Search

Digital elevation models (DEMs) are essential for quantitatively monitoring the current state and changes in the morphology of tidal flats and extracting terrain information, such as tidal channels. However, the unique environmental characteristics of tidal flats, where water and land coexist in shallow areas, make it challenging to apply traditional direct surveying methods or ship-based echo sounding. Additionally, remote sensing technologies such as airborne topographic light detection and ranging (LiDAR), drone photogrammetry, and satellite imagery are challenging to use in submerged areas. Airborne bathymetric LiDAR (ABL), which is capable of directly surveying the seabed through seawater, is a highly effective method for surveying tidal flats. However, the high turbidity and shallow water environment of tidal flats attenuate the return strength, resulting in a low signal-to-noise ratio and making airborne bathymetric LiDAR (ABL) full-waveforms extremely complex. In this study, we aim to improve the performance of ABL full-waveform processing to generate high-precision DEMs in such challenging environments. First, we analyze the characteristics of ABL waveforms under varying turbidity conditions and propose preprocessing and waveform decomposition techniques to improve seabed point extraction rates in tidal flat environments. To achieve this, experiments and validations are conducted using the data acquired by the Seahawk system along the west coast of Korea. [ABSTRACT FROM AUTHOR]

An overview of modern bed load measurement methods in rivers with fine alluvium is performed. Four groups of the methods are identified: measuring with bed load samplers, dune-tracking with a single-beam echo-sounder, dune-tracking with a multi-beam echo-sounder and measurement using acoustic Doppler current profilers. Strengths and weaknesses of each method are considered. Due to the fact that bed load transport occurs in the form of dunes the most promising methods seem to be based on the use of echo-sounders since they make it possible to take into account the integrity of bed forms directly. [ABSTRACT FROM AUTHOR]

The time series of near‐bottom temperatures collected from September 2018 until August 2020 from an array of three current‐ and pressure‐recording inverted echo sounders showed quasi‐seasonal and quasi‐monthly (∼28 days) variations at a depth of ∼1,300 m near the Chukchi slope in the western Arctic Ocean. They revealed an increase of ∼0.1°C during the winter‐spring period compared with the summer‐fall period. These variations were observed in the data‐assimilated Hybrid Coordinate Ocean Model (HYCOM) outputs near the observation site (correlation coefficient >0.7). They confirmed that variations in near‐bottom temperature are related to changes in the intensity of the Atlantic Water (AW) boundary current, concurrent with the deepening of the lower AW layer by approximately 50 m. The difference in sea surface height (SSH) between the Canada Basin and the Chukchi Shelf increased because of the negative wind stress curl (WSC) and retarded the AW boundary current according to the geostrophic effect. When the near‐bottom temperature increased during the winter‐spring period, the SSH in the Chukchi Shelf was lower than that in the summer‐fall period because of the less negative WSC. Quasi‐monthly variations were related to SSH on the Chukchi Shelf owing to the negative WSC. HYCOM outputs from 1994 to 2015 showed that the AW boundary current weakened more recently than in the past due to the increased melting of sea ice. The results imply that a longer sea‐ice‐free season in the Arctic amplifies changes in the AW boundary current and deep ocean temperature owing to increased atmospheric forcing. Plain Language Summary: Atlantic Water (AW) entering the Arctic Ocean from the Nordic Seas is considered a heat reservoir because it is warmer than the Arctic Ocean. The AW flows along the boundaries around the basin margins, known as the AW boundary current. The AW boundary current gradually deepened after entering and sat at approximately 200–800 m near the Chukchi slope. The AW boundary current exhibited quasi‐seasonal and quasi‐monthly (approximately 28 days) variations, confirmed using near‐bottom temperature data and data‐assimilated Hybrid Coordinate Ocean Model outputs. The variations are due to the geostrophic current caused by the pressure gradient due to the difference in the sea surface height (SSH) between the Chukchi Shelf and Canada Basin, which are located in the southwest and northeast of the Chukchi slope, respectively. Due to the difference in the SSH around the Chukchi slope, the geostrophic current is in the opposite direction to the AW boundary current and can suppress it. Sea surface height is affected by wind stress curl, and sea ice dampens atmospheric forcing. These findings imply that a longer sea‐ice‐free season in the Arctic can amplify changes in the AW boundary current. Key Points: The near‐bottom temperature observed at a depth of ∼1,300 m near the Chukchi slope showed quasi‐seasonal and quasi‐monthly variationsThe variations are related to the wind‐induced change in intensity of the Atlantic Water (AW) boundary current along the Chukchi slopeHYCOM outputs showed a more common occurrence of weaker AW boundary currents when sea ice melted compared to that in the past [ABSTRACT FROM AUTHOR]

The chemistry of H2O, CO, and other small molecular species in an isolated pre-stellar core, L1544, has been assessed in the context of a comprehensive gas-grain chemical model, coupled to an empirically constrained physical/dynamical model. Our main findings are (i) that the chemical network remains in near equilibrium as the core evolves towards star formation and the molecular abundances change in response to the evolving physical conditions. The gas-phase abundances at any time can be calculated accurately with equilibrium chemistry, and the concept of chemical clocks is meaningless in molecular clouds with similar conditions and dynamical time-scales, and (ii) A comparison of the results of complex and simple chemical networks indicates that the abundances of the dominant oxygen and carbon species, H2O, CO, C, and C+ are reasonably approximated by simple networks. In chemical equilibrium, the time-dependent differential terms vanish, and a simple network reduces to a few algebraic equations. This allows rapid calculation of the abundances most responsible for spectral line radiative cooling in molecular clouds with long dynamical time-scales. The dust ice mantles are highly structured and the ice layers retain a memory of the gas-phase abundances at the time of their deposition. A complex (gas-phase and gas-grain) chemical structure therefore exists, with cosmic-ray induced processes dominating in the inner regions. The inferred H2O abundance profiles for L1544 require that the outer parts of the core and also any medium exterior to the core are essentially transparent to the interstellar radiation field. [ABSTRACT FROM AUTHOR]

Since the installation at the Antarctic Jang Bogo Station (JBS) in 2017, Korea Polar Research Institute (KOPRI) has been operating the Vertical Incidence Pulsed Ionospheric Radar (VIPIR) equipped with Dynasonde analysis (JVD). The two‐dimensional ion velocity is one of the key ionospheric parameters obtained from the JVD. The ionospheric ion velocities are compared with simultaneous, but independent, measurements of the Doppler velocity obtained from SuperDARN East radar at Dome C. The JVD ion velocity vector is projected to the line‐of‐sight direction of the SuperDARN observation over the JBS to be directly compared with each other. The result of comparison shows a reasonable agreement with the correlation coefficient of 0.72. The linear regression coefficient of about 0.5 represents that the JVD ion velocity is generally smaller than the SuperDARN observations by the regression coefficient, which may result from the different height ranges of the measurements. It is also found that the correlation coefficient increases with increasing magnetic activity (Kp), which suggests that the small‐scale ionospheric density irregularities tend to move with large‐scale plasma motion that is driven by enhanced plasma convection with increasing Kp. Plain Language Summary: The ion drift velocity in the polar ionosphere is one of the key parameters for understanding not only the dynamics of the ionosphere but also the magnetosphere‐ionosphere coupling processes and the magnetospheric energy transfer to the neutral atmosphere via ion‐neutral interactions. There are several ground‐based observational techniques to monitor the ion velocities in the polar region. For example, the incoherent scatter radars (ISRs) can determine the ion motion in the polar region, but usually require expensive resources for their maintenance and operation, which makes them affordable only to large organizations or international consortiums such as EISCAT. Another widely utilized observational system for the ion velocities in the polar region is the SuperDARN radars but they are relatively scarce in Antarctica. The most affordable technique for monitoring the ionosphere is the ionospheric sounding systems capable of observing not only the ionospheric densities but also the ion velocities in the bottomside ionosphere. An advanced sounding system has been operated at Jang Bogo Station in Antarctica since 2017 to produce ionospheric parameters including ion density and velocities. The observed ion velocities are compared with simultaneously observed SuperDARN ion velocities over the JBS and we discuss similarities and differences between the two measurements. Key Points: Validation of Dynasonde analysis (JVD) ion drift velocities by using simultaneous but independent SuperDARN observationsJVD ion velocities are generally in a good agreement with SuperDARN radar observationsSmall‐scale ionospheric density irregularities tends to move with large‐scale plasma contours as the geomagnetic activity increases [ABSTRACT FROM AUTHOR]

