Lower Androscoggin Watershed Hydrologic Unit 8 Seamless 1-m DEM Pilot, 2013 to 2020

To advance the USGS 3D National Topography Model (3DNTM) including the next generation of the 3D Elevation Program (3DEP) and the 3D Hydrography Program, USGS is producing a new one-meter resolution seamless digital elevation model (DEM) product. The project is funded by the Inflation Reduction Act. This dataset is a 1-m seamless DEM prototype that was created from several different 3D Elevation Program (3DEP) Original Product Resolution source DEMs. The DEM covers the spatial extent of the Lower Androscoggin River Watershed 8-digit hydrologic unit (01040002), as delineated in the USGS Watershed Boundary Dataset. This prototype data is being released as a precursor to the new product that will be seamless across 3DEP collection projects. The metadata and data organization of this prototype may not match the final design of the new product line.

The National Geospatial Technical Operations Center and the Earth Resources Observation and Science Center of the U.S. Geological Survey researched and created a new Seamless 1-m Digital Elevation Model (DEM). This is a joint project by these two centers as part of the new National Geospatial Directorate (NGD). A Seamless 1-m DEM (S1M) requires merging multiple lidar projects with unique lineages to include the lidar sensor, bare-earth DEM generation methodology, source resolution, datums/projection, unit of measure, and geoid (mean sea level model). The goal is to generate a seamless raster elevation dataset aligned both vertically and horizontally to a common reference system for the conterminous United States. Due to the size of watersheds, and the fact they do not respect political or Universal Transverse Mercator (UTM) boundaries, the NGD chose the North American Datum of 1983 (2011) USA Contiguous Albers Equal Area Conic projection for this dataset (EPSG: 6350). The NGD also converted older geoids referenced to North American Vertical Datum of 1988 (EPSG: 5703), to the current GEOID18 model. The raster elevation product, the Federal Geographic Data Committee metadata, and the spatially referenced metadata files are contained in the downloadable bundle. This collection of high-resolution elevation data is available in a user-friendly Cloud Optimized Georeferenced Tagged Image File Format (GeoTIFF). The elevation model has floating point numeric values. Areas where data is incomplete due to lack of full data coverage or NoData are represented with the numeric value of -999999. Spatially referenced metadata are contained within an open-source GeoPackage that stores footprints for each of the input source areas along with source data characteristics. For this pilot project, the NGD merged the original product resolution source DEMs from five lidar projects collected between 2013 to 2020 in the Lower Androscoggin Hydrologic Unit 8 (HU8) watershed, HU ID 01040002. The final derived DEM has a spatial resolution of 1 meter, elevations ranging from -0.1098 meters to 1916.04 meters, and covers 2,218 square miles (5,745 square kilometers).