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TitleComparing Landsat and RADARSAT for current and historical dynamic flood mapping
AuthorOlthof, I; Tolszczuk-Leclerc, S
SourceRemote Sensing vol. 10, issue 5, 780, 2018 p. 1-19, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20190179
PublisherMDPI AG
Mediaon-line; digital
File formatpdf (Adobe® Reader®); html
ProgramRemote Sensing Science, Land Surface Characterization
Released2018 05 18
AbstractMapping the historical occurrence of flood water in time and space provides information that can be used to help mitigate damage from future flood events. In Canada, flood mapping has been performed mainly from RADARSAT imagery in near real-time to enhance situational awareness during an emergency, and more recently from Landsat to examine historical surface water dynamics from the mid-1980s to present. Here, we seek to integrate the two data sources for both operational and historical flood mapping. A main challenge of a multi-sensor approach is ensuring consistency between surface water mapped from sensors that fundamentally interact with the target differently, particularly in areas of flooded vegetation. In addition, automation of workflows that previously relied on manual interpretation is increasingly needed due to large data volumes contained within satellite image archives. Despite differences between data received from both sensors, common approaches to surface water and flooded vegetation mapping including multi-channel classification and region growing can be applied with sensor-specific adaptations for each. Historical open water maps from 202 Landsat scenes spanning the years 1985-2016 generated previously were enhanced to improve flooded vegetation mapping along the Saint John River in New Brunswick, Canada. Open water and flooded vegetation maps were created over the same region from 181 RADARSAT 1 and 2 scenes acquired between 2003-2016. Comparisons of maps from different sensors and hydrometric data were performed to examine consistency and robustness of products derived from different sensors. Simulations reveal that the methodology used to map open water from dual-pol RADARSAT 2 is insensitive to up to about 20% training error. Landsat depicts open water inundation well, while flooded vegetation can be reliably mapped in leaf-off conditions. RADARSAT mapped approximately 8% less open water area than Landsat and 0.5% more flooded vegetation, while the combined area of open water and flooded vegetation agreed to within 0.2% between sensors. Derived historical products depicting inundation frequency and trends were also generated from each sensor's time-series of surface water maps and compared.
Summary(Plain Language Summary, not published)
The Emergency Geomatics Services (EGS) relies on imagery from several satellites with different specifications to provide timely data during an emergency event, such as flooding. EGS needs to ensure that information generated from different sources of satellite data are consistent, so that changes between consecutive images relate to actual flood progression or situational changes on the ground, and not to different data sources. In addition, historical flood mapping is needed both to generate flood maps in near real time, and for Public Safety to assess flood hazard based on past events. This paper compares flood maps from two main workhorse satellites used during flooding; one optical (Landsat) and the other Canada's own RadarSat. Approximately 200 historical flood maps are generated from each sensor's data. Coincident flood maps are compared to each other and to flood depth from water gauges. Historical flood maps, including maximum flood extent derived from each data source are also compared.

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