Machine learning denoising of high-resolution X-ray nanotomography data

High-resolution X-ray nano­tomography is a quantitative tool for investigating specimens from a wide range of research areas. However, the quality of the reconstructed tomogram is often obscured by noise and therefore not suitable for automatic segmentation. Filtering methods are often required for a detailed quantitative analysis. However, most filters induce blurring in the reconstructed tomograms. Here, machine learning (ML) techniques offer a powerful alternative to conventional filtering methods. In this article, we verify that a self-supervised denoising ML technique can be used in a very efficient way for eliminating noise from nano­tomography data. The technique presented is applied to high-resolution nano­tomography data and compared to conventional filters, such as a median filter and a nonlocal means filter, optimized for tomographic data sets. The ML approach proves to be a very powerful tool that outperforms conventional filters by eliminating noise without blurring relevant structural features, thus enabling efficient quantitative analysis in different scientific fields

Understanding climate change driven coastal erosion and inundation impacts on Torres Strait communities and the development of adaptation options

[Extract] The Commonwealth of Australia, represented by the Department of Climate Change and Energy Efficiency, contracted James Cook University to undertake a study titled: Understanding climate change driven coastal erosion and inundation on Torres Strait communities and the development of adaptation options. The project undertakes an assessment of the risks of climate change driven coastal erosion and inundation of Torres Strait island communities, identifies and assesses specific adaptation options, and documents those options preferred by the communities. The project extends the work of a project completed on the central islands of Masig, Poruma, Warraber and Iama (see details in Section 2). It focuses on the 14 Torres Strait island communities on 13 islands that were not covered in the earlier project (Figure 1). These communities are: Erub (Darnley), Mer (Murray) and Ugar (Stephen) (volcanic islands); Kubin and St. Pauls (on Moa Island), Badu, Mabuiag, Dauan, Waiben (Thursday), Kiriri (Hammond), Muralug (Prince of Wales), Ngurupai (Horn) (continentaltype islands); Boigu and Saibai (low muddy islands

The age and stratigraphic significance of sea-rafted Loisels Pumice in northern New Zealand

Loisels Pumice is a sea-rafted pumice of uncertain origin, found on the east coast of the North Island of New Zealand. Since a radiocarbon age range was compiled from different and indirectly dated pumice layers by McFadgen (1982), Loisels Pumice has been used as a stratigraphic marker layer of known age in late Holocene coastal deposits. We contend that the date of primary deposition has been incorrectly determined and applied. We examined field sections from the far north of the North Island to identify and date the primary deposition of Loisels Pumice and to describe the physical characteristics and value of such a deposit. We also critically examined sites identified in the literature. Only one deposit was potentially primary, and the age of pumice deposition could be closely bracketed. From this section, we propose an age range of 915–1030 cal AD for the first stranding of Loisels Pumice in northern New Zealand. Analysis of sections shows that stratigraphic and geomorphic interpretation may be used to identify sites with the potential to be primary, but primary and secondary deposits cannot be identified by descriptive statistics. We conclude that the age of first stranding of Loisels Pumice cannot be reliably derived by compiling an age range bracket using maximum and minimum dates from different sections. Loisels Pumice should not be used as a coastal marker layer to establish synchrony between sites, and recent interpretations based on this method should be re-appraised

Fast-ferry generated waves in South-West Tallinn Bay

Waves generated by high-speed ferries sailing at near-critical speeds (depth Froude number ~1) may\ud substantially affect the coastal zone. As typical for large-amplitude waves in shallow water, waves from fast ferries frequently have a substantially nonlinear nature and are often able to seriously damage the coastal environment. We report wake characteristics of fast-ferries sailing in Tallinn Bay in June 2009. Waves were measured using an echosounder in the nearshore at Pikakari Beach at a depth of 2.7 m, 2.4 km from the sailing line. The record contains ~150 wake events for which primary wake parameters as the maximum wave height, wake energy and its flux were estimated. The shape of the highest vessel waves was analyzed in terms of cresttrough asymmetry. Maximum wave heights (up to 0.7 m) occurred exclusively for the longest waves with periods ~10 s. These waves are substantially nonlinear with wave crests exceeding wave troughs typically by a factor of 1.3. Incoming ferries generally excited smaller waves compared to a previous study of outgoing ferry\ud wakes in north-west Tallinn Bay. This apparently reflects the high spatial variability of wake waves along the\ud impacted coastal sections and is not an evidence of an overall decrease in the ship wave intensity

Implications of fast-ferry wakes for semi-sheltered beaches: a case study at Aegna Island, Baltic Sea

The almost-tideless Tallinn Bay, the Baltic Sea. is one of the few places in the world where high-speed ferries\ud frequently operate close to the shoreline and where wake-waves may have a significant effect on the morphology\ud and the sediment dynamics on medium-energy beaches, in particular, because of the difference of the wake propagation direction from that of dominant wind waves. The properties of ship waves were measured continuously during four weeks in summer 2008 offshore from a semi-sheltered beach located ~2700 m from the sailing line. Beach profiles were measured up to several times a day for more than 20 days. An adjacent jetty restricts sediment transport from the east. Overnight and during high-energy wave conditions. wind generated waves build the beach adjacent to the jetty. During calm periods the beach is not replenished and significant loss of sediment across the beach profile is evident due to ship wakes. The beach therefore, never reaches an equilibrium shape, as might normally be expected on the up-drift side of a groin. Instead, the area offshore adjacent to the jetty serves as a sink for the beach sediments

