PIV field measurements of surface flow on a river by using a helicopter

2001 ◽  
Vol 21 (2Supplement) ◽  
pp. 61-62
Author(s):  
Ichiro FUJITA ◽  
Shiro AYA ◽  
Masahiro TAMAI ◽  
Kohsei TAKEHARA ◽  
Hitoshi MIYAMOTO ◽  
...  
Keyword(s):  
Field Measurements ◽  
Surface Flow

Experiments on the stability and transition of wind-driven water surfaces

2001 ◽  
Vol 446 ◽  
pp. 25-65 ◽  
Author(s):  
FABRICE VERON ◽  
W. KENDALL MELVILLE
Keyword(s):  
Surface Current ◽  
Field Measurements ◽  
Surface Flow ◽  
Transition To Turbulence ◽  
Surface Velocity ◽  
Small Scale ◽  
Gas Transfer ◽  
Water Surfaces ◽  
Langmuir Circulations ◽  
The Stability

We present the results of laboratory and field measurements on the stability of wind-driven water surfaces. The laboratory measurements show that when exposed to an increasing wind starting from rest, surface current and wave generation is accompanied by a variety of phenomena that occur over comparable space and time scales. Of particular interest is the generation of small-scale, streamwise vortices, or Langmuir circulations, the clear influence of the circulations on the structure of the growing wave field, and the subsequent transition to turbulence of the surface flow. Following recent work by Melville, Shear & Veron (1998) and Veron & Melville (1999b), we show that the waves that are initially generated by the wind are then strongly modulated by the Langmuir circulations that follow. Direct measurements of the modulated wave variables are qualitatively consistent with geometrical optics and wave action conservation, but quantitative comparison remains elusive. Within the range of parameters of the experiments, both the surface waves and the Langmuir circulations first appear at constant Reynolds numbers of 370 ± 10 and 530 ± 20, respectively, based on the surface velocity and the depth of the laminar shear layer. The onset of the Langmuir circulations leads to a significant increase in the heat transfer across the surface. The field measurements in a boat basin display the same phenomena that are observed in the laboratory. The implications of the measurements for air–sea fluxes, especially heat and gas transfer, and sea-surface temperature, are discussed.

scholarly journals Surface Flow Measurement From a Helicopter and Field Measurements of the Confluence Region of the Yodo River

2006 ◽  
Vol 26 (Supplement2) ◽  
pp. 35-38
Author(s):  
Kosuke HIRAI ◽  
Masashi OZONO ◽  
Takashi DEGUCHI ◽  
Ryota TSUBAKI ◽  
Ichiro FUJITA ◽  
...  
Keyword(s):  
Flow Measurement ◽  
Field Measurements ◽  
Surface Flow ◽  
Confluence Region

scholarly journals Optical Ortho-Rectification for Image-Based Stream Surface Flow Observations Using a Ground Camera

2021 ◽  
Vol 3 ◽  
Author(s):  
Ryota Tsubaki ◽  
Runye Zhu
Keyword(s):  
Optical System ◽  
Image Acquisition ◽  
Field Measurements ◽  
Surface Flow ◽  
Velocity Estimation ◽  
Image Resolution ◽  
Direction Parallel ◽  
New Approach ◽  
Stream Surface ◽  
Raster Image

Image-based stream flow observation consists of three components: (i) image acquisition, (ii) ortho-rectification, and (iii) an image-based velocity estimation. Ortho-rectification is a type of coordinate transformation. When ortho-rectifying a raster image, pixel interpolation is needed and causes the degradation of image resolution, especially in areas located far from the camera and in the direction parallel to the viewing angle. When measuring the water surface flow of rivers with a wide channel width, reduced and distorted image resolution limits the applicability of image-based flow observations using terrestrial image acquisition. Here, we propose a new approach for ortho-rectification using an optical system. We employed an optical system embedded in an ultra-short throw projector. In the proposed approach, ortho-rectified images were obtained during the image acquisition phase, and the image resolution of recorded images was almost uniform in terms of physical coordinates. By conducting field measurements, characteristics of the proposed approach were validated and compared to a conventional approach.

scholarly journals AN ATEMPT OF FIELD MEASUREMENTS OF SURFACE FLOW ON A RIVER BY USING A HELICOPTER AIDED IMAGE VELOCIMETRY

