Introduction
Vegetation indices are mathematical formulas that use specific image bands to assess plant health. DroneDeploy's Plant Health layer uses these indices to help you visualize and analyze crop vitality.
This article explains how vegetation indices work and describes the different types available in DroneDeploy.
How vegetation indices work
Vegetation indices are calculated using the electromagnetic spectrum. The electromagnetic spectrum is the range of all types of electromagnetic radiation.
Image bands are specified wavelength ranges within the electromagnetic spectrum that the drone's camera captures. Each band corresponds to a different part of the spectrum, such as visible or infrared, which allows you to detect different characteristics about plant health.
Images captured by multispectral cameras predominantly contain information from the visible to near-infrared spectrums.
The visible spectrum
The visible spectrum is detectable by human eyes. Each color corresponds to a specific band. Standard cameras capture light in the red, green, and blue bands, resulting in true-color images that accurately reflect colors as perceived by the human eye. These images are useful for visual interpretation and analysis.
Vegetation indices such as VARI use standard cameras to help visualize plant health. Read more on the mathematical formula for VARI below.
The near-infrared spectrum
Even though near-infrared (NIR) bands are invisible to the human eye, they play a vital role in evaluating vegetation health. Plants respond to NIR light in ways that indicate their overall health. By capturing data in NIR bands, you can estimate the chlorophyll content in plants, which gives clues to the plant's viability before visible changes in coloration occur.
When using DroneDeploy, the camera type determines which Vegetation Index options are available. Please refer to Filter and Algorithm Types Based on Camera Type for more information.
Types of vegetation indices
Visible Atmospherically Resistant Index (VARI)
VARI is a vegetation index that evaluates the 'greenness' in plants, where greener plants are assumed to be in healthier condition. VARI is useful for mitigating atmospheric interference which enhances the ability to detect coloration differences between plants.
VARI uses Red, Green, and Blue bands to assess plant health. Since VARI only uses bands in the visible spectrum, this index is appropriate for cameras that capture in standard RGB (see Filter and Algorithm Types for more information).
VARI is calculated using the following equation:
Normalized Difference Vegetation Index (NDVI)
Normalized Difference Vegetation Index (NDVI) is an industry standard vegetation index that assesses plant health by comparing the difference between near-infrared and red bands of the electromagnetic spectrum. NDVI measures the chlorophyll content and photosynthetic activity of plants.
Higher NDVI values indicate healthier, denser vegetation, while lower values suggest stress, drought, or sparse plant cover. Since NDVI uses the near-infrared band, this index requires a multispectral camera (see Filter and Algorithm Types for more information).
NDVI is calculated using the following equation:
Enhanced Normalized Difference Vegetation Index (ENDVI)
Enhanced Normalized Difference Vegetation Index (ENDVI) is a variation of NDVI. ENDVI improves sensitivity to vegetation by incorporating the green and blue bands, which enhances the detection of chlorophyll content. ENDVI is only available for modified cameras that take false-color images.
ENDVI is calculated using the following equation:
Green Normalized Difference Vegetation Index (GNDVI)
Green Normalized Difference Vegetation Index (GNDVI) is another variation of NDVI. GNDVI uses green reflectance instead of red reflectance. The green band improves the index's ability to detect healthy vegetation, as healthy plants reflect more green light. GNDVI is only available for modified cameras that take false-color images.
GNDVI is calculated using the following equation:
Soil Adjusted Vegetation Index (SAVI)
Soil Adjusted Vegetation Index (SAVI) is a vegetation index that minimizes the influence of soil brightness when assessing plant health. Bright or reflective soils can lead to inaccurate readings of plant health by reflecting more light when soil is exposed. SAVI is only available for images taken with our supported multispectral cameras.
SAVI is calculated using the following equation:
Optimized Soil Adjusted Vegetation Index (OSAVI)
Optimized Soil Adjusted Vegetation Index (OSAVI) modifies the SAVI equation by adjusting the soil correction factor to 0.16 instead of 0.5 to allow for greater soil variation. OSAVI is meant to capture vegetation health with landscapes that have variations in soil brightness, such as landscapes with relatively sparse vegetation where the soil can be seen through the canopy. OSAVI is not well-suited for landscapes with high canopy cover (>50%).
OSAVI is calculated using the following equation:
Renormalized Difference Vegetation Index (RDVI)
Renormalized Difference Vegetation Index (RDVI) is a variation of NDVI, where the equation is normalized to reduce the influence of soil brightness. By normalizing the reflectance values, RDVI mitigates the impact of soil reflection when assessing plant health. This leads to more accurate results for landscapes with sparse vegetation.
RDVI is calculated using the following equation:
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