Measuring River Surface Velocity Using UAS‐Borne Doppler Radar

Compared to traditional river surface velocity measurement techniques such as in-situ point measurements with electromagnetic current meters, remote sensing techniques are attractive because measurements are fast, low cost and contactless. Based on Unmanned Aerial Systems (UAS) equipped with optical equipment (e.g., HD camera) and Doppler radar, surface velocity can be efficiently measured with high spatial resolution. UAS-borne Doppler radar is particularly attractive, because it is suitable for real-time velocity determination and has fewer limitations (no seeding of the flow required, no daylight required, works for both narrow and wide rivers).In this paper, videos from a UAS RGB video camera were analysed using both Particle Image Velocimetry (PIV) and Space-Time Image Velocimetry (STIV) techniques. Furthermore, we recorded full waveform signal data using a 24 GHz continuous wave Doppler radar (e.g., Geolux RSS-2-300) at multiple waypoints across the river. Different from previous processing methods, which only considered the processed velocity from Doppler radar itself, we propose an algorithm for picking the correct river surface velocity from the raw data. The algorithm fits two alternative models to the raw data average amplitude curve to derive the correct river surface velocity: a Gaussian one peak model, or a Gaussian two peaks model.Results indicate that river flow velocity and drone-induced propwash velocity can be found in the river’s lower flow velocity portions (i.e., surface velocity between 30 cm/s and 80 cm/s), while the drone-induced velocity can be neglected in fast and highly turbulent flows (i.e., surface velocity > 80 cm/s). To verify the river flow velocity derived from Doppler radar, a mean PIV value within the footprint of the Doppler radar at each waypoint was calculated. Finally, quantitative comparisons of electromagnetic velocity sensor data (OTT MF Pro) with STIV, mean PIV and Doppler radar revealed that UAS-borne Doppler radar could reliably measure the river flow velocity.

The present dissertation has investigated the influence of injection parameters on air/fuel mixture and combustion processes in a DISI engine, through advanced diagnostics. It is possible to distinguish three parts of the work: the spray macroscopic parameters characterization, the spray break-up investigation and the study of the effects of injection timing and duration on the combustion process. In the first stage, the influence of injection pressure and duration on the fuel mass rate and the spray morphology has been analysed. A fuel injection rate meter based on the Bosch Tube principle has provided useful information about the time resolved behaviour of the delivered mass highlighting both transient, such as needle lift and nozzle closing operation, and quasi steady stages of the injection event. 2D Mie-scattering imaging and Particle Image Velocimetry technique have been used for characterizing the liquid spray morphology in terms of tip penetration, cone angle and velocity vector distribution. Even if the injection parameters affect the overall spray geometry, the characterization of the inner structure of the spray is fundamental for featuring the atomization phenomena which influence the fuel - air interaction. Therefore, Phase Doppler Anemometry (PDA) and Laser Doppler Velocimetry (LDV) have been applied for providing information about the velocity and size of droplets. Trials have been performed at different injection pressures and distances from the nozzle, along two different axes: the first one corresponding to the jet axis, the second one on the jet edge. Especially at the higher injection pressure, accurate tests have been possible only at a certain distance from the nozzle, where the spray is more dilute and the laser beam can cross the jet core. For this reason X-ray absorption measurements have been performed in order to investigate high-dense regions of fuel sprays, immediately downstream of the nozzle, providing quantitative measurements of the fuel. X-rays penetrate the dense part of fuel spray because of its weak interaction with the hydrocarbon chain due to their low atomic number. X-ray radiography and tomography have been used to investigate the spray core and reconstruct the 3D inner structure. The information about the spray development has been used to optimize the injection strategies of an optically accessible DISI engine operating at mid load condition, at a fixed speed of 2000 rpm. UV-visible imaging has been performed on the engine for investigating the influence of the injection duration and timing on the flame front propagation, while natural emission spectroscopy has been applied to characterize the formation and the evolution of the main compounds featuring the spark ignition and combustion processes. Exhaust emission measurements (HC, CO and NOx) have been correlated with pressure related data and optical results.

This paper presents a comparison of microwave radar surface velocity estimates to the estimates derived from video observations in the surf zone. The data presented here were collected during the Nearshore Canyon Experiment (NCEX) in the fall of 2003. The radar estimates are inferred from the Doppler shift of the backscattered radiation while video velocity estimates were produced using particle image velocimetry (PIV) technique. Comparisons of longshore velocity estimates show high spatial correlation within the central surf zone. The comparisons of the near cross-shore velocity shows the importance of bore velocity removal while showing high spatial correlation when the bias is removed. Both alongshore and cross-shore velocity estimates display discrepancies in the breaker and the swash zones.

