Deriving exclusion maps from C-band SAR time-series in support of floodwater mapping

https://doi.org/10.1016/j.rse.2021.112668Get rights and content
Under a Creative Commons license
open access

Highlights

  • There are areas where the SAR backscatter is not sensitive to surface changes.

  • Exclusion map informs on areas where floods cannot be detected using SAR data.

  • Long time series of Sentinel-1 allow to derive 20 m resolution exclusion maps.

  • Exclusion map is crucial information when responding to a flood emergency.

Abstract

Synthetic Aperture Radar (SAR) intensity is used as an input to many flood-mapping algorithms. The appearance of floodwater tends to cause a substantial decrease of backscatter intensity over scarcely vegetated terrain. However, limitations exist in areas where the SAR backscatter is not sufficiently sensitive to surface changes, e.g. shadow areas due to topography or obstacles on the ground, densely forested areas, sand, etc. Thus, we argue that it is of paramount importance to complement any SAR-based flood extent map with an exclusion map (EX-map) indicating all areas where the presence of water cannot be derived from SAR intensity observations. In this study, we introduce a methodology for generating an EX-map based on the analysis of time-series of SAR backscatter data. In particular, the identification of the EX-map is based on the combined use of three temporal indicators based on backscatter statistics, i.e. temporal median, minimum and standard deviation. As a test case, EX-maps were derived from Sentinel-1 data acquired during the 2014–2019 time period from six representative study sites. Reference maps were generated using a global land cover map, Digital Elevation Model (DEM)-derived shadow/layover masks, global urban footprint (GUF) data and a Sand Exclusion Layer (SEL). The cross-comparison revealed that the EX-map was consistent with reference maps obtained from other data sources.

Keywords

Sentinel-1
Flood risk management
Time series analysis
SAR
EX-map (exclusion map)

Cited by (0)