Study Sites And Survey

The study areas are situated in Spain, Morocco, and Burkina Faso along a transect running from semi-arid to sub-humid Mediterranean and sub-tropical desert climate to tropical wet-dry regions (Fig. 13-2). Thus, they cover climatic regions where precipitation regimes are the most favorable for gully erosion. The gully environments range from agricultural areas and rangeland to deserts. Beginning between 1995 and 2008, 23 gullies of varying types, sizes, and ages have been monitored in intervals of usually one or two years.

Depending on wind conditions, a hot-air blimp (see Chapter 8.3.3) or a large rokkaku-type kite (see Chapter 8.4.1) is employed as a platform for analog (up to 2002) or digital single-lens reflex (SLR) cameras, allowing for photographic surveys from flying heights up to 350 m. The survey is usually conducted at various heights and scales in order to collect detailed photographs as well as overviews with stereoscopic overlap. At all gully sites, ground control points (GCPs) measured with a total station in a local coordinate system are permanently installed with steel pipes and marked with signals for the photographic survey (see Chapter 9.4). From the resulting stereoscopic images with extremely high ground resolutions of 0.5-10 cm, various techniques of analysis for measuring gully development and loss of soil material have been carried out with image-processing systems, geographic information systems (GIS), and digital photogrammetry stations.

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