Orthomosaic representing Head of the Meadow Beach, Truro, MA on March 10, 2023

RGB (red blue green) averaged orthomosaic was created in Agisoft Metashape v. 1.8.1 using the following general steps (see Over and others, 2021):
1. Project was created with imagery (located in larger work citation 2023011FA_Truro_f1.zip) and position (located in larger work citation 2023011FA_Truro_f1_photolocations.csv) data brought in using the NAD83(2011)/UTM19N and NAVD88 datums. A 0.15 m GNSS/IPS offset in the z direction was used to represent the approximate offset of the GNSS mount and camera on the Helikite. Photos were aligned at a low accuracy and then GCPs were automatically detected in the point cloud. Ten GCPs (2023011FA_Truro_nav_GCPs.csv) were located.
2. GCP horizontal and vertical accuracy was set 0.02/0.05 m and accuracies for the camera positions were set to 0.10 m. The photos were re-aligned with high accuracy (the pixels are not subsampled for increased processing speed) using a keypoint limit of 40,000 and unlimited tie points.
3. Metashape software refined and optimized, using least squares, the camera positions, GCPs, and lens model using gradual selection and optimization parameters of: Reprojection uncertainty = 15, Projection accuracy = 4, and Reprojection error = 0.3 to minimize the distance between the measured points and the software created points (see Over and others, (2021) for a detailed discussion on these parameters).
4. A dense point cloud was generated using high-quality (images are not subsampled) and a low frequency filtering algorithm. The dense point cloud was then edited by hand to remove erroneous points before generating an interpolated digital surface model (the software refers to all models as "elevation models", but a surface model includes vegetation/canopy returns whereas a terrain model would be only bare earth returns).
5. The digital surface model was used to build an RGB averaged orthomosaic, which was then exported from the software at a resolution of 10 cm and in NAD83(2011)/UTM Zone 19N (ESPG:6348).