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¿What is the NDMI index?
The Normalized Difference Moisture Index (NDMI) is obtained from images provided by Sentinel 2 / Landsat 8 and compares the near infrared band with the short-wave infrared band, which is sensitive to the absorption of leaf moisture, making it a good indicator of water in the plant.
NDMI = (IRNear – IR Shortwave)/(IRNear + IR Shortwave)
¿When is it used?
NDMI index is used for.:
- Regular monitoring of water content in crops.
- Determination of zones with water stress for a field/farm.
- Anticipated harvest logistics.
- Determination of combustibility levels in areas vulnerable to fire.
NDMI index maps vary in color spectrum from white beige to violet.
As there is more moisture content in the vegetation, the palette moves towards the intense blues/violet and the index approaches the maximum value, 1.
The following images compare NDVI / NDMI in several fields where moisture loss is observed as the crop evolves towards maturity (both indexes decrease):
In another example you can see how some of the corn in the field was lost due to flooding.
In the white part -low water content- the corn is senescing early, while the sector of the field represented with light blue and brown colors, the corn crop grew and developed in favorable conditions.