Variability Of Surface Currents Research Articles

Wind-Driven Motions of the Ocean Surface Mixed Layer in the Western Arctic

Abstract Observations of sea ice and the upper ocean from three moorings in the Beaufort Sea quantify atmosphere–ice–ocean momentum transfer, with a particular focus on the inertial-frequency response. Seasonal variations in the strength of mixed layer (ML) inertial oscillations suggest that sea ice damps momentum transfer from the wind to the ocean, such that the oscillation strength is minimal under sea ice cover. In contrast, the net Ekman transport is unimpacted by the presence of sea ice. The mooring measurements are interpreted with a simplified one-dimensional ice–ocean coupled “slab” model. The model results provide insight into the drivers of the inertial seasonality: namely, that a combination of both sea ice internal stress and ocean ML depth contribute to the seasonal variability of inertial surface currents and inertial sea ice drift, while under-ice roughness does not. Furthermore, the importance of internal stress in damping inertial oscillations is different at each mooring, with a minimal influence at the southernmost mooring (within the seasonal ice zone) and more influence at the northernmost mooring. As the Arctic shifts to a more seasonal sea ice regime, changes in sea ice cover and sea ice internal strength may impact inertial-band ice–ocean coupling and allow for an increase in wind forcing to the ocean.

Lagrangian Characterization of Surface Transport From the Equatorial Atlantic to the Caribbean Sea Using Climatological Lagrangian Coherent Structures and Self‐Organizing Maps

AbstractThis study presents an assessment of the transport of suspended material by surface ocean currents, which have a critical role in determining the connectivity and distribution of living and non‐living material. Lagrangian experiments reveal pathways from the Equatorial Atlantic to 10 strategic regions within the Caribbean Sea, determined by considering the space‐time variability of climatological Lagrangian Coherent Structures, which act as recurrent attracting pathways and transport barriers. Due to windage or Stokes drift, wind forcing is a significant factor in determining the spatial locations where particles cluster and the time needed to reach the Caribbean from the Equatorial Atlantic. Pathways shift westward within the Caribbean and take less time to arrive with increasing wind influence. Depending on the wind effect, the particles show higher confluence in different areas of the Caribbean. A case study is presented for the Mexican Caribbean nearshore area, isolated from ocean‐current trajectories. Here, wind weakens the transport barrier responsible for this isolation and causes particle confluence toward that region. Spatial patterns of the Eulerian velocity identified through Self‐Organizing Maps, with time dependence given by their best matching units, can reproduce the characteristic Lagrangian patterns of surface current climate variability. Our study demonstrates the application of tools from dynamical systems and unsupervised neural networks to understand Lagrangian patterns and identify the processes that drive them. These findings improve our understanding of transport mechanisms of suspended material by surface ocean currents in the Western Atlantic and the Caribbean Sea, which is essential for managing and conserving marine ecosystems.

Seasonal effects, spatial distribution, and possible sources of microplastics in the Chao Phraya River estuary, Thailand

Microplastics (MPs) in estuaries are sources of plastic debris that enter the marine environment. However, there is limited information on the seasonal effect on the accumulation of MPs in the estuaries of Thailand. The abundance and spatial distribution of MPs in the dry and wet seasons were investigated in the Chao Phraya River estuary, and possible emission sources were traced. Dominant factors affecting the distribution patterns of MPs have also been reported. All collected water samples contained MPs, with a mean abundance of 4.0 ± 2.8 × 105 particles/km2 in the wet season and 5.2 ± 3.3 × 105 particles/km2 in the dry season. Fragments were mostly observed, with polypropylene and polyethylene being the dominant polymers. The findings also showed that accumulation of MPs was directly influenced by the river discharge rate into the estuary. Further, the spatial distribution of MPs was closely related to seasonal variations in sea surface currents. Microplastic pollution status with seasonal variations and possible emission sources could provide important information to the government and local environmental organizations for MP pollution prevention and future MP studies in estuarine environments.

