Relations Between P- to L-Band Radar Tomography and Sub-Daily Tree Water Dynamics in a Boreal Forest

Paper in proceeding, 2025

In this study, for the first time, sub-daily radar reflectivity variations are compared with a hydraulic forest model. Multi-polarimetric time series at P- to L-band (435, 600 and 1270 MHz) over a coniferous boreal forest stand, acquired by the BorealScat-2 tomographic tower radar, are analyzed. Attenuation was measured by observing a large trihedral reflector in the forest. The hydraulic forest model was parameterized based on tree sensor data, and driven by evapotranspiration measurements. The forest canopy reflectivity is found to co-vary mainly with the crown water potential and content at P-band, and with the attenuation at L-band. A frequency dependence is apparent, with a positive linear relation at P-band transitioning to a negative nonlinear relation at L-band. The attenuation co-varies mainly with the stem water potential and content at P-band, while it varies in between that of the crown and stem at L-band. In conclusion, it is shown that radar can be used to sense forest hydraulic properties, with prospects of possibly driving forest hydraulic models.