Field crews used three differential GNSS (Global Navigation Satellite System) rover instruments survey 254 reference elevation points roughly along two north-south transects and six east-west transects at approximately 5-meter intervals between points. Transects were loosely-established as they were only intended to collect a representative sample of reference points from around the study area. 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. The SP80 rover operated by Brosnahan was connected by receiver WiFi to a data collector running SurvCE Version 4.06. Brosnahan surveyed two south–north transects from the tidal flats to the marsh. Irwin operated the ProMark 800, connected by internal GSM to the data collector running SurvCE Version 4.90.44, to survey 6 west–east transects. In some cases operators reversed direction or surveyed locations off the trajectory of the transect.
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 separated into GCP locations and transect points by referring to the operator-entered label stored in the Note column. The Note column indicates the transect label or a description of the point surveyed (e.g. ‘BOARD’). All points used as reference points to assess the accuracy of 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.
