Seeing through the clouds
The Sentinel-1 satellite constellation uses radar instead of photographs. This means that the satellites can see “through the clouds” and are not dependent on sunlight. As a result, new images are available every three to six days, with a level of detail in which each pixel corresponds to an area of 10 by 10 metres.
However, radar has the disadvantage of being sensitive to factors such as frost and seasonal changes in foliage. To distinguish between these factors and actual disturbances such as logging, the researchers combined the satellite data with modelled temperature data from ERA5-Land and forest type information from the Copernicus programme.
Previously, frost and seasonal changes in foliage made it appear to the satellite that disturbances were occurring. By including temperature and forest type data in the analysis, there are far fewer “false” detections. The system can now monitor forests throughout the year – from snow-covered boreal coniferous forests to dry Mediterranean deciduous forests.
High accuracy, rapid detection
Checks on data from various European regions show that combining this data makes the detection system highly reliable. In over 91% of cases, disturbances reported by the system were found to actually involve logging, forest fires, storm damage or pests. On the other hand, 25% of actual disturbances were not detected; the system sometimes misses parts of natural disturbances with lower intensity, such as forest fires where many trees remain standing.
New disturbances are detected on average within 27 days of the actual moment of occurrence. With an additional retrospective correction method, this delay can even be reduced to an average of one day.
Throughout the year
The system provides insight into when disturbances occur throughout the year. This reveals differences between winter harvesting in Northern Europe, spring felling in Central Europe and summer fires in Southern Europe. Another important advantage is that small-scale interventions, such as group felling in Romania, also become visible.
Support for policy and enforcement
The new warning system provides up-to-date and detailed information that can support policymakers, managers and enforcers in sustainable forest management and nature policy. It enables a faster response to changes in European forests, thereby ensuring better care for one of our most important natural resources.
Publicly accessible
The detected disturbances are publicly accessible via https://wurnrt-raddeurope.projects.earthengine.app/view/radd-europe