## 1 Introduction  
### Why Rapid Damage Assessment Is Crucial after a Disaster  
Table 1 shows the ten most important natural disasters in the time period between 1980 and 2012 sorted by the number of fatalities. Earthquakes and tropical storms are among the most dangerous natural hazards for human life. According to [PERSON] _et al._[1], global change will cause an increase of both frequency and intensity of heavy rainfall, hurricanes and cyclones leading to an increase of floods and destructions. In addition secondary effects, such as landslides triggered by heavy rainfall, will occur more often. To enable fast crisis response, e.g., to support rescue, humanitarian and reconstruction operations in the crisis area, damage mapping is very important. The areas affected by the destruction have to be identified and it is also crucial to detect which roads, railroads, airports and ports are still intact to be used for the crisis support [2, 3]. The same is also vital for crisis response after other types of natural disasters, such as earthquakes and volcanic eruptions. Remote sensing plays a key role in the support of fast disaster response. Space-borne sensors enable the monitoring of a wide field of view (tens of km to more than 100 km) at low costs with a regular revisit time (several days, depending on the orbit altitude). Furthermore, satellites have the great advantage of fast response capacities. However, it could take up to several days until a specific polar orbiting satellite with a Synthetic Aperture Radar (SAR) sensor onboard flies on a track which enables the recording of the area affected by the disaster. Constellations of satellites (e.g., COSMO-SkyMed [4], or the upcoming Radarsat constellation [5], and Sentinel-1 _cf._ Section 5) and the synergetic exploitation of different SAR platforms (e.g., TerraSAR-X [6] with COSMO-SkyMed) strongly reduce the response times. Using Earth Observation (EO) data, the rescue teams could directly concentrate on the most damaged areas without the need of first checking the entire crisis area on the ground [3, 7, 8, 9, 10]. A very important cooperation which should be mentioned in this regard is the International Charter of Space and Major Disasters [11], an international cooperation of space agencies that aims to support fast crisis response by providing EO data free of charge to those affected by a natural or man-made disaster [12]. Moreover, founded by the European Commission the Copernicus (former Global Monitoring for Environment and Security--GMES [13]) Emergency Management Service (GIO EMS [14]) covers a wide range of emergency situations resulting from man-made or natural disasters. Before becoming an operational service in April 2012, GIO EMS was prepared by the pre-operational GMES precursor project Services and Applications for Emergency Response (SAFER [15]). The United Nations Institute for Training and Research (UNITAR) Operational Satellite Applications Programme (UNOSAT) [16] concentrates its rapid mapping actions especially at Third World countries. Furthermore, Sentinel Asia, an international cooperation for monitoring natural disasters using EO data, focuses especially at the Asian and Pacific region [17]. Additional to the aforementioned international co-operations, national services such as the Center for Satellite Based Crisis Information (ZKI) operated by the German Aerospace Center DLR [12, 18] orthe French SEvice R gional de Traitement d'Image et de T d d d d ection (SERTIT [19]) provide rapid mapping capacities to support response to national and international disasters. This paper is structured as follows: After showing the necessity of rapid damage assessment after a crisis, Section 1.2 gives a brief introduction into SAR and its advantages compared to optical sensors. Section 1.3 shows the principle on SAR interferometry (InSAR). Section 2 describes the multi-temporal SAR damage assessment methods this paper focuses on: interferometric coherence and SAR intensity correlation.