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Ndvi question
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gwagner
Posted 11/2/2019 07:30 (#7824084 - in reply to #7818496)
Subject: RE: Ndvi question



The short answer is no.

The long answer is; NDVI is short for Normalized Difference Vegetation Index. There are 2 kinds of NDVI’s one is Red NDVI (rNDVI) and the other is Green NDVI (gNDVI). For this discussion rNDVI will be used (for gNDVI you will replace the red band of light with the green).

The pigment in plant leaves, chlorophyll, strongly absorbs visible light (from 0.4 to 0.7 µm)(or blue to red band; i.e. visible light) for use in photosynthesis. The cell structure of the leaves, on the other hand, strongly reflects near-infrared light (from 0.7 to 1.1 µm)(light we as humans cannot see). The more leaves a plant has, the more these wavelengths of light are affected, respectively (Red light is absorbed and NIR is reflected).

In general, there is much more reflected radiation in near-infrared wavelengths than in visible wavelengths. To measure NDVI you need a sensor that will record the NIR band which the Mavic pro 2 cannot (it only measures visible light). You can add an additional sensor to the aircraft (example Sentera has one) to record NIR. Then applying the correct math to the sensor which is rNDVI = (Red band – NIR) / (Red band + NIR) (or gNDVI= (Green band – NIR) / (Green band + NIR)) you can determine true NDVI reading. For agricultural purposes the resulting values will be between 0.3 and 0.8, where 0.08 is very good plant health and 0.03 not so good.

In other words, you cannot a get true NDVI images without a NIR sensor no matter what remote sensing suppliers are trying to sell you. Some use fancy language so you think you are getting NDVI, beware.



Edited by gwagner 11/2/2019 07:31
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