Monitoring flood extent in the lower Amazon River floodplain using ALOS/PALSAR ScanSAR images

• Published in: Remote sensing of environment Vol. 130; pp. 51 - 61
• Main Authors: Arnesen, Allan S., Silva, Thiago S.F., Hess, Laura L., Novo, Evlyn M.L.M., Rudorff, Conrado M., Chapman, Bruce D., McDonald, Kyle C.
• Format: Journal Article
• Language: English
• Published: New York, NY Elsevier Inc 15.03.2013; Elsevier
• Subjects: algorithms; Amazon River; Animal, plant and microbial ecology; Applied geophysics; basins; Biological and medical sciences; Brazil; carbon; cloud cover; Earth sciences; Earth, ocean, space; Exact sciences and technology; floodplains; Fundamental and applied biological sciences. Psychology; General aspects. Techniques; hydrology; Incidence angle; Internal geophysics; Kyoto & Carbon Initiative; lakes; land cover; logit analysis; mathematical models; moderate resolution imaging spectroradiometer; monitoring; Multi-temporal analysis; Object-based image analysis; remote sensing; seasonal variation; Synthetic aperture radar; Teledetection and vegetation maps; time series analysis; vegetation types; Wetlands; South America; Asia; Honshu; Japan; Brazil; Amazon Basin; Amazon River; Far East; Incidence angle; Multi-temporal analysis; Kyoto & Carbon Initiative; Object-based image analysis; Synthetic aperture radar; Wetlands; floods; Large dimension; Photographic image; data; Continuous; 2010; Information; precipitation; wetlands; 2007; 2006; carbon; Cloudiness; lakes; relief; Ability; maps; inundations; Method; monitoring; floodplains; Water level; Multidate observation; seasonal variations
• ISSN: 0034-4257; 1879-0704
• DOI: 10.1016/j.rse.2012.10.035

The Amazon River floodplain is subject to large seasonal variations in water level and flood extent, due to the large size and low relief of the basin, and the large amount of precipitation in the region. Synthetic Aperture Radar (SAR) data can be used to map flooded area in these wetlands, given its ability to provide continuous information without being heavily affected by cloud cover. As part of JAXA's Kyoto & Carbon Initiative, extensive wide-swath, multi-temporal SAR coverage of the Amazon basin has been obtained using the ScanSAR mode of ALOS PALSAR. This study presents a method for monitoring flood extent variation using ALOS ScanSAR images, tested at the Curuai Lake floodplain, in the lower Amazon River, Brazil. Twelve ScanSAR scenes were acquired between 2006 and 2010, including seven during the 2007 hydrological year. Water level records, field photographs, optical images (Landsat-5/TM and MODIS/Terra and Aqua) and topographic data were used as auxiliary information. A data mining algorithm allowed the implementation of a hierarchical, object-based classification algorithm, able to map land cover types and flooding status in the study area for all available dates. Land cover based on the entire time series (classification levels 1 and 2) had overall accuracies of 90% and 83%, respectively. Level 3 classifications (one map per image date) were validated only for the lowest and highest water stages, with overall accuracies of 76% and 78%, respectively. Total flood extent (Level 4) was mapped with 84% and 94% accuracies, for the low and high water stages, respectively. Regression models were fitted between mapped flooded area and water levels at the Curuai gauge to predict flood extent. A polynomial model had R2=0.95 (p<0.05) and an overall root mean square error (RMSE) of 241km2, while a logistic model had R2=0.98 (p<0.05) and RMSE=127km2. ► Flood extent was monitored from 2007 to 2010 for a lake in the Lower Amazon Floodplain. ► PALSAR ScanSAR, TM and MODIS images were combined using object-based image analysis. ► Final mapping accuracy was ~76% for land cover and ~90% for flood status. ► Logistic models predicted flooded area better than polynomial or simple regressions. ► The present method could be used to monitor flood extent for the entire Amazon.