Majid et al. (2025) Virtual water gauge from the Synthetic Aperture Radar (SAR) altimeters for small reservoirs in tropical regions

Identification

• Journal: Advances in Space Research
• Year: 2025
• Date: 2025-11-20
• Authors: Mohd Adha Abdul Majid, Nurul Hazrina Idris, Mohd Nadzri Md Reba, Stefano Vignudelli
• DOI: 10.1016/j.asr.2025.11.060

Research Groups

• Tropical Resource Mapping Research Group, Department of Geoinformation, Universiti Teknologi Malaysia (UTM).
• Geoscience and Digital Earth Centre (INSTeG), Research Institute for Sustainability and Environment, Universiti Teknologi Malaysia (UTM).
• Strategic Application Division, Malaysian Space Agency (MYSA).
• Consiglio Nazionale Delle Ricerche (National Research Council), Pisa, Italy.

Short Summary

This study evaluates the effectiveness of Sentinel-3 SAR altimetry for monitoring water surface elevation in small tropical reservoirs in Malaysia. The research demonstrates that SAR altimetry can achieve high correlations (>0.95) with in-situ gauges, providing a viable "virtual gauge" for complex tropical landscapes.

Objective

• To evaluate the performance of Synthetic Aperture Radar (SAR) altimetry from Sentinel-3 (A and B) for monitoring water surface elevation (WSE) in small reservoirs (<500 km²) characterized by complex tropical landscapes and limited ground-based monitoring.

Study Configuration

• Spatial Scale: Three reservoirs in Malaysia: Kenyir (326.4 km²), Temengor (137.3 km²), and Chenderoh (8.6 km²).
• Temporal Scale: Analysis based on the operational periods of Sentinel-3A and Sentinel-3B missions (data spanning up to late 2025/2026 as per publication context).

Methodology and Data

• Models used: Waveform classification (quasi-specular, multi-peak, and complex); six atmospheric and geophysical correction sets including ECMWF tropospheric models; ocean tide models (FES2014, GOT v4.10, TPXO9-ATLAS); and geoid models (EIGEN6C4, EGM2008).
• Data sources: Sentinel-3 SAR altimetry (Level-2 products); in-situ water level gauge observations for validation.

Main Results

• Correlation: All reservoirs showed a correlation exceeding 0.95 (p < 0.05) between satellite data and in-situ observations.
• Absolute Error (RMSE): 49 cm for Kenyir, 50 cm for Temengor, and 80 cm for Chenderoh.
• Relative Error (NRMSE): Low relative errors (<7% of water-level range) for Kenyir and Temengor; higher relative error (39%) for Chenderoh due to its very narrow water-level variability (~2 m).
• Waveform Characteristics: Chenderoh exhibited 100% quasi-specular returns (Class I), while Kenyir and Temengor showed higher proportions of multi-peak and complex waveforms, indicating higher land contamination.
• Optimal Corrections: Set 3 and 5 performed best for Kenyir, Set 6 for Temengor, and Set 1 and 2 for Chenderoh.

Contributions

• Demonstrates the feasibility of using Sentinel-3 SAR altimetry for monitoring small-scale inland water bodies in tropical regions with high topographic complexity.
• Identifies specific atmospheric and geophysical correction configurations that optimize water level retrieval for different reservoir scales.
• Establishes a framework for "virtual water gauges" in regions where physical gauge infrastructure is limited or difficult to maintain.

Funding

• Not explicitly detailed in the provided text snippet.

Citation

@article{Majid2025Virtual,
  author = {Majid, Mohd Adha Abdul and Idris, Nurul Hazrina and Reba, Mohd Nadzri Md and Vignudelli, Stefano},
  title = {Virtual water gauge from the Synthetic Aperture Radar (SAR) altimeters for small reservoirs in tropical regions},
  journal = {Advances in Space Research},
  year = {2025},
  doi = {10.1016/j.asr.2025.11.060},
  url = {https://doi.org/10.1016/j.asr.2025.11.060}
}

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