Beach Profile Data Collected from Sand Key Beach in Clearwater, Florida (May 19, 2021)

PLANNING Transects were created using the MathWorks MATLAB R2016a computing environment. Cross-shore transects were planned perpendicular to the beach by utilizing a measured 2010 lidar shoreline to find an average shoreline angle. Thirty cross-shore transects (lines 1 to 30) are spaced approximately 25 meters (m) apart and span approximately 725 m in the alongshore direction. Five alongshore transects (lines 31 to 35), spanning the length of the study area, are cast approximately 10 m apart in the cross-shore, spanning from the dune toe to the shoreline. Transect line planning was done in a similar way to Henderson and others (2015), the difference being the software used to create the transect lines and spacing of transect lines.

ACQUISITION Transect lines were surveyed, on foot, by a person equipped with a GPS receiver and a GPS antenna affixed to a SECO© surveying backpack, which was connected to a Windows laptop PC running HYPACK 2016 survey acquisition software. Kinematic GPS data were recorded at 5 Hertz (Hz) with an Ashtech ProFlexTM 500/800 Global Navigation Satellite System (GNSS) receiver and an Ashtech GNSS geodetic survey antenna. The time associated with the beginning and end of surveying each transect line was recorded on the laptop in HYPACK by the surveyor. These data acquisition steps are similar to those reported for the 'Wheel-Mounted GPS' system in Nelson and others (2017), the difference being the GNSS recording interval, GNSS survey equipment model, and that this survey used a backpack-mounted antenna to measure pre-defined transect lines.

GPS POST-PROCESSING Raw GPS kinematic data recorded on the surveying receiver was post-processed using GNSS post-processing software GrafNav (Waypoint Product Group) version 8.9 to achieve more accurate horizontal position and elevation data. The kinematic GPS data recorded by the surveying receiver were processed in NAD 83 geographic coordinates to concurrent static GPS data recorded by a local base station of known position (NAD 83). The base station used was an Ashtech ProFlexTM 500/800 GNSS receiver and Ashtech GNSS geodetic survey antenna established on the roof of the USGS SPCMSC, also known as ABBY, whose position was determined as the time-weighted average of coordinate values obtained from the National Geodetic Survey's (NGS) On-Line Positioning User Service (OPUS). The final, differentially-corrected, precise GPS positions were exported from GrafNav in American Standard Code for Information Interchange (ASCII) text format, with projected horizontal coordinates in NAD 83, UTM Zone 17N, and vertical coordinates in NAVD 88, GEOID12B. These post-processing steps are similar to those reported in Henderson and others (2015) and Nelson and others (2017).

DATA PROCESSING Beach profile horizontal position and elevation data for each individual transect were extracted from the post-processed GPS data based on the surveying times recorded with HYPACK using the MathWorks MATLAB R2017a computing environment. The data were smoothed in the cross-shore direction to reduce the noisiness of the highly sampled elevation data, using a moving 1-m wide Hanning filter in MATLAB. The data were quality-controlled in MATLAB to remove invalid data points by eliminating points with poor GPS data quality, visually inspecting plots of horizontal positions and discarding points not on the cross-shore beach profile lines (e.g., points just prior to and just after a transect), and visually inspecting plots of elevation and discarding points with erroneous GPS data (e.g., spikes in the GPS data). Lastly, the elevation data were adjusted by subtracting the elevation of the GPS antenna above the ground, when attached to the surveying backpack, during the survey (1.886 m). The final beach profile data were written to individual text files (.xyz) in tabular format, with columns representing: 1) Easting (NAD83, UTM Zone 17N), 2) Northing (NAD83, UTM Zone 17N), and 3) Orthometric Elevation (NAVD 88, GEOID12B).