This layer maps floating algae and surface aquatic vegetation on water bodies using the Floating Algae Index (FAI). It is derived from Sentinel-2 L2A surface reflectance imagery (Copernicus, ~20 m) processed on Google Earth Engine. Higher FAI values (greens to reds) indicate denser algal films or mats on the water surface, while low values (blues) indicate clear water with no floating algae.
The Floating Algae Index (FAI) detects floating algae and surface aquatic vegetation on water bodies through a spectral baseline-subtraction technique. Sentinel-2 acquisitions over the selected period are cloud- and shadow-masked using the Scene Classification Layer (SCL), optionally restricted to water pixels, and averaged into a composite; the FAI is then computed per pixel and rendered as a continuous gradient.
| Code | Provider | Resolution | Year |
|---|---|---|---|
| WRD_S2XXX_99 | ESA / Copernicus (Sentinel-2 L2A, COPERNICUS/S2_SR_HARMONIZED via Google Earth Engine) | ~20 m | 2017-present |
FAI = B8A - [B4 + (B11 - B4) * lambda], with lambda = (865 - 665) / (1610 - 665) = 0.211, using the narrow NIR band B8A (865 nm), red B4 (665 nm) and SWIR1 B11 (1610 nm). This baseline subtraction isolates the near-infrared reflectance peak of floating vegetation against the surrounding water (after Hu, 2009).