Sea Turtle Nesting Decision Points and Cross-Shore Beach Profile Data Collected on June 18, 2019, from Melbourne Beach, Florida

PLANNING Sea turtle nesting decision points, either nest or apex of false crawl (no nest), were identified and marked by FWC contractors on the morning of the survey.

ACQUISITION Transect lines were surveyed on foot by a person equipped with a GNSS receiver and antenna affixed to a SECO© surveying backpack. Transects started at the water’s edge, continued through either the turtle nest or the false crawl apex and into the dune until vegetation stopped the surveyor. The surveyor stopped for approximately 10 seconds (s) at either the nest or the apex of the false crawl, while walking the transect, making it easier to subsequently identify those locations during the DATA PROCESSING step. Kinematic GNSS data were recorded at 10 Hertz (Hz) with an Ashtech ProFlexTM 800 GNSS receiver and an Ashtech GNSS survey antenna.

GNSS DATA POST-PROCESSING Raw kinematic GNSS data recorded on the surveying receiver were post-processed using GrafNav (NovAtel’s Waypoint GNSS Post Processing Software) version 8.7 to achieve the maximum horizontal position and elevation data accuracies. The kinematic GNSS data recorded by the surveying receiver were processed in NAD83 geographic coordinates to concurrent static GNSS data recorded by a local base station of known position (NAD83). The base station used was the FPRN, (https://www.fdot.gov/Geospatial/fprn.shtm) site at Sebastian, Florida (site name = SBST). The final, differentially corrected, precise GNSS positions were exported from GrafNav in American Standard Code for Information Interchange (ASCII) text format as projected horizontal coordinates in NAD83, UTM Zone 17N, and vertical coordinates in NAVD88, GEOID12B. These post-processing steps are similar to those reported in Henderson and others (2016), the difference being that this survey utilized FPRN-CORS reference station data while Henderson and others (2016) established and collected data from their own reference station.

DATA PROCESSING Beach profile horizontal position and elevation data for each transect and nesting decision point location (nest or apex of false crawl) were extracted from the post-processed GNSS data using the MathWorks MATLAB R2020a computing environment. First, the elevation data were adjusted by subtracting the elevation of the GNSS antenna above the ground. This measurement is taken while the backpack is attached to the surveyor and measured from the antenna reference point (ARP) to the ground (1.51 meters (m)). The elevation data were then smoothed in the cross-shore direction using a moving 0.5 m wide Hanning filter (Plant and others, 2002) to reduce vertical noise resulting from the walking motion of the surveyor. Next, the data were quality-controlled to remove invalid data points by eliminating points identified as having poor GNSS data quality by GrafNav, visually inspecting horizontal position plots and discarding points not on the cross-shore beach profile lines, and visually inspecting elevation plots and discarding erroneous GNSS data (for example, large spikes in the elevation data). The 0.5 m wide Hanning filter and quality control steps were chosen to be consistent with previous data releases of this type (e.g. Brown and others, 2018). In some cases, there was not enough usable data to define a profile or the decision point so those transect/decision point data were excluded. Lastly, the data were interpolated onto an evenly spaced 0.10 m cross-shore transect. 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 (NAVD88, GEOID12B). The data processing methods described here closely follow those developed by Brown and others (2018). The naming convention of the transects and nesting decision points is as follows: LOC_YYMMDD_SS_T#, where LOC is a three letter abbreviation of the location (MEL = Melbourne, SHU = South Hutchinson, JEN = Jensen, JUP = Jupiter, and JUN = Juno), YYMMDD is the date, SS is the turtle species (Cc for Caretta caretta, Loggerhead sea turtle; Cm for Chelonia mydas, Green sea turtle; and Dc for Dermochelys coriacea, Leatherback sea turtle), T is the type of crawl (N = Nest and FC = False Crawl), and # is the transect/decision point number mapped on that survey date. The decision point locations were written to a comma-separated values (.csv) file containing the same naming convention as the profiles and the x, y, and z coordinates.