Potential of RADARSAT-2 data on identifying sugarcane lodging caused by typhoon

Sugarcane lodging monitoring in large area is a fundamental requirement for damage reduction, yield prediction and loss evaluation. Synthetic Aperture Radar (SAR), regardless of meteorological conditions, provides a promising tool to monitor the status of agricultural crops. The polarimetric features extracted from Polarimetric SAR (PolSAR) have proved to be sensitive to wheat lodging, but for sugarcane lodging monitoring, there are three influences that make it more complicated: heterogeneity of sugarcane scattering, variations of sugarcane growing conditions, and sugarcane growth. In this paper, a new process was proposed to identify sugarcane lodging. Firstly, object-based image segmentation was operated to reduce the heterogeneity of sugarcane scattering. Complex Wishart classifier was used to identify sugarcane field from other land cover types, and 18 polarimetric features were extracted from 6 consecutive RADARSAT-2 data. Then time-series trends of the polarimetric features were used to overcome the influence of variations of sugarcane growing conditions. We found that it was impossible to identify the lodging sugarcane based on a single-time data. At last, the influence of sugarcane growth was reduced by finding the polarimetric features, for which the time-series trends before and after lodging happened were opposite. The study area was located in Leizhou Peninsula, China. During the observation period, large areas of sugarcane fields were in lodging situation when two strong typhoons passed. This study indicated great potential capability of C-band RADARSAT-2 data for monitoring sugarcane lodging.