Low-altitude aerial imagery collected from a Helikite at Head of the Meadow Beach, Truro, MA on March 10, 2023

These JPEG images were collected with a camera (Sony a6000) wired to the GNSS receiver 15 cm vertically offset from the focal point and duct taped together, then hung from the Helikite (2023011FA_Truro_imagery_browse.JPG) so that the camera faced downward. The Helikite was on a 60 m string and kitesurfing harness; together the Helikite and gear were walked up and down the beach to achieve overlapping images. The horizontal positions and elevations of each image (2023011FA_Truro_f1_photoLocations.csv) were recorded from the GNSS receiver (EMLID Reach M2) and processed in PPK mode and processed using a base station set-up in the parking lot. It is recommended when using the imagery for photogrammetric purposes to also use the ground control point locations (see 2023011FA_Truro_nav_GCPs.csv).

The GNSS navigation data was processed in Emlid Studio (v 1.4) using the drone data processing workflow. The positions were processed in the NAD83(2011) datum, which provided the Latitude, Longitude, and Ellipsoid attributes. Then Geoid 18B was applied using NAVD88 as the vertical datum and UTM Zone 19N for the horizontal coordinate reference system to produce the Northing, Easting, and Altitude attributes. The GPS offset was not accounted for in this step so the offset should be accounted for when deriving further products. All of the attributes here are provided in the 2023011FA_Truro_f1_photoLocations.csv but only the latitude, longitude, and altitude (NAVD88) were embedded in the image header using Emlid Studio.

The images acquired with the camera were geotagged and processed to add additional information required by the USGS to the EXIF headers using ExifTools (https://exiftool.org/, version: 12.06), and the files were renamed to a unique identifier using Namexif (http://www.digicamsoft.com/softnamexif.html, version 2.1) to avoid any possibility of duplicate names. These steps are described here. For more information on the EXIF tags here and automatically populated by the camera see https://exiftool.org/TagNames/EXIF.html
1. Using the GNSS navigation from the previous step, ExifTools was used to tag each photo with the following tags: Credit, Copyright, UsageTerms, ImageDescription, Artist, XMP:ExternalMetadataLink, XMP:UsageTerms, XMP:AttributionURL, XMP:PreservedFilename, GPSTimeStamp, GPSAltitudeRef, GPSLatitudeRef, GPSLongitudeRef, GPSAreaInfo, GPSMapDatum, GPSLatitude, GPSLongitude, and GPSAltitude stored in a CSV file with the command:' -exiftool -csv="C:\directory\name\Geotags_EXIF.csv" C:\directory\name\of\photos *.JPG
The first row of the CSV are the tag names; the first column is SourceName (unique image names). Keywords were added with the following command in the directory with all the photographs: exiftool -keywords="aerial imagery" -keywords="Head of the Meadow Beach" -keywords=Massachusetts -keywords="2023-011-FA" -keywords=USGS -overwrite_original *.JPG
To read out the photo information to a CSV when in the directory with the photos the command is: exiftool -csv *.JPG > directory/name/allheaders_out.csv
2. All the JPEG images were renamed with Namexif (https://us.digicamsoft.com/softnamexif.html v 2.2 accessed April 2020) to ensure unique filenames and compliance with the USGS Coastal and Marine Hazards and Resources Program's best practices for image naming convention. Images were renamed with the field survey ID prefix; flight number, and ID that distinguishes USGS cameras by make/camera number, the image acquisition date, coordinated universal time (UTC) in ISO8601 format, and a suffix with the original image name. For example, image name '2023011FA_f01s6000_20230310T165822Z_image####.jpg', 2023011FA is the survey ID, f01 is the flight number, s6000 is the camera make (SONY) and model (6000), and 20230310 is the UTC date in the format YYYYMMDD. A 'T' is used to separate UTC date from UTC time in format HHMMSS followed by a Z, and image####.jpg is the original raw photo name appended to the end of the new filename.