Speaker
Description
The summer of 2026 was exceptionally dry and warm across Europe, and its ecological impact is now becoming measurable. At the ICOS ecosystem station in Brasschaat, Belgium (ICOS code Be-Bra), eddy-covariance measurements from the 40 m tower indicate that canopy photosynthesis fell roughly 19% below the long-term average. (https://www.vrt.be/vrtnws/nl/2026/08/24/brasschaatse-bossen-kreunden-deze-zomer-onder-de-droogte-laatst/) It is the lowest carbon uptake recorded since observations began at the site in 1997. What is missing is the link to spaceborne observation: it is not yet established whether this anomaly is detectable from space, nor how representative the tower footprint is of the surrounding forest - tower measurements integrate over only a few hundred metres around the mast. Whether drought impacts of this magnitude leave a detectable signature in spaceborne observations, and how far across the landscape they extend, remains untested for this site.
Drought alters canopy water content, dielectric properties and structure through stomatal closure, foliage loss and reduced water storage. SAR is sensitive to all these quantities, especially in C- and L-band. As droughts cause water deficits in trees and eventually lead to early foliage loss, the S-1 radiometric signal and polarimetric signatures are tested regarding their sensitivities to these effects.
This contribution presents an initial assessment of how spaceborne SAR observations captured the 2026 drought anomaly at Brasschaat using summer 2025 as a contrasting reference period under more typical meteorological conditions. Ground-based GNSS sensors at this site, installed as part of the TU Delft GNSS-T network provides continuous information on vegetation water dynamics. Combined with ICOS data, these provide continuous, non-destructive proxies for vegetation and soil water dynamics at temporal resolutions far exceeding the satellite revisit, and offer an independent reference against which SAR observables can be interpreted. We explore how these datasets can be combined with SAR signatures to attribute observed radar anomalies to plant water status.
Here we present preliminary results based on Sentinel-1 imagery. Ongoing analysis may incorporate additional SAR observables, sensors or in-situ variables pending availability. We will discuss the interpretability and limitations of the observed signals and what they imply for the design of future missions including Sentinel-1 Next Generation, ROSE-L and potential sub-daily SAR concepts.