Abstract
Satellite remote sensing plays an important role in the monitoring of surface water for historical analysis and near real-time applications. Due to its cloud penetrating capability, many studies have focused on providing efficient and high quality methods for surface water mapping using Synthetic Aperture Radar (SAR). However, few studies have explored the effects of SAR pre-processing steps used and the subsequent results as inputs into surface water mapping algorithms. This study leverages the Google Earth Engine to compare two unsupervised histogram-based thresholding surface water mapping algorithms utilizing two distinct pre-processed Sentinel-1 SAR datasets, specifically one with and one without terrain correction. The resulting surface water maps from the four different collections were validated with user-interpreted samples from high-resolution Planet Scope data. It was found that the overall accuracy from the four collections ranged from 92% to 95% with Cohen’s Kappa coefficients ranging from 0.7999 to 0.8427. The thresholding algorithm that samples a histogram based on water edge information performed best with a maximum accuracy of 95%. While the accuracies varied between methods it was found that there is no statistical significant difference between the errors of the different collections. Furthermore, the surface water maps generated from the terrain corrected data resulted in a intersection over union metrics of 95.8%–96.4%, showing greater spatial agreement, as compared to 92.3%–93.1% intersection over union using the non-terrain corrected data. Overall, it was found that algorithms using terrain correction yield higher overall accuracy and yielded a greater spatial agreement between methods. However, differences between the approaches presented in this paper were not found to be significant suggesting both methods are valid for generating accurate surface water maps. High accuracy surface water maps are critical to disaster planning and response efforts, thus results from this study can help inform SAR data users on the pre-processing steps needed and its effects as inputs on algorithms for surface water mapping applications.
Highlights
Satellite remote sensing offers a means to monitor water resources and their change in time across large areas
We investigated the use of vertical receiving (VV) and VH for surface water mapping in the Lower Mekong region and found that using VH polarization causes a larger number of false positives
The two surface water maps using the Bmax Otsu method performed with accuracy distributions around 92%–95.5% using the Ground Range Detected (GRD) dataset and 92%–93.5% using the radiometric terrain correction (RTC) dataset
Summary
Satellite remote sensing offers a means to monitor water resources and their change in time across large areas. Stream gauge-based monitoring provides a simple means to identify floods based on pre-determined water level thresholds set to individual gauge locations, bu fail to capture the spatial extent of flooding, a critical component in disaster response and damage assessments [6]. To address these shortcomings, many methods have been developed leveraging satellite remote sensing to map the surface water extent, during floods.
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