Introducing the remote sensing of hazardous terrain

With human population and associated environmental degradation continuing to increase, it is inevitable that more and more people will be living in zones of hazardous terrain, and therefore the risk of disaster will increase. Add to this the growing evidence for global warming and the increased severity of geohazards related to larger and more frequent storms (i.e. storm surges, coastal erosion, landslides, fluvial flooding, erosion) and both the frequency and severity of disasters is set to increase (e.g. Kesavan & Swaminathan 2006; Smolka 2006; van Aalst 2006). Remote sensing (measuring and mapping the Earth's surface from aircraft or satellites) can help us to rapidly assess, and therefore better manage, geohazards. Remote sensing and hazardous terrain mapping can play key roles in the management and mitigation of natural disasters (e.g. Cutter 2003; Zeil 2003), with applications grouped into three main stages. (1) Pre-disaster.Maps showing the distribution of geohazards and their relative severities can be used by key decision makers in government, the insurance industry and the local population, to minimize the danger to people and infrastructure. For this stage, geomorphological mapping based on stereoscopic aerial photography has been widely used for many years (e.g. Verstappen & Van Zuidan 1968; Doornkamp et al. 1979; Mantovani et al. 1996). A new development is mapping based on spectral responses and digital elevation models (DEMs), either regionally using satellite sensors (e.g. Liu et al. 2004; Andrews Deller 2006; Theilen-Willige 2006), or in detail using airborne hyperspectral sensors and laser altimetry (e.g. Brown 2004; Deronde et al. 2004). Furthermore, early warnings of disasters caused by slope instability, seismic activity or volcanic eruption should be feasible within a few years, using constellations of radar satellites to detect ground deformation (e.g. Kerle & Oppenheimer 2002; Bruno et al. 2005; Singhroy 2006). (2) Event crisis.With the onset of a disaster, medium-resolution (15–250 m pixel) satellite imagery (e.g. Landsat or MODIS) is useful for assessing the regional extent and relative severities of the various impacts. With rapid-onset disasters, such as earthquakes, explosive volcanic eruptions or landslides, aerial photography or very high resolution (0.5–2 m pixel) satellite imagery (e.g. Ikonos, Quickbird) is needed to assist rapid search and rescue operations. A useful summary of remote sensing applications in the emergency response to a major disaster, the 2004 Sumatra earthquake and Indian Ocean tsunami, has been given by Kelmelis et al. (2006). (3) Post disaster.Geomorphological and geo-ecological mapping, based on the interpretation of aerial photography or spectral and DEM data from satellites, can assist disaster recovery by highlighting locations with essential resources (e.g. water, wood fuel) and materials for reconstruction, such as timber and sand–gravel or clay deposits. Earth resource maps of Banda Aceh, produced by the British Geological Survey in the 1970s, were very useful in the reconstruction of that region after the 2004 earthquake and tsunami (M. Culshaw, pers. comm. 2005). The hazardous terrains examined in this publication include landslides, flooding, contaminated land, shrink–swell clays, subsidence, fault zones and volcanic landforms (Table 1). Featured remote sensing systems include aerial photography, thermal scanning, hyperspectral sensors, laser altimetry, radar interferometry and multispectral satellites, notably Landsat and ASTER. Related techniques, such as the processing of DEMs and data analysis using geographical information systems (GISs), are also discussed.