For development of PWR spacer grids, it is necessary to confirm mechanical strength and thermal-hydraulic characteristics. Mitsubishi has applied Computational Fluid Dynamics (CFD) to thermal-hydraulic design of spacer grids. To satisfy the requirement of high thermal performance spacer grid, the compatibility of low-pressure loss and high Critical Heat Flux (CHF) performance is necessary; therefore, parametric CFD analyses have been carried out for new spacer grid designs. Related to spacer grid design, i.e., strap structures and mixing vane, the parametric analyses have been carried out to estimate pressure-loss of each spacer grid. Moreover, thermal analyses, where heat generation from fuel rods was taken into account, have been carried out to evaluate coolant mixing capability, which is assumed to relate the CHF performance, by comparing fluid peak temperature of each grid design. In our previous study (ICONE11-36087), the rod type Laser Doppler Velocimetry (rod LDV) and Particle Imaging Velocimetry (PIV) technique were applied to cross-flow and axial flow measurements in rod gaps and sub-channels to obtain reference data for verification of CFD estimation. Estimated velocity fields at the downstream of the grid were quantitatively compared with the measurements. As a result, it was confirmed that the CFD modeling estimated flow behavior in the rod bundle appropriately. In this study, CFD under single-phase condition, which took into account heat generation from rods, was performed to simulate flow conditions of water DNB test with the same design grid of the previous study. The correlation between estimated enthalpy distribution around fuel rods by the CFD and the CHF rods in the DNB test was examined. This study was performed in collaboration with Westinghouse Electric Company and Mitsubishi Heavy Industries, Ltd.

The paper presents a comparison between two sets of experimental results in a centrifugal flow pump. The tested impeller is the so‐called SHF impeller for which many experimental data have been continuously produced to built databases for CFD code validations with various levels of approximation. Measurements have been performed using optical techniques: 2D particle image velocimetry (PIV) technique on an air test model and 2D laser doppler velocimetry (LDV) technique on a water model, both for different flow rates. For the present study, results obtained by these optical techniques are compared together in terms of phase averaged velocity and velocity fluctuations inside the impeller flow passage for design flow rate.

An investigation of MHD effects on a Flibe (Li2BeF4) simulant fluid has been conducted under the US-Japan JUPITER-II collaboration program using “FLIHY” pipe flow facility at UCLA. The present paper reports a development of unique experimental techniques using aqueous solution of potassium hydroxide as a Flibe simulant. In order to apply a particle image velocimetry (PIV) technique for magnetic field condition, special optical devices were developed. The PIV measurements of MHD turbulent pipe flow at Re = 5300 were performed, and modification of the mean flow velocity as well as turbulence suppression was observed. A flat velocity profile in the pipe center and a steep velocity gradient in the near-wall region at Ha = 20 exhibits typical characteristics of Hartmann flow.

When small particles, e.g., glass, flour, pollen, etc., come in contact with a fluid-liquid interface they disperse so quickly to form a monolayer on the interface that it appears explosive, especially on the surface of mobile liquids like water. This is a consequence of the fact that the adsorption of a particle in an interface causes a lateral flow on the interface away from the particle. In this study we use the particle image velocimetry (PIV) technique to measure the transient three-dimensional flow that arises due to the adsorption of spherical particles. The PIV measurements show that the flow develops a fraction of a second after the adsorption of the particle and then persists for several seconds. The fluid below the particle rises upwards and on the surface moves away from the particle. These latter PIV results are consistent with the surface-velocity measurements performed in earlier studies. The strength of the induced flow, and the time duration for which the flow persists, both decrease with decreasing particle size.Copyright © 2013 by ASME

