Monitoring Sand Spit Variability Using Sentinel-2 and Google Earth Engine in a Mediterranean Estuary

Abstract

Estuarine degradation is a major concern worldwide, and is rapidly increasing due to anthropogenic pressures. The Mediterranean Guadiaro estuary, located in San Roque (Cadiz, Spain), is an example of a highly modified estuary, showing severe negative effects of eutrophication episodes and beach erosion. The migration of its river mouth sand spit causes the closure of the estuary, resulting in serious water quality issues and flora and fauna mortality due to the lack of water renewal. With the aim of studying the Guadiaro estuary throughout a 4-year period (2017–2020), the Sentinel-2 A/B twin satellites of the Copernicus programme were used thanks to their 5-day and 10 m temporal and spatial resolution, respectively. Sea–land mapping was performed using the Normalized Difference Water Index (NDWI) in the Google Earth Engine (GEE) platform, selecting cloud-free Sentinel-2 Level 2A images and computing statistics. Results show a closure trend of the Guadiaro river mouth and no clear sand spit seasonal patterns. The study also reveals the potential of both Sentinel-2 and GEE for estuarine monitoring by means of an optimized processing workflow. This improvement will be useful for coastal management to ensure a continuous and detailed monitoring in the area, contributing to the development of early-warning tools, which can be helpful for supporting an ecosystem-based approach to coastal areas.

Mapping the National Seagrass Extent in Seychelles Using PlanetScope NICFI Data

“…Compared to a single PlanetScope image, the NICFI basemaps use statistics to bypass issues when lacking good images during certain time periods [42,43] while retaining the high spatial resolution of PlanetScope images for seagrass classification [44]. Although the atmospheric correction is terrestrial, previous use of terrestrially corrected surface reflectance images in other satellite imagery, such as the Sentinel-2 Level 2A Surface Reflectance Product on GEE, was found to still produce useful results [23,45]. As with the standard PlanetScope imagery, the spatial resolution of the NICFI basemaps is better than Sentinel-2 or Landsat 8 at 4.77 m (Table 1) [12].…”

Wind–Wave Conditions and Change in Coastal Landforms at the Beach–Dune Barrier of Cesine Lagoon (South Italy)

“…Due to the nature of the coastal land-water interface, the shoreline position continually changes through time [59]. Based on the guideline of geographic-object analysis [57,58], time series of instantaneous shoreline extracted from freely available high-resolution (up to less than 0.5 m) satellite images are increasingly used in the reconstruction of geomorphological trends [60][61][62][63]74,75].…”

Detecting Shoreline Changes on the Beaches of Hainan Island (China) for the Period 2013–2023 Using Multi-Source Data

“…With the accumulation of high-resolution satellite images and advancements in observation technology and coastal evolution theory, it is now possible to obtain a large amount of high-frequency coastline data. Platforms such as Google Earth Engine offer access to resources such as the Landsat series and Sentinel-2, facilitating the comprehensive study of shoreline dynamics [17,18]. However, extracting shorelines from diverse remote sensing data sources necessitates a thorough consideration of the spectral characteristics of remote sensing images to ensure compatibility with shorelines' image characteristics in varying geographical environments.…”