Cotton Phenology Detection Using Sentinel-1 Time Series Data

Sentinel-1 Synthetic Aperture Radar (SAR) data proves valuable in detecting crop phenological stages. This study explores the effectiveness of time series SAR indices from Sentinel-1 in monitoring cotton phenology, an aspect not extensively investigated. During the process, seasonal extrema and breakpoints of SAR indices were derived over a cotton plantation in Brazil from December 2021 to July 2023. The results indicate that the seasonal maximum and minimum of Dual-polarization Radar Vegetation Index (DpRVIc) align with cotton emergence and flowering dates, respectively. Additionally, the seasonal minimum of Cross-Ratio (CR) and Gamma0_VH aligns with cotton boll formation and square formation dates, respectively. During evaluation, most detected phenology stages are within ±12 days of field observation dates. However, some emergence and square formation detections exhibit large outliers, necessitating further investigation. This study underscores the significant potential of time-series Sentinel-1 data for cotton phenology monitoring, providing valuable insights for improved agricultural practices.