Mapping Plant Functional Types in Floodplain Wetlands: An Analysis of C-Band Polarimetric SAR Data from RADARSAT-2

Natalia Morandeira,Claudia Facchinetti,Patricia Kandus,Francisco Grings

doi:10.3390/rs8030174

Abstract

The inclusion of functional approaches on wetland characterizations and on biodiversity assessments improves our understanding of ecosystem functioning. In the Lower Paraná River floodplain, we assessed the ability of C-band polarimetric SAR data of contrasting incidence angles to discriminate wetland areas dominated by different plant functional types (PFTs). Unsupervised H/α and H/A/α Wishart classifications were implemented on two RADARSAT-2 images differing in their incidence angles (FQ24 and FQ08). Obtained classes were assigned to the information classes (open water, bare soil and PFTs) by a priori labeling criteria that involved the expected interaction mechanisms between SAR signal and PFTs as well as the relative values of H and α. The product obtained with the shallow incidence angle scene had a higher accuracy than the one obtained with the steep incidence angle product (61.5% vs. 46.2%). We show how a systematic analysis of the H/A/α space can be used to improve the knowledge about the radar polarimetric response of herbaceous vegetation. The map obtained provides novel ecologically relevant information about plant strategies dominating the floodplain. Since the obtained classes can be interpreted in terms of their functional features, the approach is a valuable tool for predicting vegetation response to floods, anthropic impacts and climate change.

Highlights

The largest wetlands of South America are associated with the floodplains of the Amazonas, Orinoco and Paraná-Paraguay Rivers [1]
Description of the Scenes and Field Samples. In both RADARSAT-2 scenes, co-polarizations (HH and VV) showed similar backscattering coefficients for most of the field samples belonging to different classes (Figure 3), except for plant functional types (PFTs)
The results suggest that our hypotheses between PFT and Synthetic Aperture Radar (SAR) signal interactions were accurate only for the case of shallow incidence angles

Summary

Introduction

The largest wetlands of South America are associated with the floodplains of the Amazonas, Orinoco and Paraná-Paraguay Rivers [1]. These ecosystems feature high biodiversity and are important for society due to flood regulation, habitat provision for fish and wildlife, natural forage provision for cattle, and carbon sequestering, among other factors [2,3]. Optical data often fail in Remote Sens. Synthetic Aperture Radar (SAR) data have been noted as a promising tool to discriminate wetland vegetation types and to assess their dynamics, mainly due to the ability to detect water below the vegetation [8,9,10,11]. In the Paraná River floodplain, the downstream deltaic portion has been addressed with

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Results

Conclusion