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Session

📌Poster Session and Networking Aperitivo 🍷
Location: Lower Lobby

Presentation 48

A Novel Corner-Reflector Approach for Active Microwave Monitoring of Forest VOD

David Moravec^1,2, Evripidis Avouris¹, Vít Ježek², Matthias Forkel¹

1: Dresden University of Technology (TUD); 2: Czech University of Life Sciences Prague (CZU)

Forest water availability is a major driver of forest growth, transpiration, productivity, and carbon turnover at the global scale1. Monitoring spatial and temporal dynamics of forest water content is therefore essential. Satellite remote sensing provides large-scale observations, and several water-related indicators already exist, such as multispectral indices, live fuel moisture content (LFMC) from optical and microwave data2,3 or vegetation optical depth (VOD) from passive microwave instruments4,5. However, current products are limited either by insufficient canopy penetration (optical domain) or coarse spatial resolution (passive microwave domain), which restricts their applicability in forest ecosystems.

High-resolution active microwave systems can overcome these limitations. Yet, current methods have not achieved the accuracy required to retrieve forest water content, and applications remain focused mainly on sparse vegetation6,7. Here, we introduce a novel approach using corner reflectors as stable reference targets to improve active microwave retrievals of forest water content. The strong and well-defined backscatter response of corner reflectors reduces modelling uncertainties and simplifies theoretical models such as the Water Cloud Model.

This enables direct assessment of vegetation attenuation and scattering effects from the canopy and allows the derivation of physically interpretable parameters related to forest VOD. Previous microwave tower experiments have demonstrated the feasibility of retrieving vegetation status using reflector-based configurations8,9. We will present the theoretical basis, system design, and first experimental results demonstrating the potential of corner-reflector-based SAR observations as a reference measurement within the framework of PolInSAR techniques or the BIOMASS mission.

1. Konings, A. G. et al. Detecting forest response to droughts with global observations of vegetation water content. Global Change Biology 27, 6005–6024 (2021).

2. Yebra, M. et al. A global review of remote sensing of live fuel moisture content for fire danger assessment: Moving towards operational products. Remote Sensing of Environment 136, 455–468 (2013).

3. Rao, K., Williams, A. P., Flefil, J. F. & Konings, A. G. SAR-enhanced mapping of live fuel moisture content. Remote Sensing of Environment 245, 111797 (2020).

4. Schmidt, L. et al. Assessing the sensitivity of multi-frequency passive microwave vegetation optical depth to vegetation properties. Biogeosciences 20, 1027–1046 (2023).

5. Bueso, D. et al. Soil and vegetation water content identify the main terrestrial ecosystem changes. National Science Review 10, nwad026 (2023).

6. El Hajj, M. et al. First Vegetation Optical Depth Mapping from Sentinel-1 C-band SAR Data over Crop Fields. Remote Sensing 11, 2769 (2019).

7. Vreugdenhil, M. et al. Sentinel-1 Cross Ratio and Vegetation Optical Depth: A Comparison over Europe. Remote Sensing 12, 3404 (2020).

8. Lemmetyinen, J. et al. Attenuation of Radar Signal by a Boreal Forest Canopy in Winter. IEEE Geosci. Remote Sensing Lett. 19, 1–5 (2022).

9. Fleischman, J. G., Ayasli, S., Adams, E. M. & Gosselin, D. R. Foliage attenuation and backscatter analysis of SAR imagery. IEEE Trans. Aerosp. Electron. Syst. 32, 135–144 (1996).