EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Interpreting Vegetation Optical Depth (VOD) using detailed destructive vegetation sampling of a corn canopy

Saeed Khabbazan1, Ge Gao1, Paul Vermunt1, Susan Steele-Dunne1, Jasmeet Judge2, and Mariette Vreugdenhil3
Saeed Khabbazan et al.
  • 1Department of Water Resources, TU Delft, Stevinweg 1, 2628 CN, Delft, The Netherlands
  • 2University of Florida, Department of Agriculture and Biological Engineering, Gainesville, FL, USA
  • 3Department of Geodesy and Geoinformation, TU Wien, 1040 Vienna, Austria

Vegetation Optical Depth (VOD) is directly related to Vegetation Water Content (VWC), which can be used in different applications including crop health monitoring, water resources management and drought detection. Moreover, VOD is used to account for the attenuating effect of vegetation in soil moisture retrieval using microwave remote sensing.

Commonly, to retrieve soil moisture and VOD from microwave remote sensing, VWC is considered to be vertically homogeneous and relatively static.  However, nonuniform vertical distribution of water inside the vegetation may lead to unrealistic retrievals in agricultural areas. Therefore, it is important to improve the understanding of the relation between vegetation optical depth and distribution of bulk vegetation water content during the entire growing season.

The goal of this study is to investigate the effect of different factors such as phenological stage, different crop elements and nonuniform distribution of internal vegetation water content on VOD. Backscatter data were collected every 15 minutes using a tower-based, fully polarimetric, L-band radar. The methodology of Vreugdenhil et al. [1] was adapted to estimate VOD from single-incidence angle backscatter data in each polarization.

In order to characterize the vertical distribution of VWC, pre-dawn destructive sampling was conducted three times a week for a full growing season. VWC could therefore be analyzed by constituent (leaf, stem, ear) or by height.

A temporal correlation analysis showed that the relation between VOD and VWC during the growing season is not constant. The assumed linear relationship is only valid during the vegetative growth stages for corn.  Furthermore, the sensitivity of VOD to various plant components (leaf, stem and ear) varies between phenological stages and depends on polarization.

Improved understanding of VOD can contribute to improved consideration of vegetation in soil moisture retrieval algorithms. More importantly, it is essential for the interpretation of VOD data in a wide range of vegetation monitoring applications.

[1] M. Vreugdenhil,W. A. Dorigo,W.Wagner, R. A. De Jeu, S. Hahn, andM. J. VanMarle, “Analyzing the vegetation parameterization in the TU-Wien ASCAT soil moisture retrieval,” IEEE Transactions on Geoscience and Remote Sensing, vol. 54, no. 6, pp. 3513–3531, 2016.

How to cite: Khabbazan, S., Gao, G., Vermunt, P., Steele-Dunne, S., Judge, J., and Vreugdenhil, M.: Interpreting Vegetation Optical Depth (VOD) using detailed destructive vegetation sampling of a corn canopy, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8161,, 2020