Satellite crop monitoring: beyond the green map
What indices like NDVI actually measure, where they work, where they fail, and how to turn satellite imagery into agronomic decisions.
What the indices actually measure
NDVI, NDWI and EVI are mathematical combinations of spectral bands that estimate vegetative vigor, water in vegetation and biomass. They do not “see” disease or deficiency, they see their effect on the plant. That is why the absolute value matters less than the behavior: a field at NDVI 0.7 may be thriving or in free fall, and only the historical series reveals which.
From index to decision
Satellite crop monitoring becomes a decision tool when it answers three questions: where behavior departed from what was expected, since when, and compared to what. Anomaly against the field’s own history, against neighboring fields of the same crop, and against the regional pattern, each comparison tells a different story and suggests a different action, from an urgent visit to simple follow-up.
Limitations no one should hide
Clouds interrupt optical series at the most critical periods in tropical regions. Spatial resolution defines the minimum size of a detectable problem. And no index replaces field confirmation: satellite points to where to look, not what to apply. Any serious precision agriculture platform must be honest about these limits, and design the workflow around them.
In the decision-maker’s routine
In practice, the value is in prioritization: a technical team covering dozens of farms cannot visit all of them weekly, but it can visit first the ones showing stress signals. That logic, signal, prioritization, action, confirmation, is what connects the Satellite & Indices module to the rest of the AgroPhytus ecosystem.