L-Band Radar Backscatter and Tree Water Dynamics: Insights from the BorealScat-2 System

This study investigates the influence of diurnal variations in sap flux density and vapor pressure deficit (VPD) on L-band radar backscatter patterns, using BorealScat-2 data to focus on polarization and height-specific correlations for understanding forest water dynamics. Multi-polarization and height-resolved backscatter profiles from BorealScat-2 were analyzed alongside sap flux and VPD measurements. Temporal heatmaps highlighted distinct backscatter dynamics, with the mid-to-upper canopy (14 to 20 m) having influence on radar signals. Diurnal cycles of backscatter intensity correlated strongly with sap flux density under varying VPD conditions, demonstrating the radar’s sensitivity to canopy water dynamics. Co-polarized backscatter (HH and VV) consistently exhibited stronger and more stable correlations with sap flux compared to cross-polarized signals. By integrating BorealScat-2 radar data with physiological and meteorological variables, this study underscores the potential of L-band radar backscatter as a proxy for transpiration and forest water exchange processes. The findings enhance understanding of the interplay between environmental factors and radar scattering mechanisms, contributing to advancements in radar-based monitoring of forest hydrology and evapotranspiration.