Remote Sensing-Based Numerical Methods for Water Surface Area Estimation

Abstract

Monitoring water bodies in Iraq is vital in light of increasing climatic and human pressures, especially for Lake Hamrin, a major source of drinking and irrigation water in Diyala Governorate. This research relied on Sentinel-2 L2A images from the Copernicus program for the period 2019–2025 to determine changes in the lake's surface area. The Normalized Water Index (NDWI) was used to extract the water boundaries, then convert the geographic coordinates to metric (UTM) coordinates to accurately draw the shoreline. Two numerical methods were applied to calculate the water surface area of Lake Hamrin the Shoelace and Simpson’s methods. Comparing the results with reference values extracted from the Copernicus platform, it was found that the shoelace method yielded a lower error (0.7–3.1%) than the Simpson method (1.3–5.1%). This is attributed to the complexity of the coastal shape of Lake Hamrin. Shoelaces provide a more accurate representation of coastal details, while Simpson's method tends to simplify the boundaries. However, the differences between the two methods diminish when the water level is low, as in 2021–2023, as the shape of the lake becomes more regular.