What is a Vegetation Index?
A Vegetation Index (VI) is a spectral calculation that is done between two or more bands of the source data designed to enhance the contribution of vegetation properties and allow for comparisons of photosynthetic activity across your area of interest.
When the VI calculation takes place, it cycles pixel by pixel through your entire dataset and runs a calculation on the spectral values of that pixel. This will assign a value representing some version of plant health for each pixel in the image. These values are then turned into the colorized map you see on screen when the calculation is complete.
VI’s allow you to see relative differences in the general plant health across your entire field. Because these are relative differences in plant health across your field it is important to apply only to the areas you are interested in. For an example if you include a gravel road in the bounds of your vegetation index run the lower side of your VI range is going to be thrown off by this non living material included in your area of interest.
The methodology behind these calculations are slightly different for each VI that we offer. Below we have reviewed each Vegetation Index applicable to Visual (RGB) data in PrecisionMapper.
Vegetation Indices for Visual Data
Visual data has 3 bands of the spectrum that can be used in the calculation of Vegetation Indices against the orthomosaic- Red, Green, and Blue.
Most plants are green because they contain a pigment called chlorophyll. Chlorophyll fuels the process of Photosynthesis in living plants by allowing them to absorb energy from light. Chlorophyll absorbs light in the red (long wavelength) and the blue (short wavelength) regions of the visible light spectrum. Green light is not absorbed but reflected, making the plant appear green.
For calculation of plant health values with Visual data the greenness of the vegetation is the most revealing property of the plant. Therefore each Vegetation Index for Visual data relies heavily on the greenness seen in the source imagery.
We have 3 vegetation indices that can be used with your Visual data.
- Visual NDVI- Visual Normalized Difference Vegetation Index
- GLI- Green Leaf Index
- VARI- Visual Atmospheric Resistance Index
|Supported Sensors||Visual (RGB)|
|Supported Resolution||20 cm/pixel or less|
|Estimated Processing Time||2 Hours or less|
|Outputs ||Georeferenced Image, PDF Map, KML|