Optical and Microwave Remote Sensing in Monitoring Mangrove Phenology

Abstract

Mangrove forests are critical coastal ecosystems that play an important role in the global carbon cycle, yet they are increasingly threatened by human disturbance and habitat loss. Effective phenology monitoring is therefore essential for conservation and restoration. This paper reviews recent progress in applying optical and microwave remote sensing to mangrove phenology monitoring, with a focus on Sentinel-2 optical imagery and Sentinel-1 SAR data. Optical remote sensing can effectively capture vegetation physiological changes through indices such as NDVI and EVI, but its performance is strongly limited by persistent cloud cover in mangrove regions. In contrast, microwave remote sensing enables all-weather observation and can compensate for optical data gaps, although both phenological and non-phenological factors influence its backscatter signals. The paper further discusses the complementarity of the two data types and summarises current fusion strategies at the data, feature, and decision levels. It concludes that integrating optical and microwave remote sensing, together with ground validation under a space-air-ground framework, offers strong potential for developing more reliable and continuous mangrove phenology monitoring systems.