Surface Velocity Measurements Research Articles

Remote sensing of wave-orbital velocities in the surfzone

Wave-orbital velocities are estimated with particle image velocimetry (PIV) applied to rapid sequences of images of the surfzone surface obtained with a low-cost camera mounted on an amphibious tripod. Time series and spectra of the remotely sensed cross-shore wave-orbital velocities are converted to the depth of colocated acoustic Doppler velocimeters (ADVs), using linear finite depth theory. These converted velocities are similar to the velocities measured in situ (mean nRMSE for time series=16% and for spectra=10%). Small discrepancies between depth-attenuated surface and in situ currents may be owing to errors in the surface velocity measurements, uncertainties in the water depth, the vertical elevation of the ADVs, and the neglect of nonlinear effects when using linear finite depth theory. These results show the potential to obtain spatially dense estimates of wave velocities using optical near-field remote methods during field campaigns and continuous monitoring operations.

River Surface Velocity Measurement for Rapid Levee Breach Emergency Response Based on DFP-P-LK Algorithm.

In recent years, the increasing frequency of climate change and extreme weather events has significantly elevated the risk of levee breaches, potentially triggering large-scale floods that threaten surrounding environments and public safety. Rapid and accurate measurement of river surface velocities is crucial for developing effective emergency response plans. Video image velocimetry has emerged as a powerful new approach due to its non-invasive nature, ease of operation, and low cost. This paper introduces the Dynamic Feature Point Pyramid Lucas-Kanade (DFP-P-LK) optical flow algorithm, which employs a feature point dynamic update fusion strategy. The algorithm ensures accurate feature point extraction and reliable tracking through feature point fusion detection and dynamic update mechanisms, enhancing the robustness of optical flow estimation. Based on the DFP-P-LK, we propose a river surface velocity measurement model for rapid levee breach emergency response. This model converts acquired optical flow motion to actual flow velocities using an optical flow-velocity conversion model, providing critical data support for levee breach emergency response. Experimental results show that the method achieves an average measurement error below 15% within the velocity range of 0.43 m/s to 2.06 m/s, demonstrating high practical value and reliability.

Dynamic response of equiatomic and non-equiatomic CrMnFeCoNi high-entropy alloys under plate impact

A typical Fe-rich non-equiatomic CrMnFeCoNi high-entropy alloy (HEA), Cr10Mn10Fe60Co10Ni10, and the equiatomic Cr20Mn20Fe20Co20Ni20 HEA, are investigated via plate impact experiments along with in situ free surface velocity measurements. Both the initial and postmortem samples are characterized with transmission electron microscopy and electron backscatter diffraction. These two HEAs contain a single face-centered cubic phase, are texture-free, and have similar grain sizes. Dynamic yield stress and spall strength of the non-equiatomic CrMnFeCoNi are lower by ∼55 % and 15 % than those of its equiatomic counterpart, respectively. After shock compression, dislocation slips, stacking faults, Lomer-Cottrell locks and nanotwins are found in the postmortem samples of both HEAs. Due to the reduced stacking fault energy in the non-equiatomic HEA, more deformation twins and newly formed hexagonal close-packed phases are found. For spallation, intergranular voids are larger in size but smaller in quantity than intragranular voids for both HEAs. Both intragranular or intergranular voids show strong dependence on grain boundary misorientation.

Impact of assimilating satellite surface velocity observations in the Mercator Ocean International analysis and forecasting global 1/4° system

Representing and forecasting global ocean velocities is challenging. Velocity observations are scarce and sparse, and are rarely assimilated in a global ocean configuration. Recently, different satellite mission candidates have been proposed to provide surface velocity measurements. To assess the impact of assimilating such data, Observing System Simulation Experiments (OSSEs) have been run in the Mercator Ocean International analysis and forecasting global 1/4° system. Results show that assimilating simulated satellite surface velocities in addition to classical observations has a positive impact on the predicted currents at the surface and below to some extent. Compared to an experiment that assimilates only the classical observations, the surface velocity root-mean-squared error (RMSE) is reduced, especially in the Tropics. From a certain depth depending on the region (e.g. 200 m in the Tropics) however, slight degradations can be spotted. Temperature and salinity RMSEs are generally slightly degraded except in the Tropics where there is a small improvement at the surface and sub-surface. Sea surface height results are mixed, with some areas having reduced RMSE and some increased. The OSSEs reported here constitute a first study and aim to provide first insights on the features that improve by assimilating surface velocity data, and those which need to be worked on.

