By measuring the reflectance of the plants at various wavelengths, it is possible to collect a lot of information about the status of the plants. In the above example, you can see the visual representation of the field, as seen by sensors onboard the tractor. From these data we can derive vegetation indices that help us estimate the vegetation cover and the Leaf Area Index (LAI). As the population of plants increases, the amount of biomass causes an increase in the overall near-infrared reflectance and a reduction in the red reflectance. From previous research, there are known relationships between the indices using those two regions of the spectrum and the amount of vegetation, a measure of which is the Leaf Area Index. From these estimates we can derive the population of the plants.