NDVI

 

About NDVI

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The Normalized Difference Vegetation Index (NDVI) is an index of plant "greenness" or photosynthetic activity, and is one of the most commonly used vegetation indices. Vegetation indices are based on the observation that different surfaces reflect different types of light differently. Photosynthetically active vegetation, in particular, absorbs most of the red light that hits it while reflecting much of the near infrared light. Vegetation that is dead or stressed reflects more red light and less near infrared light. Likewise, non-vegetated surfaces have a much more even reflectance across the light spectrum.

By taking the ratio of red and near infrared bands from a remotely-sensed image, an index of vegetation "greenness" can be defined. The Normalized Difference Vegetation Index (NDVI) is probably the most common of these ratio indices for vegetation. NDVI is calculated on a per-pixel basis as the normalized difference between the red and near infrared bands from an image:



Where NIR is the near infrared band value for a cell and RED is the red band value for the cell. NDVI can be calculated for any image that has a red and a near infrared band. The biophysical interpretation of NDVI is the fraction of absorbed photosynthetically active radiation.

Many factors affect NDVI values like plant photosynthetic activity, total plant cover, biomass, plant and soil moisture, and plant stress. Because of this, NDVI is correlated with many agricultural and ecosystem attributes that are of interest to researchers and managers (e.g., net primary productivity, canopy cover, bare ground cover). Also, because it is a ratio of two bands, NDVI helps compensate for differences both in illumination within an image due to slope and aspect, and differences between images due things like time of day or season when the images were acquired. Thus, vegetation indices like NDVI make it possible to compare images over time to look for agricultural and ecologically significant changes.

    Crop Management Benefits
  • Canopy coverage & density detection
  • NDVI with time provides accurate growth trending
  • Frost Damage Detection
  • Large Scale Pest Outbreaks
  • Optimizing crop rotation durations
  • Ecological Benefits
  • Vegetation dynamics or plant phenological changes over time
  • Biomass production
  • Grazing impacts or attributes related to grazing management (e.g., stocking rates)
  • Changes in rangeland condition
  • Vegetation or land cover classification
  • Soil moisture
  • Carbon sequestration or CO2 flux