Hydrologic and dielectric properties of woody plant tissue: implications for remote sensing of canopy water status

The measurement of xylem water potential provides information about the current water available to plants. Furthermore, the knowledge of actual stand transpiration and canopy water conductance provides essential information for estimating canopy carbon, water and energy budgets. Thus, successfully coupling remote sensing measurements directly to canopy water status would close a gap in our ability to estimate these parameters using remote sensing techniques. Connecting canopy water status to variations in observed radar backscatter via the plant dielectric constant will demonstrate the capability of using remotely sensed radar data in ecological studies of canopy water relations. This paper examines in situ observations of hydrologic and dielectric properties of several tree species under different environmental conditions. Characteristics of the dielectric constant measured for the woody plant material are examined together with simultaneous observations of such hydrologic parameters as xylem water potential and xylem water flow. Dielectric constant is monitored with field portable probes or with multichannel measurement systems designed specifically for continuous monitoring of dielectric properties. The importance of this work for radar remote sensing is discussed