Single-Beam Bathymetric Data collected with Personal Watercraft around Fire Island, New York (2014) in XYZ ASCII text file format

GPS Acquisition: Horizontal and vertical positioning of each vessel and backpack was were collected determined using a base-rover configuration. Data were recorded at 10 Hertz (Hz) using Ashtech ProFlex™ 500 Global Navigation Satellite System (GNSS) receivers with Thales choke ring antennas. Three stationary base stations (REST, VC, and U374) were occupied during the surveys. The stationary base at published NGS benchmark U374 (Permanent Identification number (PID#) KU0206) was equipped with an Inmarsat Broadband Global Area Network (BGAN) satellite uplink system for remote monitoring of the base station. U374 consisted of an Ashtech Proflex 500 GNSS receiver and an Ashtech choke ring antenna with a vertical offset of 1.24 meters (m). GPS data acquired by the PWCs, backpack, wheel-mount, and the REST and VC base stations were downloaded at the end of each survey day. A small segment of the U374 data was downloaded via the BGAN network nightly to ensure the system was operating properly. Reference station coordinates were verified with Continuously Operating Reference Stations (CORS) stations using OPUS, (http://www.ngs.noaa.gov/OPUS/). OPUS computed reference positions had a vertical error of 0.007 m and horizontal errors of 0.8 cm and 0.6 cm for East-West and North-South, respectively.

Single-Beam Sounding Acquisition: The single-beam bathymetric data were collected on two Yamaha (2010 and 2013) VX Deluxe personal watercraft. HYPACK version 2013 was used for positioning and navigation during the survey. Depth soundings were recorded at 10 Hz using an Odom Ecotrac CV-100 Digital Hydrographic Echo Sounder system with 200 kHz transducers with 4-degree (vessel 1) and 9-degree (vessel 2) 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) sensor. Data were processed using SonTek CastAway CTD software version 1.5.

Single-Beam Differentially Corrected Navigation Processing: Positions and elevations associated with each sounding were post-processed using differential corrections derived from the base/rover setup. 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 vessel and each survey day.

Single-Beam Processing: Soundings were merged with processed DGPS data and sound velocity profiles using Matlab to visually analyze single-beam soundings and correct for errors such as elevation outliers and dropouts associated with wave breaking in the surf zone. When this is 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 then corrected for the speed of sound associated with the mean water temperature and salinity. A moving average filter was then applied to the soundings in order to reduce instrument noise and noise associated with the pitch and roll of the PWC. The soundings were referenced to the height of the GPS antenna and subsequently to the World Geodetic System 1984 (WGS84) ellipsoid.

Single-Beam Datum Transformation: NOAA’s VDatum v3.3 was used to transform single beam data points (x, y, and z data) from their 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 either crossed or were within a horizontal distance of 0.25 m of each other. Any track line associated with a crossing that had an elevation differing by greater than 0.6 m, compared to crossing lines, was removed. Evaluation of the remaining track line crossings indicated there was an overall mean difference of 3.8 cm (based on 210 crossings) and (root mean square) RMS error of 16.5 cm (based on 696 crossings). Applying the square root of the sum of the datum conversion uncertainty (5.4 cm) and the sounding uncertainty (16.5 cm) results in a combined vertical error of 17.4 cm. Horizontal uncertainty is assumed to be at most half of the vertical uncertainty (8.7 cm).

Export Transects: Using Matlab, 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. Vessel 1 elevations were adjusted to those of vessel 2 for consistency (3.8 cm). The data were then combined into a single ASCII file consisting of position, elevation, line number, vessel number, and time of sampling.

Keywords section of metadata optimized by correcting variations of theme keyword thesauri and updating/adding keywords.

Added keywords section with USGS persistent identifier as theme keyword.