Abstract
An automated tool for pre-operational mapping of floods and inland waters using Sentinel-1 data is presented. The acronym AUTOWADE (AUTOmatic Water Areas DEtector) is used to denote it. The tool provides the end user (Italian Department of Civil Protection) with a continuous, near real-time (NRT) monitoring of the extent of inland water surfaces (floodwater and permanent water). It implements the following operations: downloading of Sentinel-1 products; preprocessing of the products and storage of the resulting geocoded and calibrated data; generation of the intermediate products, such as the exclusion mask; application of a floodwater/permanent water mapping algorithm; generation of the output layer, i.e., a map of floodwater/permanent water; delivery of the output layer to the end user. The open floodwater/permanent water mapping algorithm implemented in AUTOWADE is based on a new approach, denoted as buffer-from-edge (BFE), which combines different techniques, such as clustering, edge filtering, automatic thresholding and region growing. AUTOWADE copes also with the typical presence of gaps in the flood maps caused by undetected flooded vegetation. An attempt to partially fill these gaps by analyzing vegetated areas adjacent to open water is performed by another algorithm implemented in the tool, based on the fuzzy logic. The BFE approach has been validated offline using maps produced by the Copernicus Emergency Management Service. Validation has given good results with a F1-score larger than 0.87 and a kappa coefficient larger than 0.80. The algorithm to detect flooded vegetation has been visually compared with optical data and aerial photos; its capability to fill some of the gaps present in flood maps has been confirmed.
Highlights
And continuous monitoring of the extent of surface water bodies is very important in the management of the living environment
It can be noted that the output map is basically derived from the maps of thresholdingderived water area (TDWA) and thresholding-derived flooded15area (TDFA)
Of them because of the increase of soil moisture due to rain; the need to focus on objects adjacent to open water having Normalized Difference Vegetation Index (NDV I) > 0.2 to limit confusion between backscatter increases due to soil moisture variations and the presence of a double bounce structure formed by the horizontal water surface and vertical stems
Summary
And continuous monitoring of the extent of surface water bodies is very important in the management of the living environment. Several past studies (e.g., [3,4,5]) demonstrated that synthetic aperture radar (SAR) systems are suitable tools for surface water mapping. They combine a high spatial resolution (from hundreds of meters to approximately 1 m, depending on the SAR acquisition mode) with the capability, typical of microwaves, to provide data during day and night and even in the presence of cloud cover.
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