Questo layer mostra la variazione della torbidità di un corpo idrico tra due periodi annuali, calcolata dall'indice NDTI (Normalized Difference Turbidity Index, NDTI = (B4 - B3) / (B4 + B3)) su immagini Sentinel-2 (COPERNICUS/S2_SR_HARMONIZED) a risoluzione 10 m, sui soli pixel d'acqua. Il valore è la differenza tra il composito NDTI del periodo finale e quello del periodo iniziale. I valori positivi (colori caldi) indicano un aumento della torbidità (più particelle in sospensione, minore trasparenza), mentre i valori negativi (colori freddi) indicano acque più limpide.
This layer quantifies how water turbidity has changed between two annual periods, using the Normalized Difference Turbidity Index (NDTI) derived from Sentinel-2 surface reflectance. NDTI exploits the contrast between the Red and Green bands, which increases as suspended particles scatter more light. The analysis is restricted to water pixels (land is masked) and clouds are masked before compositing.
| Code | Provider | Resolution | Year |
|---|---|---|---|
| WRD_SCLXX_99 | ESA / Copernicus (Sentinel-2, COPERNICUS/S2_SR_HARMONIZED) | 10 m | 2017 to present |
For each of the two periods a cloud-free, water-only NDTI composite is built as NDTI = (B4 - B3) / (B4 + B3), where B4 is Red (665 nm) and B3 is Green (560 nm). The delta layer is the pixel-wise subtraction of the initial-period composite from the final-period composite (final minus initial); positive values indicate increased turbidity and negative values indicate clearer water. Sentinel-2 data are available from April 2017 onward; the base processing scale is 10 m and is adapted upward (20 m or 25 m) for very large areas.