Scientists at the University of New Hampshire's Forest Watch program use an expensive spectral reflectance measuring instrument to study the health of white pines in New England. Below is a typical pattern for a healthy set of white pine needles.
The Y-axis of the graph represents the amount of reflected light from the pine needles. Large values indicate that most of that wavelength of light is reflected, low values indicate that much of those wavelengths is being absorbed.
The X-axis represents the wavelength of light (if needed, review of the electromagnetic spectrum). The seven bands of light that Landsat measures are marked by shaded vertical boxes.
Notice that plants absorb most of the red and blue light shining on the needles. In the near infrared, plants reflect a tremendous amount of light, which is why plant leaves are so light colored in near infrared digital photographs.
Now compare the differences in reflected light patterns from two sets of white pine needles, one that is healthy and a second with stressed needles. Notice that the stressed leaves reflect less near infrared compared to the healthy needles, and reflect more red and blue light. This latter pattern allows us to use plant stress detection filters to see the health of plants when walking through fields and forests.
From satellite, we use a combination of near infrared and red light to monitor plant health. This is explored in the Vegetation Analysis Investigation.
Go To Using Analysis Tools
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