Abstract
Abstract. Reed marshes, the world’s most widespread type of wetland vegetation, are undergoing major changes as a result of climate changes and human activities. The presence or absence of water in reed marshes has a significant impact on the whole ecosystem and remains a key indicator to identify the effective area of a wetland and help estimate the degree of degeneration. Past studies have demonstrated the use of interferometric synthetic aperture radar (InSAR) to map water-level changes for flooded reeds. However, the identification of the different hydrological states of reed marshes is often poorly understood. The analysis given in this paper shows that L-band interferometric coherence is very sensitive to the water surface conditions beneath reed marshes and so can be used as classifier. A method based on a statistical analysis of the coherence distributions for wet and dry reeds using InSAR pairs was, therefore, investigated in this study. The experimental results were validated by in-situ data and showed very good agreement. This is the first time that information about the water cover under herbaceous wetlands has been derived using interferometric coherence values. This method can also effectively and easily be applied to monitor the hydrological conditions beneath other herbaceous wetlands.
Highlights
Wetlands are a critical link between water and the land surface, serving as the most productive and biodiverse ecosystem on Earth (Halls 1997), and reed marshes are the most widespread wetland vegetation type worldwide
The dominant wetland type is reed marshes, which have an area of 800 km2 and account for the largest source of raw material used for paper making anywhere in the world (Weiguo et al 2005)
To calculate the parameters of the probability density function (PDF), sampling boxes covering areas representative of the dry reeds and wet reeds in the Liaohe River Delta were defined according to results of the field campaigns
Summary
Wetlands are a critical link between water and the land surface, serving as the most productive and biodiverse ecosystem on Earth (Halls 1997), and reed marshes are the most widespread wetland vegetation type worldwide. It is important to monitor the hydrological conditions in reed marshes as this is an effective way of obtaining information about the health of the ecosystem (Bayley 1995) and maintain the biodiversity of wetlands. The monitoring of flooded surface conditions beneath reed marches is difficult because of the similarity of the spectral signatures of the vegetation in different flooded states. Advanced SAR techniques such as the use of interferometric SAR (InSAR) fringe patterns, polarimetric indexes and objected-oriented segmentation have been applied to obtain information about water levels and to enhance the separability of different wetland types (Arnesen et al 2013; Hong et al 2010; Martinez and Toan 2007). Inundation dynamics under a forest canopy can be studied using the differences in radar response that result from changes in the amount of emerged biomass (Voormansik et al 2014)
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