Copernicus Sentinel-1 C-band radar data have long been used to track the health of the world’s forests. Now scientists have shown that combining these data with L-band satellite observations can improve the monitoring of forest disturbances, such as deforestation or wildfires, in tropical environments.
This promising finding – published in the International Journal of Applied Earth Observation and Geoinformation – demonstrates the potential for future synergies between Sentinel-1 and ROSE-L, a planned Copernicus Sentinel Expansion Mission that will deliver L-band radar observations.
Artist’s impression of the future ROSE-L Copernicus Sentinel Expansion mission
Copyright:ESA
As part of the study, which focused on the island of Sumatra in Indonesia, researchers explored the possibility of generating more accurate and timely satellite-based estimates of forest disturbances from human activities like logging or agricultural expansion. Such information could help governments to enforce the sustainable management of tropical forest ecosystems.
The research team drew on L-band synthetic aperture radar (SAR) observations from Japan’s ALOS-2 satellite and C-band SAR observations from Sentinel-1 of the European Union’s Copernicus Earth observation programme. The ALOS-2 ScanSAR and Sentinel-1 ground range detected data used in the study offered resolutions of approximately 100 metres and 20 metres, respectively.
Study site: Sumatra, Indonesia
Copyright:Balling et al., 2024
The aim was to capitalise on the distinct attributes of L-band and C-band observations. Johannes Balling, remote sensing scientist at Wageningen University and lead author of the study explained, “Shorter wavelength C-band SAR is suited for detecting even disturbances of leaves and smaller tree branches in the outer layers of the canopy, while longer wavelength L-band SAR penetrates deeper into to the forest canopy, enabling the detection of disturbances of larger branches. Combining these capabilities could allow us to create a more complete and more detailed picture of different types of forest damage.”
Balling and the research team used ALOS-2 and Sentinel-1 data separately and then in combination to test this hypothesis. The resulting forest disturbance estimates were compared with other data sources, including imagery from Planet Labs, to assess their accuracy.
It was found that combining data from ALOS-2 and Sentinel-1 improved detection rates by up to 38 percent, while detection timeliness increased by about 16 days.
ALOS-2 and Sentinel-1 track forest disturbances
Copyright:Contains modified Copernicus Sentinels data (2018-2021)/processed by Balling et al., 2024; also contains data provided by JAXA and Planet Labs PBC.
ALOS-2 was particularly effective in identifying large-scale forest disturbances characterised by post-disturbance tree remnants. However, it was less adept at identifying smaller-scale disturbances due to the medium-resolution data used in the analysis. In contrast, Sentinel-1 was able to detect smaller forest disturbances, filling gaps in the detections based on ALOS-2 data.
The improved detection timeliness was due to the increased frequency of satellite observations and the ability of L-band SAR to identify disturbance events characterized by post-disturbance tree remnants earlier than C-band SAR, which only detected these disturbances after the tree remnants had been removed.
In summary, Balling said, “Our findings confirm that combining C-band and L-band data can deliver significant improvements in the monitoring of forest disturbances, providing an exciting glimpse of how data from the upcoming ROSE-L mission could support forest monitoring when analysed in combination with Sentinel-1.”
Artist’s impression of Copernicus Sentinel-1 C-band SAR mission
Copyright:ESA
One of six selected Copernicus Sentinel Expansion Missions, ROSE-L is expected to launch later this decade to fill a gap in L-band detection capabilities.
ROSE-L is expected to provide data of a higher resolution than was used in the current study, which could result in a more detailed picture of forest disturbances.
Balling added, “Another key benefit of ROSE-L is that, as part of the Copernicus programme, ROSE-L data will be more accessible than L-band data are today, which will make this type of analysis more achievable for scientists, countries and other stakeholders than is now the case.”
In addition to forest monitoring, ROSE-L will provide key information for a range of other applications, including agriculture and food security, maritime surveillance and Arctic monitoring.
The study was completed as a collaboration between: Wageningen University, Laboratory of Geo-Information Science and Remote Sensing, Wageningen, the Netherlands; and Helmholtz GFZ German Research Centre for Geosciences, Remote Sensing and Geoinformatics, Potsdam, Germany.
About the Copernicus Sentinels
The Copernicus Sentinels are a fleet of dedicated EU-owned satellites, designed to deliver the wealth of data and imagery that are central to the European Union's Copernicus environmental programme.
The European Commission leads and coordinates this programme, to improve the management of the environment, safeguarding lives every day. ESA is in charge of the space component, responsible for developing the family of Copernicus Sentinel satellites on behalf of the European Union and ensuring the flow of data for the Copernicus services, while the operations of the Copernicus Sentinels have been entrusted to ESA and EUMETSAT.
Did you know that?
Earth observation data from the Copernicus Sentinel satellites are fed into the Copernicus Services. First launched in 2012 with the Land Monitoring and Emergency Management services, these services provide free and open support, in six different thematic areas.
The Copernicus Land Monitoring Service (CLMS) provides geographical information on land cover and its changes, land use, vegetation state, water cycle and Earth's surface energy variables to a broad range of users in Europe and across the World, in the field of environmental terrestrial applications.
It supports applications in a variety of domains such as spatial and urban planning, forest management, water management, agriculture and food security, nature conservation and restoration, rural development, ecosystem accounting and mitigation/adaptation to climate change.
References:
Johannes Balling, Bart Slagter, Sietse van der Woude, Martin Herold, Johannes Reiche, ALOS-2 PALSAR-2 ScanSAR and Sentinel-1 data for timely tropical forest disturbance mapping: A case study for Sumatra, Indonesia, International Journal of Applied Earth Observation and Geoinformation, Volume 132, 2024, 103994,ISSN 1569-8432.