Simultaneous measurement of surface velocity and plasma density with interferometric velocimetry.

The apparent velocity measured by an interferometric surface velocimeter is a function of both the surface velocity and the time derivative of the refractive index along the measurement path. We employed this dual sensitivity to simultaneously measure km/s surface velocities and 1018cm-3 average plasma densities with combined VISAR (velocity interferometer system for any reflector) and PDV (photonic Doppler velocimetry) measurements in experiments performed on the Z Pulsed Power Facility. We detail the governing equations, associated assumptions, and analysis specifics and show that the surface velocity can be extracted without knowledge of the specific plasma density profile.

Experimental Heat Transfer Analysis of a New Turbulator in a Concentric Heat Exchanger Tube: A Full Factorial Design Approach

Abstract People have been looking for alternative energy sources because current sources may be depleted. Furthermore, it is critical to utilize available energy sources as effectively as possible. Turbulators are among the topics to consider when it comes to energy efficiency. In practice, turbulators are often used in exchangers to enhance heat transfer. Putting newly constructed turbulators in determined locations of the constant surface temperature heat exchanger, velocity, temperatures, pressure, and flow measurements have been performed in the inlet and outlet. In the case of using different numbers of turbulators, their placement in different locations, their arrangement at different distances, and their use at different Reynolds, the changes in pressure drop, Nusselt number, friction factor, efficiency, exergy loss rate, and NTU were determined with the full-factor experimental design. When the test data were evaluated, it was seen that as the number of turbulators increased, the thermal efficiency, friction factor, and pressure loss also increased. Using turbulators in different numbers, at different positions, at different distances, and with different Reynolds numbers, the effect ratio on the pressure loss, Nusselt number, and friction factor parameters was detected. In the analyses made, the most efficient parameters on heat transfer were determined, respectively, as Reynolds number (64.55%), the position of turbulators (19.73%), the distance between turbulators (6.09%), and the number of turbulators (5.94%).

Ice acceleration and rotation in the Greenland Ice Sheet interior in recent decades

In the past two decades, mass loss from the Greenland ice sheet has accelerated, partly due to the speedup of glaciers. However, uncertainty in speed derived from satellite products hampers the detection of inland changes. In-situ measurements using stake surveys or GPS have lower uncertainties. To detect inland changes, we repeated in-situ measurements of ice-sheet surface velocities at 11 historical locations first measured in 1959, located upstream of Jakobshavn Isbræ, west Greenland. Here, we show ice velocities have increased by 5–15% across all deep inland sites. Several sites show a northward deflection of 3–4.5° in their flow azimuth. The recent appearance of a network of large transverse surface crevasses, bisecting historical overland traverse routes, may indicate a fundamental shift in local ice dynamics. We suggest that creep instability—a coincident warming and softening of near-bed ice layers—may explain recent acceleration and rotation, in the absence of an appreciable change in local driving stress.

Vertical Velocity Diagnosed From Surface Data With Machine Learning

AbstractSubmesoscale vertical velocities, w, are important for the oceanic transport of heat and biogeochemical properties, but observing w is challenging. New remote sensing technologies of horizontal surface velocity at O(1) km resolution can resolve surface submesoscale dynamics and offer promise for diagnosing w subsurface. Using machine learning models, we examine relationships between the three‐dimensional w field and remotely observable surface variables such as horizontal velocity, density, and their horizontal gradients. We evaluate the machine learning models' sensitivities to different inputs, spatial resolution of surface fields, the addition of noise, and information about the subsurface density. We find that surface data is sufficient for reconstructing w, and having high resolution horizontal velocities with minimal errors is crucial for accurate w predictions. This highlights the importance of finer scale surface velocity measurements and suggests that data‐driven methods may be effective tools for linking surface observations with vertical velocity and transport subsurface.

