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Planet satellite imagery of primary forest removal in Kalimantan Barat, Indonesia on GFW map

Primary forest removal in Kalimantan Barat, Indonesia. Image © 2022 Planet Labs Inc. Accessed through GFW.

By 
Anika Berger, Teresa Schofield, Amy Pickens, Johannes Reiche and Yaqing Gou
Posted on March 9, 2022
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Looking for the Quickest Signal of Deforestation? Turn to GFW’s Integrated Alerts

By 
Anika Berger, Teresa Schofield, Amy Pickens, Johannes Reiche and Yaqing Gou
Posted on March 9, 2022
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Languages: Leerlo en español, Leia em portugues, Baca dalam bahasa indonesia, Lire en français

Global Forest Watch (GFW) is committed to bringing the most accurate forest data to users as quickly as possible. We are continually expanding the near-real-time deforestation alerts available on the GFW platform and are excited to introduce an updated layer. The integrated deforestation alerts layer combines the analytical power of GLAD, GLAD-S2 and RADD deforestation alerts to provide a faster, more confident view of forest disturbances than any one individual system. Prompted by user feedback, this update simplifies workflows and harnesses the best of each alert type to support a variety of monitoring purposes.

Which Alert Systems are Being Integrated?

GFW currently offers three individual deforestation alert systems. GLAD-L (often called “GLAD”) is GFW’s longest-standing alert product from the University of Maryland’s (UMD) Global Land Analysis and Discovery (GLAD) lab and uses imagery from NASA’s Landsat satellites. UMD introduced the higher resolution GLAD-S2 alerts in May 2021, which use a similar methodology to GLAD-L, but are sourced from the European Space Agency’s Sentinel-2 satellites. And finally, Radar for Detecting Deforestation (RADD) alerts produced by Wageningen University use Sentinel-1 radar data. These alerts have the additional capability of detecting forest change through cloud cover that often blocks the view of the other satellites.

Deforestation alert layers offered on GFW

What Does the Integrated Alerts Layer Offer?

integrated deforestation alerts layer combines the analytical power of GLAD, GLAD-S2 and RADD deforestation alerts

These three systems alert us of forest change happening in different parts of the world, gather different levels of resolution, and are updated at varying frequencies. The integrated option enables users to derive meaningful summary statistics that incorporate each of the individual systems. Using a common grid for all three alert products, the integrated layer understands that multiple systems have reported an alert in any given location and displays it through confidence levels:

Confidence levels of integrated deforestation alerts

This new layer comes with an important change: we are now reporting on the area affected by alerts as opposed to the count of alert pixels. As the integrated alert comes from systems with varying resolution, it is necessary to report areas rather than the number of alert pixels. However, be aware that the alerts are designed to quickly identify forest disturbances rather than precisely delineate forest loss – as a result, the areas presented on GFW may under or overestimate the actual area of forest loss.

Combining the alerts offers several benefits:

1. Users Will Always Have the Earliest Information Available

By combining all three alert systems into one layer, we are harnessing the different timing of the satellites to increase the chances of getting an unobscured look at the forest and therefore detect change faster. Users looking at integrated alerts in Peru from 2020 would have been alerted to forest loss on average 11 days earlier than by referring to any one system alone. This improvement in timeliness varies by region and across seasons, as the alert systems complement each other by providing their own strengths. For example, in consistently cloud-covered areas, the radar-based alert system provides the advantage of detecting forest loss through clouds. In areas with a regular dry season, however, the higher revisit time of the optical alert systems gives a more frequent opportunity to detect disturbances every 5-8 days where the radar system may take up to 12 days to detect change.

2. The Overlap of Multiple Systems Increases Confidence to Prioritize Alerts

If two or more alert systems detect a change in the same location, we have the highest confidence that these alerts indicate real disturbance. For individual systems, there is a delay before a first detection can be verified by additional satellite passes and thus reach “high confidence”. The integrated layer displays where multiple systems overlap, providing increased confidence faster than waiting for individual systems to reach high confidence through additional satellite images, which can take weeks or months. For forest monitors who rely on high confidence alerts to respond to deforestation events, we hope this new layer facilitates using the various alert systems in conjunction with one another and can promote faster follow up by identifying these highest confidence alerts as soon as a second system detects the same disturbance.

3. Different Tree Cover Loss Types Are Captured Across a Variety of Landscapes

The integrated alerts option helps to fill the gaps that the use of any one system alone might present. One of the greatest strengths of higher resolution RADD and GLAD-S2 alerts is their ability to capture smaller changes in the forest than the 30-meter GLAD-L product. This presents promising developments for detecting small canopy gaps from logging activities, which are widespread across the Amazon Basin. Now that all three systems are available in the Amazon basin, they can be used in concert to identify illegal activities quickly and with the highest confidence possible, a critical tool for both law enforcement and Indigenous Peoples and local communities working to combat deforestation.

The integrated deforestation alerts layer demonstrates the ability of multiple alert systems to detect small changes, such as tree removal along logging roads in the Peruvian Amazon.

Get Started with Integrated Alerts

With three alert systems to choose from, we aim to simplify users’ workflow in identifying priority alerts. The integrated layer provides the most information on recent forest change for users who want to be notified of forest loss with the highest confidence possible. Though we see these systems as complimentary to each other, users may still opt to select individual systems for alert notifications and analysis if these suit their needs.

What’s Next?

This integrated deforestation alerts layer is just the first step in combining the potential of multiple alert systems. A more comprehensive study is coming that will identify how to further integrate the systems into one downloadable dataset, assess how the different systems vary across regions, and factor in nearby pixels that detect the same disturbance. Stay tuned for future advancements in the field of forest monitoring.

For an in-depth look at how the integrated layer was designed and how to use it, see the Help Center.


Amy Pickens is a postdoc at University of Maryland and operates the GLAD alert systems.

Johannes Reiche is an associate professor at Wageningen University and operates the RADD alert system.

Yaqing Gou is a postdoc at Wageningen University and researches the various alert systems.

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