Earth Observation and Machine Learning Reveal the Dynamics of Productive Upwelling Regimes on the Agulhas Bank

The combined application of machine learning and satellite observations offers a new way for analysing complex ocean biological and physical processes. Here, an unsupervised machine learning approach, Self Organizing Maps (SOM), is applied to discover links between surface current variability and phytoplankton productivity during seasonal upwelling over the Agulhas Bank (South Africa), from 23 years (November-March 1997-2020) of daily satellite observations (surface current, sea surface temperature, chlorophyll-a). The SOM patterns extracted over this dynamically complex region, which is dominated by the Agulhas Current (AC), revealed 4 topologies/modes of the AC system. An AC flowing southwestward along the shelf edge is the dominant mode. An AC with a cyclonic meander near shelf is the second most frequent mode. An AC with a cyclonic meander off shelf and AC early retroflection modes are the least frequent. These AC topologies influence the circulation and the phytoplankton productivity on the shelf. Strong (weak) seasonal upwelling is seen in the AC early retroflection, the AC with a cyclonic meander near shelf modes and in part of the AC along the shelf edge mode (the AC with a cyclonic meander off shelf mode and in part the AC along the shelf edge mode). The more productive patterns are generally associated with a strong southwestward flow over the central bank caused by the AC intrusion to the east Bank orviaan anticyclonic meander. The less productive situations can be related to a weaker southwest flow over the central bank, strong northeast flow on the eastern bank, and/or to a stronger northwest flow on the central bank. The SOM patterns show marked year-to-year variability. The high/low productivity events seem to be linked to the occurrence of extreme phases in climate variability modes (El Niño Southern Oscillation, Indian Ocean Dipole).

Surface Current Variations and Hydrological Characteristics of the Penghu Channel in the Southeastern Taiwan Strait

Coastal ocean dynamics application radar (CODAR) SeaSonde high-frequency (HF) radars deployed along the coast of Taiwan were used to reveal ocean surface current variations both hourly and through climatological seasons in the Penghu Channel (PHC), southeastern Taiwan Strait (TS), from December 2014 to December 2020. The ocean current in the PHC has a semidiurnal tidal cycle, and the seasonal main flow, wind direction, and wind strength significantly affect the direction and speed of the flow passing through the PHC. The speed of the tidal current in the PHC area can reach more than 1 m/s, and the monthly average flow speed in the PHC is between 0.12 (winter) and 0.24 m/s (summer). Several buoys indicated that the southward flow along the western coast of Taiwan drifted through the PHC in fall and winter. The HF radar observations confirmed the same, implying that this occurred during the strong northeastern monsoon. For a weak northerly wind or even southerly wind, the flow in the PHC can be northward. Different wind directions can affect the speed of the flow passing through the PHC and the branch flow in the northern PHC. The HF radar results are highly consistent with the spatial characteristics of satellite data regarding the sea surface temperature, sea surface salinity, and chlorophyll concentrations; however, there are significant differences from the satellite-derived ocean current.

Tidal current classification insights for search, rescue and recovery operations in the Yellow and East China Seas and Korea Strait

We investigated spatial relationships between barotropic tidal currents and tides (i.e., tidal elevations) in the tidally predominant Yellow and East China Seas and Korea Strait (YESKS) continental shelf region to understand which tidal current and tide (TCE) characteristics underpin essential insights for maritime search, rescue and recovery operations. As baseline information for such operations, tidal current types were classified using FES2014 model TCE harmonic constant data and phase lag relationships for the predominant M2 constituent, to determine maximum flood currents. In terms of surface current spatial variation, the M2 currents were classified into three types: standing, progressive, and mixed tidal waves. In addition to these horizontal patterns, Acoustic Doppler Current Profiler (ADCP) records from three stations on the west coast of Korea during summertime 2007 and wintertime 2015 were harmonically analyzed to reveal the vertical structure of M2 constituent tidal currents, including ellipse parameter gradients. M2 tidal current types were found to vary through the water column, with the maximum tidal current delayed by up to 40° (∼1.4 h) in near surface waters compared to bottom waters. M2 tidal current types also varied vertically, with changes in its ellipse phase: for example, from a near-surface mixed tidal wave to a standing tidal wave near the seabed. Finally, to explore other TCE conditions relevant to rescue and recovery operations, distributions of the age of the tide and of the tidal current ellipse were compared, with results exhibiting similar distributions for both parameters, including >1.5 days in the Yellow Sea and <1.5 days in Korea Strait. In conclusion, as demonstrated by the spatially and vertically complex tidal current type patterns found in the YESKS, detailed three dimensional understandings of TCE processes are needed to successfully support maritime search, rescue and recovery operations in this and other regions.