There is considerable interest in developing quantitative methods for analyzing present‐day fluvial landscapes with a view to extracting information about tectonic forcing and drainage evolution, together with the influence of lithologic substrates and of paleoclimatic variations. In view of the multifactorial nature of this complex problem, it has previously been proposed that natural geomorphic experiments could play a significant role in developing a quantitative understanding of landscape growth and decay. Here, we describe and analyze a stacked sequence of five buried transient landscapes that punctuate marine strata along the fringes of the North Atlantic Ocean. We propose that these landscapes constitute a suite of natural experiments, which illuminate significant aspects of quantitative fluvial geomorphology. Our preliminary analysis of four of these buried landscapes suggests that the amplitude of external tectonic forcing plays a significant role in fluvial landscape evolution. In future, we hope that this suite of natural experiments will be further exploited by the fluvial community with a view to identifying the most appropriate analytical techniques. Plain Language Summary: Uplifting surfaces of the Earth are sculpted by erosion which is controlled by river drainage processes. Understanding exactly how these processes operate is difficult because so many different factors can vary. For example, the rock surface can be hard or soft, the rate at which water flows along river channels depends upon changing climate, and landscapes are strongly affected by up‐and‐down movements caused by hot and cold currents within the Earth's interior. Recently, we have discovered spectacular ancient landscapes that lie buried deep beneath the Earth's surface. These hidden landscapes were spotted using a sophisticated form of echo sounding and they show that ancient drainage patterns are strikingly similar to present‐day patterns. These uniquely preserved landscapes are large‐scale natural experiments, which can help us to understand how modern landscapes evolve. Key Points: Stacked sequence of five buried landscapes is described and analyzedLongitudinal river profiles are extracted and successfully matched by inverse modeling based upon generalized version of stream power lawThese natural geomorphic experiments will aid studies of fluvial processes [ABSTRACT FROM AUTHOR]

The influence of supraglacial debris cover on glacier mass balance in the Karakoram is noteworthy. However, understanding of how debris cover affects the seasonal and long-term variations in glacier mass balance through alterations in the glacier's energy budget is incomplete. The present study coupled an energy–mass balance model with heat conduction within debris layers on debris-covered Batura Glacier in Hunza Valley to demonstrate the influence of debris cover on glacial surface energy and mass exchanges during 2000–2020. The mass balance of Batura Glacier is estimated to be -0.262±0.561 m w.e. yr -1 , with debris cover accounting for a 45 % reduction in the negative mass balance. Due to the presence of debris cover, a significant portion of incoming energy is utilized for heating debris, leading to a large energy emission to the atmosphere via thermal radiation and turbulent sensible heat. This, in turn, reduces the melt latent heat energy at the glacier surface. We found that the mass balance exhibits a pronounced arch-shaped structure along the elevation gradient, which is associated with the distribution of debris thickness and the increasing impact of debris cover on the energy budget with decreasing elevation. Through a comprehensive analysis of the energy transfer within each debris layer, we have demonstrated that the primary impact of debris cover lies in its ability to modify the energy flux reaching the surface of the glacier. Thicker debris cover results in a smaller temperature gradient within debris layers, consequently reducing energy reaching the debris–ice interface. Over the past 2 decades, Batura Glacier has exhibited a trend towards less negative mass balance, likely linked to a decrease in air temperature and reduced ablation in areas with thin or sparse debris cover. [ABSTRACT FROM AUTHOR]

The structure and distribution of sub-glacial water directly influences Antarctic ice mass loss by reducing or enhancing basal shear stress and accelerating grounding line retreat. A common technique for detecting sub-glacial water involves analyzing the spatial variation in reflectivity from an airborne radar echo sounding (RES) survey. Basic RES analysis exploits the high dielectric contrast between water and most other substrate materials, where a reflectivity increase ≥ 15 dB is frequently correlated with the presence of sub-glacial water. There are surprisingly few additional tools to further characterize the size, shape, or extent of hydrological systems beneath large ice masses. We adapted an existing radar backscattering simulator to model RES reflections from sub-glacial water structures using the University of Texas Institute for Geophysics (UTIG) Multifrequency Airborne Radar Sounder with Full-phase Assessment (MARFA) instrument. Our series of hypothetical simulation cases modeled water structures from 5 to 50 m wide, surrounded by bed materials of varying roughness. We compared the relative reflectivity from rounded Röthlisberger channels and specular flat canals, showing both types of channels exhibit a positive correlation between size and reflectivity. Large (> 20 m), flat canals can increase reflectivity by more than 20 dB , while equivalent Röthlisberger channels show only modest reflectivity gains of 8–13 dB. Changes in substrate roughness may also alter observed reflectivity by 3–6 dB. All of these results indicate that a sophisticated approach to RES interpretation can be useful in constraining the size and shape of sub-glacial water features. However, a highly nuanced treatment of the geometric context is necessary. Finally, we compared simulated outputs to actual reflectivity from a single RES flight line collected over Thwaites Glacier in 2022. The flight line crosses a previously proposed Röthlisberger channel route, with an obvious bright bed reflection in the radargram. Through multiple simulations comparing various water system geometries, such as canals and sub-glacial lakes, we demonstrated the important role that topography and water geometry can play in observed RES reflectivity. From the scenarios that we tested, we concluded the bright reflector from our RES flight line cannot be a Röthlisberger channel but could be consistent with a series of flat canals or a sub-glacial lake. However, we note our simulations were not exhaustive of all possible sub-glacial water configurations. The approach outlined here has broad applicability for studying the basal environment of large glaciers. We expect to apply this technique when constraining the geometry and extent of many sub-glacial hydrologic structures in the future. Further research may also include comprehensive investigations of the impact of sub-glacial roughness, substrate heterogeneity, and computational efficiencies enabling more complex and complete simulations. [ABSTRACT FROM AUTHOR]

The article presents the results of studies of bottom landscapes carried out with the use of an echo sounder with a side-scan location function and supplemented by video filming from an underwater vehicle in a bay of one of the islands in the northern skerry area of Lake Ladoga in June 2022. The results of the echo sounding were used to develop a three-dimensional bathymetric model of the examined Haukaisenlahti Bay on Kukhka Island and to identify significant differences in comparison with published navigation maps for Haukaisenlahti Bay. The formation of the bed topography and the state of the shores in both above-water and underwater zones are determined by the specific features of the geological structure of this part of the water area, resulting from the different resistance to weathering processes in different geological formations. Six main types of facies were identified in the underwater landscape of the bay. The outlook and the change of facies are associated with the presence of hard rocky surfaces and hard clastic material followed by loose soils at greater depths. The outlook of the facies is also determined by the specific features of the bathymetric structure of the bay and the predominance of various associations of living organisms, the development of which depends on the type of surface and soil. The study confirmed the prospects of the use of echo sounders with a side-scan location function to study and map underwater landscapes of Lake Ladoga in combination with a remote video recording from an uninhabited vehicle. [ABSTRACT FROM AUTHOR]

Antarctic silverfish (Pleuragramma antarcticum) play a crucial intermediary role in connecting top predators and krill in the food web of the Antarctic Ocean. Despite their crucial role, research on their abundance is lacking. In this study, we estimated the abundance of juvenile Antarctic silverfish as foundational data for predicting their abundance. The density of juvenile Antarctic silverfish was estimated using an acoustic backscattering theoretical model. The mean volume backscattering strength was used to investigate the vertical and horizontal distributions of juvenile Antarctic silverfish in the Antarctic Ross Sea. The survey area was located near Cape Hallett, Antarctica, where Antarctic krill (Euphausia superba), ice krill (E. crystallorophias), and Antarctic silverfish coexist. The survey was performed four times using the Korean Antarctic research ship, RV Araon (R/V, 7507 GT). Frame trawls were conducted to identify the length and weight of the target fish species in the survey area. Captured Antarctic silverfish captured measured 3–9 cm. The maximum target strength (TS) was −92.93 dB at 38 kHz, −86.63 dB at 120 kHz, and 85.89 dB at 200 kHz. The average TS was −100.00 dB at 38 kHz, −93.00 dB at 120 kHz, and −106.90 dB at 200 kHz. Most juvenile Antarctic silverfish were found at a depth of 100 m and were distributed closer to sea ice. Between nearshore and polynya waters, the fish demonstrated a proclivity for polynya waters. [ABSTRACT FROM AUTHOR]

Accelerated bridge construction (ABC) has been widely used in the United States since the late 1990s following a national ABC initiative by the Transportation Research Board (TRB) in 1996. The press-brake-formed tub girder (PBFTG) system is one of the innovative bridge systems that has been developed recently for the accelerated construction of simple and short span bridges. The PBFTG shape is optimized to achieve the maximum structural capacity and torsional stiffness due to the distribution of the steel around the centroid of the shape, a major limitation in conventional W-shape and plate I-girders. Despite the promising advantages of PBFTG systems, it received less attention than conventional superstructure systems, especially when dealing with their live load distribution factors (LLDFs). Stemmed from these limitations, LLDFs for moment and shear of one and multiple design-loaded lanes for exterior and interior beams in PBFTG bridges are computationally investigated. More than 190 bridges are modeled using a validated finite-element (FE) approach to cover a wide range of geometric parameters of PBFTG bridges, including spacing between beams (S), bridge span (L), skew angle (θ), and number of lanes (NL). Detailed FE models show that LLDFs of PBFTG bridges are highly dependent on the selected geometric parameters. A regression analysis is performed leading to a new proposed set of equations for studies showing that the LLDFs of PBFTG bridges are highly dependent on the selected geometric different types of LLDFs for fascia and interior beams in PBFTG bridges. The results of the parametric study suggest that the current AASHTO equations are unconservative for both single lane and multilane moment and shear LLDFs for fascia and interior PBFTGs compared with proposed equations (except for single lane moment LLDFs of interior beams). [ABSTRACT FROM AUTHOR]

