Normalized difference vegetative index readings through remote sensing can be used for many functions including, but not limited to stress of plant, health of plant, and water use by plant. One must understand the surrounding environment and plant canopy in order to understand 7 NDVI readings. Normalized difference vegetative index readings are used to sort the condition, amount, and type of vegetation in an area. Solar irradiance and reflectivity of the surface determines the amount of light that can be reflected. A simple reflection measurement is not acceptable for vegetation indices. A vegetation index (VI) is created by using data from multiple spectral bands. It is important to note that each instrument used to measure VI is different and can result in different readings. A plants canopy, soil background, and atmosphere can affect accuracy of readings received (Jackson and Huete, 1991).
1. What Is A VI, Or Vegetation Index?
You should know that vegetation’s spectral reflectance across different bands measured by the sensor serves as an indicator of the presence of plants or trees and their overall state. So, VI is a mathematical combination of two or more such spectral bands that enhances the contrast between vegetation (having high reflectance) and bare soil, manmade structures, etc. as well as quantifies plant’s characteristics, such as biomass, vigor, density, etc.
How Does NDVI Work?
Basically, it works by mathematically comparing the amount of absorbed visible red light and the reflected near-infrared light. And here’s why.
The chlorophyll pigment in a healthy plant absorbs most of the visible red light, while the cell structure of a plant reflects most of the near-infrared light. It means that high photosynthetic activity, commonly associated with dense vegetation, will have fewer reflectance in the red band and higher reflectance in the near-infrared one. By looking at how these values compare to each other, you can reliably detect and analyze vegetation cover separately from other types of natural land cover.
What Does An NDVI Measure In Crops?
Simply put, NDVI measures the state and health of crops or crop vigor. This vegetation index is an indicator of greenness and has a strong correlation with green biomass, which is indicative of growth. NDVI values are also known to have a high correlation with crop yield, meaning it can be used as a tool for measuring crop productivity and predicting future yield.
When it comes to crops, there’s a bunch of applications. NDVI can be used to:
1) Measure biomass and assess the state and health of crops
2) Identify pests, diseases, fungus, or overly dried spots in the field before the damage is done
3) Observe vegetation dynamics throughout the growing season
4) Establish normal growing conditions for the crops in the specific area with NDVI Time Series
5) Estimate crop yields (never alone, only combined with other parameters used for prediction)
6) Detect areas of concern within the field faster, and spend water, crop nutrients, and pesticides more effectively
7) Monitor pasture conditions and productivity
8) Monitor drought and assist in forecasting fire-hazardous areas
17. Can NDVI Be Used To Optimize Fungicide Application?
Definitely, yes. First, you can use NDVI maps of your field to validate the results of applying various fungicides and see which one leads to healthier and more resistant crops. Second, the NDVI image can be used as a prescription map showing you the areas, where crops may have been suffering from fungal disease, so fungicide can be applied accordingly. It will cost you less than spraying the entire field.
What NDVI Value Represents Healthy Vegetation, A Positive One Or A Negative One?
As you may know, the results of the NDVI calculation range from -1 to 1. Negative values correspond to areas with water surfaces, manmade structures, rocks, clouds, snow; bare soil usually falls within 0.1- 0.2 range; and plants will always have positive values between 0.2 and 1. Healthy, dense vegetation canopy should be above 0.5, and sparse vegetation will most likely fall within 0.2 to 0.5. However, it’s only a rule of thumb and you should always take into account the season, type of plant and regional peculiarities to know exactly what NDVI values mean.