Normalized Difference Vegetation Index to monitor crop health is determined from

Correct option is D

Explanation of the Correct Option (d): Reflectance of near-infrared and red band
· NDVI (Normalized Difference Vegetation Index) is calculated using the formula: NDVI = (NIR − Red) / (NIR + Red)
· Healthy green vegetation:
· Strongly absorbs red light (for photosynthesis)
· Strongly reflects near-infrared (NIR) radiation
· The contrast between:
· High NIR reflectance
· Low red reflectance provides a reliable measure of crop vigor, biomass, and health.
· Hence, NDVI is determined using near-infrared and red bands.
Explanation of Other Options
Option (a): Reflectance of red band
· Incorrect because:
· NDVI requires two spectral bands, not one.
Option (b): Reflectance of blue and red band
· Incorrect because:
· Blue band is not used in NDVI calculation.
Option (c): Reflectance of shortwave and red band
· Incorrect because:
· Shortwave infrared (SWIR) is used in other indices, not NDVI.
Key Points Related to the Question
· NDVI range: −1 to +1
· Higher NDVI → healthier and denser vegetation
· NDVI is widely used in:
· Crop health monitoring
· Drought assessment
· Yield estimation
· Common sensors: Landsat, Sentinel-2, MODIS