How satellite crop monitoring works
Satellite crop monitoring means tracking the health and development of your fields from orbiting satellites — without drones, without in-field sensors, and without enterprise software. The two Sentinel-2 satellites, operated by the European Space Agency, photograph every field on Earth every five days at no cost to you. From this data, vegetation indices like NDVI, NDMI, and NDRE reveal exactly how your crop is doing, week by week, in numbers.
If you have ever wondered “is my field okay?” without being there to look — satellite monitoring is the answer.
What satellite monitoring reveals
From free Sentinel-2 imagery, you can measure:
- Canopy health and density (NDVI, EVI) — is the crop growing as expected for its stage?
- Water stress (NDMI) — is the crop running dry, days before it looks thirsty?
- Nitrogen / chlorophyll status (NDRE) — is the crop well-fed or running short?
- Floods and drainage (NDWI) — where is water sitting in the field?
- Fire risk and burn damage (NBR, dNBR) — is the land in danger, or how badly did it burn?
- Seasonal trends — how does this year compare to last year and the 5-year average?
The key insight: a trend is more valuable than a snapshot. A single NDVI reading of 0.5 tells you little. An NDVI that has dropped from 0.7 to 0.5 in two weeks tells you something is wrong. This is why monitoring systems compare against history, not just absolute thresholds.
The six-step process
- Identify the field — draw or define the boundary (a rectangle, a polygon, or saved field shape).
- Pull the satellite image — Sentinel-2 captures the location every 5 days, cloud permitting.
- Filter clouds and shadows — only clean pixels are used; hazy images are rejected.
- Compute vegetation indices — the raw reflectance bands are combined into NDVI, NDMI, and other indices.
- Compare against history — the current values are compared to previous months, years, and seasonal norms.
- Interpret — the numbers are translated into plain words: “Your crop is healthy and well-watered” or “Water stress is increasing — consider irrigating.”
This is exactly what AgroReports does, end to end, for free.
Key metrics
| Approach | Coverage | Frequency | Cost | Setup |
|---|---|---|---|---|
| Satellite (Sentinel-2) | Every field on Earth | Every 5 days | Free | None — just draw the boundary |
| Drones | Limited flight range | On-demand (you fly it) | €1,000–15,000 + time | Buy, learn to fly, process imagery |
| In-field sensors | One point per sensor | Continuous | €200–2,000/sensor + maintenance | Install, calibrate, maintain, replace |
Satellites win on coverage and cost. Drones win on resolution and timing control. Sensors win on real-time frequency. They are complementary, not competitive — but for most farmers, satellite monitoring is the only one that is free, zero-setup, and covers the whole farm.
What satellite monitoring cannot do
- It cannot replace walking the field. A satellite tells you where and when something is wrong; it rarely tells you what. Ground-truthing remains essential.
- It cannot see through clouds. Persistent cloud cover creates data gaps. Good systems use composites (multi-date medians) and tell you when data is unreliable.
- Resolution has limits. At 10 m/pixel, Sentinel-2 cannot see individual plants. It sees the average of a 10×10 m patch — fine for fields, inadequate for individual vines or trees.
- It cannot name a disease. Satellite detects the stress signature (declining NDVI/NDMI); it cannot identify the pathogen.
Free report: Monitor your field from satellite — draw the boundary, and AgroReports computes all relevant indices, compares against 3–5 years of history, and writes a plain-language report. Free, no signup. Check my field →
Is satellite crop monitoring really free?
Yes. The Sentinel-2 satellites are funded by the European Space Agency and the European Commission; their data is public and free. The raw imagery is downloadable by anyone. What AgroReports adds is the processing: cloud masking, index computation, historical comparison, and plain-language interpretation — so you get an answer instead of raw data.
How often is satellite crop data updated?
Sentinel-2 revisits every location on Earth every five days (two satellites working in tandem). However, clouds can block the view — in cloudy regions or seasons, the usable update frequency may be longer. Good monitoring systems use cloud-free composites (combining multiple dates) to fill gaps and flag when the data quality is low.
Do I need a drone for satellite monitoring?
No. Satellite monitoring uses orbiting satellites — you do not need to buy, fly, or maintain any hardware. Drones offer higher resolution and on-demand timing, but at significant cost and effort. For most farmers, satellite data is sufficient and vastly more practical.
How accurate is satellite crop monitoring?
Accurate enough to guide decisions when used correctly. The indices correlate well with ground observations of canopy health, biomass, and water stress — published R² values for NDVI vs field-measured biomass typically exceed 0.8 for most crops. The caveats: cloud contamination degrades quality, and no index replaces ground-truthing for diagnosis. The best approach combines satellite trends with targeted field visits.