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ARS Home » Northeast Area » Beltsville, Maryland (BARC) » Beltsville Agricultural Research Center » Hydrology and Remote Sensing Laboratory » Research » Publications at this Location » Publication #374746
Research Project: Integrating Remote Sensing, Measurements and Modeling for Multi-Scale Assessment of Water Availability, Use, and Quality in Agroecosystems

Location: Hydrology and Remote Sensing Laboratory

Title: The backscattering contribution of soybean pods at L-band

Author
item ZHOU, Y. - George Washington University
item SHARMA, A. - George Washington University
item KURUM, M. - Mississippi State University
item LANG, R.H. - George Washington University
item O'NEIL, P.E. - Goddard Space Flight Center
item Cosh, Michael

Submitted to: Remote Sensing of Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2020
Publication Date: 7/21/2020
Citation: Zhou, Y., Sharma, A., Kurum, M., Lang, R., O'Neil, P., Cosh, M.H. 2020. The backscattering contribution of soybean pods at L-band. Remote Sensing of Environment. 248:111977. https://doi.org/10.1016/j.rse.2020.111977.
DOI: https://doi.org/10.1016/j.rse.2020.111977

Interpretive Summary: Soil moisture remote sensing with the L-band frequency is complicated by the geometry of the vegetation at the surface. Soybean plants in particular have plant components with different shapes, including what could be characterized as cylinders (stems), plates (leaves), and orbs (pods). These components evolve over the growing cycle of the plant with implications on how the vegetation is interpreted in the radar scattering model. In this study, it was shown that L-band radar can accurately monitor soil moisture beneath soybean plants with good accuracy, and it is even possible to estimate the pod development using the characteristics of the radar signal. The results of this study will influence remote sensing algorithm development and soybean yield estimation.

Technical Abstract: L-band (1.25 GHz) radar measurements of a soybean canopy indicate that the emergence of seed pods is a significant contributor to the backscatter during the late stages of the growing season. In order to validate the measured data, a realistic scattering model of the soybean canopy is developed. The parameters of the soybean canopy and underlying soil used in the model vary over the growing season based on in situ measurements. Scattering amplitudes for soybean leaves are modeled analytically by using a thin disk approximation; stem and pods are jointly modeled using a numerical electromagnetic field solver. These scattering amplitudes are together incorporated into a coherent scattering model developed at George Washington University (GW) to obtain the backscattering coefficient for VV- and HH-polarizations. The modeling results show good agreement with the radar field measurements, having RMSEs of 0.51 dB for VV-pol and 1.1 dB for HH-pol. Both measurement and model results show that the change of soil moisture can be accurately monitored by L-band backscatter. It is also found that the difference between HH- and VV-polarized backscatter increases as the size of the soybean pods becomes larger. Regarding this phenomenon, an innovative method is developed here to estimate the number of pods in a soybean canopy based on polarimetric radar backscatter at L-band.