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Do clouds affect NDVI?
Yes, it affects the values of NDVI, and it may not give the desired results sometimes. The clouds effect on NDVI is then eliminated by selecting for each pixel the greatest value on any day during the 14-day period (the highest NDVI value is assumed to represent the maximum vegetation “greenness” during the period).
Do clouds have high NDVI?
Vegetated areas will generally yield high values for either index [VI or NDVI] because of their relatively high near-IR relectance and low visible reflectance. In contrast, clouds, water, and snow have larger visible relfectance than near-IR reflectance. Thus, these features yield a negative index.
Why does water have a negative NDVI value?
4.1. The mounting amount of the positive NDVI values indicates the increase in the amounts of green vegetation. The NDVI values near zero and decreasing negative values indicate nonvegetated features, such as barren surfaces (rock and soil), water, snow, ice, and clouds.
Can Nir see through clouds?
In each case, pilot vision improves, but clouds and fog remain a problem. Water droplets are usually smaller than 100 microns, which is small, but still much larger than the span of an infrared or visible-light wave, so neither infrared light nor visible light can pass easily through clouds.
Why is NIR useful?
One of the reasons why NIR analysis is so useful is that it can use reflected energy and this means that NIR analysis can be done with little or no sample preparation. Reflected energy is complex. First, because there are two components, specular (or mirror-like) and diffuse.
Is infrared long or short wave?
Short-wave infrared energy comes directly from the sun, but is not felt as heat. It converts into heat when it strikes an object. Long-wave infrared energy is the heat radiated from an object, which has received short-wave infrared radiation.