High-resolution orthoimagery and digital surface models of Fern Ridge Lake, Oregon, during annual low pool, January and February, 2023

In cooperation with the U.S. Army Corps of Engineers (USACE), the U.S. Geological Survey (USGS) deployed ground control points and coordinated aerial photograph acquisition of Fern Ridge Lake, a multi-purpose reservoir in western Oregon impounded by the 13-m tall Fern Ridge Dam. Aerial photographs were acquired by the Civil Air Patrol (CAP) during winter 2023 when water levels were at or near typical annual “low pool” or minimum pool, a target elevation (108 m NGVD 29) for flood-control operations. Photographs were acquired at two different altitudes with a WaldoAir XCAM Ultra 50 camera mounted on a Cessna aircraft and captured the entire reservoir area as defined by full pool (or maximum conservation pool elevation), including major tributaries entering the reservoir such as the Long Tom River and Coyote Creek, upstream of Fern Ridge Dam. Dam operations at the 3,700-hectare Fern Ridge Lake, located 39 kilometers upstream of the confluence of the Long Tom River and the Willamette River, along with other hydrogeomorphic conditions, result in a diverse array of geomorphic processes and landforms within the reservoir. To document reservoir floor geomorphology, the USGS applied structure-from-motion (SfM) techniques to these aerial photographs, following the workflow outlined in Over and others (2021), and generated three-dimensional xyz point clouds, digital surface models (DSMs), and orthomosaics of Fern Ridge Lake at low pool. 

This data release includes ground control points, dataset footprints, original aerial photographs, processed point clouds, DSMs, and orthomosaics of Fern Ridge Lake with varying aerial extents and resolutions that were all developed from imagery acquired in January and February of 2023: (1) the January 30  model (FernRideLake_10cm) covered the entire reservoir area with an average point density of 7.47 points per square meter, DSM resolution of 36.6 centimeters per pixel, and orthomosaic ground resolution of 9.15 centimeters per pixel; (2) the January 31 model (FernRidgeLake_5cmLongTomRiver) covered the Long Tom River within the reservoir with an average point density of 25 points per square meter, DSM resolution of 20 centimeters per pixel, and orthomosaic ground resolution of 5 centimeters per pixel; (3) the combined February 2 and February 8 model (FernRidgeLake_5cmCoyoteCreek) covered Coyote Creek within the reservoir with an average point density of 36.3 points per square meter, DSM resolution of 16.6 centimeters per pixel, and orthomosaic ground resolution of 4.15 centimeters per pixel. All DSMs and orthomosaics are formatted as Cloud Optimized GeoTIFFs (COGs) for enhanced web visualization (GDAL 2024). 

This documentation describes a polygon shapefile including the footprints (spatial coverage) of SfM DSMs and orthomosaics of Fern Ridge Lake, Oregon, developed from imagery acquired on January 30, January 31, February 2, and February 8, 2023.