Single-Beam XYZ Point Coastal Bathymetry Data Collected in June 2014 from Fire Island, New York from the Shoreface

GPS Acquisition: GPS base stations were erected at benchmarks REST (near the town of Robins Rest) and U374 (NGS benchmark Permanent Identification number (PID#) KU0206) located on Fire Island. Base stations were equipped with Ashtech ProFlex 500 Global Navigation Satellite System (GNSS) receivers. The survey personal watercraft (PWC) (rovers) were equipped with ProFlex 500 GNSS receivers. The base and rover receivers recorded their positions concurrently at 10 Hertz (Hz) throughout the survey. Reference stations coordinates were verified with Continuously Operating Reference Station (CORS) sites using the Online Positioning User Service (OPUS), available at http://www.ngs.noaa.gov/OPUS/). U374 used reference stations ZNY1, NYRH, CTDA, while REST used stations NYCI, NYRH, and MOR6. OPUS computed both reference stations had horizontal errors of 0.4 cm and vertical errors of 0.2 cm.

Single-Beam Sounding Acquisition: The single-beam bathymetric data were collected on two Yamaha (2010 and 2013) VX Deluxe personal watercraft. Each PWC was fitted with a single-beam transducer below the waterline off the starboard stern, 1.11 m beneath the GPS antenna position. HYPACK version 2013 was used for positioning and navigation during the survey. Depth soundings were recorded at 10 Hertz (Hz), using an Odom Ecotrac CV-100 Digital Hydrographic Echo Sounder system with 200 kHz transducers with 4-degree (10 June 2014) and 9-degree (remainder of survey) transducers. Soundings were merged into a raw data file (.raw) and a sounding file (.bin) in Hypack. Each file was named according to transect number and coordinated universal time (UTC). Water column sound velocity measurements were collected periodically throughout the survey, using a SonTek CastAway conductivity, temperature, and depth (CTD) meter. Data were processed using SonTek CastAway CTD software version 1.5.

Single-Beam Differentially Corrected Navigation Processing: Horizontal positions and vertical elevations associated with each single-beam sounding were post-processed using differential corrections derived from the base/rover setup. Two GPS reference stations were used for the survey and were located at benchmarks U374 and REST. Applying the reference station coordinates, GPS data acquired from the rover were processed to the concurrent GPS session data at the base station- using GrafNav version 8.5 software (Waypoint Product Group). The horizontal and vertical coordinates were recorded in the World Geodetic System of 1984 (WGS84) reference frame and exported as an ASCII file for each personal watercraft and each survey day.

Single-Beam Data Processing: Single-beam soundings were merged with differentially processed GPS data and sound velocity profiles using Matlab R2014b. Each transect was visually inspected for elevation outliers and dropouts associated with wave breaking in the surf zone were manually corrected. Typically, the highest intensity return is generated by the seafloor surface. Breaking waves in the surf zone can create air bubbles in the water column and create an erroneous peak in waveform intensity, which causes errors in the interpreted seafloor reflection. When this situation was suspected, a corrected seafloor elevation was manually digitized by analyzing the complete waveform signal recorded by the Odom within the .bin data file. The soundings were corrected for the average speed of sound (table 1). A moving average filter was applied to the soundings to reduce instrument noise and the noise associated with the pitch and roll of the PWC. The depth soundings (from the transducer to the seafloor) were then adjusted to the depth from the GPS antenna and subsequently to the WGS84 ellipsoid.

Single-Beam Datum Transformation: NOAA's VDatum v3.3 was used to transform single-beam data points(x,y,z data) from their data acquisition datum (WGS84) to the North American Datum of 1983 (NAD83) reference frame and the North American Vertical Datum of 1988 (NAVD88) elevation using the National Geodetic Survey (NGS) geoid model of 2012A (GEOID12A). For conversion from the WGS84 ellipsoid to NAVD88 there is a total of 5.4 cm of uncertainty in the transformation (http://vdatum.noaa.gov/docs/est_uncertainties.html).

Single-Beam Error Analysis: The accuracy of the single-beam soundings was evaluated by identifying locations where survey track lines crossed and soundings from each line were horizontally within 0.25 m of each other. Any track line with a root mean square (RMS) error of 12.2 cm for a total of 732 crossings. Since the mean error between wave runners was 0.5 cm, which is below the minimum resolution of the echosounder, no correction offset was applied to the individual echosounders. Applying the square root of the sum of the datum conversion uncertainty and the sounding uncertainty resulted in a combined vertical error of 13.3 cm. Horizontal uncertainty is assumed to be half of the vertical uncertainty (6.7 cm) at most.

Single-Beam Error Analysis: The accuracy of the single-beam soundings was evaluated by identifying locations where survey track lines crossed and soundings from each line were horizontally within 0.25 m of each other. Any track line with a root mean square (RMS) error of 12.2 cm for a total of 732 crossings. Since the mean error between wave runners was 0.5 cm, which is below the minimum resolution of the echosounder, no correction offset was applied to the individual echosounders. Applying the square root of the sum of the datum conversion uncertainty and the sounding uncertainty resulted in a combined vertical error of 13.3 cm. Horizontal uncertainty is assumed to be half of the vertical uncertainty (6.7 cm) at most.

Merging Transects: Using Matlab R2015b, partial lines (the result of restarting the line in the middle of a transect) were subsequently merged with similar segments to create one seamless line. When repeats were present, only a single line was retained. The data were then combined into a single ASCII file consisting of position, elevation, line number, vessel number, and time of sampling.

Extract Shoreface XYZ: The single-beam XYZ data was imported into Esri ArcGIS version 10.2.2 using the Create Feature Class From XY Table tool, in ArcCatalog. Using ArcMap, a polygon feature was created, which surrounded data points within the shoreface of Fire Island. The polygon vertices were converted to points using the Feature Vertices to Points tool, Add XY Coordinates tool, and exported as an ASCII file using the Export Feature Attribute to ASCII tool. This ASCII file was subsequently imported into Matlab 2015b. Any PWC data within or on this polygon was then extracted and saved as an ASCII file.

Added keywords section with USGS persistent identifier as theme keyword.