Field Activity Details for field activity 2025-007-FA

Other ID: Long Pond Falmouth

Status: Pending

Organization(s): USGS, Woods Hole Coastal and Marine Science Center

Funding Program(s): CMG-WH Core Competency - Marine Technology (LQ000GU)

Principal Investigator(s): Seth Ackerman, David Foster

Affiliate Investigator(s): Chuck Martinsen, Natural Resources, Town of Falmouth, MA; Michael Reghitto, DPW, Water Division, Town of Falmouth

Information Specialist(s): Seth Ackerman, David Foster

Data Type(s): Sonar: Multibeam

Scientific Purpose/Goals: Evaluation of a shallow water multibeam sonar and a chirp sub-bottom sonar in a controlled environment, Long Pond, Falmouth, MA. AIM group to complete a topographic lidar and orthophoto survey along the perimeter of Long Pond.

Vehicle(s):

Start Port/Location: Falmouth, MA

End Port/Location: Falmouth, MA

Start Date: 2025-03-31

End Date: 2025-08-19

Equipment Used: Norbit - iWBMS (SP)

Information to be Derived: Bathymetry and acoustic backscatter. Orthophoto and topographic lidar. Lidar and bathymetry merged into a DEM.

Summary of Activity and Data Gathered: Description: Long Pond, located in the Town of Falmouth (Falmouth) and Commonwealth of Massachusetts, is the primary public water source for Falmouth. Water elevations of the reservoir, specifically during periods of drought, is critical to ensure Falmouth can provide safe, potable drinking water to the community. The U.S. Geological Survey (USGS) provided a single-beam echosounder and sidescan sonar survey in 2011 that provided general bathymetric morphology and acoustic backscatter of the pond-floor sediments. The USGS in cooperation with Falmouth Department of Public Works, Water Division, completed a multibeam echosounder survey in April 2025 to update the bathymetry and acoustic backscatter maps with 90 percent coverage of the pond floor at significantly higher resolution (25 cm and 20 cm grid cells, respectively) than the 2011 survey. In addition, the bathymetry was rectified to a vertical datum (NAVD 88), which allowed for integration with existing topographic lidar data and newly acquired drone topographic lidar data. Multibeam sonar data were not collected on the following dates because work did not occur on weekend days, weather, or scheduling conflicts: 20250403, 20250405-20250409, 20250411-2025013. POS MV files were not recorded on 20250402 after 13:35.39 UTC. raw bathymetry and backscatter Bathymetry and backscatter data were collected using a Norbit iWBMS multibeam echo sounder (MBES). The sonar was mounted to a Norbit PORTUS pole attached to a bracket on the starboard side of the Falmouth Department of Public Works (DPW) 14-foot aluminum skiff. The Norbit sonar bracket, used to mount the integrated iWBMS sonar, was located 0.17 m below the waterline when deployed. The navigation reference point (NRP) is 0.07 m below the bracket mount point, for a total draft of 0.24 m. Vessel navigation and attitude data were acquired using an Applanix POS MV Wavemaster II system, configured with two Trimble GNSS antennas located at either end of a 2m baseline. The antennas were oriented fore and aft and mounted atop the MBES pole and the wet pod IMU, which is integrated with the sonar head. During data acquisition, Real-Time Kinematic (RTK) corrections were applied via NTRIP (Networked Transport of RTCM) protocol using data broadcast from the MA CORS (Continuously Operating Reference Stations) network. A Valeport SWiFT SV Profiler sound probe mounted underwater on the sonar bracket monitored sound speed near the sonar head during acquisition, and a hand-deployed AML Oceanographic MINOS X sound velocity profiler was used to collect water column sound speed profiles each survey day. The Norbit WBMS GUI (version 11.3.0) and data collection tool DCT (version 2.0.0) was used to control the sonar, which was operated with frequency-modulated pulses transmitted between 360 and 440 kHz. The swath width of the 512 across-track equidistant soundings was typically around 4-5 times the water depth. The depth gates, which delineate the sonar listening range, were adjusted manually during the survey depending on water depth. The Norbit GUI then used the manually adjusted gate depths to optimize ping rates accordingly. Data were monitored and recorded using the Norbit WBMS GUI and Norbit DCT. The Norbit DCT logged navigation, attitude, bathymetry and time-series backscatter data into the Teledyne Reson s7k format for each recorded file. The line files were created by the Norbit DCT according to the following naming convention:“YYYYMMDD_HHMMSS" DRONE SURVEY SUMMARY

Staff: Sandra Brosnahan, Wayne Baldwin, William Danforth, Liesel Vanderveen, Patrick Berube, Eric Moore, Alexander Nichols

Affiliate Staff:

Notes:

Location:

Long Pond, Town of Falmouth reservoir

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Data Acquired