River flood mapping in urban areas combining Radarsat-2 data and flood return period data

Abstract

24Near-real-time flood maps are essential to organize and coordinate emergency services' 25 response actions during flooding events. Thanks to its capacity to acquire synoptic and detailed 26 data during day and night, and in all weather conditions, Synthetic Aperture Radar (SAR) 27 satellite remote sensing is considered one of the best tools for the acquisition of flood mapping 28 information. However, specific factors contributing to SAR backscatter in urban environments, 29 such as shadow and layover effects, and the presence of water surface-like radar response 30 areas, complicate the detection of flood water pixels. This paper describes an approach for 31 near-real-time flood mapping in urban and rural areas. The innovative aspect of the approach is 32 its reliance on the combined use of very-high-resolution SAR satellite imagery (C-Band, HH 33 polarization) and hydraulic data, specifically flood return period data estimated for each point of 34 the floodplain. This approach was tested and evaluated using two case studies of the 2011 35Richelieu River flood (Canada) observed by the very-high-resolution RADARSAT-2 sensor. In 36 both case studies, the algorithm proved capable of detecting flooding in urban areas with good 37 accuracy, identifying approximately 87% of flooded pixels correctly. The associated false 38 negative and false positive rates are approximately 14%. In rural areas, 97% of flooded pixels 39 were correctly identified, with false negative rates close to 3% and false positive rates between 40 3% and 35%. These results highlight the capacity of flood return period data to overcome 41 limitations associated with SAR-based flood detection in urban environments, and the relevance 42 of their use in combination with SAR C-band imagery for precise flood extent mapping in urban 43 and rural environments in a crisis management context. 44 45 Keywords: Flood mapping; Synthetic Aperture Radar, C-Band; Flood return period 46 47Simple hydraulic considerations have also been used in several image-processing algorithms to 96 guide the detection of flooded pixels in urban and rural areas (see Pierdicca et al., 2008 ; 97 Pulvirenti et al., 2011 ;Mason et al., 2012. In this approach, 98 information from surface elevation data, which have the advantage of being available for most 99 rivers worldwide, is exploited. However, such algorithms restrict the integration of hydraulic 100 considerations to simple elevation and proximity analysis. To our knowledge, no example can 101 be found in the recent literature of the explicit integration of hydraulic data within SAR image-102 processing algorithms for flood detection in urban and rural areas. Such data, which could 103 include information about a river's flooding pattern or the specific hydraulic characteristics of a 104 floodplain, could be of great use in areas where SAR-based flood detection remains a 105 challenge. 106Therefore, the objective of the present study is to demonstrate how a combination of very high 107 resolution SAR imagery and hydraulic da...

Flood Mapping in a Complex Environment Using Bistatic TanDEM-X/TerraSAR-X InSAR Coherence

“…Noticeably, the present study gives a relatively straightforward and promising flood mapping approach that takes advantage of the bistatic interferometry of short wavelength (3 cm) X-band data. Among the recent research studies that dealt with inundation mapping for the same flooding event (Richelieu River in 2011) using SAR imagery, the study of Tanguy et al [32] can be mentioned. The authors used the RADARSART-2 C-band data with a longer wavelength (5.5 cm) and included information on the flood hazard at each point of the study area to reduce errors in the derived flood extent map.…”

“…The maximum flow rate was 1550 m 3 /s at the "Richelieu aux rapides Fryers" gauging station. On 22 June 2011, the water level of Richelieu River returned to its normal values below bankfull [32].…”

Delimitation of Flood Areas Based on Calibrated DEM and Geoprocessing: Case Study on Uruguay River, Itaqui City, Southern Brazil

“…The return period (Tr), also known as recurrence 10 interval or recurrence time, was employed as the time which a specific hydrological event can be matched or exceeded at any given year (McCuen, 1998). In the present study, the return period (Tr), in years, was defined by the following equation, where p is the probability of a hydrological event be matched or exceeded (Tanguy et al, 2017), Eq. (1):…”

A Spectral Unmixing Method with Ensemble Estimation of Endmembers: Application to Flood Mapping in the Caprivi Floodplain

“…These methods make use of: (a) reflected solar radiation [3,14]; (b) emitted thermal radiation [15]; and (c) microwave backscatter and/or emission [11,16]. Reflected solar radiation methods are effective for assessing seasonal patterns of inundation in areas that have minimum vegetation and cloud cover [4,17].…”

“…The water features will appear darker in the image as compared to non-water features. For instance, authors in [16] successfully (accuracy > 85%) delineated floods by combining very high-resolution Radarsat-2 (C-band, HH polarization) data with flood return period data estimated for each point of the floodplain from a digital elevation model (DEM). SAR has become an important source of data to map flooded areas as the land surface can be observed regardless of the cloud cover, and during day or night.…”