The thermal expansion occurring when a laser beam is incident on the surface of a solid can be used to excite ultrasonic waves in the solid medium, without causing damage to the material. The resulting wavefield is characterized by a dominant shear wave and a weak compressional wave. This Letter demonstrates the possibility of generating a dominant compressional wavefield by coating the surface with a layer of clear ice. This is achieved by exploiting a minimum in the attenuation spectrum of light in ice, which occurs at around 500 nm and renders the coating transparent to green laser radiation. Ice coatings could, therefore, provide a path for the development of more sensitive laser-based nondestructive testing methods that have traditionally been affected by the poor excitability of compressional waves, especially along the direction orthogonal to the surface. [ABSTRACT FROM AUTHOR]

Plastic pollution has become an enormous environmental problem, endangering ecosystems, livelihoods, safety and human health. Large quantities of plastics are trapped in or transported by rivers. Monitoring methods mostly focus on plastics floating at the surface or deposited on riverbanks, while a substantial part of plastics may be transported below the water surface. Available underwater monitoring methods rely on nets and large equipment, making them labour-intensive, expensive and invasive. The measurements are, therefore, limited to occasional point measurements. In this paper, we explore the potential of echo sounding for the monitoring of suspended macroplastic (plastic items bigger than 5 mm). We performed tests in a controlled (basin), a semi-controlled (harbour) and an uncontrolled (river) environment using the high-end Acoustic Doppler Current Profiler (ADCP). This device is already in use for the estimation of flow velocity and suspended sediment concentrations using the wide network of ADCPs in the Netherlands and other countries. In the undisturbed controlled environment, 25 items varying in size, material, and orientation could be detected up to at least 4.6 m from the ADCP. The semi-controlled experiments showed that most of these items can also be detected among other naturally occurring scatterers, such as aquatic life, organic material and air bubbles. The field tests under natural conditions, combining ADCP and net measurements, showed that ADCP data can be calibrated towards a correct order of magnitude estimate of plastic transport. The coupling of the ADCP data to item characteristics such as size, material and orientation is still challenging, but more research into, for example, the signature of items may enable distinguishing item characteristics. This fundamental knowledge, combined with repetitions of validated field measurements under different flow conditions, is needed for the development of a robust monitoring method. Such a method may enable continuous or cross-sectional monitoring of suspended plastics and give insight into historic and plastic transport through 30-year long datasets. These insights can help improve and determine the effect of current mitigation and cleaning efforts. [ABSTRACT FROM AUTHOR]

Submarine volcano 8.10, which is part of the South Iturup group of submarine volcanoes in the Kuril Island Arc (KIA), was studied using a proven technology of quantitative interpretation of hydromagnetic survey materials in combination with echo sounding, continuous seismoacoustic profiling, and analysis of petromagnetic properties and chemical composition of dredged rocks. The technology makes it possible to interpret directly from the original data without resorting to the procedure of their preliminary restoration in the nodes of a regular grid. The studies found that dredged andesite-basalts and andesites are representatives of different lava flows that have a single magma source but differ in the conditions and dynamics of crystallization. The main carrier of the natural residual magnetization of andesite-basalts is titanomagnetite with low Ti content and that for andesites is magnetite. Feeding channels and peripheral magma chambers are identified in the volcanic edifice. Submarine volcano 8.10 and other studied KIA volcanoes formed during geomagnetic inversions. The presence of hydroacoustic anomalies at the top of the volcano indicates that manifestations of underwater gas-hydrothermal activity in the southern part of the KIA are more significant than was thought until recently. [ABSTRACT FROM AUTHOR]

We have investigated the static and dynamic behavior of "pseudo-3D" trilayer square artificial spin ice structures. The trilayer stack comprises of two ferromagnetic Ni81Fe19 (Permalloy, Py) layers with 30 and 70 nm thickness, separated by a nonmagnetic copper layer of varying thickness from 2 to 40 nm. We show that the copper thickness enables interlayer coupling between layers to be finely controlled, leading to bespoke magnetization states and resonance spectra tuning. Our results demonstrate a further route to control the interaction in artificial spin ices beyond planar structures, enabling tunable magnetization dynamics, a potentially programmable degree of freedom for magnonic and microwave devices. [ABSTRACT FROM AUTHOR]

Side-scan sonar is designed and used for a variety of survey work, in both military and civilian fields. These systems provide acoustic imageries that play a significant role in a variety of marine and inland applications. For this reason, it is extremely important that the recorded sonar image is characterized by high resolution, detail and sharpness. This article is mainly aimed at the demonstration of the impact of side-scan sonar resolution on the imaging quality. The article also presents the importance of acoustic shadow in the process of analyzing sonar data and identifying underwater objects. The real measurements were carried out using two independent survey systems: hull-mounted sonar and towed side-scan sonar. Six different shipwrecks lying in the Baltic Sea were selected as the objects of research. The results presented in the article also constitute evidence of how the sonar technology has changed over time. The survey findings show that by maintaining the appropriate operational conditions and meeting several requirements, it is possible to obtain photographic-quality sonar images, which may be crucial in the process of data interpretation and shipwreck identification. [ABSTRACT FROM AUTHOR]

Tiny cryoconite holes are commonly found on glacier surfaces. Despite a long history of research on them, their influence on glacier‐scale mass balance and runoff are not well understood. We model the absorption of solar radiation at the bottom of cylindrical cryoconite holes, incorporating the three‐dimensional geometry. The simulated holes achieve a limiting steady‐state depth, where the daily melt rate at the bottom of the holes matches that at the glacier surface. This implies a feedback loop restricting the excess ice melt due to the presence of dark supraglacial impurities. The modeled steady‐state depth scales approximately linearly with the radius, consistent with in situ observations at several glaciers across the world. Given the areal coverage and radius distribution of cryoconite holes on a glacier, this scaling yields first‐order estimates of their melt contribution. Plain Language Summary: Dark particles deposited on glacier surfaces absorb more solar radiation than the surrounding ice, and melt into the surface to create approximately cylindrical holes with a layer of dark "cryoconite" substance at their bottom. Such cryoconite holes are commonly seen on glacier surfaces all over the world. These holes continue to deepen, reducing the exposure of the dark cryoconite to solar radiation, and eventually leading to a steady‐state depth. We combine modeling and in situ observations to show that the steady depth is approximately proportional to the radius of the hole. This simple geometric property proves useful in estimating the net contribution of all the cryoconite holes present on a glacier to its mass balance and runoff. Our estimates suggest that these holes efficiently negate the melt‐enhancing effects of the dark impurities on glacier surface. Key Points: Effects of shortwave radiation on cryoconite holes modeled in three dimensionsUnder steady clear‐sky conditions, cryoconite holes deepen up to a steady depth which scales with radiusThis depth‐diameter scaling yields estimates of cryoconite‐hole contribution to glacier mass balance [ABSTRACT FROM AUTHOR]

Multiple autonomous underwater vehicles (AUVs) have gradually become the trend in underwater operations. Identifying and detecting these new underwater multi-targets is difficult when studying underwater moving targets. A 28-element transducer is used to test the echo of multiple AUVs with different layouts in a lake. The characteristics of the wideband echo signals are studied. Under the condition that the direction of arrival (DOA) is not known, an autofocus coherent signal subspace (ACCSM) method is proposed. The focusing matrix is constructed based on the received data. The spatial spectrum of the array signal of multiple AUVs at different attitudes is calculated. The algorithm estimates the DOA of the echo signals to overcome the shortcomings of traditional wideband DOA estimation and improve its accuracy. The results show that the highlights are not only related to the number of AUVs, but are also modified by scale and attitude. The contribution of the microstructure of the target in the overall echo cannot be ignored. Different parts of the target affect the number of highlights, thus resulting in varying numbers of highlights at different attitude angle intervals. The results have significant implications for underwater multi-target recognition. [ABSTRACT FROM AUTHOR]