<p>Image-based methods for measuring surface flow velocities in rivers have several advantages, one of them being that the sensor (camera) is not in contact with the water and its mounting position is very flexible hence there is no need of expensive structures to mount it. Additionally, it is possible to measure the whole river width. On the other hand, environmental factors, like wind, can affect the surface velocity and the have an impact on the accuracy of the measurements.</p><p><span>Herein we present an analysis of the wind effect on </span><span>the image based surface velocity at </span><span>Rhine river</span><span>, at the border between Switzerland and Austria. At this location the river width is of approximately 100 meters under low flow conditions, while the width of its floodplain is of about 200 m. </span><span>A</span><span>n</span> <span>ATMOS 22 ultrasonic anemometer </span><span>was installed </span><span>at the site to measure the wind </span><span>intensity</span><span> as well as </span><span>its</span><span> direction. </span></p><p><span>A time series of flow velocities and wind </span><span>from May to October 2019 </span><span>was analyzed. During this period, the </span><span>average disch</span><span>a</span><span>rge </span><span>was </span><span>320 m</span><sup><span>3</span></sup><span>/s and the average </span><span>flow </span><span>velocity 1.7 m/s. While the average wind velocity was of </span><span>2</span><span>.</span><span>3</span><span>m/s which roughly follows the same direction of the river flow.</span></p><p>A rating curve following a power law function was fitted to the image based surface flow measurements. It was found that for maximum wind speeds of 10 m/s, blowing in the opposite direction of the river flow, there was a deviation of 8%. For the average wind speed of 2.3m/s, the deviation was found to be 3%.</p>

The micro particle image velocimetry (MPIV) technique has been widely adopted for the measurements of velocity field in microfluidic devices. To simply the investigation of the transient phenomena in a usual biological microfluidic device, this study, a novel high frequency MPIV technique without fluorescence, was developed by combining a high-speed CMOS camera, a long working distance zoom microscope, a high power LED along with reversed image algorithm. The depth of the measurement plane is defined by the focusing characteristics of the probing optics through volume illumination. With efficacious contrast base, the unfocused particle images, which are out of the measurement plane, create background noise that decreases the single-to-noise ratio of the particle image fields. The velocity fields of fluid in the micro device were visualized for a time resolution of 125μs and a spatial resolution of 2.2×2.2m^2. The result shows that the numerical predictions are very similar to the measurement of high frequency MPIV inside the micro flow device. Consequently, by using the novel MPIV technique, the time resolution can be abbreviated and the tracing particles require no decorating with fluorescing.

With the global population on the rise and arable land diminishing, the need for sustainable and precision agriculture has become increasingly important. This study explores the application of unoccupied aerial systems (UAS) in precision agriculture, specifically focusing on Montmorency cherry orchards in Payson, Utah. Despite the widespread use of UAS for various crops, there is a notable gap in research concerning cherry orchards, which present unique challenges due to their physical structure. UAS data were gathered using an RTK-enabled DJI Mavic 3M, equipped with both RGB and multispectral cameras, to capture high-resolution imagery. This research investigates two primary applications of UAS in cherry orchards: tree height mapping and crop health assessment. We also evaluate the accuracy of tree height measurements derived from three UAS data processing software packages: Pix4D, Drone2Map, and DroneDeploy. Our results indicated that DroneDeploy provided the closest relationship to ground truth data with an R2 of 0.61 and an RMSE of 31.83 cm, while Pix4D showed the lowest accuracy. Furthermore, we examined the efficacy of RGB-based vegetation indices in predicting leaf area index (LAI), a key indicator of crop health, in the absence of more expensive multispectral sensors. Twelve RGB-based indices were tested for their correlation with LAI, with the IKAW index showing the strongest correlation (R = 0.36). However, the overall explanatory power of these indices was limited, with an R2 of 0.135 in the best-fitting model. Despite the promising results for tree height estimation, the correlation between RGB-based indices and LAI was underwhelming, suggesting the need for further research.

Nonstationary velocity fields that arise during the development of flows behind shock (blast) waves initiated by pulsed surface sliding discharge in air at a pressure of (2–4) × 104 Pa have been experimentally studied by the particle image velocimetry (PIV) technique. Plasma sheets (nanosecond discharges slipping over a dielectric surface) were initiated on walls of a rectangular chamber. Spatial analysis of the shape of shock-wave fronts and the distribution of flow velocities behind these waves showed that the pulsed energy deposition is homogeneous along discharge channels of a plasma sheet, while the integral visible plasma glow intensity decreases in the direction of channel propagation.

