Assessing vegetation water potential of winter wheat on field-scale by ground-based L-band radiometry

Jagdhuber, Thomas [German Aerospace Center, Microwave and Radar Institute, Wessling, Germany] Jonard, François [UCL] Piles, Maria [University of Valencia, Image Processing Lab., Spain] Flurher, Anke [German Aerospace Center, Microwave and Radar Institute, Wessling, Germany] Chaparro, David [Universitat Politecnica de Catalunya, CommSensLab & IEEE/UPC, Barcelona, Spain] Meyer, Thomas [Agrosphere (IBG-3), Forschungszentrum Jülich, Germany]

The vegetation water potential (VWP) indicates the level of water stress anticipating eventually drought-induced damage of plants. Therefore, VWP is an essential ecological indicator. As proposed in [1], the relative water content (RWC) can be a valid metric for plant water status and can be utilized to estimate VWP. Rao et al. showed in [2] that the vegetation optical depth (VOD) from X-band satellite radiometry can be converted into RWC estimates with the caveat that water and biomass influence the VOD signal. Therefore, only periods with constant biomass should be evaluated in order to isolate the water component of VOD. Fink et al. investigated in [3] the possibility to extract the gravimetric water content of vegetation (GWC) from the VOD signal. GWC can be converted into RWC and, importantly, it is not affected by biomass dynamics. The GWC-estimation methodology of [3] was already tested on field-scale in [4]. For this study, the dataset of [5] is used to estimate VOD, GWC, RWC and finally VWP for one winter wheat field along the growing season. The applied dataset was recorded at the remote sensing field laboratory of the Forschungszentrum Jülich (FZJ) in Selhausen (Germany) from April to August 2017. The winter wheat field was monitored with the ground-based L-band radiometer instrument ELBARA-II of FZJ. Simultaneously, in situ measurements for key plant (e.g. GWC, height, biomass, leaf area index, and phenology) and soil (e.g. moisture) properties were recorded directly within the field. As a specialty, the soil emission was blocked by a metal grid on top of the ground allowing only vegetation emission and reflection (no soil influence) to reach the sensor. Time series analysis of VOD, GWC, RWC and VWP and their correlation with in situ measurements will be presented in order to understand plant water status and water potential dynamics along the wheat growing season.