Electromagnetic scattering from a corn canopy at L and C bands

• Main Authors: Yang Du, Wenzhe Yan, Shi, J. C., Zeng-Yuan Li, Er-Xue Chen
• Format: Conference Proceeding
• Language: English
• Subjects: Dielectrics; Electromagnetic scattering; Mathematical model; Remote sensing; Rough surfaces; Surface roughness

The ability to retrieve and monitor soil moisture and vegetation water content (VWC) is of great importance. Yet accurate retrieval of such information from microwave observations presents a big challenge, which calls for the development of high fidelity scattering models. In the literature, a "discrete scatter" approach was usually deployed, which attempted to determine first the scattering behavior of the individual constituent of the canopy, then that of canopy as a whole by summing up either incoherently [1] [?] or coherently [2]-[3]. To simplify the problem, constituents of the canopy are modeled as canonical geometrical objects. For corn canopy, the stalks are modeled as dielectric circular cylinders with finite length, and the leaves are represented as thin dielectric disks with elliptic cross section. Since scattering from each of the canonical object serves as the base for further "assembling", it is expected to be accurately determined. However, mush is still desired in this regard. For a dielectric cylinder of finite length, in studying its scattering behavior the generalized Rayleigh-Gans approximation (GRGA) [4] is usually applied, which approximates the induced current in a finite cylinder by assuming infinite length. This method is valid for a needle shaped scatterer with radius much smaller than the wavelength. Yet caution must be taken even at L band when EM scattering from the stalk of a corn plant is to be evaluated using GRGA. It is also well known that GRGA fails to satisfy the reciprocity theorem [2]. In the evaluation of scattering amplitude of leaves, the GRGA method is usually used. However, caution must be taken here. At C band the wavelength is 5.6 cm, which is comparable to the length of minor axis of corn leaves, which presents an unfavorable condition in applying GRGA and thus appreciable error is expected in the predicted scattering amplitude. When corn canopy is at its early stage of growth, or when the incidence angle is not large, contribution from the underlying ground is appreciable and thus its accurate prediction is important. Yet this roughness effect has not been adequately addressed in canopy scattering models, where what is typically applied is conventional analytical method such as Kirchhoff approximation (KA), or the small perturbation method (SPM) [5], or the more advanced yet still improvement-needed integral equation method (IEM) [6]. In this study, we choose to apply a more rigorous treatment of the rough sur