According to Reiche, existing alerting systems rely mostly on optical images: regular satellite photos of the Earth. “You often wouldn't see anything on these for months, because there would be thick cloud cover above the African rainforest, particularly during the rainy season. Countries like the Congo and Gabon have some of the heaviest cloud coverage in the world.” This meant that illegal logging used to go unnoticed for months, by which time it was too late to intervene.

“The high-resolution radar images produced by Sentinel-1 allow us to look straight through the clouds, 365 days a year,” explains Reiche enthusiastically. Last year he trialled the RADD system in a smaller region: Indonesia, where rainforest is being cleared for palm oil plantations. Thanks to a collaboration with Global Forest Watch – the international forestry watchdog – and Google (which stores the vast amount of radar satellite data analysed by the alerting system), Reiche's team at WUR has now been able to scale up to cover the entire African rainforest.

As well as allowing us to look through cloud cover, radar imaging also means we can zoom in to the forest, which is exactly what is needed in Africa, says Reiche. That’s because deforestation is happening in relatively small patches, in contrast to South America and Indonesia where large areas are often cleared for soya and palm oil plantations. Broadly speaking, there are two main causes of deforestation in the Congo Basin. Commercial entities cut tropical hardwoods destined for trade, while local residents cut trees, processing the wood into charcoal and using the cleared land for agriculture.

The commercial entities – local traders, but also major players from China, for example – only remove the trees they need for export purposes. “That’s known as selective logging,” says Reiche. “They create paths through the jungle and then to the left and right of those paths they just cut the commercially valuable trees they can sell.” That kind of deforestation is only visible if you zoom in very closely on the map. The same is true for the patches of rainforest cleared by local residents. The RADD technology can zoom in closely to a 10x10 metre patch, meaning you can see gaps in the forest canopy after trees have been logged.

The visibility that this system provides may be great, but how does that stop illegal logging? “Our alerting system is being used by the Global Forest Watch,” says Reiche. “They’ve been monitoring global deforestation for years and also have excellent partnerships with the governments of tropical countries, as well as with other organisations fighting against deforestation. These include NGOs such as Greenpeace and WWF, but also local stakeholders such as the rangers who protect national parks. The Global Forest Watch app will soon give those rangers access to the RADD alerts too: they'll be able to see on their mobile phone where areas are in the process of being logged, so they can intervene.”

The environmental conservation organisation WWF is delighted with Wageningen’s RADD alerting system, says its adviser Jorn Dallinga, who happens to be a WUR alumnus. “We now have a much better idea of where trees are being logged and we can act on that. When all we had was the optical satellite imagery it was often too late to intervene. Now we can swing into action more promptly, and it's essential that we do so because deforestation is occurring at a rapid pace in the Congo Basin. The African tropical rainforest is rich in biodiversity, and is home to endangered animal species such as the forest elephant and the mountain gorilla. Its peat soils also provide a natural way of capturing CO₂, and releasing it will lead to even greater acceleration in climate change.”

So is the idea now to immediately go and tackle any new RADD deforestation alerts? Yes, ideally, says Dallinga. “But it's often complicated to enforce locally, because of limited capacity, ambiguous mandates and regulations. You’re also dealing with a range of different groups, including local communities who cut trees for their own use, and traders who sell tropical hardwood illegally. Those traders might actually be employing the local community to cut trees for them.”