Abstract
This article focuses on bistatic coherence as an additional feature complementing amplitudes in classification space, permitting to monitor temporal changes in water extent on the wetland comprising surface water and inundated vegetation. The research was conducted on a herbaceous wetland. The TanDEM-X images were acquired during the science phase in bistatic mode with long perpendicular baselines. Two different sets of observations were computed: polarimetric amplitudes (PAs) and interferometric coherences in single-pass mode. Next, the datasets composed of a multitemporal stack of images were classified using object-based image analysis. The main outcome of the experiment is that bistatic coherences increased greatly the overall accuracy (OA) of expected thematic classes. The OA shows that thematic categories were classified with higher accuracy when the bistatic coherence complemented PAs. The OA is greater than 85% for all analyzed datatakes. The accuracy achieved using amplitudes only was higher than 70% but varied overtime. The bistatic coherence at X-band turned out to be really helpful in mapping high vegetation, which can be an indicator that this methodology can be directly used in the monitoring of common reed mowing or mapping highly invasive vegetation. Additionally, we could observe that short inundated vegetation was also mapped correctly, allowing flooded areas in this floodplain to be mapped with great precision throughout the growing season.
Highlights
We focus on bistatic coherences as additional features complementing amplitudes in “classification space” permitting the monitoring of temporal changes in water extent on the wetland comprising 1) surface water and 2) partially inundated vegetation
The work presented in this article was possible thanks to TDX data acquired during the science phase, for the first time in the bistatic mode, over this wetland
The usefulness of bistatic coherence for herbaceous wetland mapping was studied on the Biebrza wetland for the first time in our research
Summary
Special emphasis shall be put on the wetlands exploited partially as meadows where the vegetation cover and water stagnation time shall be mapped. The latter factor is extremely important because it shows the areas of the potential risk of organic soils degradation or peat crumbling due to a decrease of moisture. Peatland shrinking caused by water deficit is a very negative phenomenon observed across Europe and Worldwide [1] This problem is addressed in numerous publications, e.g., in [3]–[6]. Another important issue that should be observed and monitored on wetlands is the natural grasslands mowing activity. This thematic category is interesting especially in the floodplains because its identification and monitoring permits a better understanding of hydrological connectivity between separated oxbows and floodplain lakes, the succession of vegetation, and the conditions of living for ichthyo and avifauna [2], [9], [10]
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