Satellites monitor plant health by detecting invisible near-infrared light.

This monitoring process relies on the Normalized Difference Vegetation Index (NDVI), a formula developed in 1973 by researchers at Texas A&M University. Healthy vegetation contains high amounts of chlorophyll, which absorbs visible red light for photosynthesis. However, the internal structure of healthy leaves, specifically the spongy mesophyll cells, strongly reflects near-infrared (NIR) radiation to prevent overheating.When a plant is stressed or dying, its cellular structure collapses and it reflects less NIR light while reflecting more red light. NASA's Landsat program and the European Space Agency's Sentinel-2 satellites carry multispectral sensors that capture these specific wavelengths from hundreds of miles above Earth. By calculating the ratio between red and NIR light, scientists can determine the 'greenness' and vigor of vegetation with high precision.This technology allows for the detection of agricultural issues up to two weeks before physical wilting occurs. Today, organizations like the United Nations Food and Agriculture Organization (FAO) use this data to predict food shortages and monitor global deforestation. The ability to see beyond the visible spectrum provides a vital early warning system for global food security and environmental conservation.