L-band vegetation optical depth as an indicator of plant water potential in a temperate deciduous forest stand
- 1Stanford University, Earth System Science, Stanford, United States of America (natan.holtzman@gmail.com)
- 2Department of Ecology, Evolution and Marine Biology, University of California Santa Barbara, Santa Barbara, CA, USA
- 3Department of Electrical and Computer Engineering, University of Massachusetts, Amherst, MA, USA
- 4Département des Sciences de l'Environnement, Université du Québec à Trois-Rivières (UQTR), Trois-Rivières, Québec, Canada
- 5Département de géographie, Université de Montréal, Montréal, Québec, H2V 2B8, Canada
- 6USDA ARS Hydrology and Remote Sensing Laboratory, Beltsville, MD, USA
- 7Département de Géomatique Appliquée, Université de Sherbrooke, Sherbrooke, Québec, Canada
- 8NOAA-CESSRST, The City College of New York, City University of New York, New York, NY, USA
- 9Department of Earth and Atmospheric Sciences, City College of New York, City University of New York, New York, NY, USA
- 10Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
Vegetation optical depth (VOD) retrieved from microwave radiometry correlates with the total amount of water in vegetation. In addition to depending on overall biomass, the total amount of water in vegetation varies with relative water content, which is monotonically related to plant water potential, a quantity that drives plant hydraulic behavior. Thus there is a possible relationship between VOD and plant water potential. Previous studies have found evidence for that relationship on the scale of satellite pixels tens of kilometers across, but these comparisons suffer from significant scaling error. Here we used small-scale remote sensing to test the link between remotely sensed VOD and plant water potential. We placed an L-band radiometer on a tower above the canopy looking down at red oak forest stand during the 2019 growing season in the northeastern United States. We retrieved VOD with a single-channel algorithm based on continuous radiometer measurements and in-situ soil moisture data. We also measured water potentials of stem xylem and leaves on trees within the stand.
VOD exhibited a diurnal cycle similar to that of leaf and stem water potential, with a peak at approximately 5 AM. Over the whole growing season, VOD was also positively correlated with both the water potential of stem xylem and the xylem's dielectric constant (a proxy for water content). The presence of moisture on the leaves did not affect the observed relationship between VOD and xylem dielectric constant. We used our observed VOD-water potential relationship to estimate stand-level values for a radiative transfer parameter and a plant hydraulic parameter, which compared well with the published literature. Our findings support the use of VOD for plant hydraulic studies in temperate forests.
How to cite: Holtzman, N., Anderegg, L., Kraatz, S., Mavrovic, A., Sonnentag, O., Pappas, C., Cosh, M., Langlois, A., Lakhankar, T., Tesser, D., Steiner, N., Colliander, A., Roy, A., and Konings, A.: L-band vegetation optical depth as an indicator of plant water potential in a temperate deciduous forest stand, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13033, https://doi.org/10.5194/egusphere-egu21-13033, 2021.
