Satellite deforestation alerts (GLAD, RADD)
Satellite deforestation alerts are near-real-time signals of probable forest disturbance detected from satellite imagery. Public systems include the GLAD alerts from the University of Maryland, based mainly on optical data, and RADD alerts from Wageningen University, based on Sentinel-1 radar, which sees through clouds.
Also known as: GLAD alerts · RADD alerts · forest disturbance alerts · deforestation alerts
Why does it matter?
A forest baseline shows what existed in 2020; alerts show what has changed since. Continuous monitoring lets companies detect new clearing near or inside supplying plots, rather than relying on a one-off check at onboarding.
How does it work?
- GLAD alerts, developed by the Global Land Analysis and Discovery laboratory at the University of Maryland, detect tree cover disturbance from optical imagery such as Landsat and Sentinel-2.
- RADD (Radar for Detecting Deforestation) alerts, from Wageningen University, detect disturbance in humid tropical forests from Sentinel-1 radar.
- Alerts are published as rasters with dates and confidence levels, and differ in coverage, resolution and latency.
Overlaying alerts on plot polygons gives plot-level risk signals: alert area, date relative to the cut-off date, and confidence.
Common pitfalls
- Treating low-confidence alerts as confirmed.
- Ignoring alerts in buffer zones just outside a plot, where expansion often starts.
- Using alerts on non-forest land, such as tree crops, where disturbance may be normal farm management.
- Checking alerts once, then never again.
Farmer1st combines public alert systems with baselines and field verification in a multi-source deforestation assessment up to today, through its geo and polygons service.
Frequently asked questions
Does an alert prove deforestation?
No. An alert indicates a probable disturbance, such as clearing, fire or logging. Whether it is EUDR deforestation depends on whether the land was forest and has been converted to agricultural use, which needs further evidence.
Why use radar alerts in the tropics?
Frequent cloud cover limits optical imagery. Radar, such as that used by RADD, observes the surface regardless of clouds, which improves timeliness in humid tropical regions.
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