Surface Current Variations and Oceanic Fronts in the Southern East China Sea: Drifter Experiments, Coastal Radar Applications, and Satellite Observations

AbstractOcean currents in the southern East China Sea (ECS) are complex and have long lacked systematic observational data. Observations from coastal radars in northern Taiwan, along with several drifters and satellite data, reveal a detailed ECS surface flow structure and thermal front. Drifter trajectories followed the seasonal flow field and were oscillatory and trapped due to strong tidal currents. Three drifters crossed the oceanic front off the northern coast of Taiwan following the tidal motion with a rapid change in the sea surface temperature by 2.5°C, which was recorded within a small distance of 500 m. A significant seasonal water mass exchange cycle occurred in the southern ECS. Starting in October, the Kuroshio Current intrudes onto the ECS shelf, causing the formation of a southwestward Northern Taiwan Coastal Current that mixes with the China Coastal Current to form a southward flow in the northern Taiwan Strait. Beginning in March, the ocean current off northwestern Taiwan shifts northward and then gradually flows eastward into the Kuroshio region. With satellite‐derived and model‐simulated surface currents contradicting each other over long periods of time, hourly coastal radar data have not only successfully explained the spatiotemporal variations in the sea surface temperature, salinity, and chlorophyll concentration observed by satellites but have also resolved the long‐standing disputes over the surface currents in the southern ECS.

Sea Surface Current Velocity Retrieving from TanDAM-X Satellite Data

This is the first investigation for the use of TanDEM-X data, satellite for the Malaysian coastal waters. This aims at utilizing an optimization of the Hopfield neural network to retrieve variation of sea surface current along Malaysian coastal waters. In doing so, a multi-objective evolutionary algorithm based on the Pareto front is used to minimize the error produced due to non-linearity between TanDEM-X data and sea surface movements. This work aimed at retrieving sea surface current from TanDEM-X data along the coastal waters of Malaysia. Two approaches have been implemented, the Hopfield neural network algorithm and Pareto optimal solution. The study shows that the Pareto optimal solution has a higher performance than the Hopfield neural network algorithm with a lower RMSE of ±0.009. Furthermore, a Pareto optimal solution can determine the sea surface current pattern variation along the coastal water from TanDEM-X data. In conclusion, TanDEM-X data shows an excellent promise for retrieving sea surface currents.

Wintertime Variability of Currents in the Southwestern Taiwan Strait

AbstractA 57‐days record of surface currents observed from high‐frequency radars on the Chinese coast, along with wind records, are analyzed to investigate wintertime variability of surface currents in the southwestern Taiwan Strait. The M2 tide dominates tidal variability, and the semimajor axes of semidiurnal tidal current ellipses coincide well with bathymetry contours suggesting interactions with a propagating tidal wave. However, phase progressions suggest that this wave undergoes an angular reflection near the Taiwan Bank (TWB). Diurnal currents are less correlated to bathymetry perhaps because many different diurnal tide waves interact here. Surface currents are strongly related to winds at subtidal frequencies. Subtidal along‐strait currents have a correlation of 0.8 with along‐strait winds. However, three different spatial current patterns appear depending on the strength of along‐strait winter monsoon. Downwind currents occur when northeasterly wind is stronger than 10 m s−1. For medium winds, a gradual change in the pattern of currents is observed, including an offshore flow north of the TWB. In low winds conditions, when winds can be either northeasterly or (sometimes) southwesterly, the eastward flow along the northern edge of the TWB increases to 20 cm s−1; elsewhere flow is to the northeast. This forms a counter‐wind current when winds are from the northeast. By investigating the momentum balance, we find that in along‐strait direction wind stress and pressure gradient are important over the TWB, and a geostrophic balance dominates north of bank. In the cross‐strait direction, momentum is dominated by a geostrophic balance over the entire region.

The Dynamic of Convergence Zone Displacement in Western Pacific Ocean on 2015 Super El Niňo Event

Warm pool and the existence of equatorial processes in the Pacific Ocean have an important role on El-Nino Southern Oscillation (ENSO). The eastward advection of warm and less saline water from the western Pacific together with the westward advection of cold and more saline water from the central-eastern Pacific induces a convergence of water masses at the eastern edge of the warm pool. The aim of this study is to determine convergence zone displacement in Western Pacific Ocean based on oceanography parameters such as temperature, salinity and surface current from insitu Argo Float, satellite and model data. The convergence zone displacement was characterized by proxies variable of isotherm 28,5 °C and isohaline 34,6 psu. The convergence zone is zonally displaced in association with EI Niño-La Niña and wind-driven surface current variations. The displacement of the convergence zone moved as far east as 136 °W in the eastern Pacific during the 2015 Super El Niňo. Otherwise, convergence zone moved westward near 154 °E in the western Pacific, during La Niňa periods. During Super El Niňo, the stronger-than-normal speed of the North Equatorial Counter Current (NECC) was increased by 0,8 m/s and appears to have been a major factor in convergence zone reaching the far eastern Pacific. A strong significant positive correlation (R= 0.88, 0.82 and 0.84) between SST and skipjack tuna catch on Super El Niňo, La Niňa and Normal respectively suggested that changes in skipjack CPUE occurred in phase with movement of convergence zone.