Variability in the properties of wakes generated by high-speed ferries

The largest impact on the coast of waves generated by high-speed ferries is usually caused by the highest and longest components of transcritical wakes. Building reliable statistics of these parts of vessel-generated waves is usually nontrivial because of the high variability in the properties of wakes and their infrequent occurrence. Tallinn Bay is one of the few places where high-speed ferries frequently operate at transcritical speeds close to the shoreline. We report the results of measurements performed in 2008 at the entrance of Tallinn Bay. The time series of water surface elevations were collected in 2.5-3 in water depth, similar to 100 m offshore from an almost non-reflecting beach, similar to 2700 m from the sailing line. The data from 418 wakes on 15 days allows the construction of distribution functions of different wake properties (maximum height, wake energy,and energy flux) with an acceptable accuracy. The periods of the highest waves vary insignificantly and are closely related to the cruise speed of the vessels. An appropriate measure of the properties and variability of wakes is the maximum wave height. Wakes from `classic' high-speed ships are very variable. Wakes from large, basically conventional, but strongly powered ferries show quite limited variability, thus, both the average and extreme wake properties of such ships can be more easily adjusted by changing their sailing regime

Understanding climate change driven coastal erosion and inundation impacts on Torres Strait communities and the development of adaptation options

[Extract] The Commonwealth of Australia, represented by the Department of Climate Change and Energy Efficiency, contracted James Cook University to undertake a study titled: Understanding climate change driven coastal erosion and inundation on Torres Strait communities and the development of adaptation options. The project undertakes an assessment of the risks of climate change driven coastal erosion and inundation of Torres Strait island communities, identifies and assesses specific adaptation options, and documents those options preferred by the communities. The project extends the work of a project completed on the central islands of Masig, Poruma, Warraber and Iama (see details in Section 2). It focuses on the 14 Torres Strait island communities on 13 islands that were not covered in the earlier project (Figure 1). These communities are: Erub (Darnley), Mer (Murray) and Ugar (Stephen) (volcanic islands); Kubin and St. Pauls (on Moa Island), Badu, Mabuiag, Dauan, Waiben (Thursday), Kiriri (Hammond), Muralug (Prince of Wales), Ngurupai (Horn) (continentaltype islands); Boigu and Saibai (low muddy islands

Preface. Special issue on ocenaography, meterology and coastal engineering

This publication does not have an abstract\u

Monsoonally influenced circulation around coral reef islands and seasonal dynamics of reef island shorelines

Synchronous measurements of reef flat waves and nearshore currents were made around the perimeter of three coral reef islands in the central Maldives. Nearshore current velocities were shown to be tidally modulated in most instances with maximum velocities associated with lower tidal stages. Peak currents were consistently observed on the windward and lateral flanks of island shorelines (0.3–0.4 ms− 1). The relatively low elevation of reef surfaces and medium to low energy incident wave energy (Hs ~ 0.2–0.3 m) accounts for low tidal stage peaks in velocity as this corresponds to the period when wave setup-induced current processes are maximised. Significantly, all nearshore currents were unidirectional and alongshore. The generation of unidirectional alongshore flow patterns results from island configuration which deflects flow and variations in reef geometry that control: spatial variations in wave-setup around the reef platform edge and at the island shoreline, which can drive alongshore currents; the presence of a nearshore moat that channelizes flow in the nearshore: and variations in reef geometry where topographic low points act as preferential drainage points. Results show that changes in monsoon conditions, that modulate wind and wave patterns from the west to northeast, can force substantial changes in reef platform and nearshore current flows, but that the degree of change is dependent on reef platform shape and position in the atoll. The circular study island was found to exhibit a near-complete reversal in unidirectional flow from northeast flow in the westerly monsoon to southwest flow in the northeast monsoon. However, the elongate and triangular shaped reef platforms exhibited more localised changes in flow patterns. Significantly, those shorelines that exhibit the greatest changes in shoreline currents correspond to the sections of coast that exhibit the largest morphological adjustments between seasons. Results provide significant insights for the morphodynamics of reef platform islands. In particular, the nearshore process regime is dominated by alongshore processes. Furthermore, reef platform shape and the magnitude of change in direction of wave approach to reef platforms provide critical indicators of the morphodynamic behaviour of reef platform islands

Shoreline effects of vessel wakes, Marlborough Sounds, New Zealand

The science of vessel wake generation and propagation is well advanced, but the environmental effects of wakes are less well understood. The introduction of large vehicle and passenger-carrying fast ferries (HSC) in the 1990s resulted in numerous reports of environmental damage worldwide. In the Marlborough Sounds, New Zealand, regulatory agencies have struggled with the management of vessel wakes from both HSC and conventional vessels operating between the North Island and South Island. Gravel beaches along the route responded very quickly to the higher energy levels associated with the introduction of HSC, and there has been little change since that time, except in situations associated with geological instability. There has been no recovery of beaches towards pre high-energy conditions following HSC speed restrictions in 2000. Evidence of wake influences on very low-energy beaches in the far-field, over 7 km from the vessel path shows that long wave lengths associated with HSC can result in geomorphically significant waves and sediment transport. These findings are in\ud accordance with other recently published results reported by other authors in the Baltic Sea