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Abstract
Wetlands are one of the most important ecosystems on Earth. There is an urgent need to quantify the biophysical parameters (e.g., plant height, aboveground biomass) and map total remaining areas of wetlands in order to evaluate the ecological status of wetlands. In this study, Environmental Satellite/Advanced Synthetic Aperture Radar (ENVISAT/ASAR) dual-polarization C-band data acquired in 2005 is tested to investigate radar backscattering mechanisms with the variation of hydrological conditions during the growing cycle of two types of herbaceous wetland species, which colonize lake borders with different elevation in Poyang Lake region, China. Phragmites communis (L.) Trin. is semi-aquatic emergent vegetation with vertical stem and blade-like leaves, and the emergent Carex spp. has rhizome and long leaves. In this study, the potential of ASAR data in HH-, HV-, and VV-polarization in mapping different wetland types is examined, by observing their dynamic variations throughout the whole flooding cycle. The sensitivity of ASAR backscattering coefficients to vegetation parameters of plant height, fresh and dry biomass, and vegetation water content is also analyzed for Phragmites communis (L.) Trin. and Carex spp. The research for Phragmites communis (L.) Trin. shows that HH polarization is more sensitive to plant height and dry biomass than HV polarization. ASAR backscattering coefficients are relatively less sensitive to fresh biomass, especially in HV polarization. However, both are highly dependent on canopy water content. In contrast, the dependence of HH- and HV- backscattering from Carex community on vegetation parameters is poor, and the radar backscattering mechanism is controlled by ground water level.
Highlights
Wetlands are among Earth’s most productive systems
C-band ENVISAT/ASAR fine mode alternating-polarization imager are utilized in Poyang Lake wetland of Jiangxi province, China, to investigate the temporal radar backscattering mechanism and to understand the relationships between radar backscattering coefficients and wetland biophysical characteristics
For the purpose of mapping different wetlands in Poyang Lake region, C-band fine-mode ASAR imagery, especially in HH polarization mode, shows its potential to detect and map wetlands species colonizing those areas with different elevations
Summary
Wetlands are among Earth’s most productive systems These ecosystems fix and store organic matter, and release dissolved and particulate organic carbon to adjacent aquatic environments or down streams [1]. Their contribution to carbon sequestration is highlighted by the fact that wetlands occupy. The productivity of many wetland plants is as great as they are the most hearty agricultural crops [3]. This type of ecosystem is currently a small, persistent sink for carbon dioxide (CO2) and a large source of methane (CH4) [4]. The extent of wetlands is uncertain due to the difficulty of identifying and classifying wetlands on a global scale, the estimates of global wetlands vary from 5.3 × 1012 m2 [6] to
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