Multi-scale variability of circulation in the Gulf of Tonkin from remote sensing of surface currents by high-frequency radars

The sea surface velocity measurements obtained during the period of 2014–2016 using two high-frequency radars (HFR), which were installed on the northern coast of Vietnam, were reprocessed by using a variational approach (EOF/2dVar) to provide an extended dataset. The high temporal resolution of measurements and large spatial coverage of the radar data enabled the assessment of the surface circulation in the data-poor region of the southern Gulf of Tonkin (GoT) and the characterization of its temporal variations in a wide range of scales: from tidal frequency to annual cycle. It was found that tidal motions account for a large percentage (approximately 60%) of surface current variability in the GoT. The temporal variability of the kinetic energy of the surface currents is tightly correlated with wind variations in the monsoon-dominated atmospheric circulation system. Stratification, induced by the discharge of the Red River, also affects the tidal currents within the coastal region (~ 40 km wide) by modifying the tidal ellipses polarizations. Close to the shore, the prominent coastal flow experiences large temporal variations in response to wind and buoyancy forcing. The seasonal variability of the zonal wind component was found to play a significant role in coastal flow speed variations through the cross-shore mass exchange. The Red River freshwater discharge controls the seaward extension of the coastal flow and causes asymmetry in the seasonal variability of flow velocity. The data obtained and analysis results could be useful for the improvement of the regional circulation models, for further studies of the physical and biological processes in the GoT, and for marine resource management.

Seasonal and Tidal Variability of Surface Currents in the Western Andaman Sea Using HF Radars and Buoy Observations During 2016–2017

The characteristics of surface currents during November 2016-October 2017 are studied using observations from the high-frequency radars (HFRs) and a moored buoy (BD12) along the western Andaman Sea (WAnS). The comparison of HFR currents with the collocated currents from BD12 shows a high correlation (>0.78) on a daily scale for both the components. Moreover, the daily HFR currents compared reasonably well to the composite daily surface currents from multiple satellites for both the zonal and meridional components. The reversal of currents is observed during the northeast (November-February) and southwest (June-October) monsoons with the mean current magnitudes of 0.41 m/s northward and 0.22 m/s southward, respectively, which is predominantly influenced by the local wind stress. The seasonal reversal of currents leads to the exchange of waters between the WAnS and the Bay of Bengal through the 11° channel, which is primarily due to the Ekman mass transport. Harmonic analysis of the hourly data from HFRs shows the dominance of M2 tidal currents, followed by other semidiurnal (S2, N2), diurnal (K1, O1), and shallow water constituents (M4 and MS4). Also, the tidal constituents from both the current observations matched in their relative order of amplitudes with a reasonable correlation (0.95). Total tidal variance ranges between 10% and 50% in the WAnS, with the highest contributions from the M2 tidal currents (of 25%). Moreover, stronger M2 tidal currents are observed to skirt around Little Andaman (LA) Island extending out to 100-km offshore, with maximum amplitudes of 12 cm/s.

Responses of hyperiid (Amphipoda) communities to monsoon reversal in the central South China Sea

Significant seasonal variations in surface circulation are driven by the East Asian Monsoon in the South China Sea (SCS). Seasonal variations in copepod and hyperiid communities following the monsoon have been reported. The mechanisms controlling these monsoon-driven seasonal variations in hyperiid communities were analyzed using data from the central SCS (CSCS) during 2014–2015. Hyperiids mainly aggregated at the transitional water zones driven by the interactions of the cyclonic gyre and anti-cyclonic gyre or the western boundary current (WBC) in the CSCS. The total hyperiid abundance was related to the Northwest Luzon Cyclonic Gyre during the northeast monsoon and the East Vietnam Cyclonic Gyre during the southwest monsoon. The hyperiid community structure was significantly affected by the temperature of the upper 100-m water layer and gelatinous plankton in the CSCS from summer to fall. Different hyperiid ecological groups occurred in different water masses in the CSCS. The areas of interaction between cyclonic and anti-cyclonic gyres or the WBC and the distributions of water masses changed following seasonal variations in surface currents. The seasonal change in transitional water zones and water masses caused the seasonal variations of hyperiid community to track the monsoon reversal. Comparison of our data with previous data for the tropical SCS and other tropical oceanic areas confirms that the species composition of hyperiids is similar to that of the tropical Pacific, and that the most abundant species of hyperiid communities are very much more abundant than other species in subtropical–tropical oceans. Confirmation of symbiosis between three abundant hyperiid species (Lestrigonus bengalensis, Primno latreillei and Phronima sedentaria) and some abundant species of gelatinous zooplankton in CSCS suggests that the symbiosis helps the most abundant species to dominate significantly. The seasonal species diversity and total abundance of hyperiids usually remain relatively constant, the occurrence of strong El Niño events leads to the abnormal low total hyperiid abundance in fall, and the weak Kuroshio intrusion causes the abnormally low hyperiid species diversity in fall in the CSCS.