During the 2022/23 Antarctic summer, eight pico balloon flights were deployed from Neumayer Station III (70.6666°S, 8.2667°W), yielding valuable insights into the Antarctic stratospheric wind structure. Pico balloons maintain a lower altitude compared to larger superpressure balloons, floating between 9 and 15 km MSL. The most impressive flight lasted an astounding 98 days, completing eight circumnavigations of the Southern Hemisphere. Throughout the flights, pico balloons encountered diverse air masses, displaying zonal velocities ranging from −50 to 250 km h−1 and meridional velocities between ±100 km h−1. Total wind speeds observed were extensive, spanning from 2.0 to 270 km h−1. A significant finding revealed that lower-flying pico balloons could rise due to convection underneath the flight paths, influenced by high convective available potential energy environments, resulting in changes to the balloons' float density. Moreover, the flights demonstrated that pico balloons tended to drift farther south compared to larger stratospheric balloons, with some balloons reaching up to 8° south of the equator and 2° from the South Pole. This article explores the pressure-testing process and deployment techniques for pico balloons, showcasing their transformation from inexpensive party balloons (costing less than $20) into efficient superpressure balloons. The logistical demands for pico balloon flights were minimal, with a single person transporting all materials for the balloons (excluding lifting gas) to the Antarctic continent in carry-on luggage. The authors aim to promote the application of pico balloons to a wider scientific community by demonstrating their usefulness. Significance Statement: Pico balloons are small party-sized balloons that are capable of floating at lower altitudes than traditional superpressure balloons. In Antarctica, where research is challenging due to harsh weather and limited resources, pico balloons present an affordable and easy-to-deploy alternative to traditional research methods. By studying the distinctive wind patterns at lower altitudes around Antarctica, pico balloons can provide valuable insights into this remote region. By demonstrating the potential use of pico balloons for scientific purposes, this study aims to offer the atmospheric community a new method of conducting research on a global scale. [ABSTRACT FROM AUTHOR]

Port is one of the transportation networks that connect sea and land transportation. Thus, it can be ensured that there are many activities closely related to port such as planning, implementation, and maintenance. One of the port maintenance activities is dredging. The sea current that is always moving carries sediment towards the port causing sedimentation in the port pool area and preventing the ship from grounding. Maintenance dredging is required to remove sediment deposits in the pool port to maintain the safety depth. Before dredging, the parameter that has to be considered is the sediment type and its thickness in the area of interest. The study utilized underwater acoustic remote sensing instruments such as Sub Bottom Profiler, Side Scan Sonar, and Multibeam Echosounder to determine the type and thickness of sediments in the port pool. The validation process for the sediment types and the Standard Penetration Test value are derived from the soil investigation data. There are six borehole points at the research location which have a Standard Penetration Test value. The research location is in a shallow water area with depth values ranging from 0.5 m to 7.0 m with respect to Low Water Spring. Based on the SSS image interpretation, the research location is dominated by sediment type of clay. The area of interest is 30541.29 m² and the total volume of the sediment thickness is 82326.7 m³ with respect to the depth design. This sediment volume is dominated by the soft sediment with the volume of 79614.8 m³. The couple of underwater acoustic remote sensing and soil investigation can provide a continuous representation of the sediment thickness and an essential reference for future research on the estimation of sediment volume in the port pool. [ABSTRACT FROM AUTHOR]

Crevasses pose severe risks for mountaineers and field glaciologists. Smaller cracks between 0.5 and 2 m are still dangerous, but often not visible in medium resolution satellite imagery. If they are snow covered, they are completely undetectable by optical sensors. We set out to develop an approach to detect potentially crevassed areas by a minimum of geometric data, and to make the method generally applicable to glacier regions. On Vernagtferner, we compared a reference dataset of crevasses observed in high-resolution optical imagery with the curvature of the ice surface and the spatial gradients in driving stress. Both parameters can be derived from a digital surface model and a bedrock model, derived from ice thickness measurements. The correlation patterns show that crevasses preferably form in convex areas and in areas where the driving stress rapidly increases. This corresponds with the theory of crevasse formation. Although the method still misclassifies larger parts, the approach has the potential to define probable non-crevassed areas as well as to aid the planning of safe routes. [ABSTRACT FROM AUTHOR]

This research was conducted to study length–weight relationships (LWR) and condition factors of six Antarctic notothenioidei fish species including blackfin icefish (Chaenocephalus aceratus), single-angle icefish (Chionodraco hamatus), marbled rockcod (Notothenia rossii), black rockcod (Notothenia coriiceps), emerald rockcod (Trematomus bernacchii), and dusky rockcod (Trematomus newnesi) from the King Sejong Station on King George Island and Jang Bogo Station on the Northern Victoria Land. A total of 232 specimens were collected by fishing on the icebreaking research vessel ARAON from December 2020 to February 2021. The LWR parameters and condition factors differed depending on species, which can be affected by their distribution, species characteristics, and gravidity status. The exponent b values in LWR (W = aLb) ranged from 2.593 to 5.184. Four species including C. aceratus, C. hamatus, N. rossii, and T. bernacchii followed positive allometric growth, T. newnesi followed negative allometric growth, and only N. coriiceps showed isometric growth. These results can be helpful in understanding the ecological and growth conditions of six fish species living in the Antarctic Ocean, providing more information for future research on Antarctic fish. [ABSTRACT FROM AUTHOR]

Radio Echo Sounding (RES) surveys conducted in May 2010 and April 2011 revealed a 2 km2 flat area with increased bed reflectivity at the base of Isunnguata Sermia at the western margin of the Greenland Ice Sheet. This flat reflector was located within a localized subglacial hydraulic potential (hydropotential) minimum, as part of a complex and elongated trough system. By analogy with comparable features in Antarctica, the initial interpretation of such a feature was a potential subglacial lake. In September 2013 a co‐located seismic survey revealed a 1,750 m by 540 and 37 m thick stratified lens‐shaped bedform at the base of a subglacial trough system. Amplitude Versus Angle (AVA) analysis yields a derived reflection coefficient R = 0.09 ± 0.14 indicative of consolidated sediments possibly overlain by dilatant till. The bed and flank on the northern side of the trough consist of unconsolidated, possibly water‐bearing sediments with R = −0.10 ± 0.08, whereas on the southern side it consists of more consolidated material. We interpret the trough as a key component of the wider subglacial drainage network, for which the sediments on its northern side act as a localized water‐storage reservoir. Given the observation of seasonally forming and rapidly draining supraglacial meltwater lakes in this area, we interpret the lens‐shaped bedform as deposited by episodically ponding meltwater within the subglacial trough system. Our results highlight the importance of transient subglacial hydrological and sedimentological processes such as drainage events for the interaction of ice sheets and their substrates, to understand ice dynamics in a warming climate. Plain Language Summary: A ground based radar survey in West Greenland showed an unusually flat, highly reflective zone in an otherwise rough bed suggesting a possible subglacial lake beneath the ice. The highly reflective zone was part of a drainage system transporting meltwater under the ice sheet. We performed a detailed seismic survey across the area which, unlike radar signals, has the advantage of penetrating through the overlying ice into any rock, sediments and water below it. Analysis of our reflection data reveal that the flat area was in fact an elongated lens‐shaped bedform consisting of layered (stratified) sediments. However at a larger angle of incidence, analysis showed the bedform is possibly overlain by a thin layer of water‐bearing sediments likely saturated by ponding water. Our interpretation is that episodically draining meltwater from upstream is locally accumulating beneath the ice sheet at this locality, thereby depositing the lens‐shaped bedform over many melt seasons. Key Points: Seismic data show that a subglacial lake implied by high reflectivity in radar data is in fact a lens‐shaped sediment bedformSeismic reflectivity analysis suggests the lens‐shaped bedform is possibly overlain by a thin layer of water‐bearing sedimentsThe subglacial bedform is stratified and likely deposited through episodically ponding of upstream derived meltwater [ABSTRACT FROM AUTHOR]

The future vehicle‐to‐everything (V2X) scenarios greatly call for reliable and efficient communication links between roadside units (RSUs) and vehicles. Integrated sensing and communication (ISAC) represents one of the key candidate technologies for 6G, which provides new solutions for this problem. In this paper, the beam tracking design for V2X communication is investigated by exploiting the ISAC technique, where the RSU uses the echoes of the ISAC signals to estimate the motion parameters of the vehicles. Compared with traditional feedback‐based beam tracking, the proposed method can reduce the overall signaling costs and improve communication robustness. Furthermore, to achieve high accuracy and low latency for beam alignment, a Trajectory Adaptive Unscented Kalman Filter (TA‐UKF) beam tracking algorithm is proposed, which obtains the optimal state transition model following the change of the vehicle state. Considering practical application scenarios, an ISAC‐based adaptive beam coverage (ISAC‐AC) scheme is further developed for the beam tracking of extended targets, which can achieve the beam misalignment of vehicles in practical scenarios. Numerical results demonstrate that the proposed beam tracking and coverage strategies outperform baseline approaches. [ABSTRACT FROM AUTHOR]

Plastic pollution has become an enormous environmental problem, endangering ecosystems, livelihoods, safety and human health. Large quantities of plastics are trapped in or transported by rivers. Monitoring methods mostly focus on plastics floating at the surface or deposited on riverbanks, while a substantial part of plastics may be transported below the water surface. Available underwater monitoring methods rely on nets and large equipment, making them labour-intensive, expensive and invasive. The measurements are, therefore, limited to occasional point measurements. In this paper, we explore the potential of echo sounding for the monitoring of suspended macroplastic (plastic items bigger than 5 mm). We performed tests in a controlled (basin), a semi-controlled (harbour) and an uncontrolled (river) environment using the high-end Acoustic Doppler Current Profiler (ADCP). This device is already in use for the estimation of flow velocity and suspended sediment concentrations using the wide network of ADCPs in the Netherlands and other countries. In the undisturbed controlled environment, 25 items varying in size, material, and orientation could be detected up to at least 4.6 m from the ADCP. The semi-controlled experiments showed that most of these items can also be detected among other naturally occurring scatterers, such as aquatic life, organic material and air bubbles. The field tests under natural conditions, combining ADCP and net measurements, showed that ADCP data can be calibrated towards a correct order of magnitude estimate of plastic transport. The coupling of the ADCP data to item characteristics such as size, material and orientation is still challenging, but more research into, for example, the signature of items may enable distinguishing item characteristics. This fundamental knowledge, combined with repetitions of validated field measurements under different flow conditions, is needed for the development of a robust monitoring method. Such a method may enable continuous or cross-sectional monitoring of suspended plastics and give insight into historic and plastic transport through 30-year long datasets. These insights can help improve and determine the effect of current mitigation and cleaning efforts.

