L-band; microwave radiometry; SMAP; Soil plant atmosphere system; SPAC; transmissivity; vegetation; vegetation water potential; Forest stand; In-situ measurement; Microwave radiometry; Transmissivity; Vegetation water potential; Water potential; Computers in Earth Sciences; Atmospheric Science
Abstract :
[en] Monitoring the water status of forests is paramount for assessing vegetation health, particularly in the context of increasing duration and intensity of droughts. In this study, a methodology was developed for estimating forest water potential at the canopy scale from ground-based L-band radiometry. The study uses radiometer data from a tower-based experiment of the SMAPVEX 19-21 campaign from April to October 2019 at Harvard Forest, MA, USA. The gravimetric and the relative water content of the forest stand was retrieved from radiometer-based vegetation optical depth. A model-based methodology was adapted and assessed to transform the relative water content estimates into values of forest water potential. A comparison and validation of the retrieved forest water potential was conducted with in situ measurements of leaf and xylem water potential to understand the limitations and potentials of the proposed approach for diurnal, weekly and monthly time scales. The radiometer-based water potential estimates of the forest stand were found to be consistent in time with rPearson correlations up to 0.6 and similar in value, down to RMSE = 0.14 [MPa], compared to their in situ measurements from individual trees in the radiometer footprint, showing encouraging retrieval capabilities. However, a major challenge was the bias between the radiometer-based estimates and the in situ measurements over longer times (weeks & months). Here, an approach using either air temperature or soil moisture to update the minimum water potential of the forest stand (FWPmin) was developed to adjust the mismatch. These results showcase the potential of microwave radiometry for continuous monitoring of plant water status at different spatial and temporal scales, which has long been awaited by forest ecologists and tree physiologists.
Jagdhuber, Thomas ; Augsburg University, Institute of Geography, Augsburg, Germany ; German Aerospace Center, Microwaves and Radar Institute, Wessling, Germany
Schmidt, Anne-Sophie; German Aerospace Center, Microwaves and Radar Institute, Wessling, Germany
Fluhrer, Anke ; Augsburg University, Institute of Geography, Augsburg, Germany ; German Aerospace Center, Microwaves and Radar Institute, Wessling, Germany
Chaparro, David ; Center for Ecological Research and Forestry Applications (CREAF), Cerdanyola del Vallès, Spain ; German Aerospace Center, Microwaves and Radar Institute, Wessling, Germany
Jonard, François ; Université de Liège - ULiège > Département de géographie ; Université de Liège - ULiège > Sphères ; Université de Liège - ULiège > Département de géographie > Earth Observation and Ecosystem Modelling (EOSystM Lab)
Piles, Maria ; Image Processing Lab, University of Valencia, Paterna, Spain
Holtzman, Natan; Stanford University, School of Earth & Environmental Sciences, Stanford, United States
Konings, Alexandra G. ; Stanford University, School of Earth & Environmental Sciences, Stanford, United States
Feldman, Andrew F.; Biospheric Sciences Laboratory, NASA Goddard Spaceflight Center, Greenbelt, United States ; University of Maryland, Earth System Science Interdisciplinary Center, College Park, United States
Baur, Martin J.; University of Cambridge, Department of Geography, Cambridge, United Kingdom
Steele-Dunne, Susan ; Delft University of Technology, Department of Geoscience and Remote Sensing, Delft, Netherlands
Schellenberg, Konstantin ; German Aerospace Center, Microwaves and Radar Institute, Wessling, Germany ; Friedrich Schiller University Jena, Department for Earth Observation, Jena, Germany ; Max Planck Institute for Biogeochemistry, Department Biogeochemical Processes, Jena, Germany
Kunstmann, Harald ; Augsburg University, Institute of Geography, Augsburg, Germany
Ramon Areces Foundation NASA - National Aeronautics and Space Administration
Funding text :
Thisworkwas supported in part by the MIT-Germany Seed Fund “GlobalWater Cycle andEnvironmental Monitoring usingActive and
Passive Satellite-basedMicrowave Instruments,” and in part by theMIT-Belgium Seed Fund “Early Detection of PlantWater Stress Using Remote Sensing.” The work of David Chaparro was supported in part by the Ramón Areces Foundation postdoctoral grant, in part by the projects “la Caixa” Junior Leader Fellowship under Grant LCF/BQ/PI23/11970013 (lead: O. Binks) and Grant H2020 FORGENIUS (Improving access to FORest GENetic resources Information and services for end-USers) #862221, and in part by the Ramón Areces Postdoctoral Fellowship. Thework ofAndrewF. Feldmanwas supported in part by the NASA ECOSTRESS science team and in part by theNASATerrestrial Ecology scoping
study for a dryland field campaign (ARID).
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