Response of Multi-Incidence Angle Polarimetric RADARSAT-2 Data to Herbaceous Vegetation Features in the Lower Paraná River Floodplain, Argentina

Abstract

Wetland ecosystems play a key role in hydrological and biogeochemical cycles. In emergent vegetation targets, the occurrence of double-bounce scatter is indicative of the presence of water and can be valuable for hydrological monitoring. Double-bounce scatter would lead to an increase of σ0HH over σ0VV and a non-zero co-polarized phase difference (CPD). In the Lower Paraná River floodplain, a total of 11 full polarimetric RADARSAT-2 scenes from a wide range of incidence angles were acquired during a month. Flooded targets dominated by two herbaceous species were sampled: Schoenoplectus californicus (four sites, Bulrush marshes) and Ludwigia peruviana (three sites, Broadleaf marshes). As a general trend, σ0HH was higher than σ0VV, especially at the steeper incidence angles. By modeling CPD with maximum likelihood estimations, we found results consistent with double-bounce scatter in two Ludwigia plots, at certain scene incidence angles. Incidence angle accounted for most of the variation on σ0HH, whereas emergent green biomass was the main feature influencing σ0HV. Multivariate models explaining backscattering variation included the incidence angle and at least two of these variables: emergent plant height, stem diameter, number of green stems, and emergent green biomass. This study provides an example of using CPD to decide on the contribution of double-bounce scatter and highlights the influence of vegetation biomass on radar response. Even with the presence of water below vegetation, the contribution of double-bounce scatter to C-band backscattering depends on scene incidence angles and may be negligible in dense herbaceous targets.

Effects of Man-Made Fires on Wetlands of the Paraná River in Argentina: Perspectives of Ecological Restoration

“…The largest surface covered by riparian wetlands is located in South America, associated with the Amazonas, the Orinoco, and the Paraguay-Paraná rivers. In Argentina, wetlands cover more than 21% of its territory (Morandeira et al 2021). Degradation and loss of wetlands are global concerns because they harbor high biodiversity and ecosystem services, such as erosion control, hydrological regimen and water safety (Costanza et al 2014).…”

Cover classifications in wetlands using Sentinel-1 data (Band C): a case study in the Parana river delta, Argentina

“…Multitemporal C-Band data can enhance wetland classification schemes, by accounting flood changes and vegetation phenology (Salvia et al, 2008;Vanama et al, 2020). However, characterizing vegetation types in high-vegetated wetlands using C-band data has been challenging due to the modest potential of this band to penetrate forest canopies (Sivasankar et al, 2018;Meyer, 2019;Numbisi and Coillie, 2020;Morandeira et al, 2021). In areas where the vegetation is sufficiently dense, backscatter mean values may be similar between different vegetation types.…”