain size classifications), drop camera photographs (Garmin Virp XE 1080 pHD camera), sidescan sonar (Lowrance HDS7 Carbon sonar), and single-beam bathymetry (Seafloor Systems Dual Frequency 30/200 kHz single-beam echosounder). Upon review of the initial ground truth data, subsequent ground truth data were collected by ISGS in targeted areas to expand coverage of anticipated bottom types during the  
Figure 3: Satellite data products: (**a**) multispectral (bottom of atmosphere) reflectance, (**b**) Depth Invariant Index, and (**c**) Satellite-Derived Bathymetry. summer and fall of 2019. This included multi-beam bathymetry for qualitative assessment using a kit with the following specifications:  
Applanix-Trimble POS MV V4 kit:  
GPS antennae (2): Trimble GPS Zephyr model 2  
topside processor: PCS-29 Wavemaster  
Inertial Motion Unit: POS MV V4  
Reson-Teledyne SeaBat 7125 kit:  
Receiver: RESON EM7200-1 7125.7128 200/400 kHz  
Projector: RESON TC2181 7125 200 and 400 kHz  
RESON SVP 71; 2000 m; EM 7223 sound velocity probe  
RESON SeaBat 7125 MBES Processor Unit  
SVP-15 sound velocity kit:  
SVP-15 Sound velocity probe  
RESON SVPD-10 Power and Control Unit  
Universal Sonar Mount, standard mount with gear drive  
Acquisition software:  
QPS Quincy: integration of MBES, GPS, and sound velocity data  
Trimble Applsanix GNSS Surfer: for real-time GPS correction  
Trimble VRSlow: real-time RTK broadband GPS correction services  
Boat: Kann 8.2 m flat bottom work skiff  
Subsequent ground truth data collection also included lake-bottom videography along transects using an AquaVu 1080i Pro camera kit. Lake-bottom videography was collected using an AquaVu 1080i Pro camera kit. The camera cable was tethered to a steel davit cable weighted by a 12-pound river anchor with a carabineer to eliminate offset in the camera location, similar to a down-rigger setup used in salmon fishing on the Great Lakes. The anchor tether reduced offset (blowback or angle) of the camera relative to the boat position. The anchor depth was controlled, and the camera depth was independently controlled below the anchor depth by manually lifting and lowering the camera cable based on a real-time visual view of camera output. Live video output from the AquaVu topside monitor was fed to a computer using a HDMI video cable connected to a Magewell USB Capture 4K Plus device. Topside environmental conditions (e.g., boat motion) and boat crew narration were captured with a Microsoft HD Cinema Cam connected to the computer and mounted in an aft ceiling position inside the boat cabin. Boat position, heading, and water depth were derived from the boat navigation system which included a Garmin 6212 chartplotter, Garmin GPS 19\(\times\) HVS GPS antenna, Garmin GSD 22 Remote Sounder, and Garmin basic dual frequency (50/200 kHz) transducer. GPS and sounder data were exported from the chartplotter in NMEA 0183 format with a serial cable connected from the chartplotter to the computer. Franson GPS Gate software enabled a virtual COM port on the computer for real-time GPS, heading, speed, and time display in ArcGIS 10.5.1 for Desktop with the GPS toolbar. Open Broadcast Studio (OBS) software installed on the computer collected the AquaVu and web cam video feeds, an ArcGIS data layout window showed live boat navigation tracks and bathymetry. The OBS software setting saved video frames at a rate of 30 frames per second. In addition, the NMEA 0183 data strings from the chartplotter were independently saved with HyperTerminal software in ASCII text format. The NMEA data strings were post-processed to identify video start, video roll, and video stop records based on the GPS time stamp identified in the video display and the matching time stamp in the NMEA 0183 data log.