Abstract
BackgroundInterferometric Synthetic Aperture Radar (InSAR) has become a promising technique for monitoring wetland water levels. However, its capability in monitoring wetland water level changes with Sentine-1 data has not yet been thoroughly investigated.MethodsIn this study, we produced a multitemporal Sentinel-1 C-band VV-polarized SAR backscatter images and generated a total of 28 interferometric coherence maps for marsh wetlands of China’s Momoge National Nature Reserve to investigate the interferometric coherence level of Sentinel-1 C-VV data as a function of perpendicular and temporal baseline, water depth, and SAR backscattering intensity. We also selected six interferogram pairs acquired within 24 days for quantitative analysis of the accuracy of water level changes monitored by Sentinel-1 InSAR. The accuracy of water level changes determined through the Sentinel-1 InSAR technique was calibrated by the values of six field water level loggers.ResultsOur study showed that (1) the coherence was mainly dependent on the temporal baseline and was little affected by the perpendicular baseline for Sentinel-1 C-VV data in marsh wetlands; (2) in the early stage of a growing season, a clear negative correlation was found between Sentinel-1 coherence and water depth; (3) there was an almost linear negative correlation between Sentinel-1 C-VV coherence and backscatter for the marsh wetlands; (4) once the coherence exceeds a threshold of 0.3, the stage during the growing season, rather than the coherence, appeared to be the primary factor determining the quality of the interferogram for the marsh wetlands, even though the quality of the interferogram largely depends on the coherence; (5) the results of water level changes from InSAR processing show no agreement with in-situ measurements during most growth stages. Based on the findings, we can conclude that although the interferometric coherence of the Sentinel-1 C-VV data is high enough, the data is generally unsuitable for monitoring water level changes in marsh wetlands of China’s Momoge National Nature Reserve.
Highlights
Covering between 1–2% of the Earth’s surface, wetlands are among the most productive ecological systems and perform important eco-hydrological functions such as food supply, water storage and purification, flood control, climate change mitigation, as well as provide a desirable habitat for wildlife (Millenium Ecosystem Assessment, 2005; Costanza et al, 1997; Mitsch & Gosselink, 2015)
The higher temporal resolution of the Sentinel-1 images allowed us assessing the potential of using Interferometric Synthetic Aperture Radar (InSAR) applications for wetland dynamic analysis
Our study showed that coherence was mainly dependent on the temporal baseline, not affected by the perpendicular baseline for Sentinel-1 C-VV data collected over the marsh wetlands
Summary
Covering between 1–2% of the Earth’s surface, wetlands are among the most productive ecological systems and perform important eco-hydrological functions such as food supply, water storage and purification, flood control, climate change mitigation, as well as provide a desirable habitat for wildlife (Millenium Ecosystem Assessment, 2005; Costanza et al, 1997; Mitsch & Gosselink, 2015). Hydrological monitoring of wetlands is carried out through stage (water level) stations providing good temporal resolution over a finite number of observation points (Hong et al, 2010a). These in-situ measurements have limited capability to detect spatial patterns, as gauge stations are usually located several or even tens of kilometers from each another (Hong et al, 2010a; Wdowinski & Hong, 2015). We can conclude that the interferometric coherence of the Sentinel-1 C-VV data is high enough, the data is generally unsuitable for monitoring water level changes in marsh wetlands of China’s Momoge National Nature Reserve
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