With the recent flooding events that swept the western United States, a lot of attention has turned towards assessing flood-related damages in order to assign and focus relief efforts, and towards mitigating future damages by identifying and fortifying high-risk regions. Of particular utility to these interests has been high-resolution imagery1, both for flood-related change detection and the creation of effective hazards maps to aid future mitigation efforts. In this article, we take a look at how satellite imagery has been combined with ground efforts and GIS techniques to assess the damages and produce valuable hazards maps for future flood events.
One of the most immediate sources of geospatial information came from DigitalGlobe’s FirstLook program, which is a subscription service that provides on-demand access to pre- and post-event satellite imagery. With the breaking news of a major disaster, available satellites are immediately tasked by DigitalGlobe to make collections of the affected region; and both the new imagery and archival data are made accessible to subscribers. In the case of the Colorado flooding, this gave analysts at-hand imagery to digest and process, which in turn offered emergency response workers prioritization information to focus their efforts. These collections also proved invaluable after the rains stopped and the waters receded, as they provided geospatial data that informed mitigation efforts to lessen the impact of future flood events; and became central portions of GIS-based hazards and assessment maps.
Damage maps produced by FEMA made extensive use of satellite imagery to trace and designate levels of impact, long before data collected on the ground by government officials and insurance representatives were available in enough volume to build detailed map products. Initial damage estimates came from the degree of flooding observed as well as its persistence. Impacted areas were assessed and then lumped on the basis of flooding present in each designated zone. When house-by-house data was collected by inspection teams, robust GIS products became available by coupling the imagery analysis with damage metrics taken in the field. These maps are now a part of the National Flood Hazard Layer database.
One of the absolute strongest features of geospatial information and GIS is the community that embodies them, and the floods were a time that this community truly came together. A large repository of user-generated and crowdsourced maps poured in, both independently and as requested by the City of Boulder; and many of these are still being publicly hosted by Esri. These maps include everything from flood heights, stream discharge, measured rainfall, both quantitative and qualitative damage measurements and photographs documenting the change. A truly modern addition to this effort was the combination of satellite and aerial imagery with crowdsourced street-view photographs, geolocated by the smart devices that recorded them, as research has shown that the use of both of these types of images produces maps that are the most easily-understood and easy-to-orient by the general public3.
- Gillespie, T., Chu, J., Frankenberg, E., Thomas, D., “Assessment and Prediction of Natural Hazards from Satellite Imagery,” from the California Center for Population Research, UCLA, 2007, On-Line Working Paper
- Joyce, K., Belliss, E., Samsonov, S.V., McNeill, S.J., Glassey, P.J., “A review of the status of satellite remote sensing and image processing techniques for mapping natural hazards and disasters,” Progress in Physical Geography, vol. 33 no. 2 pp. 183-207, 2009
- Haynes, K., Barclay, J., Pidgeon, N., “Volcanic hazard communication using maps: an evaluation of their effectiveness,” Bulletin of Volcanology, vol. 70, I 2, pp123-138, 2007