Aerial Imagery and Structure-from-Motion Derived Data Products from an Aerial Digital Photographic Survey of 10 Islands in the Oregon Coast National Wildlife Refuge Complex, OR, USA

This release presents hi-resolution structure-from-motion (SfM) habitat imagery suitable for GIS. The U.S. Geological Survey (USGS) has developed SfM to become a low-cost technique for coastal change assessments. The software uses a combination of camera locations and ground control points to produce digital surface models (DSMs) and orthorectified imagery products. SfM products include high resolution RGB color imagery and offer an alternative to such expensive topographic survey techniques including aerial light detection and ranging (LIDAR) and terrestrial laser scanning. With Global Positioning System (GPS) ground control accuracies of less than 10-centimeters and small image pixel sizes, SfM can detect landscape change at the decimeter scale, comparable with airborne LIDAR. This data release includes hi-resolution aerial imagery, digital point clouds, island orthomosaics, and digital topographic surfaces (digital surface models; DSMs) derived from aerial images using SfM photogrammetry (Agisoft Metashape, Agisoft L.L.C., 2020, https://www.agisoft.com). These data are intended to support the U.S. Fish and Wildlife Service (USFWS) Oregon Coast National Wildlife Refuge Complex (OCNWRC) with landscape-level conservation science data to evaluate species abundance and impacts related to habitat change including invasive vegetation and erosion. The Refuge’s Comprehensive Conservation Plan (CCP) calls for USGS to help establish long-term seabird research to better understand the interrelationship of physical and biological factors that shape refuge lands and resources, including assessing the abundance of burrow- and crevice-nesting seabirds every 10 years. A GIS-based inventory and monitoring program for seabirds and plant species on vegetated offshore islands can be used to evaluate change and monitor habitat response to invasive plant management. 
 
USGS has collected and assembled new, high-resolution digital orthoimagery and digital surface information for 10 islands. We used SfM to generate orthoDSM layers (~0.5 meter pixel dimension) that can serve as base GIS layer for quantifying landscape features, current erosional surfaces, habitat classifications, survey effort, and burrowing seabird nest site locations. For each island site, we used a set of individual, overlapping oblique aerial images to create a georeferenced, orthorectified, mosaic image (orthomosaic, approximate GSD = 1.5 centimeters) and a 0.5 meter resolution DSM covering the entire surface areas for each of the 10 islands. 
 
Imagery was collected from a Eurocopter MH-65 Dolphin using a hand-held Canon EOS 5Dsr digital SLR camera (50.6MP Full-Frame CMOS Sensor) with attached Canon GPS Receiver GP-E2 and Canon EF 135mm f/2L USM prime telephoto lens. Images used f/5.6, min shutter speed 1/2500s, and max IS0 800. Pilots were instructed to circumnavigate each island at 750 feet ASL with a 750 feet horizontal distance from the island coastline.