In the mountain terrain, ice holes are little depressions between rock boulders that are characterized by the exit of cold air able to cool down the rock surface even in summer. This cold air creates cold microrefugia in warmer surroundings that preserve plant species probably over thousands of years under extra-zonal climatic conditions. We hypothesized that ice hole populations of the model species Vaccinium vitis-idaea (Ericaceae) show genetic differentiation from nearby zonal subalpine populations, and high functional trait distinctiveness, in agreement with genetic patterns. We genotyped almost 30,000 single nucleotide polymorphisms using restriction site-associated DNA sequencing and measured eight functional traits indicative of individual performance and ecological strategies. Genetic results showed high differentiation among the six populations suggesting isolation. On siliceous bedrock, ice hole individuals exhibited higher levels of admixture than those from subalpine populations which could have experienced more bottlenecks during demographic fluctuations related to glacial cycles. Ice hole and subalpine calcareous populations clearly separated from siliceous populations, indicating a possible effect of bedrock in shaping genetic patterns. Trait analysis reflected the bedrock effect on populations' differentiation. The significant correlation between trait and genetic distances suggests the genetic contribution in shaping intraspecific functional differentiation. In conclusion, extra-zonal populations reveal a prominent genetic and phenotypic differentiation determined by history and ecological contingency. Therefore, microrefugia populations can contribute to the overall variability of the species and lead to intraspecific-driven responses to upcoming environmental changes. [ABSTRACT FROM AUTHOR]

The dynamics of the Greenland Ice Sheet are affected by surface meltwater reaching the base of the ice, altering ice contact with the bedrock. Lack of understanding of this evolution hampers the ability to predict the effects of increasing temperatures on the Greenland Ice Sheet mass balance. Here we present a unique high-resolution study of ice velocity response to surface melting based on data from a COSMO-SkyMed satellite campaign over Upernavik Isstrøm (Northwest Greenland) for two months around the end of the 2014 melt season. We show that the velocity variations, due to both short-term (days) and seasonal variations in surface melt rates, are increasing in relative strength farther from the glacier terminus. Furthermore, we observe how ice dynamic response to frontal retreat, reaching several kilometres inland, can obscure the meltwater-induced velocity change close to the terminus. Future studies should consider the flow velocity dependence on the distance to the terminus, and local geometry, to distinguish subglacial hydrologic system changes from frontal processes and local basal conditions. [ABSTRACT FROM AUTHOR]

Over the last few years, due to various climatic, anthropogenic, and environmental factors, a large amount of submerged heritage has been unearthed and exposed to deterioration processes in the Bay of Algeciras. These impacts can be more severe in shallow waters, where the cultural heritage is more vulnerable to natural and human-induced impacts. This makes it urgent to document cultural heritage at risk of disappearing using different techniques whose efficiencies in the archaeological record need to be determined and compared. For this purpose, we have documented a shipwreck in the Bay of Algeciras using two techniques: photogrammetry and a multibeam echosounder. The photogrammetric method consists of obtaining a 3D model from numerous photographs taken of an object or a site. The processing software creates three-dimensional points from two-dimensional points found in the photographs that are equivalent to each other. Multibeam echosounders are capable of providing side scan imagery information in addition to generating contour maps and 3D perspectives of the surveyed area and can be installed in an unmanned surface vehicle. As a result, we have obtained two 3D visualisations of the shipwreck, i.e., digital copies, that are being used both for the analysis of its naval architecture and for its dissemination. Through the comparison of the two techniques, we have concluded that while a multibeam echosounder provides a detailed digital terrain model of the seabed, photogrammetry performed by divers gives the highest resolution data on objects and structures. In conclusion, our results demonstrate the benefits of this combined approach for accurately documenting and monitoring shipwrecks in shallow waters, providing valuable information for conservation and management efforts. [ABSTRACT FROM AUTHOR]

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Mars Environmental Dynamics Analyzer instrument, on board NASA's Mars 2020 Perseverance rover, includes a number of sensors to characterize the Martian atmosphere. One of these sensors is the Radiation and Dust Sensor (RDS) that measures the solar irradiance at different wavelengths and geometries. We analyzed the RDS observations made during twilight for the period between sol 71 and 492 of the mission (Ls 39°–262°, Mars Year 36) to characterize the clouds over the Perseverance rover site. Using the ratio between the irradiance at zenith at 450 and 750 nm, we inferred that the main constituent of the detected high‐altitude aerosol layers was ice from Ls = 39°–150° (cloudy period), and dust from Ls 150°–262°. A total of 161 twilights were analyzed in the cloudy period using a radiative transfer code and we found: (a) signatures of clouds/hazes in the signals in 58% of the twilights; (b) most of the clouds had altitudes between 40 and 50 km, suggesting water ice composition, and had particle sizes between 0.6 and 2 µm; (c) the cloud activity at sunrise is slightly higher that at sunset, likely due to the differences in temperature; (d) the time period with more cloud detections and with the greatest cloud opacities is during Ls 120°–150°; and (e) a notable decrease in the cloud activity around aphelion, along with lower cloud altitudes and opacities. This decrease in cloud activity indicates lower concentrations of water vapor or cloud condensation nuclei (dust) around this period in the Martian mesosphere. Plain Language Summary: During twilight, ground‐based observations of the irradiance allows the detection and characterization of high‐altitude clouds (above 30–35 km). Because the sun is at or below the horizon, the cloud layers reflect the direct light that only reaches the higher parts of the atmosphere, producing an increase in the sky brightness with respect to the cloud‐free scenario. Moreover, the decrease in the intensity with the solar zenith angle highly depends on the cloud altitude and density. Using observations made by the Radiation and Dust Sensor, part of the instrument Mars Environmental Dynamics Analyzer on board Perseverance rover, we present here a study of the twilight clouds detected at the Perseverance landing site for the first 490 sols of the mission (Mars Year 36). By modeling the irradiance at 450 and 950 nm with radiative transfer simulations, we constrained the cloud altitude, opacity, and particle radius. The number of twilights analyzed allowed us to study the seasonal trend in the cloud activity. During the cloudy period, Ls 39°–150°, we find a significant decrease in the cloud activity above 30–35 km around aphelion (Ls ∼ 70°). This implies that the seasonal distribution of clouds above 30–35 km differs from that observed at lower altitudes. Key Points: Most of the cloud detected at twilight between sol 71 and 492 of the Mars 2020 mission (Ls 39°–262°) occurred at altitudes between 40 and 50 kmAround aphelion (Ls ∼ 70°) we found the minimum in cloud activity and lower cloud opacitiesThe cloud activity at sunrise is slightly stronger than at sunset and this is likely due to the lower temperatures [ABSTRACT FROM AUTHOR]

Moving force identification (MFI) is one of the challenging tasks in structural health monitoring (SHM) of bridges. As an inverse problem, continuous attention is needed to address the ill-posedness of MFI system matrix, computational efficiency and accuracy. Therefore, a novel regularized adaptive matching pursuit (NRAMP) framework is proposed for MFI using multiple criteria and prior knowledge in this study. Firstly, a relationship between moving forces and structural responses is established. With the utilization of redundant matrix, the MFI problem is converted into one of the sparse recoveries. A new adaptive criterion related to atoms both in the sparse regularization and LSQR factorization is introduced into the regularized orthogonal matching pursuit (ROMP) process. The ill-posedness of system matrix in sparse recovery can be reduced greatly, and the unknown sparsity problem can be skipped. Furthermore, the optimal atoms of redundant matrix will be selected repeatedly based on another criterion related to prior knowledge that the static axle-weight of a vehicle is the main component of moving vehicle force. The residual in each iteration will be saved and the atoms with the smallest residual are chosen at last. Finally, to assess the feasibility of the proposed method, numerical simulations on identification of single moving force with impulse components and two unequal moving forces, and experimental verifications on MFI of a model vehicle moving on a beam in laboratory are also carried out. The results show that the relative percentage errors between the identified and true gross vehicle weight keep under 3.6% in all measured cases, and the executive time of the proposed method is far less than that due to common OMP methods. [ABSTRACT FROM AUTHOR]

