What is NDVI?

What is NDVI?

NDVI - Normalised Difference Vegetation Index - is calculated from satellite imagery data and provides an indication of overall plant health.

SWAN uses the NDVI (see illustration below), calculated from satellite imagery data, as the basis for monitoring how healthy (or green) a crop or field of turf is. NDVI is calculated from the red and near-infrared light bands, producing an index of between 0 and 1, which correlates with the greenness of the crop and its biomass.

SWAN allows you to choose parts of a field to monitor, by configuring Site Health Points or Site Health Areas. Data is obtained from two satellites.

Sentinel-2 – 10 x 10m pixels, data collected every ~5 days

Landsat-8 – 30 x 30m pixels, data collected every ~16 days.

The orbit of both satellites is sun-synchronous – this ensures the angle of sunlight hitting the Earth’s surface is maintained throughout the data set, enabling comparison between data sets obtained at different dates. More information on the Sentinel-2 satellite can be found on the ESA Sentinel website, while information on Landsat-8 is available on the USGS Landsat Missions website.

Sentinel-2 provides higher spatial resolution and is a good choice for smaller fields, or if you are interested in a particular area of your field. Landsat-8 data is intended for users who wish to have a broader overview of their site, and is more suited to larger operations. Additionally, there is a larger historical data set available.

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