Counting marmots…
This is a 5 cm resolution Digital Elevation Model (DEM) for the Gothic Townsite area, derived from Uncrewed Aircraft System (drone) imagery collected in September - November of 2021. The DEM was generated using structure-from-motion processing of RGB imagery collected with a 40-megapixel camera mounted on the UAS, flying approximately 100 m aove the terrain. Heights represent orthometric (geod) height above the EGM96 geoid model. Flights were conducted approximately weekly within 3 hours of solar noon, in full-sun conditions where possible. The flights typically took approximately 75 minutes to complete, and flightlines were oriented NNW-SSE at a 28m spacing, starting in the western proportion of the imaging area and progressing east. This means that western parts of the imaging area were typically imaged approximately 1-hour beore the eastern edges. Raw images were captured as 16-bit TIFF files approximately once every 1.2 seconds, providing approximately 75 percent forward overlap and 70 percent side overlap between adjacent images. For densely forested parts of the landscape, the forward speed of the aircraft was reduced to 8 m/sec to increase the forward overlap to 85%, improving orthomosaic performance for complex vegetation. Raw image data was georeferenced and orthorectified in Agisoft Metashape software (version 1.7), using information from the UAS system's Real-time Kinematic (RTK) global satellite navigation system as well as 8-15 ground-control points geolocated to within 2 cm. Independent assessment indicates a geographic precision of approximately 5 cm (Mean Absolute Error). Point clouds were exported from Agisoft Metashape and imported into CloudCompare software. Ground points were classified using a Cloth Simulation Filter and then manually edited to remove residual and building points. The cloud was then re-imported into Metashape, and the DEM grid was generated using the built-in inverse-distance-weighted interpolation algorithm. Note that this DEM version has been shifted by approximately 0.8 m to align with an updated reference frame for the Gothic Townsite implemented in 2026. All DEM, surface model, and canopy height products are in this reference frame. The previous version (v5) is now deprecated.
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