Abstract
Synthetic aperture radar (SAR) data have been identified as a potential source of information for monitoring surface water, including open water and flooded vegetation, in frequent time intervals, which is very significant for flood mapping applications. The SAR specular reflectance separates open water and land surface, and its canopy penetration capability allows enhanced backscatter from flooded vegetation. Further, under certain conditions, the SAR signal from flooded vegetation may remain coherent between two acquisitions, which can be exploited using the InSAR technique. With these SAR capabilities in mind, this study examines the use of multi-temporal RADARSAT-2 C band SAR intensity and coherence components to monitor wetland extent, inundation and vegetation of a tropical wetland, such as Amazon lowland. For this study, 22 multi-temporal RADARSAT-2 images (21 pairs) were used for InSAR processing and the pairs in the low water stage (November, December) showed high coherence over the wetland areas. The three-year intensity stack was used for assessing wetland boundary, inundation extent, flood pulse, hydroperiod, and wetland vegetation. In addition to the intensity, derived coherence was used for classifying wetland vegetation. Wetland vegetation types were successfully classified with 86% accuracy using the statistical parameters derived from the multi-temporal intensity and coherence data stacks. We have found that in addition to SAR intensity, coherence provided information about wetland vegetation. In the next year, the Canadian RADARSAT Constellation Mission (RCM), will provide more data with frequent revisits, enhancing the application of SAR intensity and coherence for monitoring these types of wetlands at large scales.
Highlights
As for other tropical wetlands, Amazon wetlands provide many services for society, such as water storage, stabilize river discharge, groundwater recharge, organic carbon storage, withholding sediment, ecotourism, timber production, medicinal plants, agricultural products, fish, drinking water, and grazing land [1]
This paper reports an investigation of the use of intensity and/or coherence from a stack of RADARSAT-2 images acquired in 2014-2016 for wetland extent, flood pulse and hydroperiod in the Amazon tropical floodplain region throughout the high and low water stages
The inundation extent of wetlands is one of the largest uncertainties in applying models of wetland function [38,42]. This has long been recognized in the International Geosphere Biosphere Programme Global Analysis, Integration and Modeling report, which states “Wetland extent: The largest gap in wetland characterization is the size of wetlands themselves, both in space and time” [42]
Summary
As for other tropical wetlands, Amazon wetlands provide many services for society, such as water storage, stabilize river discharge, groundwater recharge, organic carbon storage, withholding sediment, ecotourism, timber production, medicinal plants, agricultural products, fish, drinking water, and grazing land [1]. In tropical floodplains like the Amazon, often the water level is high and inundate wetland vegetation that makes significant areas as temporary open water [30] This is a factor in addition to the common factors, such as perpendicular baseline, temporal baseline, change in water level, high biomass, target motion, change in dielectric constant, and atmospheric conditions [31,32,33,34], which disturb the coherence of phase over wetlands inconsistent over time limiting the use of the InSAR technique for water level monitoring. SAR satellites, such as ALOS PALSAR, RADARSAT-2, COSMOS Sky-Med, Terra-SAR/X, Sentinel-1, and upcoming RADARSAT Constellation Mission (RCM), provide timely data for dynamic wetland monitoring activities Their advanced capabilities, such as interferometric data with short temporal baselines, polarimetric data, high resolution data, and single or dual pol standard mode consistent data products offer exciting possibilities for identifying innovative methods for wetland, flooded vegetation and water resource applications [34,35,36]. The knowledge gained from tropical and temperate wetlands will be used to propose a methodology that could lead to the use of RADARSAT-2 and RCM data for wetland monitoring
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