Estimates water transparency (Secchi disk depth, SDD) in meters over water bodies, from Sentinel-2 Surface Reflectance imagery (ESA/Copernicus, 10 m). SDD is derived from the blue-to-red reflectance ratio and shows how deep light penetrates: warm colors mark turbid, opaque water (low depth) and cool blue tones mark clear water with high transparency (high depth). Only water pixels are analyzed, over the selected time window.
The Secchi Depth layer estimates water transparency, expressed as the equivalent Secchi disk depth in meters, for inland and coastal water bodies. It is computed from Sentinel-2 Surface Reflectance imagery served through Google Earth Engine (COPERNICUS/S2_SR_HARMONIZED), using the blue and red bands.
| Code | Provider | Resolution | Year |
|---|---|---|---|
| WRD_S2XXX_99 | ESA/Copernicus (Sentinel-2 Surface Reflectance) | 10 m | 2017 to present |
For each cloud-free acquisition in the selected window, SDD is derived from the blue-to-red reflectance ratio as SDD = a · ln(B2 / B4) + b (B2 Blue 490 nm, B4 Red 665 nm; default calibration a = 1.7, b = 1.6), clamped to the 0-30 m range. Clouds and shadows are removed via the Sentinel-2 Scene Classification (SCL) band and only water pixels are retained; the per-acquisition values are then averaged into a mean composite over the requested period. Values are rendered on a 0-10 m scale from warm colors (opaque, turbid water) to blue (clear, highly transparent water).