Assessing Long-Term Water Dynamics in the Danube Delta Lakes using Sentinel-1 Radar Imagery

The EcoDaLLi project is an integrative initiative designed to contribute to the European Green Deal’s freshwater objectives by supporting the restoration, protection, and sustainable management of the Danube River Basin and its delta. As part of the broader mission "Restore Our Ocean, Seas & Waters by 2030," the project employs a systemic approach to ecosystem restoration through the implementation of innovative solutions and improved governance frameworks. By focusing on the Danube Basin, one of Europe’s most ecologically significant areas, EcoDaLLi aims to strengthen climate resilience, enhance biodiversity conservation, and promote sustainable water resource management. Additionally, Unitatea Executivă pentru Finanțarea Învățământului Superior, a Cercetării, Dezvoltării și Inovării (UEFISCDI) from Romania has awarded a special funding grant to support the present research.

A core scientific objective of the project is to document and analyze the dynamic behavior of the water surfaces in the Danube Basin. The present research relies on satellite radar imagery from the Sentinel-1 constellation, made available through the Copernicus Program. The radar data’s ability to penetrate cloud cover and record consistent surface reflections makes it highly suitable for long-term multi-temporal monitoring of water bodies, especially in a complex and variable environment such as the Danube Delta.

The initial phase involves the systematic collection of radar imagery, focusing on the VV polarization channel, which offers superior water isolation characteristics compared to other channels. In the second phase, a rigorous preprocessing workflow is applied to the raw imagery, including orbital corrections, radiometric normalization, and noise reduction. These steps are critical for ensuring data consistency and enabling precise extraction of water body extents. The processed data is then subjected to detailed geospatial analysis using advanced GIS tools, enabling the derivation of key hydrological metrics. These metrics include maximum and minimum water extent, presence and recurrence of water bodies, and seasonal variations.

The analysis will employ methodologies such as Continuous Change Detection and Classification (CCDC) to track and quantify spatial and temporal changes across the monitored lakes. Statistical models will further be used to correlate observed hydrological changes with climatic and environmental factors. The resulting datasets will provide a robust foundation for understanding the long-term hydrological dynamics of the Danube Delta’s lakes and their role in regional ecosystem functioning. Moreover, the results will offer guidelines for local and regional stakeholders, supporting evidence-based policy-making and adaptive management strategies.

Acknowledgments

This work was supported by a grant of the Ministry of Research, Innovation and Digitization, CNCS/CCCDI - UEFISCDI, project number PN-IV-P8-8.1-PRE-HE-ORG-2023-0089, within PNCDI IV.