Beach Profile Data Collected from Madeira Beach, Florida (July 25, 2024)

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 (Doran and others, 2017) to find an average shoreline angle. The transects were generated at locations of groins (cross-shore perpendicular structures that are connected to land and extend into the ocean) and at 3 alongshore locations, equally spaced, between adjacent groins in the area of interest, by utilizing imagery from Google Earth to determine the location of the groins. This resulted in 25 cross-shore transects (lines 35 to 59) spaced approximately 23 meters (m) apart and spanning approximately 555 m in the alongshore direction. An additional cross-shore transect was planned in the middle of the study area (line 60). Five alongshore transects (lines 1 to 5), spanning the length of the study area, were 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® 2022 survey acquisition software. Kinematic GPS data were recorded at 5 hertz (Hz) with an Ashtech™ ProFlex™ 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. For this survey, 26 cross-shore transects (lines 35 to 60) and 5 alongshore transects (lines 1 to 5) were collected.

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. 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™ ProFlex™ 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) Online Positioning User Service (OPUS, https://geodesy.noaa.gov/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 R2023a computing environment. The data were smoothed in the cross-shore direction to reduce the noisiness of the data, similar to the smoothing method done by Stockdon and others (2009). The noisiness is due to the high temporal sampling frequency and the walking motion of the human surveyor. The choice of a moving 1-m wide Hanning filter (Blackman and Tukey, 1959) was sufficient to reduce noise along the profile while preserving the elevation of the profile. 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 (1.65 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). One cross-shore transect (line 49) was deemed to have highly questionable elevation values, and that transect was excluded from this release.