Limitations in the use of Sentinel-1 data for morphological change detection in rivers

ABSTRACT

The identification of morphological changes occurring along river channels is essential to support river process understanding, assess sediment budgets and evaluate the effectiveness of river management. Among available remote sensing techniques, space-borne synthetic aperture radar (SAR) could potentially provide a powerful complement to optical imagery for this task. However, very few studies have been carried out on the use of SAR datasets to study erosion and deposition processes in river channels. In this work, we investigate the potential of change detection analysis based on Sentinel-1 data, by comparing variations of radar backscattering to river morphology changes identified through high-resolution drone acquisitions. We considered a time series of two years of Sentinel-1 data relative to a period where, despite a moderate fluvial event occurred, morphological changes have been significantly detected in multitemporal drone point clouds. Satellite optical imagery (planet.com) and hydro-meteorological data were used to support the analysis and interpret results. The results show that the spatial and temporal resolution of Sentinel-1 is currently not suitable for accurate discrimination of morphological changes related to river dynamics at local scale. Other spaceborne sensors with sub-metric ground sampling distance and/or daily revisit time would be probably suitable; however, so far, this option would need the use of commercial solutions with a consistent increase of the costs of the investigation.

Summary

• First attempt to evaluate whether Sentinel-1 data can provide quantitative estimates of fluvial morphological changes;

• Multitemporal comparison of Sentinel-1 backscattering and coherence data against UAV-SfM 3D point clouds difference;

• Sentinel-1 data found to be not suitable to track relatively small morphological changes (<2 m in the vertical direction) and the consequent changes in the surface characteristics which are typical of river dynamics;

• SAR-based detection of fluvial changes in rivers are intrinsically affected by severe limitations due to varying soil water content and vegetation cover;

• Higher resolution and/or different spectral sensor may lead to different results but, so far, would require important acquisition costs.

KEYWORDS:

• SAR
• photogrammetry
• river morphological changes
• Sentinel 1

Acknowledgement

We thank Prof. Patrice Enrique Carbonneau, Durham University, for his support in the steps of Dem of Difference generation and analysis. We thank all memers of the ‘IRIS - Italian Research and development Initiative for Spaceborne river monitoring’ project for their contribution in the field activities carried out for the ground truth data collection used in this work.

Disclosure statement

No potential conflict of interest was reported by the author(s).