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Vuthy Men¹, Shingo Ichikawa², Shogo Tokunaga², and Susumu Onaka²

^{1 Water Resources and Energy Department, Nippon Koei Co., Ltd., 5-4, Kojimachi, Chiyoda-ku, Tokyo 102-8539, Japan, [email protected]}

^{2 Coast and Port Department, Nippon Koei Co., Ltd., 5-4, Kojimachi, Chiyoda-ku, Tokyo 102-8539, Japan}

Abstract: For small and low-lying countries, having a thorough understanding of shoreline’s position and how it changed over the years is essential for effective coastal conservation, management, and national land protection efforts, particularly given the heightened risk of coastal hazards and sea-level rise. This study presented an automated method for extracting shorelines from open-source satellite imagery in South Maldives using unsupervised machine learning. The method involves resampling the Near-Infrared (NIR) image to improve spatial resolution, georeferencing, and followed by applying the K-means clustering algorithm to distinguish between land and water areas. The resulting boundary line is then corrected and georeferenced to match the actual shoreline position and transformed into a smooth line using a new modification algorithm. The accuracy of the automated method was evaluated by comparing its results to those obtained through manual extraction from high-resolution WorldView2 images in Laamu atoll. This study found that the automated method produced more accurate results from Sentinel-2 image than from Landsat image, with R-squared ranging from 0.94 to 0.95, MAE from 2.34 m and 3.24 m, MSE from 9.21 m to 19.12 m and RMSE from 3.04 m to 4.37 m. This approach offers a quick and cost-effective means of extracting shorelines from open-source satellite imagery, enabling coastal engineers and scientists to explore shoreline changes at a regional scale with high accuracy while saving time, money, and labor compared to manual extraction or high-cost satellite imagery purchases.

Keywords: Shoreline Extraction, Sentinel-2, Landsat, K-means, Machine Learning, Maldives.

Citation: ---

Submitted: --- / Revised: --- / Accepted: --- / Published: ---

This work is licensed under a Creative Commons Attribution 4.0 International License.