Semidiurnal tidal currents can exceed 5 ms − 1 in Minas Passage, Bay of Fundy, where a tidal energy demonstration area has been designated to generate electricity using marine hydrokinetic turbines. The risk of harmful fish–turbine interaction cannot be dismissed for either migratory or local fish populations. Individuals belonging to several fish populations were acoustically tagged and monitored by using acoustic receivers moored within the Minas Passage. Detection efficiency ρ is required as the first step to estimate the probability of fish–turbine encounter. Moored Innovasea HR2 receivers and high-residency (HR) tags were used to obtain detection efficiency ρ as a function of range and current speed, for near-seafloor signal paths within the tidal energy development area. Strong tidal currents moved moorings, so HR tag signals and their reflections from the sea surface were used to measure ranges from tags to receivers. HR2 self-signals that reflected off the sea surface showed which moorings were displaced to lower and higher levels on the seafloor. Some of the range testing paths had anomalously low ρ , which might be attributed to variable bathymetry blocking the line-of-sight signal path. Clear and blocked signal paths accord with mooring levels. The application of ρ is demonstrated for the calculation of abundance, effective detection range, and detection-positive intervals. High-residency signals were better detected than pulse position modulation (PPM) signals. Providing that the presently obtained ρ applies to tagged fish that swim higher in the water column, there is a reasonable prospect that probability of fish–turbine encounter can be estimated by monitoring fish that carry HR tags. [ABSTRACT FROM AUTHOR]

Reduction in river discharge and sediment load has left deltaic lobes in the world's many river deltas starving, but knowledge of how the subaqueous topography of these abandoned subdeltas responds to environmental changes is limited. In this study, we aimed to determine the long-term dynamics of the subaqueous seabed of abandoned delta lobes to advance current knowledge. As a case study, we selected an abandoned subdelta on the Yellow River Delta of the Bohai Sea, China, for which three-decade long (1984–2017) bathymetric data and long-term river discharge and sediment load records are available. We analyzed the seafloor surface change and quantified the void space from the sea water surface to the seafloor. In addition, we surveyed the seafloor surface with an M80 unmanned surface vehicle carrying a multibeam echo sounder system (MBES) in 2019 to obtain high-resolution microtopography information. We found that a net volume of 5.3 × 108 m3 of sediment was eroded from the study seabed within an area of 3.6 × 108 m2 during 1984–2017. This volumetric quantity is equivalent to 6.89 billion metric tons of sediment, assuming a bulk density of 1.3 t/m3 for the seabed sediment. The seabed erosion from 0 to −5 m, from −5 to −10 m, and below −10 m has showed a similar increasing trend over the past 33 years. These findings suggest that seabed erosion in this abandoned subdelta will very likely continue, and that other abandoned delta lobes in the world may have been experiencing similar seabed erosion due to the interruption of the sediment supply and sea level rise. It is not clear if the seabed erosion of abandoned delta lobes would have any effect on the stability of the coastal shoreline and continental shelf. [ABSTRACT FROM AUTHOR]

In soft‐bottom marine ecosystems, bedform variation is induced by wind‐ and tidal‐driven hydrodynamics. The resulting megaripples, sand waves and sandbanks form a spatially and temporally heterogeneous seafloor landscape. The strong physical forces imposed by the migration of these bedforms are important determinants for the occurrence of different macrozoobenthic species. Quantifying the effect of these forces can help in differentiating natural‐ and anthropogenically induced physical stressors. However, large‐scale mapping of seabed morphology at high resolution using multibeam echosounder is challenging, costly and time‐consuming, especially in shallow seas, prohibiting wide swaths. Instead, their bathymetry is typically studied using single‐beam transects that are interpolated to bathymetric grids with a relatively coarse resolution (20 m). However, this leaves out information on smaller scale (<20 m) bedforms that can be ecologically relevant. In the Dutch Wadden sea, a shallow tidal system, we characterized bedform variation at high resolution using single‐beam data for the first time. We calculated a 2‐D Terrain Ruggedness Index (TRI) at sub‐meter resolution along the single‐beam transects and interpolated the results to a full 3‐D grid. We then validated the result by relating TRI to independently modeled hydrodynamic parameters and to the distribution of macrozoobenthic species. We found that TRI successfully integrates the variation of tidal‐driven bed shear stress and wave‐driven orbital velocity. In addition, we found TRI to be a good predictor of the occurrence of macrozoobenthic species. The inferred small‐scale bedforms provide valuable information for separating the relative importance of natural dynamics versus anthropogenic disturbances such as dredging and bottom trawling activities. We discuss that by repurposing already available single‐beam data in this way, bedforms can be characterized at high resolution without the need for additional equipment or mapping campaigns, yielding novel input to decision‐making on marine management and conservation. [ABSTRACT FROM AUTHOR]

Copyright of Railway Investigation & Surveying is the property of Railway Investigation & Surveying Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Russian sector of the arctic shelf is the longest in the world. Quite a lot of places of massive discharge of bubble methane from the seabed into the water column and further into the atmosphere were found there. This natural phenomenon requires an extensive complex of geological, biological, geophysical, and chemical studies. This article is devoted to aspects of the use of a complex of marine geophysical equipment applied in the Russian sector of the arctic shelf for the detection and study of areas of the water and sedimentary strata with increased saturation with natural gases, as well as a description of some of the results obtained. This complex contains a single-beam scientific high-frequency echo sounder and multibeam system, a sub-bottom profiler, ocean-bottom seismographs, and equipment for continuous seismoacoustic profiling and electrical exploration. The experience of using the above equipment and the examples of the results obtained in the Laptev Sea have shown that these marine geophysical methods are effective and of particular importance for solving most problems related to the detection, mapping, quantification, and monitoring of underwater gas release from the bottom sediments of the shelf zone of the arctic seas, as well as the study of upper and deeper geological roots of gas emission and their relationship with tectonic processes. Geophysical surveys have a significant performance advantage compared to any contact methods. The large-scale application of a wide range of marine geophysical methods is essential for a comprehensive study of the geohazards of vast shelf zones, which have significant potential for economic use. [ABSTRACT FROM AUTHOR]

A typical ultrasonic sensor has a major lobe that extends beyond 45 degrees. Because the wide beam of the ultrasonic sensor's main lobe, which is used for straightforward distance measurement, has a low angular resolution, conventional methods such as incidence angle and linear angle measurements cannot accurately determine the azimuthal angle. Determining whether one or more objects are present in a single beam is also challenging. In this study, the azimuthal angles of two or more objects placed beneath a single beam are determined by the Doppler frequency shift. An ultrasonic sensor is mounted on an automobile to transmit and receive an ultrasound when the car moves towards stationary objects. The sensor picks up the object's reflected Doppler shift signal. The azimuth angle of the objects is determined by estimating the received Doppler shift signal using a standard signal processing method. Near-field motion detection systems and autonomous driving heavily rely on the ability to evaluate the azimuthal angle of objects in a vehicle's surroundings using the Doppler Effect. These are examples of low-cost technology and active safety, which the experimental results support. Based on the results and error estimation, there is an average error of less than 3% between measured and computed values. [ABSTRACT FROM AUTHOR]

Coastal fish communities are under increasing levels of stress associated with climate variation and anthropogenic activities. However, the high degree of behavioral plasticity of many species within these communities allow them to cope with altered environmental conditions to some extent. Here, we combine meteorological information, data from hydroacoustic surveys, and recordings of goliath grouper sound production to examine the response of coastal fish communities to heavy rainfall events in South Florida, USA, that resulted in the release of excess storm water into surrounding estuaries and coastal waters. We observed a nearly 12,000% increase in water column acoustic backscatter following a heavy rainfall event of September 16th, 2015. Interestingly, estimates of school backscatter, a proxy for biomass, increased by 172% with the onset of the perturbation. Schooling fish density also increased by 182%, as did acoustically derived estimates of mean schooling fish length (21%). Following the perturbed period, school backscatter decreased by 406%, along with schooling density (272%), and mean schooling fish length (35%). Hydrophone and hydroacoustic data also revealed that goliath grouper (Epinephelus itajara) spawning aggregations were persistent in the region throughout the duration of the study and continued to exhibit courtship behavior during the perturbed period. Our observations demonstrate the high level of resistance common in coastal species but raises new questions regarding the threshold at which fish communities and reproductive activities are disrupted. As coastal land use continues to increase, and the effects of global climate change become more pronounced, more Before-After Control Impact (BACI) studies will provide improved insight into the overall response of nearshore communities to future perturbations and the cumulative effect of repeated perturbations over extended periods. [ABSTRACT FROM AUTHOR]

