Maine NSS Bathymetric Elevation Data – Frequently Asked Questions

Q1. How is the bathymetric data collected?     Back

Bathymetric data is collected using a Nearshore Survey System (NSS). The components of the NSS include:

  1. A SeaDoo Switch pontoon jetboat (lovingly named “Nessie” by the MGS scientists) that provides a comfortable working platform on the water.
  2. A pole-mounted Leica GS14/CS15 RTK-GPS used for positioning the system.
  3. A small, waterproof computer mounted in Nessie’s hull used to navigate and store collected bathymetric data. The computer runs Eye4Software’s Hydromagic bathymetric surveying software, which is used for pre-mission planning, data capture, and data post-processing.
  4. A through-hull mounted single-beam CEE ECHO shallow water transducer which sends out acoustic signals at 20 readings per second. These signals are multiplexed with RTK GPS positioning using the Hydromagic software.
  5. A touchscreen monitor mounted on the helm which displays the Hydromagic software data capture screens, which include the position of Nessie in relation to the pre-set transects, information on navigation, GPS configurations, and incoming data.

Data is collected by navigating along pre-set transects spaced about 20 meters apart and these transects are generally repeated each year, as applicable.

Q2. Which study areas are surveyed as part of the NSS bathymetric data collection, and why are they being surveyed?     Back

Several locations along the Maine shoreline where beach nourishment and nearshore placement of dredged sediments occur on a regular basis are monitored as part of MGS mapping in order to understand the movement of sediments over time. These areas include, from south to north:

  1. Wells Beach, Wells (2018-2022)
  2. Saco beaches, Saco (2016-2022, 2025)
  3. Little River Rock, Old Orchard Beach (2018, 2019, 2022, 2023, 2025)
  4. Scarborough River, including Pine Point, Anchorage, Ferry and Western beaches, and Scarborough River channel (2016-2025)

In addition, MGS scientists are occasionally asked to survey other locations for special purposes. These areas include:

  1. Blue Hill Bay, Blue Hill (2017), in support of ground-truthing newly captured NOAA topo-bathy LIDAR data and to test the NSS for eel-grass mapping.
  2. Spring Point and Willard Beach, South Portland (2018), in support of eel-grass mapping efforts.
  3. Fore River and East End Beach, Portland (2018), in support of eel-grass mapping efforts.
  4. Mackworth Island, Falmouth (2018), in support of eel-grass mapping efforts.
  5. Lanes Island, Yarmouth (2018), in support of eel-grass mapping efforts.
  6. Leonard Lake, Ellsworth (2020), in support of capturing bathymetric data upstream from a dam in downtown Ellsworth.
  7. Kennebec River region, including Waterville, Winslow, Fairfield, Benton, Clinton, Skowhegan, Norridgewock (2020), to capture bathymetric data in the river upstream and downstream from proposed potential dam removal projects.
  8. Scarborough marsh, select areas (2025), in support of filling gaps in topo-bathy LIDAR data for marsh modeling.

Q3. When are the study areas surveyed?     Back

In support of understanding the fate of dredged materials and beach nourishment sediments, surveys are generally conducted on an annual basis sometime in late Summer and early Fall (July or August through October or November) for the sake of getting good weather and consistent data year after year. The season in which a specific area was mapped is noted in the map layer name. For other locations, the timing of surveys is highly variable and dependent upon the purpose of the survey. The year and season are noted in the map layer name, as needed.

Q4. How is the data processed?     Back

Pre-mission planning, data capture, and data post-processing are accomplished using Eye4Software Hydromagic software. After data is collected, raw echosounder data is viewed and processed to remove any noise and unwanted or bad return data. Next, the processed data is converted into 1 point-per-second soundings and output referenced to NAD83 UTM Zone 19N and Geoid18B North American Vertical Datum 1988 (NAVD 1988). Finally, processed data is imported into ArcGIS software for visualization and conversion to rasters. A natural-neighbor interpolation methodology is used to output rasters with a 10-m cell size.

Q5. What data is visualized in the map viewer?     Back

Bathymetric elevation points from every year and study area where data was captured, as well as interpolated elevation rasters that were created from that point data are available for visualization. No rasters are available along the Kennebec River because the spatial distribution of collected raw data points was not adequate for raster interpolation. For these areas, individual elevation points are available.

Q6. How is the data visualized?     Back

The bathymetric elevation rasters are displayed as shaded color ramps with a value range from 1 meter to -11 meters NAVD88, except for Leonard Lake which has a scale of 1.5 meters to 19.5 meters NAVD88 (since it is an inland lake).

Last updated on January 7, 2026