Surface Water Mapping and Flood Monitoring in the Mekong Delta Using Sentinel-1 SAR Time Series and Otsu Threshold

The annual flood and the alteration in hydrological regimes are most vital concerns Vietnamese Mekong Delta (VMD). Although synthetic aperture radar (SAR) Sentinel-1 imagery is widely used for water management, only a few studies have data mapping surface monitoring events VMD. This study developed an algorithm to implement (i) automatic Otsu threshold on series of images extract (ii) time analyses derived maps detect extent near-real-time (NRT). Specifically, cross-polarized VH was selected after assessment different polarizations. dynamic thresholding applied identify optimal each pre-processed image separate from non-water pixels producing maps. were visually compared with Sentinel-2 Full Resolution Browse (FRB) statistically examined Multispectral Instrument (MSI) maps, which generated by applying normalized difference index (NDWI) modified (MNDWI) images. visual comparison showed strong correspondence between FRB three periods, including rice’s sowing season, period, maturation stage. A good statistical agreement suggested that performance map effective river areas (R2 = 0.97 RMSE 1.18%), while it somewhat lower paddy field 0.88 3.88%). Afterward, NRT change-detection-based Every single pixel at t respectively referred its state water/non-water flooded/non-flooded previous t−1 be classified into flooded or non-flooded pixel. enables updates step generate temporal large-scale areas. provides tool rapidly support management risk reduction future improvement current discussed.