Editorial on Remote Sensing Application in Coastal Geomorphology and Processes

1. Introduction

Coastal zones are characterized by exceptional environmental, social, and economic importance, while, at the same time, being particularly vulnerable to climate-related changes. Coastal processes such as sediment dynamics, erosion, and accretion are essential factors that influence the evolution of coastal zones. Understanding the geomorphological processes that shape coastal areas and their evolution is fundamental for effective coastal management and adaptation strategies. However, studying and monitoring these processes is challenging due to the complex and dynamic nature of the coastal environment. Remote sensing applications have enormous potential to monitor this intrinsically dynamic environment via remote observations and measurements, which can provide important insights into coastal conditions and coastal evolution at different geomorphologic settings and timescales.

Remote sensing technologies such as optical, radar, and LiDAR, offer unique advantages for studying sediment dynamic processes on deltas, beaches, dunes, and barrier islands; coastal processes in erosional landscapes, such as rocky cliffs, forcing mechanisms of coastal processes such as waves, tides, and currents; and coastal geomorphology and evolution. Additionally, close-range remote sensing applications, such as planes or UAVs, as well as onsite cameras or webcams, offer valuable data for studying the coastal environment at a high spatiotemporal resolution and accuracy [1,2,3,4,5].

This Special Issue, entitled “Remote Sensing Application in Coastal Geomorphology and Processes”, presents an overview of the latest advances and applications of remote sensing in coastal geomorphology and its processes, providing a platform where researchers can share their innovative approaches, methodologies, and findings in this field. Topics include, but are not limited to, delta systems evolution, nearshore bar behaviour, shoreline changes, human-related impacts on coastal zones, salt marsh predicted evolution, early warning systems for high-energy events and climatic variability.

The nine articles in this Special Issue of Remote Sensing highlight the use of remote sensing to study various aspects of coastal geomorphology and its processes. The contributions to this Special Issue stress the widespread potential of remote sensing to provide crucial insights into coastal conditions and evolution at wide timescales.

2. Contributions to the Special Issue

Wang et al. [6] investigated the long-term evolution of Jiuduansha, a mega delta in the Yangtze estuary, using satellite images captured between 1965 and 2021 together with K-means classification, probability statistics and GIS spatial analysis to generate annual probability waterlines and determine the continuous time series of geomorphological features, position of waterlines, and centroid change. The study reveals that the delta has undergone rapid growth, with erosion in the south and deposition in the north mainly caused by human activities. The paper provides an in-depth understanding of the long-term evolution of mega deltas highlighting the importance of considering human activities in the management and conservation of mega deltas.

Janušaitė et al. [7] used very-high resolution satellite data to analyse the cross-shore nearshore bar behaviour on a wave-dominated multi-bar coast of the Curonian Spit. The study assesses the interannual and seasonal bar cross-shore behaviour and alongshore variability in bar cross-shore migration rates at multiple timescales. This suggested that small alongshore variations in nearshore hydrodynamics, caused by the local wave climate and its interplay with shoreline orientation, determine the morphological and temporal variability of the multi-bar system in the Curonian Spit. This study illustrates the capabilities of very-high-optical satellite imagery in the field of nearshore morphodynamics, which can provide new insights into nearshore bar behaviour.

Ai et al. [8] used Landsat 8 OLI and Sentinel 2A MSI images to map the three typical types of coastal reclamation in Guangdong Province: ports, aquaculture ponds, and salt pans. The study compares pixel-based and object-oriented classification methods and evaluates the performance of different algorithms and determined the optimal one, according to statistical analysis, which was then used to map the main types of reclamation in the coastal zone of Guangdong Province. The results show that the object-oriented classifier, performs the best overall in reclamation classification, with relatively high-resolution Sentinel 2A MSI images. The overall results can provide key supporting data for decision making in coastal management and preservation.

Wu et al. [9] analysed the position and status of the Yangtze River Delta (YRD) coastline using high-resolution satellite imagery and an NDWI threshold method. The natural and artificial coastlines in the YRD region accounted for 42.73% and 57.27% of coastal areas in 2013 and 41.56% and 58.44% in 2018, respectively. The coastline generally advanced towards the sea, causing a land area increase of 475.62 km². The changes in the YRD coastline were mainly caused by a combination of large-scale artificial construction and natural factors such as silt deposition. The study provides insights into the distribution of coastline types and changes in the YRD coastline, which can help improve future environmental protection policies for coastal zones.

