Sentinel-3 SAR Altimetry for Accurate Water Level Retrieval in Small Tropical Reservoirs
Mohd Adha Abdul Majid (a,b), Nurul Hazrina Idris (c*,d), Mohd Nadzri Md Reba (d)

a) Department of Geoinformation, Faculty of Built Environment and Surveying, Universiti Teknologi Malaysia, Malaysia
b) Strategic Application Division, Malaysian Space Agency, Malaysia
c) Tropical Resource Mapping Research Group, Department of Geoinformation, Faculty of Built Environment and Surveying, Universiti Teknologi Malaysia, Malaysia. *nurulhazrina[at]utm.my
d) Geoscience and Digital Earth Centre, Research Institute for Sustainability and Environment, Universiti Teknologi Malaysia, Malaysia

Abstract

Monitoring water surface elevation (WSE) is essential for effective water resource management in tropical regions with strong monsoonal influences. However, traditional in-situ methods and conventional satellite altimetry often lack the spatial resolution and reliability needed for small, remote reservoirs with complex topography. This study examines the feasibility of using Sentinel-3 synthetic aperture radar (SAR) altimetry to retrieve WSE in small tropical reservoirs by testing tailored geophysical and atmospheric correction strategies in three inland reservoirs in Peninsular Malaysia - Kenyir (326.4 km2), Temengor (137.3 km2), and Chenderoh (8.6 km2). Three correction configurations were evaluated, and altimetry-derived WSE was validated against in-situ gauge data. Among them, Model Set 1 - integrating European Centre for Medium-Range Weather Forecasts (ECMWF)-based atmospheric corrections (dry at zero altitude, wet at measured altitude), the Finite Element Solution Release Year 2014 (FES 2014) tide model, and the European Improved Gravity Model of the Earth by New Techniques (EIGEN6C4) geoid - consistently delivered the best performance. Kenyir, with its large surface area and stable terrain, showed minimal sensitivity to correction models, achieving a correlation coefficient of 0.99, root mean square error (RMSE) between 42 cm and 46 cm, and mean absolute error (MAE) between 34 cm and 37 cm. Temengor performed best under Set 1, with a correlation coefficient of 0.99, RMSE of 20 cm, and MAE of 13 cm. Despite Chenderoh^s smaller size and likely influence of narrow-channel hydrodynamics, fair accuracy was achieved, with a correlation coefficient of 0.84, RMSE of 26 cm, and MAE of 22 cm. These findings confirm that Sentinel-3 SAR altimetry, when paired with site-specific correction strategies, enables reliable WSE monitoring in small tropical reservoirs, supporting hydrological modelling, reservoir management, and climate-resilient planning in scarce-data regions.

Keywords: SAR altimetry, Water surface elevation, Small reservoirs, Sentinel-3, Tropical hydrology

Topic: Topic B: Applications of Remote Sensing