Search

Mapping shorelines is critical for coastal management and conservation, as shorelines are essential indicators for understanding coastal geomorphology and dynamics. Nonetheless, as shorelines are often lengthy and rugged, in-situ surveys are labor-intensive and costly. Oppositely, spaceborne remote sensing data provide cost-efficient alternatives, yet, most earlier studies rely on manual digitization or thresholding band ratio-based water indices to delineate instantaneous shorelines, which locations are affected by varying water color and tides. Consequently, cross-temporal assessments of environmental and anthropogenic impacts on coastal stability remain challenging. The present study develops an edge detection-based, dual-temporal, nationwide, tide-coordinated, and sediment cell-based shoreline dataset in Japan, i.e., the TSSD-JP. Both 1980s and 2020s shorelines along the Japanese coasts are extracted using cross-mission multispectral data and an automated shoreline extraction method. The results are validated with national coast surveys and global shoreline databases, confirming a positional accuracy better than 80% at 50 m. Moreover, founded on the extracted dual-temporal shorelines, 30+ year coastal changes are measured. An increased land area of 293.21 km2 at a rate of 8.50 km2/yr is estimated. Evident accretions in bay regions of southern Honshu due to extensive land reclamation and engineering constructions are observed. Since the analysis is conducted on natural management units with a physical basis, potential biases caused by jurisdictional boundaries are overcome. Practically, because TSSD-JP is derived from freely accessible data and tools, its universal applicability is guaranteed. Thence, the proposed approach can be applied to different nations' intertidal zones to assess the coastal vulnerability and resilience as well as support local governments' shoreline management plans (SMPs). [Display omitted] [ABSTRACT FROM AUTHOR]

ABSTRACT Tojo, K. and Udo, K., 2018. Analysis of beach recovery after the 2011 Tohoku Earthquake Tsunami based on shoreline extraction by ISODATA technique. In: Shim, J.-S.; Chun, I., and Lim, H.S. (eds.), Proceedings from the International Coastal Symposium (ICS) 2018 (Busan, Republic of Korea). Journal of Coastal Research, Special Issue No. 85, pp. 171–175. Coconut Creek (Florida), ISSN 0749-0208. The 2011 Tohoku earthquake tsunami caused the disappearance of beaches over a wide area. Understanding of the beach recovery process after the tsunami is important for long-term coastal management. This study aimed to develop a highly accurate method of shoreline extraction using satellite and aerial images and to clarify characteristics of beach recovery by analyzing shoreline changes in the tsunami-affected area. Shorelines extracted by the Iterative Self Organizing Data Analysis Technique (ISODATA) with tidal- and wave-corrections agree well with those obtained from topography measurements. In addition, the shorelines extracted from 406 images from before the tsunami to four years after it at 44 beaches demonstrated the shorelines tended to be recovered at plain coasts and not to be recovered at ria coasts. It is confirmed that the method based on ISODATA is highly accurate and significantly reduces the time and labor. [ABSTRACT FROM AUTHOR]

Foam is often present in satellite images of coastal areas and can lead to serious errors in the detection of shorelines especially when processing high spatial resolution images (<20 m). This study focuses on shoreline extraction and shoreline evolution using high spatial resolution satellite images in the presence of foam. A multispectral supervised classification technique is selected, namely the Support Vector Machine (SVM) and applied with three classes which are land, foam and water. The merging of water and foam classes followed by a segmentation procedure enables the separation of land and ocean pixels. The performance of the method is evaluated using a validation dataset acquired on two study areas (south and north of the bay of Sendaï—Japan). On each site, WorldView-2 multispectral images (eight bands, 2 m resolution) were acquired before and after the Fukushima tsunami generated by the Tohoku earthquake in 2011. The consideration of the foam class enables the false negative error to be reduced by a factor of three. The SVM method is also compared with four other classification methods, namely Euclidian Distance, Spectral Angle Mapper, Maximum Likelihood, and Neuronal Network. The SVM method appears to be the most efficient to determine the erosion and the accretion resulting from the tsunami, which are societal issues for littoral management purposes. [ABSTRACT FROM AUTHOR]

This study explored closed-circuit television (CCTV) networks in northeastern Toyama Prefecture, Japan, as a new data source for tsunami detection following the 2024 Noto Peninsula earthquake. We analyzed CCTV footage and extracted time-series water level fluctuations at Yokoyama, Shimoiino, and Ekko. Spectral analysis of these waveforms revealed several long-period peaks (more than 100 s) in power spectral density (PSD), suggesting the presence of tsunami components. Notably, relatively large PSD peaks at approximately 5–10 min were observed at all CCTV locations in this study and at offshore wave observation points (Tanaka and Toyama). At Yokoyama, a maximum run-up of approximately 3 m was confirmed around 16:28. Although water level fluctuations at Shimoiino and Ekko were detected, identifying tsunami components proved challenging due to their small magnitude compared to other wave components. Despite these challenges, this study demonstrates the potential of CCTV networks for tsunami detection, and further research is needed to achieve real-time detection. [ABSTRACT FROM AUTHOR]

In this study, we analyze the influence of the Great East Japan Earthquake, which occurred on 11 March 2011, on the shoreline of the northern Ibaraki Coast. After the earthquake, the area experienced subsidence of approximately 0.4 m. Shoreline changes at eight sandy beaches along the coast are estimated using various satellite images, including the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer), ALOS AVNIR-2 (Advanced Land Observing Satellite, Advanced Visible and Near-infrared Radiometer type 2), and Sentinel-2 (a multispectral sensor). Before the earthquake (for the period March 2001–January 2011), even though fluctuations in the shoreline position were observed, shorelines were quite stable, with the averaged change rates in the range of ±1.5 m/year. The shoreline suddenly retreated due to the earthquake by 20–40 m. Generally, the amount of retreat shows a strong correlation with the amount of land subsidence caused by the earthquake, and a moderate correlation with tsunami run-up height. The ground started to uplift gradually after the sudden subsidence, and shoreline positions advanced accordingly. The recovery speed of the beaches varied from +2.6 m/year to +6.6 m/year, depending on the beach conditions. [ABSTRACT FROM AUTHOR]