Radiation resistance matrix for baffled simply curved plates for sound power applications

Sound power, a standard metric used to quantify product noise, is determined through the vibration-based sound power (VBSP) method. This method involves measuring surface velocities and utilizing an acoustic radiation resistance matrix, R, dependent on the structure's geometry. While R matrix expressions have been established for baffled flat plates, fully closed cylinders, and fully closed spheres, this work presents the first analytical expression tailored for baffled simply curved plates with uniform curvature. This development, based on eigenfunction expansion and the uniform theory of diffraction, extends the VBSP method's capabilities for accurate sound power assessment from these structures. Experimental validation involved testing three plates of varying curvature in a reverberation chamber, comparing the VBSP method with the ISO 3741 pressure-based standard. One of the curved plates underwent additional testing in an anechoic chamber following the ISO 3745 standard, confirming the VBSP method's accurate sound power measurements down to the 160 Hz one-third octave band. The same plate was tested in uncontrolled acoustic environments — a busy hallway and an outdoor location. The VBSP results showed strong agreement with ISO 3741, affirming the method's robustness for measuring sound power from baffled simply curved plates in acoustically challenging real-world conditions. This underscores the practicality of the VBSP method, enabling accurate sound power measurements of baffled curved plates in the presence of substantial background noise and environmental variability.

Image Processing Techniques for Dynamic Surface Velocity Measurement in Rivers

Image Processing Techniques for Dynamic Surface Velocity Measurement in Rivers

Evolution of ice rises in the Fimbul Ice Shelf, Dronning Maud Land, over the last millennium

AbstractWe investigate two ice rises, Kupol Moskovskij and Kupol Ciolkovskogo, in the Fimbul Ice Shelf, East Antarctica, situated ~60 km from each other but differing in their glaciological settings. We apply a thermo-mechanically coupled Elmer/Ice model to profiles going across these ice rises and use it to investigate their past evolution covering present to several millennia ago. We constrain the model results using field measurements, including surface-velocity measurements, and surface mass balance estimated by isochronous radar stratigraphy dated with firn cores. We find that the ice rises are thickening at present (2012–2014), which started only in recent decades. Investigation of deeper radar reflectors suggests a stronger upwind-downwind contrast in surface mass balance in the past for both ice rises, with varying details. This result matches what was previously found on Blåskimen Island ice rise, which is also in the Fimbul Ice Shelf. Moreover, Kupol Moskovskij, situated at a shear margin, shows signs of recent changes in its ice-divide position, while Kupol Ciolkovskogo shows a more stable divide position. This study highlights the long-term influence of surface mass balance on ice rises, as well as the strong influence of local glaciological settings on their evolution.

Simultaneous Measurements of Surface Spanwise Waves and Velocity in a Turbulent Boundary Layer

Among the different passive and active techniques for skin friction drag reduction for turbulent boundary layers, near wall forcing through moving walls is one of the most promising techniques at low Reτ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_\ au$$\\end{document}. Fewer studies have looked at the mechanism at high Reτ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_\ au$$\\end{document}, closer to flight conditions, largely because, in this regime, numerical simulations become harder and experiments more challenging. To that end, there is the need of a systematic study for different surface waves and flow conditions. This work introduces a new model using a kagome lattice and an experimental setup which combines simultaneous measurements of surface displacement and velocity in the boundary layer. Here the results from a shortened version of the model at Reτ≈\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_\ au \\approx$$\\end{document} 1000 are presented to demonstrate the capability of the experimental setup which is developed in view of further investigation at higher Reynolds number.

Surface Current Measurement Using Large Scale Particle Image Velocimetry (LSPIV) in Ender Estuary, Cirebon

The Large-Scale Particle Image Velocimetry (LSPIV) method is an image- based technique that uses a non-intrusive approach or avoids direct physical contact with the water being studied to measure the velocity of water flow. The present study aims to identify surface velocity using LSPIV captured by Unmanned Aerial Vehicle (UAV) in Ender estuary, Cirebon. Field observation for surface velocity was conducted at three locations during flood and ebb tides. The surface current results of LSPIV compared with in situ velocity measurement by a current meter. The results of the LSPIV method are strongly influenced by the data acquisition process such as lighting, interrogation area, and video recording angle. Based on comparing the surface flow between results of LSPIV and observation data, the coefficient correlation (R) is 0.84 for velocity magnitude and R = 0.92 for flow direction. The Root Mean Square Error (RMSE) of 0.024 m/s for velocity magnitude and 4.81 degree for flow direction, and the Mean Absolute Error (MAE) range from 0.002 to 0.059 m/s (1 to 12 degree) for the velocity magnitude and the flow direction, respectively. Furthermore, the Mean Absolute Percentage Error (MAPE) value of 10.41% (8.84%) for magnitude and direction, respectively. Therefore, LSPIV was applied successfully to obtain surface velocity measurements.

