High-resolution measurements of scattering in wheat canopies-implications for crop parameter retrieval

Abstract

Polarimetric X-and C-band measurements by the University of Sheffield ground-based synthetic aperture radar (GB-SAR) indoor system provide three-dimensional images of the scattering processes in wheat canopies, at resolutions of around a wavelength (3-6 cm). The scattering shows a pronounced layered structure, with strong returns from the soil and the flag leaves, and in some cases a second leaf layer. Differential attenuation at horizontal (H) and vertical (V) polarization, due to the predominantly vertical structure of the wheat stems, gives rise to marked effects. At both C and X bands, direct return from the canopy exceeds the soil return at large incidence angles for VV polarization, but is comparable to or less than the soil return in all other cases. At HV, the apparent ground return is probably due to a double-bounce mechanism, and volume scattering is never the dominant term. Direct sensing of the crop canopy is most effective at X band, VV, and large incidence angles, under which conditions the return is dominated by the flag leaf layer. Field measurements with the outdoor GB-SAR system suggest, however, that for sensitivity to biomass and reduced susceptibility to disturbances by rainfall, a two-channel C-band system operating at a medium range of incidence angles is preferred.Index Terms-Agriculture, backscatter modeling, synthetic aperture radar (SAR).

Cereal Yield Modeling in Finland Using Optical and Radar Remote Sensing

“…durum), soybean (Glycine max L.) maize (Zea mays L.) and rice (Oryza sativa L). Previous studies have described attempts to apply both optical and microwave SAR (Synthetic Aperture Radar) satellite data for crop yield modeling and crop inventory monitoring, e.g., Brown et al [1], Henning et al [2], Maas and Dunlap [3] and Kondratyev et al [4] for wheat and maize, Shibayama and Akiyama [5] and Le Toan et al [6] for rice.…”

“…Moriondo et al [25] studied wheat yield variation with CROPSYST model using NDVI (Normalized Difference Vegetation Index) and FAPAR Index (Fraction of Absorbed Photosynthetically Active Radiation) estimates. Brown et al [1] and Henning et al [2] studied crop canopy and microwave SAR (Synthetic Aperture Radar) backscattering interactions. Prasad et al [26] evaluated the use of Spectral Reflectance Indices (SRI) similar to VGI indices applied in this study, for assessing grain yield variabil ity in winter wheat genotypes under Great Plains (USA) growing conditions.…”

Can C-band synthetic aperture radar be used to estimate soil organic carbon storage in tundra?

“…These data cover the same incidence angle range and swath but spatial resolution is finer, although still medium, with ∼ 120 m (Closa et al, 2003). Data availability of this mode is lower since it was acquired on request only.…”

“…Surface roughness thus plays an important role for spatial differences in backscatter during frozen conditions in tundra regions. Specifically, data acquired in HH (horizontally sent and received) polarization are expected to represent soil conditions better than VV (vertically sent and received) polarization (Brown et al, 2003). Vertically (with respect to the Earth surface) polarized waves interact more with vertically structured vegetation parts (stems) than horizontally polarized waves.…”

“…There are to date only very few studies which make use of frozen period acquisitions (Duguay et al, 2015;Widhalm et al, 2015a). The advantage for using winter data is that only roughness and volume scattering contributes to the return signal intensity.…”