Conference Agenda

The resilience of terrestrial ecosystems to droughts and stress is key for the future of the terrestrial carbon balance. Satellite observations of sub-daily variations in vegetation water content (VWC) could provide us information on health, stress and resilience of key ecosystems across the globe. Water dynamics in vegetation are central in these ecosystems, as they are closely coupled to carbon assimilation at the plant stomata. Understanding diurnal variations in VWC provides insight into the water status, stress and health of plants. However, sub-daily water dynamics in ecosystems are still poorly understood and weakly represented in terrestrial biosphere models. Furthermore, there are no existing or planned satellite missions capable of resolving fluctuations in VWC on sub-daily scales.

To address this critical knowledge and observation gap, SLAINTE was being developed as one of ESA’s New Earth Observation Mission Ideas with a first mission concept submitted in response to ESA’s 12th Call for Earth Explorers (Steele-Dunne et al., 2024, Matar et al., 2024). It comprised a constellation of identical, decametric, monostatic SARs to capture sub-daily variations in vegetation water storage (e.g. via vegetation optical depth (VOD), vegetation water content (VWC), plant water potential (PWP) and surface soil moisture (SSM). One of the key challenges during the development of the SLAINTE mission concept was the limited availability of sub-daily radar backscatter data, both real and synthetic. Real observations are restricted to a few tower sites. Generating synthetic data, on the other hand, requires sub-daily vegetation water content information that is difficult to obtain through destructive sampling, as it is both expensive and logistically demanding.

Here, this challenge is addressed by using continuous, non-destructive ground-based measurements of vegetation water storage dynamics at various forested sites throughout Europe. These observations provide the high-temporal-resolution input needed to drive a physically-based, bistatic and polarimetric radiative transfer (RT) model. The simulations produce synthetic time series of radar backscattering coefficient at sub-daily resolution, allowing us to quantify and characterize the influence of sub-daily variations in plant water dynamics, vegetation structural parameters and biogeophysical properties on the backscattering coefficient. Disentangling and isolating pertinent signals (such as plant internal and surface water content) from confounding factors (e.g. forest geometry, vertical water redistribution effects), will allow us to better understand the sensitivity of radar backscatter to key variables. In this presentation, we will show initial results from simulations of Loobos, a forested site in the Netherlands. We will use these results to demonstrate the value of RT simulations to further strengthen the science case, consolidate observation and measurement requirements and develop retrieval approaches for future sub-daily SAR missions.

References:

Matar, J., Sanjuan-Ferrer, M. J., Rodriguez-Cassola M., Steele-Dunne, S. & De Zan, F. (2024). A Concept for an Interferometric SAR Mission with Sub-daily Revisit. EUSAR 2024; 15th European Conference on Synthetic Aperture Radar, pp. 18-22. IEEE, 2024.

Steele-Dunne, S., Basto, A., De Zan, F., Dorigo, W., Lhermitte, S., Massari, C., Matar J. et al. (2024). SLAINTE: A SAR mission concept for sub-daily microwave remote sensing of vegetation. EUSAR 2024; 15th European Conference on Synthetic Aperture Radar, pp. 870-872. VDE, 2024.