Coral reef applications of Sentinel-2: Coverage, characteristics, bathymetry and benthic mapping with comparison to Landsat 8

Hedley, John D.; Roelfsema, Christiaan M; Brando, Vittorio E.; Giardino, Claudia; Kutser, Tiit; Phinn, Stuart; Mumby, Peter J.; Barrilero, Omar; Laporte, Jean; Koetz, Benjamin

doi:10.1016/j.rse.2018.07.014

Cited by 173 publications

(124 citation statements)

References 52 publications

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“…The multi-scene compositing approach addressed limitations inherent in conventional methods and reduced the impact of turbidity, performing better than the standard "pick the best scene" method that relies on a single image (Figures 3 and 4c vs. Figure 4a in Cape Lookout; and Figure 10e vs. Figure 10a,c in Saint Joseph Bay). The final corrected SDB produced robust depths up to the limit of the lidar surveys, with typical errors ≤0.4 m. These excellent results from Sentinel-2 compared favorably with those produced in relatively low turbidity water in south Florida [22,44], and in regions with transparent waters [10,18,20,30]. Whereas some researchers suggested there is still work to be performed regarding the identification of the optimal period throughout the year where bathymetric errors are minimized [18,29], others asked for novel strategies to allow seabed mapping without the laborious analysis per image and the visual inspection of the "clearest scene" [19].…”

Section: Discussionmentioning

confidence: 63%

“…The study areas were Saint Joseph Bay, Florida (29.75 scales [9,10,22]. This paper proposes the first multiple-image technique with Sentinel-2A and Sentinel-2B that allows semi-automated SDB estimation in areas of variable turbidity.…”

Section: Study Areasmentioning

confidence: 99%

“…A spatial filter (median filter 3x3) was conducted on the bands in order to remove some noise and inter-pixel variability. Recent experience with Sentinel-2 imagery indicated spatial filtering enhanced bathymetric products [10,22,44]. In this investigation, the spectral red-edge band at 704 nm (Rrs704) was used as a proxy for turbidity over optically shallow waters [22].…”

Section: Atmospheric Correctionmentioning

confidence: 99%

“…Several reviews of the methodologies are available in the literature [8,9]. Although the acquisition of imagery is not a problem today, image processing is more complex than data collected from conventional surveys, as it requires special treatment for a correction of the atmosphere, the air-water interface, and especially the local water characteristics [10]. Whereas SDB has been typically applied over environments with clear water (particularly coral reefs), its broader application has been constrained by water clarity, the most challenging constraint to routine satellite seabed mapping [8].…”

mentioning

confidence: 99%

“…This approach uses the capabilities of the Sentinel-2 Multi Spectral Imagers (MSI) of the Copernicus programme, which include 10 m spatial resolution in the visible bands, five-day routine revisit, and freely available data. In this context, researchers have hypothesized that a higher temporal resolution would allow the development of guidelines for repeatable shallow water mapping approaches at regional to global scales [9,10,22].…”

mentioning

confidence: 99%

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Towards Routine Mapping of Shallow Bathymetry in Environments with Variable Turbidity: Contribution of Sentinel-2A/B Satellites Mission

Caballero

Stumpf

2020

Remote Sensing

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Satellite-Derived Bathymetry (SDB) has significant potential to enhance our knowledge of Earth's coastal regions. However, SDB still has limitations when applied to the turbid, but optically shallow, nearshore regions that encompass large areas of the world's coastal zone. Turbid water produces false shoaling in the imagery, constraining SDB for its routine application. This paper provides a framework that enables us to derive valid SDB over moderately turbid environments by using the high revisit time (5-day) of the Sentinel-2A/B twin mission from the Copernicus programme. The proposed methodology incorporates a robust atmospheric correction, a multi-scene compositing method to reduce the impact of turbidity, and a switching model to improve mapping in shallow water. Two study sites in United States are explored due to their varying water transparency conditions. Our results show that the approach yields accurate SDB, with median errors of under 0.5 m for depths 0-13 m when validated with lidar surveys, errors that favorably compare to uses of SDB in clear water. The approach allows for the semi-automated creation of bathymetric maps at 10 m spatial resolution, with manual intervention potentially limited only to the calibration to the absolute SDB. It also returns turbidity data to indicate areas that may still have residual shoaling bias. Because minimal in-situ information is required, this computationally-efficient technique has the potential for automated implementation, allowing rapid and repeated application in more environments than most existing methods, thereby helping with a range of issues in coastal research, management, and navigation. surveys are constrained by access, logistics and extremely high deployment cost. It is estimated that multibeam echo sounding (at best resolution) would take more than 200 ship-years and billions of dollars to complete a swath survey of the seafloor [6]. The problem is substantial; consider that some 50% of the USA territories-as an example-were surveyed by using old hydrographic methods that do not meet today's requirement [7]. In the opinion of the IHO, sea bottom information derived from satellite imagery, widely known as Satellite-Derived-Bathymetry (SDB), should be considered as a potential technology to improve the collection, timeliness, quality, and availability of bathymetric data worldwide. In this regard, IHO has started to evaluate SDB strategies and the IHO S-44 standards are currently under revision. Furthermore, SDB offers a low-cost and non-intrusive suitable solution because no mobilization is required, removing health and safety risk, and any environmental impact.Approaches to SDB mapping vary on aim and rationale, spatial scale, and source of satellite system information. The concept is based on detection of sunlight reflected from the seafloor, and algorithms that use spectral information from this light to calculate water column depth. Several reviews of the methodologies are available in the literature [8,9]. Although the acquisition of imagery ...

