Data with Drew: Vegetation Indices

The cameras we use on fixed wing and drone aircraft capture visual picture images (RGB), near infrared images (NIR), and thermal images. A formula is used to analyse the NIR data returned and provides Pollen Systems with two main metrics to measure plant vigor: NDVI (Normalized Difference Vegetation Index) and NDRE (Normalized Difference Red Edge). These vegetation indices are each unique ways to assess the health of your fields, and offer helpful insights for farm management.

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NDVI is one of the first indices designed to estimate the presence of vegetation in satellite images. It represents a ratio between light reflected by plants in the visible red light spectrum and the Near Infrared spectrum, and is related to the chlorophyll in those plants. the more chlorophyll present, the higher the index becomes. Therefore, we know it to be a solid estimate of photosynthesis in a plant, and by extension, plant health and vigor. It runs from -1 to 1, where -1 is represents water, 0 represents bare soil, and 1 represents extremely vigorous vegetation.

More recently, NDRE has emerged as another index that fills a role NDVI does not. While both estimate chlorophyll content, NDRE replaces visible red light with a wavelength that borders the infrared and visible red wavelengths: Red Edge. Since it does not rely on visible red light, NDRE can collect readings below dense canopy cover where NDVI is blocked. This is especially useful late-season to determine which plants need support.

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When looking at both maps together, we often see where canopy health is high compared to lower branches, or how to distinguish ground cover from crops of interest. Our partner Micasense produces cameras specifically designed to capture the wavelengths of light needed for NDVI and NDRE, and we are excited to continue using their technology in service of your farms and vineyards. Hopefully this has been a helpful reminder to keep learning and keep growing!