Flood Discharge Measurement by STIV Coupled with Maximum Entropy Method Using Parameter Estimation by Numerical Analysis

The coupling of surface velocity measurement by image analysis and the maximum entropy method (MEM) is a non-contact measurement technique to estimate river discharge during flood with high accuracy. The MEM can represent complex vertical velocity distributions including velocity dips, but there is a challenge that the measurement of the cross-sectional velocity distribution by Acoustic Doppler Current Profiler (ADCP), etc. must be required at least once to determine the entropy parameter, which is a specific value at the cross section. This study proposes a new framework for determining the entropy parameter at new measurement sites based on the results of 3-D flow simulations. The framework is applied to two measurement sites, and the cross-sectional velocity distribution and the discharge estimated by the MEM with the entropy parameter are evaluated. The result shows that the framework enables the setting of an appropriate entropy parameter at a given site, and that the discharge estimated using the entropy parameter has a relative error of less than 10% to those measured by the ADCP.

Measuring Velocity and Discharge of High Turbidity Rivers Using an Improved Near-Field Remote-Sensing Measurement System

Large-scale particle image velocimetry (LSPIV) is a computer vision-based technique renowned for its precise and efficient measurement of river surface velocity. However, a crucial prerequisite for utilizing LSPIV involves camera calibration. Conventional techniques rely on ground control points, thus restricting their scope of application. This study introduced a near-field remote-sensing measurement system based on LSPIV, capable of accurately measuring river surface velocity sans reliance on ground control points. The system acquires gravity-acceleration data using a triaxial accelerometer and converts this data into a camera pose, thereby facilitating swift camera calibration. This study validates the system through method verification and field measurements. The method verification results indicate that the system’s method for retroactively deriving ground control-point coordinates achieves an accuracy exceeding 90%. Then, field measurements were performed five times to assess the surface velocity of the Datong River. These measured results were analyzed and compared with data collected from the radar wave velocity meter (RWCM) and the LS1206B velocity meter. Finally, a comprehensive sensitivity analysis of each parameter was conducted to identify those significantly impacting the river’s surface velocity. The findings revealed that this system achieved an accuracy exceeding 92% for all river surface velocities measured.

ANDROMEDE — A software platform for optical surface velocity measurements

Methods and algorithms for measuring stream surface velocities have been continuously developed over the past five years to adapt to specific flow typologies. The free software ANDROMEDE allows easy use and comparison of these methods with image processing capabilities designed for measurements in natural environments and with unmanned aerial vehicles. Conventional particle tracking velocimetry, optical flow and particle image velocimetry algorithms, as well as filtering and statistical analysis methods, are available on a single platform. The code is written in Python, exploits available Python libraries, and allows accessible open-source code development. The validation of the integrated algorithms is presented on three case studies that represent the targeted applications: the study of currents for eco-hydraulics, the measurement of low water flows and the diagnosis of hydraulic structures. The field measurements are in very good agreement with the optical measurements and demonstrate the usefulness of the tool for rapid flow diagnosis for all the intended applications.

Comparative Assessment of Different Image Velocimetry Techniques for Measuring River Velocities Using Unmanned Aerial Vehicle Imagery

The accurate measurement of river velocity is essential due to its multifaceted significance. In response to this demand, remote measurement techniques have emerged, including large-scale particle image velocimetry (LSPIV), which can be implemented through cameras or unmanned aerial vehicles (UAVs). This study conducted water surface velocity measurements in the Xihu River, situated in Miaoli County, Taiwan. These measurements were subjected to analysis using five distinct algorithms (PIVlab, Fudaa-LSPIV, OpenPIV, KLT-IV, and STIV) and were compared with surface velocity radar (SVR) results. In the quest for identifying the optimal parameter configuration, it was found that an IA size of 32 pixels × 32 pixels, an image acquisition frequency of 12 frames per second (fps), and a pixel size of 20.5 mm/pixel consistently yielded the lowest values for mean error (ME) and root mean squared error (RMSE) in the performance of Fudaa-LSPIV. Among these algorithms, Fudaa-LSPIV consistently demonstrated the lowest mean error (ME) and root mean squared error (RMSE) values. Additionally, it exhibited the highest coefficient of determination (R2 = 0.8053). Subsequent investigations employing Fudaa-LSPIV delved into the impact of various water surface velocity calculation parameters. These experiments revealed that alterations in the size of the interrogation area (IA), image acquisition frequency, and pixel size significantly influenced water surface velocity. This parameter set was subsequently employed in an experiment exploring the incorporation of artificial particles in image velocimetry analysis. The results indicated that the introduction of artificial particles had a discernible impact on the calculation of surface water velocity. Inclusion of these artificial particles enhanced the capability of Fudaa-LSPIV to detect patterns on the water surface.

