Estimating Stem Water Content From Tower-Based L-Band Tomographic Radar Using a Single-Scattering Model of a Uniform Layer: A First in Situ Experiment

Spaceborne SAR missions have the potential to estimate forest vegetation water content (VWC), but understanding the underlying scattering processes and their link to VWC is still limited. In the paper, tower-based tomographic radar observations of a boreal forest at L-band are used to measure canopy-only backscatter. Results show that the latter is anticorrelated with stem water content. Time series of both canopy backscatter and attenuation were extracted and linked to in situ stem water content using a scattering model. Results show that the proposed canopy backscatter model effectively captures the diurnal and long-term variations in stem water content, with an RMSE of 4%. The estimated model coefficients indicate that the sensitivity of extinction to stem water content dominates over the sensitivity of volume backscatter to stem water content. Moreover, the attenuation time series and corresponding model resulted in a better agreement with an RMSE of 2%. However, attenuation requires a known concealed reference target in the forest which limits its use over extended areas. While the study is limited in scope and the model has not been validated for broader generalization, these findings offer preliminary insights into the sensitivity of L-band radar to forest VWC and may support future observational strategies.