Creating an NDVI
Our first example will be a Normalized Differential Vegetative Index or NDVI. NDVIs are used to show the relative health of plants in an area of interest. An NDVI algorithm shows relative health by highlighting chlorophyll density in plants. NDVIs use only the red and infrared bands. The formula is:
NDVI = (Infrared – Red) / (Infrared + Red)
The goal of this analysis is to begin with a multispectral image containing those two bands and end up with a pseudo-color image using seven classes that color the healthier plants darker green, less-healthy plants lighter green, and bare soil brown.
Because the health index is relative, it is important to localize the area of interest. You could perform a relative index for the entire globe, but vast areas like the Sahara Desert on the low-vegetation extreme and densely forested areas like the Amazon Jungle skew the results for vegetation in the middle range. However, that being said, climate scientists do routinely create global NDVIs...