This study investigates the large-scale distribution patterns of the acoustic scattering layers and micronekton density across the Northeast Atlantic Ocean during daylight hours. A research cruise on board R/V "Kronprins Haakon" was conducted during May 2019 from Cape Verde to Bay of Biscay. Hydrological data were obtained at 20 conductivity-temperature-depth sensor (CTD) stations. To estimate the micronekton densities in front of the trawl, an autonomous echo sounder (120 or 200 kHz) on the headrope of the macroplankton trawl was used. Acoustic data were also collected along the cruise track using ship-mounted multi-frequency echo sounders (backscatter at 18 and 38 kHz was analyzed). Acoustic observations (both at 18, 38 and 120/200 kHz) showed clear patterns in the horizontal distribution of the micronekton during daytime with higher backscatter and echo densities in the south of the study area (from 17 to 37° N), and the absence of high backscatter in the surface from 37 to 45° N. Backscatter and echo densities were found to be significantly influenced by: temperature, salinity, and oxygen, as well as depth and time of the day. [ABSTRACT FROM AUTHOR]

The topographic fabric of the rift valley floor has been analyzed using the multibeam echosounder data obtained by the autonomous underwater vehicle (AUV) Abyss at two locations over a short segment of the slow-spreading Central Indian Ridge between 10°18′ and 10°57′S. The region is influenced by hydrothermal venting in the near vicinity. Two AUV dives D51 and D52 were performed over this segment at two locations that are 30 km apart and covered 5 km2 and 8 km2 seafloor area, respectively. The dive D51 covered the off-axis part of the rift valley floor in the middle part of the segment, and the dive D52 is located near to the non-transform discontinuity that covered the terminal part of an oceanic core complex (OCC). High-resolution seafloor topography as revealed by the AUV-mounted multibeam echosounder system brought out several micro-bathymetric fabric features such as a lava lake, a cratered volcano, an OCC, and the foot wall volcanic complex at the distal part of the OCC. The valley floor imaged in the D51 is marked by a lava flow encompassing an area of 1 km2 and a volcano in the NE corner. The volcano has a diameter of about 800 m with an elevation of about 200 m from the adjacent seafloor, and the partially mapped volcano crater has a relief of about 60 m. A prominent linear fissure running parallel to the ridge axis has been identified; this feature joins with the volcano. Analysis of AUV-mounted CTD data indicated three distinct temperature spikes ranging 0.009 to 0.013 °C in the region of dive D51. The observed temperature spikes appear to be related to the linear fissure on the seafloor and probably represent leaky venting of fluids from the fissure. With respect to the dive D52, the foot wall volcanic features associated with the OCC are prominent. The volcanic seafloor feature covered an area of 3.45 km2 and is conspicuous with rugged topographic fabric at the base of the OCC. These inferences and the morphotectonics of the rift valley floor as revealed by the AUV data suggest moderate hydrothermal venting in this segment of the slow-spreading Central Indian Ridge. [ABSTRACT FROM AUTHOR]

Aims. Understanding the activity is vital for deciphering the structure, formation, and evolution of comets. We investigate models of cometary activity by comparing them to the dynamics of 67P/Churyumov-Gerasimenko. Methods. We matched simple thermal models of water activity to the combined Rosetta datasets by fitting to the total outgassing rate and four components of the outgassing induced non-gravitational force and torque, with a final manual adjustment of the model parameters to additionally match the other two torque components. We parametrised the thermal model in terms of a distribution of relative activity over the surface of the comet, and attempted to link this to different terrain types. We also tested a more advanced thermal model based on a pebble structure. Results. We confirm a hemispherical dichotomy and non-linear water outgassing response to insolation. The southern hemisphere of the comet and consolidated terrain show enhanced activity relative to the northern hemisphere and dust-covered, unconsolidated terrain types, especially at perihelion. We further find that the non-gravitational torque is especially sensitive to the activity distribution, and to fit the pole-axis orientation in particular, activity must be concentrated (in excess of the already high activity in the southern hemisphere and consolidated terrain) around the south pole and on the body and neck of the comet over its head. This is the case for both the simple thermal model and the pebble-based model. Overall, our results show that water activity cannot be matched by a simple model of sublimating surface ice driven by the insolation alone, regardless of the surface distribution, and that both local spatial and temporal variations are needed to fit the data. Conclusions. Fully reconciling the Rosetta outgassing, torque, and acceleration data requires a thermal model that includes both diurnal and seasonal effects and also structure with depth (dust layers or ice within pebbles). This shows that cometary activity is complex. Nonetheless, non-gravitational dynamics provides a useful tool for distinguishing between different thermophysical models and aids our understanding. [ABSTRACT FROM AUTHOR]

The study of the fabric and microstructure of ice at the shear margin of the Antarctic ice sheet is of great significance for understanding the ice flow and its contributions to sea level rise. In this study, twenty-three one-meter-long ice cores were drilled from blue ice areas at the shear margin of the Dalk Glacier, Antarctica. The ice fabric and microstructure of these ice cores are analyzed using a G50 fabric analyzer. This study shows that the shallow ice cores in this region present a cluster fabric as a consequence of shear stress. The grain size decreases following the direction of the ice flow towards the exposed bedrock at the end of the glacier, due to the blocking and squeezing by the bedrock. The formation mechanism of the shallow ice layers is that the ice from the original accumulation area flows here, lifted by the bedrock and shaped by the summer ablation and denudation. The basal ice at the shear margin of the Dalk Glacier is strongly rubbed by the bedrock and demonstrates a cluster fabric. The analysis of stable water isotopes shows a weak negative correlation between shallow ice fabric and stable water isotopes with depth. Bedrock topography and shear stress have a greater influence on grain microstructure among different ice cores over long distances at shear margins. [ABSTRACT FROM AUTHOR]

Ocean Acoustic Waveguide Remote Sensing (OAWRS) enables fish population density distributions to be instantaneously quantified and continuously monitored over wide areas. Returns from seafloor geology can also be received as background or clutter by OAWRS when insufficient fish populations are present in any region. Given the large spatial regions that fish inhabit and roam over, it is important to develop automatic methods for determining whether fish are present at any pixel in an OAWRS image so that their population distributions, migrations and behaviour can be efficiently analyzed and monitored in large data sets. Here, a statistically optimal automated approach for distinguishing fish from seafloor geology in OAWRS imagery is demonstrated with Neyman–Pearson hypothesis testing which provides the highest true-positive classification rate for a given false-positive rate. Multispectral OAWRS images of large herring shoals during spawning migration to Georges Bank are analyzed. Automated Neyman-Pearson hypothesis testing is shown to accurately distinguish fish from seafloor geology through their differing spectral responses at any space and time pixel in OAWRS imagery. These spectral differences are most dramatic in the vicinity of swimbladder resonances of the fish probed by OAWRS. When such significantly different spectral dependencies exist between fish and geologic scattering, the approach presented provides an instantaneous, reliable and statistically optimal means of automatically distinguishing fish from seafloor geology at any spatial pixel in wide-area OAWRS images. Employing Kullback–Leibler divergence or the relative entropy in bits from Information Theory is shown to also enable automatic discrimination of fish from seafloor by their distinct statistical scattering properties across sensing frequency, but without the statistical optimal properties of the Neyman–Pearson approach. [ABSTRACT FROM AUTHOR]

Subglacial water bodies are critical components in analyzing the instability of the Antarctic ice sheet. Their detection and identification normally rely on geophysical and remote sensing methods such as airborne radar echo sounding (RES), ground seismic, and satellite/airborne altimetry and gravity surveys. In particular, RES surveys are able to detect basal terrain with a relatively high accuracy that can assist with the mapping of subglacial hydrology systems. Traditional RES processing methods for the identification of subglacial water bodies mostly rely on their brightness in radargrams and hydraulic flatness. In this study, we propose an automatic method with the main objective to differentiate the basal materials by quantitatively evaluating the shape of the A-scope waveform near the basal interface in RES radargrams, which has been seldom investigated. We develop an automatic algorithm mainly based on the traditional short-time Fourier transform (STFT) to quantify the shape of the A-scope waveform in radargrams. Specifically, with an appropriate window width applied on the main peak of each A-scope waveform in the RES radargram, STFT shows distinct and contrasting frequency responses at the ice-water interface and ice-rock interface, which is largely dependent upon their different reflection characteristics at the basal interface. We apply this method on 882 RES radargrams collected in the Antarctic's Gamburtsev Province (AGAP) in East Antarctica. There are 8822 identified A-scopes with the calculated detection value larger than the set threshold, out of the overall 1,515,065 valid A-scopes in these 882 RES radargrams. Although these identified A-scopes only takes 0.58% of the overall A-scope population, they show exceptionally continuous distribution to represent the subglacial water bodies. Through a comprehensive comparison with existing inventories of subglacial lakes, we successfully verify the validity and advantages of our method in identifying subglacial water bodies using the detection probability for other basal materials of theoretically the highest along-track resolution. The frequency signature obtained by the proposed joint time–frequency analysis provides a new corridor of investigation that can be further expanded to multivariable deep learning approaches for subglacial and englacial material characterization, as well as subglacial hydrology mapping. [ABSTRACT FROM AUTHOR]

