True color and multispectral ortho products created from UAS operations at North Core Banks, NC in October 2022

The ortho products were created in Agisoft Metashape v. 1.8.1 using the following general steps (see Over and others, 2021 for a more detailed methodology explanation): 1. For each site (NP0, NP1, and NP3) a project was created and Ricoh and Altum-PT imagery (located in larger work citation) was imported. 2. Photos were aligned at a low accuracy and then GCPs were automatically detected in the point cloud. Incorrect detections were removed manually. GCP positions (2022034FA_NCB_GCPs.csv located in the larger work citation) were added to the project in the reference systems NAD83(2011)/UTM Zone 18N and NAVD88 (geoid 18). Accuracies for the GCPs were set to 0.05 m and the camera positions for the Altum-PT images were turned off. The photos were then re-aligned with high accuracy (the pixels were not subsampled) using a keypoint limit of 60,000 and unlimited tie points. 3. The alignment process matched pixels between images to create point clouds and put the imagery into a relative spatial context using the GCPs. The resultant point clouds were filtered using one iteration of the 'Reconstruction uncertainty' filter at a level of 12, one iteration of the 'Projection accuracy' filter at a level of 3, and three iterations of the 'Reprojection accuracy' filter to get to a level of 0.3. With each filter, iteration points are selected, deleted, and then the camera model was optimized to refine the focal length, cx, cy, k1, k2, k3, p1, and p2 camera model coefficients. 4. At this point, multiple ‘chunks’ were created so that independent high quality dense clouds with a low-frequency filtering algorithm could be made from the Ricoh images and Altum-PT images. The dense point clouds were then edited by visual inspection and Metashape’s confidence filter to remove points with a low confidence near the edges and near water bodies. 4. Digital elevation model products were built from the dense clouds and then orthomosaics were built from these with refined seamlines. The first Altum-PT ortho product was transformed so that the bands were all divided by the reflectance normalization factor 32768 (half of the available digital number range or 100% reflectance for each band for 16-bit images) and reordered so that bands 1-5 are in wavelength order, Blue, Green, Red, Red edge, and Near-infrared, respectively. The normalization process produces values that are a unitless reflectance value between 0 and 1, where 1 would be 100% reflectance, i.e. lighter. This 5-band product was exported at 10 cm resolution. The second Altum-PT product was just the panchromatic band and was not transformed, the product was exported at 2.5 cm. The Ricoh product is an RGB product with 5 cm resolution. All products are in NAD83(2011)/UTM Zone 18N and region boundaries were rounded to the nearest 5 m interval. West and south bounds were rounded up and east and north bounds were rounded down. 5. All ortho image products were compressed and turned into a cloud-optimized GeoTIFFs (COG) using gdal_translate with the following command: for %i in (.\*.tif) do gdal_translate %i .\cog\%~ni_cog.tif -of COG -stats -co BLOCKSIZE=256 -co COMPRESS=DEFLATE -co PREDICTOR=YES -co NUM_THREADS=ALL_CPUS -co BIGTIFF=YES (v. 3.1.4 accessed October 20, 2020 https://gdal.org/). Where i is the name of each geoTIFF section.