The use of satellite imagery to meet the needs in emergency situations: myths and realities
It is well known that Earth observation (EO) satellites constitute a versatile source of geographic data for a large variety of applications in the fields of forestry, agriculture, land use planning, environmental monitoring, and many more. In the case of humanitarian aid, the up-to-date geospatial information that can be extracted from satellite imagery can be used for planning the establishment of refugee camps/shelters and monitoring their progression, evaluating population density, mapping road networks and infrastructure and so on. EO satellites also provide reliable and rapid observation tools that can support efforts in emergency response when natural or man-made disasters occur and thus help reduce the disruption to societies and overburden on national economic systems caused by these disasters. In the immediate aftermath of a disaster, accurate and credible information telling decision-makers what is not needed can help reduce the overall complexity of the logistical response. Critical geospatial information obtained from the satellite imagery can also be extremely useful to obtain before or while the actual field assessment is conducted, by helping prioritize information collection needs and planning the appropriate level of response.
Both archive and up-to-date information can be obtained from EO satellites thus enabling the mapping of the “before” and “after” of a disaster event soon after it happens. There are currently several very high resolution satellites that can quickly acquire imagery with a spatial resolution up to 30 cm. When a disaster strikes, human and material resources need to be deployed as quickly as possible and such detailed images can help orient emergency response. For example, the images can be used to delineate the area impacted by floods, earthquakes or forest fires; to pinpoint severely damaged bridges and roads and thus identify optimal routing for rescue operations; to locate the closest undamaged buildings suitable for shelter and so on. For this particular kind of urgent information need, spatial resolutions in the order of 40 and 50 cm are usually preferred to get maximum detail on the status of infrastructure and small dwellings.
Upon being notified of an emergency situation, the satellite operators can program their satellites to acquire imagery while on the next close-by fly-over by aiming at the affected area usually within nine to 33 hours at most. Processing of the images and transmission to relief coordinators can then usually be achieved within four to eight hours after the image is collected. This means that crucial geospatial information on the event’s impact can be in the hands of those in the front line as soon as 13 hours later, provided that meteorological conditions cooperate and satellite operators are informed of the need with timeliness.
Flood in Bosnia and Herzegovina – Pléiades 50 cm © CNES 2014, Distribution Airbus DS
What happens if the impacted area is cloud covered?
In cases where significant cloud cover might limit the imagery’s usefulness (for instance in the case of a persistent severe rainstorm or hurricane), radar satellites become a particularly interesting option as they can “see through” clouds. Even though their spatial resolution is not quite as high and their information content more difficult to grasp, they can still provide extremely valuable information on things such as flood or forest fire extent.
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