These points correspond to the 18 temporary targets placed in the field by the U.S. Geological Survey field crew and used as ground control points (GCPs) to geo-reference SfM products. Field crews distributed 18 targets evenly around the study area by referring to a pre-created map with suggested placement of GCPs. Targets were commercial 4 ft x 4 ft x 4-mil thick PVC plastic sheets diagonally quartered in alternating black and white triangles (Berntsen International, Inc. product number AT48IC-STK). Each target was labeled with a unique identifying integer.
Field crews used three differential GNSS (Global Navigation Satellite System) rover instruments to record the horizontal and vertical position of the targets. The rovers received differential GPS corrections in real time from a base station on the Massachusetts Continuously Operating Reference Station Network (MaCORS) for RTK position corrections that yield (x,y,z) data accurate to within 1-3 cm (network: NTRIP RTCM3_MAX). The RTK base station was located in East Falmouth, approximately 9 km from Black Beach. Positions were referenced to WGS 84, UTM Zone 19 North (meters horizontal) and Geoid 12a, NAVD88 (meters vertical) by the MaCORS base station.
Two rovers were Spectra Precision model SP80 GNSS receivers with antenna SPP91564_2 (radius: 0.0985 m; slant height measure point: 0.028 m; L1 offset: 0.0826 m; L2 offset: 0.0756 m; instrument height: 2.0826 m) and the other, model ProMark GNSS Receiver 800 was operated with antenna ASH802147 (radius: 0.098 m; slant height measure point: 0.04 m; L1 offset: 0.0852 m; L2 offset: 0.0922 m; instrument height: 2.0852 m). Rover antennas were mounted on 2-m survey rods with bubble levels and 5-cm (2-inch) sand feet. The receivers were connected to Carlson CHC LT30 Handheld Terminal running Carlson SurvCE software under Windows Mobile v. 6.1 Professional operating system.
Rovers were operated by Sandy Brosnahan, Barry Irwin, Jonathan Borden, and E. Robert Thieler to survey the temporary targets and survey elevations around the study area. The SP80 rover operated by Brosnahan was connected by receiver Wifi to a data collector running SurvCE Version 4.06. Brosnahan surveyed Targets 1–10 (twice surveying Target 2) on the western landmass and two south–north transects from the tidal flats to the marsh. The rover operated by Thieler was connected by Data Collector Internet to the data collector running SurvCE Version 4.07. Thieler surveyed targets 11–16 and 19–20. The ProMark 800 was connected by internal GSM to the data collector running SurvCE Version 4.90.44. It was operated by Irwin to survey Targets 1–10 (except for Target 2) and 5 west–east transects from the beach and to the marsh. Positions were only recorded when the solution was fixed.
The measurements were exported from the data collector in a text file in the RW5 format and then converted to a comma-separated values file using the Carlson Report Generator for a SurvCE RW5 Report (
https://www.carlsonemea.com/cwa/report). The three datasets were consolidated into one and then manually divided into two: GCP locations and transect points by referring to the operator-entered label stored in the Note column. The Note column indicates the target number and can be used to match the coordinate to its corresponding target. All points used as GCPs in SfM processing (see bb_20160318_pointcloud.laz metadata in the larger work) are listed in the text file. The following columns were removed because they contained values that were unnecessary or misleading: Point_ID, Cartesian_X, Cartesian_Y, Cartesian_Z, Ant_Hgt_KI, Ant_Hgt_True, Solution, PC DATE STAMP, PC TIME STAMP, and GPS END TIME. The Note column was moved to the first column position. The columns PhotoScan_ptID and Operator were added and populated manually to correspond to the GCP label in the SfM software and the rover operator.
