Evaluation of L- and S-Band Polarimetric Data for Monitoring Great Lakes Coastal Wetland Health in Preparation for NISAR

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Article

Publication Date

11-1-2025

Abstract

Highlights: What are the main findings? Inundation extent mapping demonstrated high accuracy (79–83%) at C-, S- and L-band areas with limitations related to stand structure and frequency, while du-al-frequency SAR was found to have high accuracy (~92%) for wetland type mapping. Misattribution of dominant double-bounce scatter (characteristic of wetlands) to single-bounce scatter occurs at certain vegetation moisture and SAR geometries for C-, S- and L-band areas. What are the implications of the main findings? Multi-frequency polarimetric SAR provides high-accuracy wetland mapping capabilities, regardless of cloud cover. The misattribution of double-bounce to single-bounce scattering results in errors in wetland extent mapping, but it may also be useful in monitoring wetland health since it has larger anomalies with low vegetation moisture. Coastal wetlands are a critical buffer between land and water that are threatened by land use and climate change, necessitating improved monitoring for management and resilience planning. The recently launched NASA-ISRO L- and S-band SAR satellite (NISAR) will provide regular collections of fully polarimetric SAR imagery over the Great Lakes, allowing for unprecedented remote monitoring of the large expanses of coastal wetlands in the region. Prior research with polarimetric C-band SAR showed inconsistencies with common polarimetric analysis techniques, including the erroneous misattribution of double-bounce scattering in three-component scattering models. To prepare for NISAR and determine whether SAR-based coastal wetland analysis methods established with the C-band are applicable to the L- and S-bands, the NASA-ISRO airborne system (ASAR) collected imagery over western Lake Erie and Lake St. Clair coincident with a field data collection campaign. ASAR data were analyzed to identify common Great Lakes coastal wetland vegetation species, assess the extent of inundation, and derive biomass retrieval algorithms. Co-polarized phase difference histograms were also analyzed to assess the validity of three-component scattering decompositions. The L- and S-bands allowed for the production of wetland type maps with high accuracies (92%), comparable to those produced using a fusion of optical and SAR data. Both frequencies could assess the extent of flooded vegetation, with the S-band correctly identifying inundated vegetation at a slightly higher rate than the L-band (83% to 78%). Marsh vegetation biomass retrieval algorithms derived from L-band data had the best correlation with field data (R2 = 0.71). Three component scattering models were found to misattribute double-bounce scattering at incidence angles shallower than 35°. The L- and S-band results were compared with satellite RADARSAT-2 imagery collected close to the ASAR acquisitions. This study provides an advanced understanding of polarimetric SAR for monitoring wetlands and provides a framework for utilizing forthcoming NISAR data for effective monitoring.

Publication Title

Remote Sensing

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