Wave Observation Methods using High-frequency Ocean Radar

Shim, J.S.; Kim, J.H.; Chang, B.S.; Min, I.K.; Choi, J., and Chun, I., 2020. Wave observation methods using high-frequency ocean radar. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1273–1278. Coconut Creek (Florida), ISSN 0749-0208.The Korea Institute of Ocean Science and Technology (KIOST) has been developing high-frequency (HF) ocean radar for wave observation with SETsystem Inc., which had developed HF ocean radar for ocean currents. A Bayesian directional spectrum estimation method (BDM) algorithm was developed to extract wave information from HF ocean radar and tested using surface current and wave variability experiments (SCAWVEX) data. A circular array antenna was used, which has advantages in terms of smaller installation space and narrower beamwidth. The prototype of the HF ocean radar for wave was composed of BDM algorithm and circular array antenna for optimizing the observed waves. The prototype of the HF ocean radar was installed at the East Sea Research Institute, Uljin, in the Republic of Korea (ROK). The radar system is being checked, and a future study will compare the results with those of other observation tools.

Improving Surface Current Resolution Using Direction Finding Algorithms for Multiantenna High-Frequency Radars

AbstractWhile land-based high-frequency (HF) radars are the only instruments capable of resolving both the temporal and spatial variability of surface currents in the coastal ocean, recent high-resolution views suggest that the coastal ocean is more complex than presently deployed radar systems are able to reveal. This work uses a hybrid system, having elements of both phased arrays and direction finding radars, to improve the azimuthal resolution of HF radars. Data from two radars deployed along the U.S. East Coast and configured as 8-antenna grid arrays were used to evaluate potential direction finding and signal, or emitter, detection methods. Direction finding methods such as maximum likelihood estimation generally performed better than the well-known multiple signal classification (MUSIC) method given identical emitter detection methods. However, accurately estimating the number of emitters present in HF radar observations is a challenge. As MUSIC’s direction-of-arrival (DOA) function permits simple empirical tests that dramatically aid the detection process, MUSIC was found to be the superior method in this study. The 8-antenna arrays were able to provide more accurate estimates of MUSIC’s noise subspace than typical 3-antenna systems, eliminating the need for a series of empirical parameters to control MUSIC’s performance. Code developed for this research has been made available in an online repository.

An Improved Antenna Theory Model of Lightning Return Stroke Using a Distributed Current Source–Part II: Applications

A full-wave method of Maxwell's equations is adopted for the analysis of lightning electromagnetic fields. The method is based on a numerical solution of the electric field integral equation by the method of moments (MoM). A new electromagnetic model of the lightning channel based on a thin-wire antenna with distributed current sources allows the use of Sommerfeld integrals for the evaluation of electromagnetic fields due to lightning, in stratified media. In order to extend the study to more complex systems including the lightning channel and its nearby structures, an array of conducting wires and metallic surfaces is used to represent the entire system. An efficient and cost-effective MoM method capable to compute the variation of spatial one-dimensional linear currents and two-dimensional surface currents is implemented. It permits the evaluation of the electromagnetic interference effects of lightning in a complex environment, without the use of approximate formulas. The proposed method is capable of analyzing the electromagnetic interference effects of lightning for a wide range of applications. Several case studies, including the analysis of lightning-induced disturbances on overhead lines, underground cables, and shielding enclosures, are also presented.

