EO Capability Benefits
Salt marshes are vital coastal ecosystems located at the intersection of land and sea, offering a wide range of ecological, climatic, and socio-economic benefits. They support biodiversity by serving as habitats for various species, including molluscs, crustaceans, insects, birds, and fish. Their dense vegetation acts as a natural barrier, reducing coastal erosion and protecting inland areas from storm surges and flooding. Moreover, salt marshes are significant carbon sinks, earning the designation of “blue carbon” ecosystems along with mangroves and seagrasses due to their ability to capture and store atmospheric carbon in both plant biomass and sediment.
Monitoring salt marshes enables the assessment of these services over time, helping track their health and extent amidst pressures like sea-level rise, eutrophication, and land-use change. Advanced remote sensing techniques, such as NDVI analysis through satellite and UAV imagery, allow for high-resolution, long-term observation of vegetation dynamics, productivity, and degradation, thereby informing effective conservation, restoration, and sustainable management strategies.
EO Capability Description
Monitoring water fluctuation, especially in coastal and intertidal zones like salt marshes, is critical for understanding the hydrological and ecological processes that influence ecosystem health and resilience. Variations in water levels affect sediment transport, nutrient distribution, and plant growth cycles, all of which are key factors for maintaining the structure and function of salt marshes. Changes in tidal patterns, freshwater inflow, and sea-level rise can alter the balance between submersion and exposure, directly impacting the ability of these ecosystems to sustain biodiversity and sequester carbon.
This EO capability consists of two interrelated datasets designed to identify and assess areas with potential for salt marsh development by analysing patterns of water variability and vegetation activity. The first dataset, a Water and Wetness Fluctuation Map, captures temporal changes in water coverage, while the second, a Salt Marsh Potentiality Map, highlights zones that exhibit both hydrological dynamics and vegetative growth, typical of salt marsh ecosystems.
The Water and Wetness Fluctuation Map presents a summary of water presence by calculating, for each pixel, the percentage of time it is covered by water. It highlights transitional zones that are neither permanently submerged nor always dry, creating the ideal conditions for salt marshes, which are influenced by tidal patterns.
The subsequent application of vegetation indices, such as the Normalised Difference Vegetation Index (NDVI), allows for the detection of areas with active chlorophyll, indicative of plant productivity within salt marshes. By overlaying the NDVI data with water fluctuation values and applying specific thresholds, it is possible to delineate areas likely to support salt marsh vegetation. The outcome is a detailed map showing zones with both intermittent inundation and vegetative growth, signifying potential salt marsh occurrence.
This mapping effort can be derived from satellite data from Sentinel-1 radar (SAR) and Sentinel-2 optical (multispectral) sensors. The combined use of radar and optical imagery allows for frequent and reliable monitoring. Radar data is unaffected by clouds or weather conditions, while optical data provides rich spectral information essential for vegetation analysis.
Combining radar and optical data streams makes it possible to generate monthly image composites, which in turn can be used to derive annual maps of water fluctuation and vegetation activity. By applying analytical thresholds, such as NDVI values and water coverage, it becomes feasible to identify areas with potential for salt marsh development. To further refine the analysis and exclude irrelevant inland zones, a Digital Elevation Model (DEM) can be employed to mask out areas above a defined elevation, ensuring the focus remains on coastal and low-lying environments.
By observing water fluctuations over time, researchers and managers can detect early signs of ecosystem stress, predict potential habitat shifts, and model the long-term impacts of climate change. This monitoring supports more accurate planning for coastal protection, restoration initiatives, and adaptation strategies, ensuring that the benefits provided by these ecosystems, such as shoreline stability and water purification, are preserved in the face of environmental change.
