NDVI measures vegetation health using satellite data. Healthy plants reflect more near-infrared (NIR) light and absorb red light.

• Formula: NDVI = (NIR - Red) / (NIR + Red) 

• Range:
  +0.6 to +1.0 → Healthy vegetation
  0.2 to 0.5 → Sparse/stressed vegetation
  < 0.2 → Bare soil, urban areas, or water

• Data Source :
  Based on Landsat 5, 7, 8, and 9 imagery (NASA & USGS) processed in Google Earth Engine for 1990–2024.