Estimation of Surface Current Divergence from Satellite Doppler Radar Scatterometer Measurements of Surface Ocean Velocity

Abstract The ability to estimate surface current divergence and vorticity from space is assessed from simulated satellite Doppler radar scatterometer measurements of surface velocity with an effective footprint diameter of 5 km across an 1800-km measurement swath. The focus is on non-internal-wave contributions to divergence and vorticity. This is achieved by simulating Doppler radar measurements of surface velocity from a numerical model in which internal waves are weak because of high dissipation, seasonal cycle forcing, and the lack of tidal forcing. Divergence is much more challenging to estimate than vorticity because the signals are weaker and restricted to smaller scales. With the measurement noise that was anticipated based on early engineering studies, divergence cannot be estimated with useful resolution. Recent advances in the understanding of how the noise in measurements of surface currents depends on the ambient wind speed have concluded that measurement noise will be substantially smaller in conditions of wind speed greater than 6 m s−1. A reassessment of the ability to estimate non-internal-wave contributions to surface current divergence in this study finds that useful estimates can be obtained in such wind conditions; the wavelength resolution capability for divergence estimates in the middle of the measurement swaths will be better than 100 km in 16-day averages. The improved measurement accuracy will also provide estimates of surface current vorticity with a resolution nearly a factor of 2 higher than was previously thought, resulting in wavelength resolutions of about 50, 30, and 20 km in snapshots, 4-day averages, and 16-day averages, respectively. Significance Statement The divergence of surface ocean velocity is of great interest to oceanographers because of its direct relation to the near-surface vertical velocity that has important implications for air–sea exchanges of CO2 and other gases, as well as the supply of nutrients from depth that are critical to biological productivity. Observational estimates of surface divergence are challenging because of the weakness of the divergence signals and the technical difficulties in acquiring two-dimensional observations of velocity with sufficient accuracy and spatial resolution to obtain accurate estimates of the divergence. The analysis presented here concludes that useful estimates of surface current divergence can be obtained from a future Doppler radar satellite mission that is in the early stages of development by NASA.

Simultaneous Measurement of Turbulent Surface Velocities and Fish Movement in an Open Channel Flow with Implications for Agent-Based Models

Simultaneous Measurement of Turbulent Surface Velocities and Fish Movement in an Open Channel Flow with Implications for Agent-Based Models

Clutter and Interference Cancellation in River Surface Velocity Measurement with a Coherent S-Band Radar

Using a Doppler radar to measure river surface velocity is a safe and effective technique. However, the measurement would be severely affected by undesired targets that enter the illuminated area of radar. The issue is worsened when measuring the surface velocities of wide rivers because undesired targets such as boats and ships are more likely to be present. The buoy boats fixed on the river surface and cargo ships sailing on the river would generate ground clutter and moving target interference, respectively. The clutter and interference can mask the signal produced by the Bragg scattering and seriously bias the extraction result of river surface velocity. This paper proposes two effective methods to remove ground clutter and moving target interference, respectively. One is an improved phase-based method that eliminates ground clutter after obtaining its boundaries through the phase in the frequency domain, and another is an improved constant false alarm rate (CFAR) detector that combines smallest-of selection logic and a multi-step deletion scheme to detect and remove interference in the time-Doppler spectrum. The experimental data measuring the surface velocity of the Yangtze River with a coherent S-band radar in July 2022 are used to verify the proposed methods. The results show that the proposed methods can effectively remove ground clutter and moving target interference, respectively. After clutter and interference cancellation, a more reasonable result of river surface velocity distribution can be extracted. Therefore, the methods proposed in this paper can be used to remove clutter and interference when extracting the surface velocity of rivers with numerous undesired targets.