The Normal Difference Vegetation Index evaluates vegetation by measuring a plants ability to either reflect or absorb light. This value is usually expressed as a number that falls between -1 and +1. The closer to +1 the healthier the plant..Healthy vegetation (chlorophyll) reflects more near-infrared (NIR) and green light compared to other wavelengths. But it absorbs more red and blue light. There are other indices available for analysis such as VARI, RE, SAVI, etc, and each one has it s place in field analysis, however, NDVI is probably the most generally used index but it is not without limitations.
The picture right shows the varying in reflectance values as chlorophyll depletes. Below are the simple formulas, usually calculated at the processing stage, for NDVI. Farmers and anyone else such as an Agronomist can use this information to analyse plant health. Problems detected can be either due to disease, pests, nutrient deficiency, water and a host of other reasons. What iOS important is that the farmer ia able to detect these potential problems early and target the area requiring treatment. In the long run this makes farming the land more efficient and will increase profit margins by reducing costs and increasing yields albeit crops, hay, beef or dairy.