Sentinel-1 Polarimetry to Map Apple Orchard Damage after a Storm

Climate change increases extreme whether events such as floods, hailstorms, or storms, which can affect agriculture, causing damages and economic loss within the agro-food sector. Optical remote sensing data have been successfully used in damage detections. Cloud conditions limit their potential, especially while monitoring floods or storms that are usually related to cloudy situations. Conversely, data from the Polarimetric Synthetic Aperture Radar (PolSAR) are operational in all-weather conditions and are sensitive to the geometrical properties of crops. Apple orchards play a key role in the Italian agriculture sector, presenting a cultivation system that is very sensitive to high-wind events. In this work, the H-alpha-A polarimetric decomposition technique was adopted to map damaged apple orchards with reference to a stormy event that had occurred in the study area (NW Italy) on 12 August 2020. The results showed that damaged orchards have higher H (entropy) and alpha (alpha angle) values compared with undamaged ones taken as reference (Mann-Whitney one-tailed test U = 14,514, p < 0.001; U = 16604, p < 0.001 for H and alpha, respectively). By contrast, A (anisotropy) values were significantly lower for damaged orchards (Mann-Whitney one-tailed test U = 8616, p < 0.001). Based on this evidence, the authors generated a map of potentially storm-damaged orchards, assigning a probability value to each of them. This map is intended to support local funding restoration policies by insurance companies and local administrations.

Automated summary

The study utilized the H-alpha-A polarimetric decomposition technique to map the damage caused by a storm event in apple orchards in northwestern Italy, showing significant differentiation between damaged and undamaged orchards. A probability map of storm-damaged orchards was generated to support local funding restoration policies by insurance companies and local administrations.