Using multi-source remote sensing image data from 1979 to 2019, Kang et al. [10] analyse the evolution process and characteristics of the radial sand ridges (RSRs) on the continental shelf of the South Yellow Sea. The study uses image data to extract geomorphic feature lines, such as artificial coastlines, waterlines, and sand ridge lines. The study shows that the coastline is advancing towards the sea, the exposed tidal flats are decreasing, and the overall sand ridge lines show a trend of gradually moving southeast. The findings also suggest that the trend of south-eastward movement of the radial sand ridge group will remain in the future, and the topography will become steeper. The information provided in this study is crucial for marine resource management and ecological protection.

Toolsee and Lamont [11] examined the interannual variability and longer-term trends of sea-surface temperature (SST), wind forcing and surface circulation in the sub-Antarctic Prince Edward Islands (PEIs) using satellite and reanalysis data. The authors also applied wavelet analysis to identify low-frequency time-dependent amplitudes in the time series. The study found significant interannual and decadal-scale variability in SST, wind and currents, with the strongest variance occurring at intra-annual time scales. The paper also identifies the influence of the Antarctic circumpolar wave on the variability of SST, wind, and currents at interannual and decadal time scales. These decadal variations may have a stronger influence on biological communities, which are much smaller by comparison, than long-term trends but detailed studies examining such impacts need to be conducted. In their study, the authors also highlight the need for time series observations of sufficient length to be able to adequately discern longer-term variations.

Inácio et al. [12] present a reduced-complexity model to predict the evolution of salt marshes in the context of sea-level rise. The SMRM (simplified marsh response model) combines field and remote sensing data and requires four parameters to generate outputs. The study was conducted in two test areas of Tróia sandspit (Setúbal, Portugal). A sensitivity analysis for each parameter’s influence and a comparison with another rule-based model (SLAMM) were undertaken. The results suggest that the studied salt marshes could be resilient to conservative sea-level rise scenarios but not to more severe sea-level rise projections. The developed model can be used to project the evolution of marsh areas until the end of the century and can be an alternative to more complex models such as numerical and other rule-based models demanding a larger amount of input data.

Scardino et al. [13] present a new monitoring system called LEUCOTEA that uses geophysical surveys, convolutional neural networks (CNNs) and optical flow to automatically obtain tide and storm parameters from video records. The system was developed and tested in the Mediterranean Sea and Atlantic coasts of Portugal. The CNN predictions were compared with tide gauge records, and water levels and wave heights were validated with pre-event topographic surveys in the proximity of the surveillance cameras. The results show that CNN and optical flow techniques can improve the calibration between network results and field data. The system has the potential to represent an innovative approach for early warning systems and could be useful for monitoring and study storm events.

Kong [14] proposes a new methodology for cliff monitoring that does not require georeferencing efforts, making it a cost-effective solution. The proposed approach aligns 3D point clouds of the cliff from different periods into the same coordinate system using a rigid registration protocol. The results show that the proposed methodology can yield reliable monitoring results without relying on expensive georeferencing efforts. The findings of this study would be particularly valuable for underserved coastal communities, where high-end GPS devices and GIS specialists may not be easily accessible resources. The findings of this study have important implications for coastal management and hazard mitigation efforts.

3. Summary and Future Directions

The Special Issue of Remote Sensing, entitled “Remote Sensing Application in Coastal Geomorphology and Processes”, presents a collection of nine research papers that focus on the use of remote sensing techniques in studying various coastal geomorphological processes. The papers explore topics such as the long-term evolution of mega deltas, nearshore bar behaviour, the resilience of salt marshes to sea-level rise, and the impact of climate variability on the sub-Antarctic Prince Edward Islands. In addition, the papers highlight the importance of human activities in the management and conservation of coastal ecosystems. Overall, these articles demonstrate the value of remote sensing in research on coastal geomorphology and its processes. The use of remote sensing techniques can provide a more comprehensive understanding of coastal environments and help inform management and conservation efforts. We hope that this Special Issue will inspire further research in this field, thus broadening our understanding of the complex dynamics of coastal environments.