Measuring river surface velocity is crucial for hydrological monitoring. However, traditional methods exhibit significant limitations under extreme weather conditions and emergency scenarios. In this study, we propose OF-PhyNet, an innovative hybrid neural network architecture designed as an image-based velocimetry method to improve the accuracy of river surface velocity estimation. By integrating an optical flow algorithm with a physics-informed neural network, OF-PhyNet achieves deep coupling of motion feature extraction with fluid dynamics constraints. To address the challenges posed by uneven particle distribution and illumination variations in natural rivers, we introduce a feature extraction strategy based on K-means clustering and morphological operations, which enables effective flow field segmentation and reliable identification of particle regions. Experimental validation conducted in the Heihe River Basin, using Stalker Pro II surface velocity radar (SVR) as a reference, demonstrates that OF-PhyNet achieves a mean absolute error of 0.054 m/s and a relative error of 7.22% across 12 cross-sectional measurement points, substantially outperforming PIVLab with 11.65% and the Horn-Schunck algorithm with 25.84% relative error. As a UAV-based image velocimetry approach, OF-PhyNet offers exceptional mobility for rapid flood monitoring and enables robust reconstruction of flow fields in particle-sparse regions, delivering precise non-contact river velocity measurements beyond the reach of traditional methods.

There is relatively little literature concerning the effect of Reynolds number on multi-hole aerodynamic probe performance. In particular, there is almost no discussion in the literature regarding the underlying mechanisms of Reynolds number (Re) sensitivity for such probes. In order to close this gap, detailed investigations of the effect of Re on a five-hole probe have been performed using both particle image velocimetry (PIV) techniques and oil flow visualizations. Wind- and water-tunnels were used to cover a wide range of Re. The open-access Oxford Probe was used for these studies because of the readily available data-sets and processing routines and to allow future comparisons by other authors. Complex flow dynamics including flow separation and re-attachment were identified, which cause Re-sensitivity of the calibration map at low Re even for low yaw or pitch angles. By comparing calibration maps across a wide range of Re, we demonstrate that the Oxford Probe can be employed without much loss of accuracy at lower Re levels than initially (conservatively) suggested, and quantify the errors in the extreme low-Re regime. Overall, we demonstrate the robustness of the Oxford Probe concept across a wide range of Re conditions, we more clearly defined the low-Re limit for the probe design and quantify errors below this limit, and we illustrate the fundamental mechanisms for Re-sensitivity of multi-hole probes.

Turbulent flow of a Non-Newtonian polymer fluid through concentric annuli was studied using 9 m long horizontal flow loop (inner to outer pipe radius ratio = 0.4) and Particle Image Velocimetry (PIV) technique. A high molecular weight, anionic, water soluble, acrylamide-based copolymer was used as a viscosifier. The aqueous polymer solution exhibited power law rheology with strong shear thinning behavior. Experiments with aqueous polymer solutions have been conducted at the same bulk velocity as water experiments. Mean bulk velocity values changed from 0.827 to 1.164 m/s, corresponding to solvent (water) Reynolds number from 46000 to 68000. Mean axial velocity and Reynolds stress distribution in the near wall region (considering both inner and outer walls) and in the whole annular gap were determined. Axial mean velocity profile was found to be following the universal wall law close to the wall, but it deviated from logarithmic law with an increased slope in the logarithmic zone. Radial locations of the maximum velocity values were also determined and compared to that of water flow. For the range of Reynolds numbers studied, location of maximum velocity was found to be dependent on Reynolds number. As Reynolds number increased, location of maximum velocity moved closer to inner wall. Reynolds and laminar stresses were calculated. Reynolds stresses for polymer fluid flow decreased with increasing polymer concentration and were found to be always smaller than that of water. Laminar stresses, on the other hand, were found to be always higher at higher polymer concentration, reflecting the effect of the fluid viscosity.

The convection pattern and the evolution of mushy zone, temperature and solidification structure are measured during solidification of NH4Cl-70%H2O solution in a water-cooled copper mold with transparent sidewalls. The natural convection and crystal sedimentation are measured via Particle Image Velocimetry (PIV) technique. This experiment is simulated using a 5-phase mixed columnar-equiaxed solidification model proposed by current authors [Comp. Mater. Sci. 50 (2010) 32-4]. The 5 phases comprise the extradendritic melt, the solid dendrite and interdendritic melt inside the equiaxed grains, the solid dendrite and interdendritic melt inside the columnar grains. Melt convection and crystal sedimentation are considered. It is demonstrated that the experimentally observed flow patterns and the solidification structure can be qualitatively reproduced. Reasons for the quantitative deviation between the simulation and experiment are discussed. Analysis of the modeling results in details and improvement of the calculation accuracy will be in a subsequent step.