Getting Back to Nature…

Roses are red,

Violets are blue,

What is Normalized Difference Vegetation Index?

I haven’t got a clue…

At least that was my position on the subject a few weeks ago, now however I am fully clued up on the ins and outs of NDVI.

Essentially its a method of determining the density of greenery (aka vegetation) that covers a certain area. The Sun emits many wavelengths across the Electromagnetic Spectrum (read my early blog post on the ES here) and when the Sun’s light hits various objects certain wavelengths are either reflected or absorbed depending upon the object’s characteristics.

The pigment in plants, called chlorophyll, has certain properties that mean it strongly absorbs visible light, and heavily reflects NIR. The greener a plant, ie. the healthier it is, the more visible is absorbed and NIR reflected. Using the resulting NDVI values, the health and density of vegetation can be determined (earthobservatory.nasa.gov, 2000).

Once the NDVI values have been gathered they can be used not only to map vegetation density and heath changes over a period of time, but also show the impacts that certain events have had on the environment. This could be the results of a tsunami, earthquake, flooding, conflict etc.

NDVI Darfu
NDVI value for August (right) and April (left) in 2008 in the Darfur region of Sudan.

As you can see from the images above, the vegetation health in the Darfur region is significantly better in the south of the area studied. What’s more, the changes in NDVI values across the year show a cycle of growth and depletion in vegetation health and density. Looking at the chart below, the trend is displayed again showing a fluctuation in NDVI values across the year.

Fun Fact: Earth is the only known planet where fire can burn!

References:

Campbell, J. B. & Wynne, R. H. (2011), Introduction to remote sensing, 5th edn., New York: The Guilford Press, pp. 7.

Weier, J., & Herring, D. (2000), Measuring Vegetation, Available at: https://earthobservatory.nasa.gov/Features/MeasuringVegetation, (Accessed on: 25th May, 2017).

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