Sentinel-2 ACOLITE-DSF Aquatic Reflectance for the Conterminous United States

This dynamic data release presents an aquatic reflectance product with 20-meter spatial resolution derived from Sentinel-2 satellite imagery for the conterminous United States using the Atmospheric Correction for OLI “lite” (ACOLITE). Aquatic reflectance, noted Rhow in ACOLITE documentation, is defined here as unitless water-leaving radiance reflectance and represents the ratio of water-leaving radiance (units of watts per square meter per steradian per nanometer) to downwelling irradiance (units of watts per square meter per nanometer) multiplied by π. This is also known as remote sensing reflectance (units of per steradian) multiplied by π. These data are intended for use in remote sensing of water color and differ from other satellite imagery products by using an atmospheric correction approach that is designed for aquatic applications. Level-1C top of atmosphere imagery collected with Multispectral Instrument (MSI) on the Sentinel-2A and Sentinel-2B satellites was atmospherically corrected using the dark spectrum fitting (DSF) algorithm and the Atmospheric Correction for OLI ‘lite’ (ACOLITE) version 20221114.0 processing software (https://github.com/acolite/acolite/releases/tag/20221114.0). The DSF atmospheric correction largely avoids glint and adjacency effects making the technique an improvement over other atmospheric correction for inland waters. Current default ACOLITE settings were used with the exception that; 1) output pixel size (S2_TARGET_RES) was set to 20 m, 2) the tiling dimensions (DSF_TILE_DIMENSIONS) was set to 300 pixels, 3) the non-water pixel mask (L2W_MASK THRESHOLD) was set to 0.05 and, 4) the Digital Elevation Model (DEM) to compute pressure (DEM_SOURCE) was set to the Shuttle Radar Topography Mission (SRTM). The optional residual glint correcting using the SWIR bands was not applied. Users are directed to the metadata file for a complete description of the atmospheric correction process. A Normalized Difference Water Index (NDWI) product is calculated as the difference of Band 3 (560 nm) and Band 8a (865 nm) divided by the sum of Band 3 and Band 8a, that is: NDWI = (Band 3 – Band 8a)/(Band 3 + Band a8a). The aquatic reflectance and NDWI products are stored as Cloud Optimized GeoTIFFs (COGs). Each Sentinel-2 scene includes cloud optimized geotiffs (COG) of aquatic reflectance raters for band 1, 2, 3, 4, 5, 6, 7, 8, 8a, 11, and 12, a computed Normalized Difference Water Index (NDWI) COG, and an ACOLITE settings file. The file nam