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Section: Discussionmentioning

confidence: 63%

Section: Study Areasmentioning

confidence: 99%

Section: Atmospheric Correctionmentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Towards Routine Mapping of Shallow Bathymetry in Environments with Variable Turbidity: Contribution of Sentinel-2A/B Satellites Mission

Caballero

Stumpf

2020

Remote Sensing

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Mapping Apennines river paths along different hydrological conditions from satellite images: A description of the method and potential applications

Giacomelli

Chelli

Bresciani

et al. 2023

River Research & Apps

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Climate change is producing large impacts on rivers, amplifying hydrological extremes. Prolonged drought periods result in dramatic stress for river biota and associated processes due to low discharge, reducing the interactions between rivers and their lateral environments or leading to hydrological intermittency. New quantitative methods are needed, to correlate discharge with the available riverine habitats. In this work we have mapped the wet surface and paths of two stretches of the Taro and Trebbia Apennine rivers, analyzing satellite images from periods with contrasting discharge. The considered stretches are critical due to different human pressures (large water withdrawals for agriculture and industrial use) and are particularly vulnerable to further, climate‐driven discharge reductions. The produced images offer multiple possibilities to extract qualitative and quantitative information at the whole stretch scales, including habitat reduction along with decreasing discharge, threshold discharge limiting lateral interactions, or the evaluation of longitudinal river continuity. We discuss the limitation and the potentialities of the method and the maps produced in terms of possible application in the field of river geomorphology, ecology, the definition of ecological river flow, risk assessment, and river management.

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Cloud‐native seascape mapping of Mozambique’s Quirimbas National Park with Sentinel‐2

Poursanidis

Traganos

Teixeira

et al. 2020

Remote Sens Ecol Conserv

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The lack of detailed spatial information on coastal resources, notably shallow water coral reefs and associated benthic habitats, impedes our ability to protect and manage them in the face of global climate change and anthropogenic impacts. Here, we develop a semi-automated workflow in the cloud that uses freely available Sentinel-2 data from the European Space Agency (ESA) Copernicus programme to derive information on near-shore coral reef habitats in the Quirimbas National Park (QNP), a recently declared biosphere reserve in northern Mozambique. We use an end-to-end cloud-based framework within the Google Earth Engine cloud geospatial platform to process imagery from raw pixels to cloud-free composites which are corrected for glint and surface artefacts, water column and derived estimated depth and then classified into four benthic habitats. Using independent training and validation data, we apply three supervised classification algorithms: random forests (RF), support vector machine (SVM) and classification and regression trees (CART). Our results show that random forests are the most accurate supervised algorithm with over 82% overall accuracy. We mapped over 105 000 ha of shallow water habitat inside the protected area, of which 18% are dominated by coral and hardbottom; 27.5% are seagrass and submerged aquatic vegetation and another 23.4% are soft and sandy substrates, and the remaining area is optically deep water. We employ satellite-derived bathymetry to assess slope, bathymetric position, rugosity and underwater topography of these habitats. Finally, a spectral unmixing model provides further sub-pixel-level information of habitats with the potential to monitor changes over time. This effort provides the first, consistent and repeatable and also scalable coastal information system for an east African tropical marine protected area, which hosts shallow-water ecosystems which are of great significance to local communities and building resilience towards climate change.

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Coral reef applications of Sentinel-2: Coverage, characteristics, bathymetry and benthic mapping with comparison to Landsat 8

Cited by 173 publications

References 52 publications

Towards Routine Mapping of Shallow Bathymetry in Environments with Variable Turbidity: Contribution of Sentinel-2A/B Satellites Mission

Towards Routine Mapping of Shallow Bathymetry in Environments with Variable Turbidity: Contribution of Sentinel-2A/B Satellites Mission

Mapping Apennines river paths along different hydrological conditions from satellite images: A description of the method and potential applications

Cloud‐native seascape mapping of Mozambique’s Quirimbas National Park with Sentinel‐2

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