Staying Alert: How a New Landsat-Based Tool Spots Deforestation

Forests are commodities. The biggest driver of deforestation worldwide is the economic value of trees and the land they stand on. With the high demand for agricultural land and wood products, deforestation has become an intractable problem.

To address this dilemma, the World Resources Institute, a not-for-profit, non-governmental research organization, has released a Landsat-based alert system as part of its Global Forest Watch network. When a new road appears in the dense forests of Peru, or a baseball diamond-sized patch of forest is felled in the Republic of Congo or Kalimantan in Indonesia, anyone with an Internet connection can be alerted to the loss.

That's near-weekly alerts for changes smaller in size than a football field. That combined detail and pace makes this new deforestation alert system revolutionary. Using Landsats 7 and 8 together, forests are potentially imaged every eight days. That revisit time, or data cadence, together with Landsat's 30 meter spatial resolution, allows land managers to know when small incursions into forests are being made—in time to respond before major damage has been done.

And who manages the land is broader than just forest managers. Frances Seymour, a senior fellow at the Center for Global Development, points out, "Government agencies, civil society watchdogs, and companies trying to get deforestation out of their commodity supply chains can all use these alerts to target their efforts and mobilize quick response."

Global Forest Watch (GFW) teamed up with the University of Maryland's Global Land Analysis and Discovery (GLAD) team and scientist Matt Hansen to make these near-weekly alerts happen. The three essential ingredients are freely available Landsat data distributed by the USGS, the Hansen-GLAD tree cover loss algorithms, and big data computing power like that of Google's Earth Engine.

"When old growth forests are logged, what is the legal context?" asks Hansen, "If such activity occurs in a protected area, it is likely illegal. However, official forest land use plans are lacking or not openly shared in many countries."

That lack of transparency is a point of legitimate contention. The new forest alert system aims to increase transparency. It tracks forest exploitation, including the nascent stages—new access roads, selective tree removals—so all interested stakeholders in land use development and conservation can have the same set of facts.

"We hope the alerts stimulate improved, consensus-based planning on how remaining high carbon stock, high biodiversity forests will be developed and protected," Hansen says.

Forests and Climate Change

In December 2015, the Paris Agreement recognized the urgent need to respond to climate change and to attempt to keep global warming below 2 degrees Celsius. To help do so, drafters of the agreement specifically mention efforts to conserve and enhance forests for carbon mitigation.

Policy programs like REDD+ aim to reduce emissions from tropical forests by giving intact forests an economic value—tropical nations are paid to preserve their forests (on the basis of performance). The linchpin for this type of policy concept is an accurate baseline of forest cover and an unbiased mechanism for monitoring change.

"There's no question that the revolution in remote sensing technology in recent years has already had a dramatic impact on forest management throughout the tropics," says Seymour. "These systems have changed the politics of forest management both within and between countries. They have empowered environmental activists and indigenous peoples to make visible what is really going on in the world's forests, and how it diverges from what is legal and sustainable."

What made the alerts possible?

The opening of the Landsat archive by the U.S. Geological Survey in 2008 was the spark that made massive operational systems like the GFW-GLAD alert system possible. "Free and open access to the Landsat archive has already spurred scientific innovation and provided a foundation for REDD+ monitoring, reporting and verification," wrote Douglas Morton, a research scientist at NASA Goddard.

Clouds remain the chief limitation in humid tropical forests. Researchers have called for acquiring data more often, and for radar, which can look right through clouds. Upcoming lidar and radar missions such as NASA's GEDI and the NASA-ISRO SAR Mission (NISAR) will help capture the three-dimensional structure of forests.

Seymour explains, "It's getting harder and harder for government officials and private companies to escape accountability for deforestation that happens on their 'watch.'"

What this means for a Legal Reserve

Weekly deforestation alerts changed what satellite imagery can do: instead of finding out about clearing the following year, it can be known within days.

Neutraza applies the same logic at a smaller scale, reserve by reserve. Analyses use Sentinel-2, with 10-meter resolution and a revisit of a few days, and Sentinel-1 radar when clouds get in the way. Official INPE alerts (DETER) that fall inside a reserve's boundary go into its history, next to the images.

For someone supporting a reserve, this means the certificate is not a static promise: the forest behind it keeps being watched, and any change shows up on the FRU's public page.

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Source: Staying Alert: How a New Landsat-Based Tool Spots Deforestation. Public domain text and image from a U.S. government agency.