You are here:
Validation of Sentinel-2 maximum chlorophyll-a index for U.S. waters
Citation:
Schaeffer, B., W. Salls, M. Amanatides, D. Keith, K. Loftin, R. Stumpf, B. Seegers, E. Urquhart, AND P. Werdell. Validation of Sentinel-2 maximum chlorophyll-a index for U.S. waters. Ocean Optics Conference, Dubrovnik, CROATIA, October 08 - 12, 2018.
Impact/Purpose:
The Cyanobacteria Assessment Network (CyAN) is a multi-agency project among the National Aeronautics and Space Administration (NASA), National Oceanic and Atmospheric Administration (NOAA), U.S. Geological Survey (USGS), and U.S. Environmental Protection Agency (EPA) to develop an early warning indicator system using historical and current satellite data to detect algal blooms in U.S. freshwater systems. The CyAN mission is to support the environmental management and public use of U.S. lakes and estuaries by providing a capability of detecting and quantifying algal blooms and related water quality using satellite data records. Water quality is a critical consideration in determining water resource availability for human consumption, aquatic life, and recreation (U.S. EPA, 2013). Concentrations of chlorophyll-a are used as a proxy for phytoplankton biomass, can serve as an indicator of increased anthropogenic nutrient stress, and as a measure of nuisance algal blooms.
Description:
Chlorophyll-a concentration can serve as a proxy for phytoplankton biomass, an indicator of increased anthropogenic nutrient stress, and a measure of nuisance algal blooms. Here, we compare chlorophyll-a concentrations derived from satellite imagery to those obtained by in situ sampling. Satellite chlorophyll-a concentrations were derived from the European Space Agency’s (ESA) Sentinel-2 MultiSpectral Instrument using the Maximum Chlorophyll Index (MCI). In situ data from the Water Quality Portal, serves data collected by state, federal, and tribal groups across the United States, was quality assured and entered in the Field Integrated Exploratory Lakes Database (FIELD) for validation. Initial data screening included cloud free satellite scenes, sampling depth 60 meters, and within ±3, 5, and 10 days of the satellite overpass. The spectral reflectance (before atmospheric correction) and Bottom of Rayleigh Reflection (BRR, Rayleigh removed) were evaluated as options for MCI implementation within ESA’s Sentinel Application Platform software. Validation regression results and statistical distributions for derived MCI are presented and evaluated for >300 lakes, reservoirs, and estuaries. The intended outcome of this work is to use this satellite product to inform trophic status and eutrophication level assessments across the United States.
