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Vegetation Indices

Vegetation indices are like health indicators for crops. Just like checking a person's 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.

Usage

The processVegetationIndices() mutation and retrieveVegetationIndices() query are used to generate and retrieve these analyses. They each require four arguments:

  • polygonId
  • startDate
  • endDate
  • indexType


mutation {
  processPlantHealth(
    polygonId: "[YOUR POLYGON ID GOES HERE]"
    startDate: "2023-01-01"
    endDate:   "2023-07-31"
    indexType: [CHOOSE YOUR INDEX HERE]
  )
  {
    IsSuccess
    Message
    Status
    Result {
      requestId
    }
  }
}



query {
  retrievePlantHealth(
    polygonId: "[YOUR POLYGON ID GOES HERE]"
    startDate: "2023-01-01"
    endDate:   "2023-07-31"
    indexType: [CHOOSE YOUR INDEX HERE]
  )
  {
    IsSuccess
    Message
    Status
    Result {
      tif
      png
      json
      colorlegend
    }
  }
}

Please refer to the Schema Documentation in the API Playground for more information.

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

One common vegetation index is the Normalized Difference Vegetation Index, or NDVI. It's calculated by looking at the difference between the amount of light reflected in the near-infrared and the visible red parts of the spectrum. Healthy plants tend to absorb a lot of red light and reflect a lot of near-infrared light, so a high NDVI value often means your plants are doing well.

Think of NDVI like a plant's "greenness meter." If NDVI is high, your plants are lush and healthy. If it's low, there might be an issue with your crops, like water stress, nutrient deficiency, or disease.

Normalized Difference Water Index

The Normalized Difference Water Index (NDWI) is used in precision agriculture to detect and monitor water stress in crops. NDWI measure water stress in the canopy. It can also be used in combination with other indices, such as NDVI. NDVI is sensitive to vegetation and NDWI is sensitive to water, so combining NDWI and NDVI, or other, analyses produces a more complete picture of the health and productivity of crops.

Modified Soil-Adjusted Vegetation Index

The Modified Soil-Adjusted Vegetation Index 2 (MSAVI2) is a vegetation index that is similar to NDVI, but is designed to reduce the influence of soil brightness on the index values. This means that MSAVI2 is more sensitive to vegetation than NDVI, and it can provide more accurate information about vegetation health and productivity. The MSAVI2 index is calculated by using a different combination of red and near-infrared bands than NDVI. MSAVI2 can be more effective than NDVI for identifying crop stress, especially when used in combination with other indices.

Leaf Area Index

The Leaf Area Index (LAI) is a measure of the amount of leaf area per unit of ground area. It is often used as an indicator of vegetation canopy structure and biomass. LAI values can range from 0 to over 8, with higher values indicating denser and more extensive vegetation.

Normalized Difference Red Edge

The Normalized Difference Red Edge (NDRE) index is calculated using the difference between the red edge and red bands of a multispectral image. NDRE is used to assess vegetation health and productivity as it is sensitive to variations in chlorophyll content, leaf area, and leaf structure. NDRE is particularly useful for monitoring crops that have high chlorophyll content, such as corn, soybeans, and sugarcane.

Enhanced Vegetation Index

The Enhanced Vegetation Index (EVI and EVI2) is a vegetation index that is similar to NDVI but it is designed to improve the sensitivity and dynamic range of NDVI. 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 or areas that might have challenges like aerosols or haze in the atmosphere. It's designed to minimize the impact of these factors, making it a valuable tool for monitoring vegetation health in diverse environmental conditions.

Reflectance Vegetation Index

The Reflectance Vegetation Index (RVI) is a measurement of the greenness or health of vegetation. RVI is calculated by taking the ratio of the reflectance of light in the near-infrared (NIR) band to that in the red band. Because healthy vegetation reflects more light in the NIR band than in the red band, the RVI values will be higher for healthier vegetation. RVI values are used to identify areas of the field that may be experiencing stress due to disease, nutrient deficiencies, or water.

Green Normalized Difference Vegetation Index

The Green Normalized Difference Vegetation Index (GNDVI) is calculated by taking the ratio of the reflectance of light in the near-infrared (NIR) band to that in the green band, then normalizing the result by subtracting a constant value from it. GNDVI is sensitive to the chlorophyll content of vegetation making it an indicator of vegetation health and productivity. GNDVI values are high for healthy vegetation, and low for stressed or bare soil.