Stephanie Wegscheider & Joachim Post
German Aerospace Center (DLR)
The experience of the past few years shows expanding demands for comprehensive, near-real time Earth Observation data covering wide areas, for a broad spectrum of civilian crisis situations. The reasons for this development are manifold and can be seen in the increasing vulnerability of societies and infrastructure and population growth . Additionally, regional and global cooperation of relief actors has been extended strongly.
Satellite imagery may serve as a source of information in all phases throughout the disaster cycle (see Figure 1). In the preparedness phase, risk assessment is an important tool to support disaster management and spatial planning activities in order to minimize potential future impacts. Here, remote sensing can provide important information to perform risk and vulnerability assessments, such as land use information or inventories of exposed elements and facilities. During an acute disaster crisis like an earthquake or tsunami, while the situation in the disaster area may be still chaotic and unclear, rapid mapping activities using up-to-date satellite data can provide valuable information to support emergency response actions .
The Center for Satellite Based Crises Information (ZKI), a service of the German Remote Sensing Data Center (DFD) of the German Aerospace Center (DLR), provides rapid processing and analysis of satellite imagery during natural and environmental disasters, for humanitarian relief activities and civil security issues worldwide. Contributions of ZKI are mainly made during the emergency response phase, but activities for preparedness, early warning and recovery are equally important tasks.
On Sept. 30, 2009, a severe earthquake hit the city of Padang in Western Sumatra, Indonesia, and caused more than 700 casualties. About one year later, on Oct. 25, 2010, an earthquake offshore of Sumatra triggered a tsunami which hit the Mentawai Islands, killing more than 400 people. ZKI’s activities during these two disasters will be shown as examples for the use of remote sensing data for disaster management efforts.
The Padang Earthquake of 2009
During the first day after the Padang Earthquake in 2009, the first map products became available — so-called situation maps. These provided an immediate overview on the spatial settings and properties of the affected area, while still referring to the pre-disaster situation and including up-to-date field information from local authorities about destroyed buildings. The first high-resolution post-disaster satellite imagery (QuickBird) was available on Oct. 3, three days after the earthquake. Based on this data and in comparison to pre-disaster imagery, a first rapid damage assessment was undertaken and the result was provided to local users and published on the ZKI website (see Figure 2, above). ZKI maps were used, for example, in the United Nations On-Site Operations Coordination Center (OSOCC) (Figure 3, below).
GITEWS (German Indonesian Tsunami Early Warning System) and Last Mile -Evacuation, funded by the German Ministry for Research and Education. In the frame of these projects, tsunami hazard, exposure, vulnerability and risk information had been generated   . From these assessments, additional value could be drawn and further map products were provided. One of these is a high-resolution population density map providing information on a per-building basis, which provides extremely relevant information to estimate the number of affected people. The building mask had been derived from high-resolution satellite imagery (IKONOS). In combination with a detailed digital elevation model, a precise 3-D model of the city of Padang had been generated in the framework of the Last Mile project (see Figure 4, ).The city of Padang is a study area in the projects
The fact that Padang was the subject of two research projects dealing with tsunami risk, vulnerability and early warning, created a unique situation of having manifold risk data already available at the time of the disaster. This case shows the value of risk information for preparedness measures and emergency response activities.
The Mentawai Tsunami of 2010
Although the Mentawai Islands are also part of the broad scale risk assessment performed in the frame of GITEWS , the coarse scale (1:100,000) was not sufficient to provide additional valuable information for emergency response purposes. Assessments on that scale can be used to provide an overview and first evaluations. But in order to serve as input for disaster and crisis management on local level, more detailed and high resolution analyses are needed.
The acquisition of optical satellite imagery following the Mentawai Tsunami in 2010 was hampered by clouds, as it is often the case in tropical regions. The first post-disaster imagery (ALOS AVNIR-2) was available for ZKI five days after the event, on Oct. 29. Pre- and post-disaster image pairs were used to derive the line of the maximum tsunami inundation in-land and to rapidly produce first disaster extent maps. During the following days, further satellite imagery, partly with higher spatial resolution (mainly WorldView-1 and -2), were acquired and further maps were produced and published (see Figure 5 and the ZKI website).
Various products to support emergency relief and reconstruction have been provided in a rapid manner. Generally, this information is of high value and helps in making emergency relief strategies more effective and successful. On the other hand, this rapidly generated information possesses certain deficits especially related to accuracy. Continuous research efforts, intensive cooperation with other agencies and institutions, decision makers and governmental authorities are needed to improve these products and provide more target-oriented information based on user needs.
Especially for earthquake-related hazards, in-situ observations by engineers on damage grades of buildings and infrastructure are essential information to improve satellite-based methods and risk assessments. However, this information as well as other risk and vulnerability information is most often not available or scattered around different national and international institutions. The case of the Padang earthquake illustrates how such data can be used to provide valuable emergency response information even before satellite images of the affected area are available. A better exchange of information and comprehensive collaborative research are needed to make post-disaster information products and their use more effective — and consequently improve emergency response efforts.
References T.L. Murlidharan, Economic consequences of catastrophes triggered by natural hazards, John A. Blume Earthquake Engineering Center, Report No. 143, 231p., March 2003.  T. Riedlinger, G. Strunz, S. Voigt, H. Mehl, S. Dech, Rapid mapping to support disaster management in coastal communities, International Conference on Tsunami Warning (ICTW), Bali, Indonesia, November 12-14, 2008.  G. Strunz, J. Post, K. Zosseder, S. Wegscheider, M. MÌ_ck, T. Riedlinger, H. Mehl, S. Dech, J. Birkmann, N. Gebert, H. Harjono, H. Z. Anwar, Sumaryono, R. M. Khomarudin, and A. Muhari, Tsunami risk assessment in Indonesia, Nat. Hazards Earth Syst. Sci., 11, 67ÛÒ82, 2011.  S.Wegscheider, J. Post, K. Zosseder, M. MÌ_ck, G. Strunz, T. Riedlinger, A. Muhari, and H. Z. Anwar, Generating tsunami risk knowledge at community level as a base for planning and implementation of risk reduction strategies, Nat. Hazards Earth Syst. Sci., 11, 249ÛÒ258, 2011.  H. TaubenbÌ¦ck, N. Goseberg, N. Setiadi, G. LÌ_mmel, F. Moder, M. Oczipka, H. KlÌ_pfel, R. Wahl, T. Schlurmann, G. Strunz, J. Birkmann, K. Nagel, F. Siegert, F. Lehmann, S. Dech, A. Gress, and R. Klein, ÛÏLast-MileÛ preparation for a potential disaster ÛÒ Interdisciplinary approach towards tsunami early warning and an evacuation information system for the coastal city of Padang, Indonesia, Nat. Hazards Earth Syst. Sci., 9, 1509ÛÒ1528, 2009.
Stephanie Wegscheider is research assistant at DLR since 2007. She holds a diploma in physical geography from the University of Munich (Germany). She is a remote sensing and GIS expert and works on environmental vulnerability and risk assessment. Besides, she is involved in the Center of Satellite Based Crisis Information (ZKI) and experienced in emergency response mapping and crisis information activities.
Dr. Joachim Post is research scientist at DLR. He holds a diploma in environmental sciences from University of Trier (Germany) and a Ph.D. in Geoecology from University of Potsdam (Germany). He is an expert in environmental risk and vulnerability assessments, climate and land use change impacts on the environment and eco-hydrological modeling.