Background: The international community has shown increasing interest in the Arctic and Antarctic due to the value polar regions have in terms of environmental research, natural resources, and national defense. The US Government maintains several permanent research and military facilities in polar regions. Medical evacuation (MEDEVAC) from these facilities can be limited for prolonged periods of time due to their extreme climates. Published data regarding MEDEVACs from these facilities is extremely limited. Methods: Evacuations on military aircraft registered in the Transportation Command Regulation and Command and Control Evacuation System (TRAC2ES) database in a previously de-identified dataset were queried for events from McMurdo, Antarctica. The data was analyzed to determine the number of evacuations, reasons for evacuation, and additional demographic data. Results: There were 31 evacuations from McMurdo Station and Scott Amundsen South Pole Station for 29 unique patients recorded in the available TRAC2ES dataset. Reasons for evacuation included traumatic brain/ head injury, behavioral health concerns, extremity injuries, pregnancy, and various other medical/surgical concerns. Conclusions: MEDEVAC was typically required for advanced diagnostic/treatment modalities or if a patient could no longer fulfill his/her duties. Most evacuations were not directly related to environmental exposure. Given the climate in polar regions can preclude timely evacuation for large periods of time, the need for evacuation must be anticipated and mitigated whenever possible. Better data is needed to guide staffing and mission planning in this remote location. [ABSTRACT FROM AUTHOR]

The ocean covers 71% of the Earth's surface. At present, only about 20% of the seafloor topography (ST) has been directly measured by ships, and most areas are predicted from satellite altimetry‐derived gravity products. In this study, an adaptive nonlinear iterative (ANI) method is proposed to address two major problems in gravity ST inversion: linear approximation and empirical seafloor density contrast (SDC). In ANI, the SDC is adaptively estimated as an output, while higher‐order Parker expansion and modified Bott's iteration are combined to recover nonlinear topography. We apply our new method using the DTU21GRA altimetric gravity model and single‐beam bathymetry to predict the ST in a part of the South China Sea. Results reveal that the average SDC in the study area is 1.24 g/cm3, which compares well to CRUST1.0. The root‐mean‐square (RMS) error between the nonlinear model and single‐beam checkpoints is 102.1 m, which is improved by 34.5%, 29.2%, and 18.3% compared with the non‐gravity model, topo_24.1, and linear model, respectively. The RMS error between the nonlinear model and multibeam bathymetry is 91.0 m, which is better than the linear model. Analysis of two‐dimensional profiles shows that the nonlinear model reveals more terrain details than the linear model. Plain Language Summary: Seafloor bathymetry has important significance for understanding ocean tectonic evolution and ocean circulation. Bathymetric mapping with shipborne sonar instruments is feasible but expensive and time‐consuming. After decades of efforts, only about 20% of the seafloor topography (ST) is directly mapped, and the remaining is predicted by satellite altimetry‐derived gravity products. This study uses the latest gravity model and proposes a new method to refine the ST in a part of the South China Sea. The new method has several advantages. First, it does not require preset an empirical density parameter. Second, it is based on a more rigorous mathematical relationship between seafloor bathymetry and gravity. Using this method, we find that the density contrast between seawater and topography is far less than the theoretical value; the ST estimated by the new method can reveal more detailed terrain and improve accuracy, especially in rugged areas. Key Points: Seafloor topography (ST) and density contrast are simultaneously predicted by using altimetry‐derived gravity data and ship soundingsHigher‐order Parker expansion and iteration are applied to model the nonlinearities between gravity and bathymetryA refined ST model of the South China Sea has been constructed to reveal more terrain details [ABSTRACT FROM AUTHOR]

Infusible thermoplastic Elium® family of resins from Arkema have garnered much attention in recent years as a possible replacement for thermoset resins in laminate and sandwich composite manufacturing for wind blade applications due to its ease of recyclability and the ability to utilize existing manufacturing processes without imposing complicated variations. However, physical and mechanical properties of the proposed Elium® based thermoplastic composites must be comparable to existing epoxy (thermoset) based composites using manufacturing processes relevant for large wind turbine blades. A 13-meter-long demonstration blade was manufactured for that purpose and sandwich samples were obtained from that project for a detailed study. This paper details three-point flexural properties of unidirectional E-glass fiber reinforced acrylic and epoxy based sandwich panels with identical balsa wood core materials. In addition, to evaluate the relative merit considering debond failure mode, the interfacial critical strain energy release rate, predominantly in mode-1, was compared via single cantilever beam testing. In sandwich composites constructed with balsa wood core material, resin uptake by the balsa core is traditionally impeded via the insertion of a scrim material at the facesheet to core interface. Results revealed that inclusion of scrim mesh layer at the facesheet to core interface reduced flexural properties and strain energy release rates in panels infused with acrylic resin but did not significantly reduce these properties in epoxy infused facesheets. [ABSTRACT FROM AUTHOR]

Hyperactive comets have attracted attention due to their high water production rate with an unclear mechanism, though some hypotheses have been proposed to explain it. Based on the thermal theories of the comet nuclei, this paper studied a comet surface thermal model considering the sublimation of H2O. In this paper, a method for solving the sublimation rate of water ice by infrared spectroscopy is proposed. The method adopts the assumption of subpixel temperature nonuniformity on the comet nucleus surface and uses the numerical solution of the Fredholm equation. We use the HRI‐IR spectrum (1.05–4.8 μm) data by EPOXI to analyze the pixel‐by‐pixel water sublimation rate of hyperactive comet 103P/Hartley 2. The results show that sublimation exists in most areas of the surface with or without surface roughness, and most of the water production rate (70%–90%) may come from the comet nucleus when Gauss random surface roughness is adopted. According to the sublimation law, it is estimated that the sublimation temperature of water ice on 103P is above 180 K. If the dust‐to‐ice volume ratio is 3:1, the sublimation temperature is about 200–210 K, which indicates that the water ice may sublimate underneath. This may explain why exposed water ice on the surface can hardly be observed while the active fraction of this comet is up to 100%. Plain Language Summary: Extremely active comets, known as hyperactive comets, release water at very high rates, although observations indicate that they have little exposed water ice on their surfaces. We found a significant energy deficit in the comet surface spectroscopic data, suggesting that the sublimation of water ice may be prevalent in the layers just below the nucleus surface. The sublimation of these water ices may have provided an appreciable water production rate by hyperactive comets. Key Points: The sublimation of the water ice on the comet nucleus absorbs energy, which significantly reduces the infrared radiation on the surfaceThe high water production rate of hyperactive comets may be due to the sublimation of water ice in the surface layer of the comet nucleusThe solution of the Fredholm equation is proved effective to solve the surface temperature distribution based on the observed spectrum [ABSTRACT FROM AUTHOR]

Nowadays, there is a problem related to the difficulties of the vehicles and pedestrians' movement in the cold season due to the formation of an ice layer on roads and sidewalks. As a variant of the problem solution, the mechanical ice destruction by impact-destructive working body with spherical strikers is applied. The use of the spherical strikers provides not only effective ice destruction but it also prevents from damage of the road and sidewalks pavement. In order to achieve the effectiveness of the ice destruction, it is necessary to use appropriate mathematical dependencies for calculation of the working body parameters. In the paper, mathematical model of the ice destruction process using spherical strikers has been conducted. Theoretical dependencies of the mathematical model have been corrected based on the experimental studies. [ABSTRACT FROM AUTHOR]

Deltaic channels are significant landforms at the interface of sediment transfer from land to oceanic realms. Understanding the dynamics of these channels is urgent because delta processes are sensitive to climate change and adjustments in human activity. To obtain a better understanding of the morphological processes of large deltaic channels, this study assessed the evolution and response mechanism of the South Channel and South Passage (SCSP) in the Yangtze Estuary between 1983 to 2018 using hydrology, multibeam echo sounding and historical bathymetry datasets. Decadal changes in riverbed volume and erosion/deposition patterns in the SCSP were assessed. The results showed that the SCSP experienced substantial deposition with a total volume of 26.90 × 107 m3 during 1983–2002, but significant bed erosion with a total volume of 26.04 ×107 m3 during 2003–2010. From 2011 to 2018, the estuarine riverbeds shifted from erosive to depositional, even though the deposition was relatively marginal (0.76 ×107 m3). We inferred that the SCSP have most likely changed from a net erosion phase to a deposition stage in response to local human activities including sand mining, river regulation project, and Deep Water Channel Regulation Project). The channel aggradation will possibly continue considering sea level rise and the ongoing anthropogenic impacts. This is the first field evidence reporting that the lowermost Yangtze River is reaching an equilibrium state in terms of channel erosion and, in fact, the Yangtze River Estuary channels are beginning to aggrade. The findings have relevant implications for the management of the Yangtze River and other lowland alluvial rivers in the world as global sea level continues rising and human intervention on estuarine systems persists. [ABSTRACT FROM AUTHOR]