Impact of the Atlantic Multidecadal Oscillation on the Pacific North Equatorial Current bifurcation

Variability in surface currents is mainly induced by the time-varying wind forcing. Recent studies have revealed robust pronounced changes in the atmospheric circulation over the Pacific came with the Pacific Decadal Oscillation (PDO). However, the PDO is a climate index based on sea surface temperature (SST) variations, and may not be appropriately considered as a climate forcing. Here, we suggest the Atlantic SST variability is the ultimate forcing leading to changes in the atmospheric circulation and surface winds over the North Pacific. Anomalous warm North Atlantic and cold South Atlantic leads to weak Hadley cell in the Northern Hemisphere, resulting in a northward displacement of the ITCZ as well as a positive wind stress curl anomaly in the Pacific subtropical region, which would reduce the North Pacific subtropical gyre (NPSG). Associated with reduced sea surface height in the subtropics by the weakened NPSG, the North Equatorial Current (NEC) is weakened based on geostrophy. Changes in basin-scale winds further result in the southward migration of the tropical gyre and consequential downstream ocean circulation.

EMPIRICAL ORTHOGONAL FUNCTION ANALYSIS OF SATELLITE-DERIVED CURRENTS IN THE TROPICAL ATLANTIC

An Empirical Orthogonal Function (EOF) analysis was performed using 22 years of monthly surface currents in order to investigate the main modes of variability of the Tropical Atlantic surface circulation based on satellite data. The EOF1 of the zonal component captures more than 50% of the total variance and represents the central branch of the South Equatorial Current (cSEC). The EOF2 of the zonal component (~8% variance) represents a zonal dipole with a positive signal to the west, and a negative one to the east in the Atlantic Cold Tongue (ACT). The meridional EOF1 (18% variance), with alternating positive and negative structures in the western tropical North Atlantic, representing the high dynamics associated to the North Brazil Current retroflection and its anticyclonic eddies. The meridional EOF2 (~ 12% variance) represents the high variability of the NBC, with stronger intermittent signals propagating from the eastern Atlantic. In the EOF1 of currents speed predominates the cSEC pattern (30%) and the EOF2 (8%) represents the zonal dipole between South Atlantic Warm Pool and the ACT. These dominant modes of surface current variability contribute to the understanding of the ocean-atmosphere interaction processes, zonal and meridional transport variability, and the surface dynamics in the TA. Keywords: EOF Analysis, Remote Sensing, Ocean Currents, Oceanic Dynamics, Tropical Atlantic

Fluidically Switchable Metasurface for Wide Spectrum Absorption

Metasurfaces, owing to their attractive features, provide a wide range of potential applications. Electromagnetic absorbers based on metasurfaces have significantly improved responses compared to the earlier absorbers made from composite materials. Active metasurfaces, in contrast to the passive designs, can exhibit multifunctional characteristics without repeated fabrication. This paper presents a fluidically-reconfigurable active metasurface that provides switchable wide spectrum absorption. The proposed design is comprised of liquid-metal-encased dielectric substrates, sandwiched between the top resistive pattern and bottom ground plane. With precise control of the liquid metal flow, the structure can exhibit wide absorption bandwidth switching between two frequency regimes. Further, the proposed metasurface has a significant advantage of displaying polarization-insensitive behaviour, unlike the previous fluidically-reconfigured structures. The design has been investigated by illustrating surface current distributions and several parametric variations. Finally, the proposed structure was fabricated using laser etching, and experimentally validated. This work has paved the way towards the realization of reconfigurable metasurfaces with multifunctional characteristics, thus showing great potential in microfluidic technology for diverse applications.

Hopfield neural network and pareto optimal algorithms for retrieving sea surface current from TanDEM-X data

This is first work is done on the application of TanDEM-X data satellite data for the Malaysian coastal waters. This study aims at comparison between Hopfield neural network and Pareto optimal algorithms for modelling sea surface current using TanDEM-X satellite data. In fact, X-band data have a great potential for retrieving sea surface parameters such as sea surface current movement and ocean wave spectra. Therefore, TanDEM-X is the term of the satellite operation hovering the two satellites in a strictly controlled foundation with regular distances between 250 and 500 m. The study of ocean surface current is important for understanding the coastal water circulation. The set of TanDEM-X satellite data are examined by using Hopfield neural network algorithm. The sea surface current is retrieved based on the energy function. Therefore, the Pareto optimal algorithm is used to determine the optimal solution for nonlinearity problem which is raised due to the Doppler frequency shift impact. The study shows that the Pareto optimum resolution has highest performance than Hopfield neural network rule with lowest RMSE of ±0.08. Further, Pareto optimum resolution can verify the ocean surface current pattern variation on coastal water from TanDEMX data. Last, TanDEMX data reveals a superb guarantees for retrieving ocean surface current with X-band.