Exploring the potential of using L-band InSAR for mapping flooded vegetation in tropical wetlands

Wetlands play a critical role in the global water and carbon cycles, yet monitoring their water extent remains difficult, particularly beneath dense vegetation. SAR-based techniques such as backscatter thresholding are limited by complex scattering mechanisms, while fully polarimetric SAR (PolSAR) data capable of detecting double-bounce scattering is scarce. To address these challenges, this study evaluates the potential of Interferometric SAR (InSAR) for mapping water surfaces beneath vegetation using the Atrato floodplain in Colombia as a case study. We develop an automated workflow combining InSAR fringe detection with local phase homogeneity analysis to generate probabilistic flooded vegetation maps. Applied to ALOS PALSAR-1 L-band image pairs from 2007 to 2011, the workflow captures seasonal fluctuations in flooded extent ranging from 500 to 1500 km 2 . When compared to other L-band SAR inundation products, the InSAR-based maps identify broader flooded areas, with ∼70 % agreement in pairwise comparisons. Furthermore, around 84 % of detections align with existing wetland inventories and seasonal changes in water extent are found to follow terrestrial water storage anomalies. Finally, the PolSAR analysis shows that InSAR can complement backscatter-based methods by detecting inundation in areas with weak double-bounce signals. These findings suggest that combining InSAR with backscatter-based methods can improve detection of flooded vegetation, which is particularly relevant given that the new NISAR mission will provide frequent global L-band observations. • First standardized workflow for mapping flooded vegetation using InSAR. • Detects inundation under canopy, even where volume, not double-bounce, dominates. • Potentially scalable approach for monitoring tropical wetland water dynamics.