Abstract
Abstract. Crop lodging – the bending of crop stems from the vertical – is a major yield-reducing factor in cereal crops and causes deterioration in grain quality. Accurate assessment of crop lodging is important for improving estimates of crop yield losses, informing insurance loss adjusters and influencing management decisions for subsequent seasons. The role of remote sensing data, particularly synthetic aperture radar (SAR) data has been emphasized in the recent literature for crop lodging assessment. However, the effect of lodging on SAR scattering mechanisms is still unknown. Therefore, this research aims to understand the possible change in scattering mechanisms due to lodging by investigating SAR image pairs before and after lodging. We conducted the study in 26 wheat fields in the Bonifiche Ferraresi farm, located in Jolanda di Savoia, Ferrara, Italy. We measured temporal crop biophysical (e.g. crop angle) parameters and acquired multi-incidence angle RADARSAT-2 (R-2 FQ8-27° and R-2 FQ21-41°) and Sentinel-1 (S-1 40°) images corresponding to the time of field observations. We extracted metrics of SAR scattering mechanisms from RADARSAT-2 and Sentinel-1 image pairs in different zones using the unsupervised H/α decomposition algorithm and Wishart classifier. Contrasting results were obtained at different incidence angles. Bragg surface scattering increased in the case of S-1 (6.8%), R-2 FQ8 (1.8%) while at R-2 FQ21, it decreased (8%) after lodging. The change in double bounce scattering was more prominent at low incidence angle. These observations can guide future use of SAR-based information for operational crop lodging assessment in particular, and sustainable agriculture in general.
Highlights
Crop lodging – the permanent displacement of the crop stem from its upright position or destruction of root anchorage is caused by the complex interaction between genetic, management and environmental forces (Pinthus, 1974)
For R-2, the largest densities in the two planes correspond to surface scattering (Z6, 25.03% before and 27.00% after) and volume diffusion (Z5 12.78% before 22.19% after) with moderate to high randomness with some double-bounce scattering at moderate H (Z4 2.29% before and 0% after)
This study demonstrated the feasibility of using synthetic aperture radar (SAR) data to detect the possible change in scattering mechanisms in the event of lodging in wheat; thereby allowing lodging identification to support precision management and understanding of on-going plant physiological processes
Summary
Crop lodging – the permanent displacement of the crop stem from its upright position or destruction of root anchorage is caused by the complex interaction between genetic, management and environmental forces (Pinthus, 1974). Field-based approaches for lodging assessment rely on visual inspection and physical measurement of plant properties (such as crop angle and lodged area) which can be infeasible for large areas (more than a few 100 ha). These methods depend on the skill and self-consistency of the observer. The earliest work by Gerten and Wiese (1987) captured aerial photos of a single wheat field to determine if lodged areas could be discriminated and measured from RGB and near-infrared (NIR) photos. In another study, Chapman et al (2014) conducted field experiments on 3 ha wheat fields to quantify lodged areas using aerial RGB and NIR images. Yang et al (2017) used UAV data, a digital surface
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