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Normalized Difference Vegetation Index

The Normalized Difference Vegetation Index (NDVI) is basically used to measure the growth of plants, to determine regions covered in vegetation and control the production of biomass.


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How is it calculated?

The ICGC's digital airborne cameras collect information from four regions of the electromagnetic spectrum, specifically from red, green, blue and near infrared regions (the latter cannot be detected by the human eye). The NDVI is calculated based on the information given by the red and near infrared regions, with the following formula:

NDVI = (near infrared - red) / (near infrared + red)

How is it interpreted?

When a tree is vigorous, it reflects a lot of sun radiation in near infrared and not much in red, so the NDVI is high. However, when a tree is sick, the opposite happens.

For example, if a vigorous tree reflects 50% in near infrared region and 8% in red region, the NDVI will be 0.72, according to the previous formula. However, if a sick tree reflects 40% in the near infrared region and 20% in red region, the NDVI will be 0.33.

So, taking into account that the NDVI always produces a number between -1 and 1, because of how it is calculated, we could say that an NDVI < 0 represents artificial cover or areas with water, NDVI between 0 and 0.3 represents bare soil, and a high NDVI value represents vegetation.


The following image is a normal aerial photo, where some areas of vegetation can be seen.

The following image includes near infrared, which clearly shows vegetation (red).

The following image is a non-classified NDVI value, that is, the direct result of the previous formula. In this one, the lighter areas are vigorous vegetation (high NDVI), and the darker areas are water or artificial cover (negative NDVI).

If in the previous image the

  • darker areas (NDVI < 0), which represent water or artificial cover, in red,
  • the dark areas (0 < NDVI < 0.2), which represent bare soil and dead vegetation, in orange,
  • the neither dark nor light areas (0.2 < NDVI < 0.4), which represent shrub or grassland, in yellow,
  • the light areas (0.4 < NDVI < 0.6), which represent abundant and vigorous vegetation, in light green, and
  • the lighter areas (NDVI > 0.6), which represent very dense and vigorous vegetation, in dark green,

are represented, the following image is produced, where we can easily see the areas with more and less vigorous vegetation:

This cartography is under the Creative Commons Attribution 4.0 International license.
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