If you are just starting up in the precision agriculture field with the various indexes, you will certainly have noticed that the NDVI can be calculated either by the blue spectrum, either with the red spectrum. Both coupled with the NIR (Near Infrared). But which formula to choose? Better use NDVI with blue or NDVI with the Red? What are the differences? Here you go.
Let’s start with a quick NDVI explanation. The NDVI is the most widespread and well-known vegetation index which will allow you to determine the vegetation state of health in order to verify the lack of water and the presence of parasites.
Here is how to calculate the NDVI with specific formula:
Now, what should you use? In a study, the NDVI with the red spectrum is more widespread, accurate and reliable than the one with the blue spectrum. In the NDVI with the blue spectrum non-photosynthetic materials are also considered, giving incorrect information. You must also consider that when using the blue, the NDVI value of interest can be limited, making it difficult to recognize the plants in very bad health condition. To see this, just look at the comparison of the two indexes in the image below:
So the NDVI with the blue spectrum is to be discarded? Of course not. The blue spectrum is further away from the red spectrum than the NIR. It is therefore more suitable for cameras with a single filter, such as for example the MAPIR NDVI + NIR. In this case you can calculate the NDVI with a single camera. A solution therefore faster and cheaper.