Vegetation indices

What are Vegetation Indices

Vegetation indices are like health indicators for crops. Just like checking your own health by measuring factors such as temperature, blood pressure, and heart rate, vegetation indices use the way plants reflect light to give an idea of how well the plants are doing.

Plants absorb sunlight and use it for photosynthesis, which is how they make their own food. But they also reflect some of that sunlight, especially in the visible and near-infrared parts of the light spectrum. The amount of reflection in these two parts of the spectrum can tell a lot about the crop's health.

Growers use these indices to monitor their fields over time. By taking regular measurements, growers can spot changes in plant health before they become visible to the naked eye. This allows the grower to take timely actions to address problems and optimize their crop yield.

Index values tend to range from -1 to +1, though some indices have different ranges. In all indices, high values mean your plants are doing great and growing well. Lower values suggest that something is not quite right – maybe they need more water and/or nutrients, or there's a pest problem. Vegetation indices are a useful way to keep an eye on your plots and make sure everything is growing as it should.

Indices Available in the Vultus Analysis Platform

The Vultus Analysis Platform (API) can provide an analysis of a polygon using several different vegetation indices.

Normalized Difference Vegetation Index

The Normalized Difference Vegetation Index (NDVI) is a commonly used index that assess the health and productivity of vegetation. NDVI looks at the colors of light that plants reflect. When plants are healthy and have lots of leaves, they reflect a lot of near-infrared light and not as much visible red light. NDVI takes these two types of light and compares them to tell us how much healthy plant material there is.

Normalized Difference Water Index

The Normalized Difference Water Index (NDWI) is used in precision agriculture to measure the "water health" of your plants. NDWI looks at two types of light that are reflected by plants and water. There is the light in the near-infrared part of the spectrum (which is just beyond what our eyes can see), and there is also light in the green part of the spectrum.

Plants usually reflect a lot of near-infrared light because they're healthy and full of water. But they don't reflect as much green light. Water, on the other hand, reflects more green light and less near-infrared light. So, by comparing the amount of these two types of light that is being reflected, NDWI can give us an idea of how much water is in an area.

When your crops are well-hydrated and have enough water, NDWI tends to be higher. If the NDWI value drops, it might mean that the plants are stressed because they are not getting enough water. This could be due to things like drought or problems with irrigation.

Modified Soil-Adjusted Vegetation Index

The Modified Soil-Adjusted Vegetation Index 2 (MSAVI2) is a vegetation index that's quite similar to NDVI. Like NDVI, MSAVI2 also helps growers understand how healthy and vigorous their crops are. However, MSAVI2 takes into account the presence of soil and adjusts the index accordingly.

When looking at fields from above using things like satellite images, we can see how much sunlight the plants are reflecting. Sometimes, the soil between the plants also reflects sunlight, and that can mess up our measurements. MSAVI2 takes care of this problem. It considers both the near-infrared and red light, just like NDVI does, but it adjusts the calculation to take into account the amount of sunlight reflected by the soil. This way, MSAVI2 gives us a better estimate of the actual health of our plants, without getting confused by the soil.

As with NDVI, higher MSAVI2 values indicate that plants are healthy and strong. Lower MSAVI2 values indicate attention is needed.

Leaf Area Index

The Leaf Area Index (LAI) is tool that helps growers understand how much leafy canopy cover their crops have. Looking down at a field from above we are able to see the tops of all the plants. LAI is a number that tells us how many layers of leaves would fit on top of each other if we stacked them up. A higher LAI value means there are more layers of leaves, and a lower LAI value means there are fewer layers. LAI values can range from 0 to over 8.

The more leaves crops have, the more sunlight they can capture for photosynthesis. Higher LAI generally mean crops are getting plenty of light and are growing well. Lower LAI values indicate that crops have fewer leaves and might not be getting as much sunlight as they need. This could be due to things like spacing, competition with weeds, or nutrient deficiencies.

Normalized Difference Red Edge

The Normalized Difference Red Edge (NDRE) index is a vegetation index that helps growers understand the health of plants by looking at a specific part of the light spectrum. It is particularly useful for assessing the amount of chlorophyll in crops, which is essential for photosynthesis and overall plant health.

Plants not only reflect light, but they also absorb it for photosynthesis. NDRE focuses on the "red edge" of the light spectrum, which is a range of wavelengths just beyond the visible red light. This red edge is where chlorophyll strongly absorbs light, and healthy plants have a lot of chlorophyll. NDRE is particularly useful for monitoring crops that have high chlorophyll content, such as corn, soybeans, and sugarcane.

NDRE calculates the difference between the reflectance in the red edge part of the spectrum and the near-infrared part of the spectrum. This difference tells how much chlorophyll is present in the plants. When the NDRE value is high, it indicates that there is a good amount of chlorophyll, suggesting strong and thriving vegetation. If the NDRE value is low, it might mean that plants are stressed or lacking in chlorophyll. This could be due to factors like nutrient deficiencies, disease, or inadequate water.

Enhanced Vegetation Index

The Enhanced Vegetation Index (EVI and EVI2) is a special tool that helps growers understand how healthy and green their crops are. It's a bit more advanced than other indices like NDVI because it takes into account some things like dust, aerosols, and the angle of the sun that can affect the accuracy of the measurements.

EVI takes care of these issues. It considers the blue light as well, which helps account for things like aerosols in the air. It also corrects for variations in the angle of the sun, which can change how the sunlight is reflected. This correction makes EVI more accurate, especially in areas where these factors can play a big role.

EVI is more sensitive to vegetation than NDVI and it can provide more accurate information about vegetation health and productivity. EVI2 is an improved version of the original Enhanced Vegetation Index. EVI2 is particularly useful in regions with dense vegetation.

As with other vegetation indices, high values indicate that crops are healthy, green, and flourishing. If the EVI value is lower, it might suggest that there are some factors affecting the measurements, or that crops might not be as healthy as they could be.

Reflectance Vegetation Index

The Reflectance Vegetation Index (RVI) is another tool that helps growers understand how healthy and green their crops are. RVI uses the red part of the spectrum (visible red light) compared to the near-infrared part of the spectrum. RVI uses the ratio of these two types of light to provide a sense of how healthy plants are. When the ratio is high, it means plants are healthy and green. If the ratio is lower, it might suggest that crops are stressed or not as green as they could be.

Green Normalized Difference Vegetation Index

The Green Normalized Difference Vegetation Index (GNDVI) is another tool that helps growers understand how green and healthy their crops are. GNDVI focuses on the specific color of green and provides insights into the condition of crops.

GNDVI looks at the colors of light reflected by plants, specifically in the green and near-infrared parts of the spectrum. GNDVI calculates the difference between the reflectance of these two colors to tell you about the greenness of plants. When GNDVI is high, it means plants are lush, green, and healthy. This is a good sign that they are growing well and getting the right nutrients and care. On the other hand, if the GNDVI value is low, it might suggest that crops aren't as green as they should be. This could be due to factors like nutrient deficiencies, water stress, or pest problems.