Forest canopy scattering properties with signal of opportunity reflectometry: theoretical simulations

• Main Authors: Xuerui Wu, Andrés Calabia, Jin Xu, Weihua Bai, Peng Guo
• Format: Article
• Language: English
• Published: SpringerOpen 2021-07-01
• Series: Geoscience Letters
• Subjects: Bistatic scattering; Forest canopy; Radiative transfer equation model; GNSS-reflectometry (GNSS-R); Polarization; Signal of opportunity-reflectometry (SoOP-R)
• Online Access: https://doi.org/10.1186/s40562-021-00195-7

Abstract In recent years, signal of opportunity reflectometry (SoOp-R) has become a promising remote sensing technique. This emerging technique employs the reflected signals from existing Global Navigation Satellite System (GNSS) or communication satellites to estimate geophysical parameters for Earth observation, such as wind speed, altimetry, significant wave height, soil moisture, etc. While its application for forest canopy monitoring is still in the initial stage, there are still many unknown relations between vegetation parameters and actual observations, and a proper theoretical basis needs to be established for simulation and analysis of the different observation geometries. In this paper, we develop a bistatic scattering model with various polarizations at different frequency bands. Our improved model is based on the first-order radiative transfer equation, and is developed based on the wave synthesis technique, after which it can be used for circular polarization signals in bistatic radar systems, i.e. the typical configuration of SoOp-R. We analyze the simulations of the P (0.25–0.5 GHz), L (0.5–1.5 GHz), C (4–8 GHz), and X (8–12 GHz) bands at the backscattering, specular cone, bistatic scattering, and perpendicular planes. The contributions of the different components to the total scattering are also analyzed. The results show that the coherent scattering at the specular cone is larger than the non-coherent scattering, while trunk-dominated forest canopy has strong scattering at the aforementioned different directions. Variations of canopy parameters such as trunk and branch diameters, tree density, and vegetation water content are also simulated at the specular cone plane, showing strong dependence on the final bistatic scattering observation. The simulation results show that the SoOp-R technique has a great potential for monitoring of canopy parameters.