Sentinel‐1 remote sensing data and Hydrologic Engineering Centres River Analysis System two‐dimensional integration for flash flood detection and modelling in New Cairo City, Egypt

Abstract

Digital surface models, land use and rainfall data were used to simulate water areas using Hydrologic Engineering Centres River Analysis System (HEC‐RAS) software. Multi‐temporal synthetic aperture radar (SAR) was used for the detection of flood prone area to calibrate HEC‐RAS, due to the lack of data validation in the New Cairo City, Egypt. The thresholding water detection method was applied to two Sentinel‐1 images, one pre‐ and one post‐flash flood event from April 24 to 27, 2018. The threshold method was used to detect water areas from SAR Sentinel‐1 images. Feature statistical agreement F1 and F2 values ranged from 73.4 to 77.7% between water areas extracted based on backscattering values between 19.97 and 16.53 in decibels (dB) and reference water areas obtained using an optical image of the Sentinel‐2 satellite. The similarity between simulated HEC‐RAS two‐dimensional (2D) of water areas and reference water areas based on SAR data ranged between 74.2 and 89.7% using feature statistical agreement values F1 and F2. It provides a clear suggestion that, in the absence of field observations, SAR data can be used to calibrate the model. Two flood hazard maps created based on water velocity and depth were obtained from HEC‐RAS 2D simulation. The obtained maps indicated that 11% of the roads and 50% of the buildings in New Cairo City are exposed to high hazard areas. Furthermore, 28% of the bare land is situated in a very high vulnerability area. We recommend the use of obtained hazard map in supporting emergency response, and designing effective emergency plans.

Country‐wide flood exposure analysis using Sentinel‐1 synthetic aperture radar data: Case study of 2019 Iran flood

“…Based on the backscattering intensity of the SAR image where water appears as a dark area resulting in a low backscatter recording as incident radar signals are reflected away from the radar antenna (Henderson & Lewis, 1998), one can visualize and interpret flooding based on various classification methods. This includes a simple visual interpretation approach (Matgen et al, 2007;Oberstadler et al, 1997;Sanyal & Lu, 2004), image change detection (Bazi et al, 2005;Clement et al, 2018;Nico et al, 2000), region growing algorithms (Malnes et al, 2002;Mason et al, 2012), supervised classification (Pulvirenti et al, 2013;Townsend, 2002), histogram thresholding (Chini et al, 2012;Elkhrachy et al, 2021;Pulvirenti et al, 2016), and clustering algorithm (Ruzza et al, 2019). Further, many flood detection approaches have used a combination of thresholding, region growing, and change detection utilizing a single SAR image Matgen et al, 2011).…”

A Survey of Remote Sensing and Geographic Information System Applications for Flash Floods

“…Using SAR images, it can be used to distinguish water from other objects. Therefore, Sentinel-1 has often been used in the research of flash floods in recent years [65][66][67][68].…”

Satellite-based flood inundation and damage assessment

“…Apart from multiple applications of Sentinel-1, it uses a wide area coverage with near real-time data acquisition making it a more feasible tool allowing for more efficient and cost-effective use. Over the last few decades, a considerable number of studies have been through on the SAR flood mapping method in combination with other Remote Sensing (RS) imageries (Mimich et al 2021;Jokar et al 2022) whereas other researchers suggest the use of Sentinel-1 radar image to calibrate (Elkhrachy et al 2021) or validate the extent derived using other models (Ezzine et al 2020).…”