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In addition to the spectral information, the texture of the surface of the mudflats also plays an important role. Information about this is provided by radar data, which measure the backscatter of an emitted signal and in doing so provides information about the roughness of the surface.
With radar systems, there are also a few factors that must be considered when analysing the data:
Data from the German TerraSAR-X and TanDEM-X as well as the Canadian Radarsat-2 are used for the analysis of satellite-based SAR images from 2012 and 2013. SAR images from 2007 to 2009, which were used for the systematic study of radar signatures of dry tidal mudflats, come from the ERS-2 and ENVISAT European satellites, the German TerraSAR-X, the Japanese ALOS, and the Canadian Radarsat-2. A radar with a synthetic aperture (Synthetic Aperture Radar, SAR) provides two-dimensional fields of the backscattered radar output ("radar images", "SAR images"), whose high spatial resolution is achieved by a complex recording technology and processing of the raw data. The spatial resolution of SAR images depends on the satellites, their recording mode and the radar band. The highest resolutions of under one metre (spatial size of a pixel in the SAR image) are achieved with the German TerraSAR-X (X-Band) in high-resolution spotlight mode. Data with this resolution are suitable for identification of fine structures in the mudflat, whereas lower resolutions (10 – 50 m) are used for large-scale monitoring and classification of sediments. The SAR images used were made in the L (approx. 1 GHz / 30 cm), C (approx. 5 GHz / 6 cm) and X (approx. 10 GHz / 3 cm) radar bands. The different electromagnetic wavelengths allow investigation of textured structures on the surface of the mudflats at various length scales (of the magnitude of the radar wavelengths). |
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