2002 ◽  
Vol 46 ◽  
pp. 809-814 ◽  
Author(s):  
Kohsei TAKEHARA ◽  
Ichiro FUJITA ◽  
Yasuhide TAKANO ◽  
Goji T. ETOH ◽  
Shiro AYA ◽  
...  
Keyword(s):  
Field Measurements ◽  
Surface Flow ◽  
Image Velocimetry

scholarly journals Photogrammetry for Free Surface Flow Velocity Measurement: From Laboratory to Field Measurements

Water ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 1675
Author(s):  
Hang Trieu ◽  
Per Bergström ◽  
Mikael Sjödahl ◽  
J. Gunnar I. Hellström ◽  
Patrik Andreasson ◽  
...  
Keyword(s):  
Free Surface ◽  
Particle Tracking ◽  
Field Measurements ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Hydropower Plant ◽  
Surface Velocity ◽  
Camera System ◽  
Particle Tracking Method ◽  
Calibration Methods

This study describes a multi-camera photogrammetric approach to measure the 3D velocity of free surface flow. The properties of the camera system and particle tracking velocimetry (PTV) algorithm were first investigated in a measurement of a laboratory open channel flow to prepare for field measurements. The in situ camera calibration methods corresponding to the two measurement situations were applied to mitigate the instability of the camera mechanism and camera geometry. There are two photogrammetry-based PTV algorithms presented in this study regarding different types of surface particles employed on the water flow. While the first algorithm uses the particle tracking method applied for individual particles, the second algorithm is based on correlation-based particle clustering tracking applied for clusters of small size particles. In the laboratory, reference data are provided by particle image velocimetry (PIV) and laser Doppler velocimetry (LDV). The differences in velocities measured by photogrammetry and PIV, photogrammetry and LDV are 0.1% and 3.6%, respectively. At a natural river, the change of discharges between two measurement times is found to be 15%, and the corresponding value reported regarding mass flow through a nearby hydropower plant is 20%. The outcomes reveal that the method can provide a reliable estimation of 3D surface velocity with sufficient accuracy.

scholarly journals Inferring Surface Flow Velocities in Sediment-Laden Alaskan Rivers from Optical Image Sequences Acquired from a Helicopter

2020 ◽  
Vol 12 (8) ◽  
pp. 1282 ◽  
Author(s):  
Carl J. Legleiter ◽  
Paul J. Kinzel
Keyword(s):  
Remote Sensing ◽  
Field Measurements ◽  
Video Camera ◽  
Image Sequences ◽  
Surface Flow ◽  
Optical Image ◽  
Frame Rate ◽  
Digital Mapping ◽  
Lower Frame ◽  
Flow Velocities

The remote, inaccessible location of many rivers in Alaska creates a compelling need for remote sensing approaches to streamflow monitoring. Motivated by this objective, we evaluated the potential to infer flow velocities from optical image sequences acquired from a helicopter deployed above two large, sediment-laden rivers. Rather than artificial seeding, we used an ensemble correlation particle image velocimetry (PIV) algorithm to track the movement of boil vortices that upwell suspended sediment and produce a visible contrast at the water surface. This study introduced a general, modular workflow for image preparation (stabilization and geo-referencing), preprocessing (filtering and contrast enhancement), analysis (PIV), and postprocessing (scaling PIV output and assessing accuracy via comparison to field measurements). Applying this method to images acquired with a digital mapping camera and an inexpensive video camera highlighted the importance of image enhancement and the need to resample the data to an appropriate, coarser pixel size and a lower frame rate. We also developed a Parameter Optimization for PIV (POP) framework to guide selection of the interrogation area (IA) and frame rate for a particular application. POP results indicated that the performance of the PIV algorithm was highly robust and that relatively large IAs (64–320 pixels) and modest frame rates (0.5–2 Hz) yielded strong agreement ( R 2 > 0.9 ) between remotely sensed velocities and field measurements. Similarly, analysis of the sensitivity of PIV accuracy to image sequence duration showed that dwell times as short as 16 s would be sufficient at a frame rate of 1 Hz and could be cut in half if the frame rate were doubled. The results of this investigation indicate that helicopter-based remote sensing of velocities in sediment-laden rivers could contribute to noncontact streamgaging programs and enable reach-scale mapping of flow fields.

scholarly journals Hydrological Conditions Of Drained Lake Basins Of The Anadyr Lowland Under Changing Climatic Conditions

2021 ◽  
Vol 14 (4) ◽  
pp. 41-54 ◽  
Author(s):  
Оleg D. Tregubov ◽  
Vladimir E. Glotov ◽  
Pavel Ya. Konstantinov ◽  
Vladimir V. Shamov
Keyword(s):  
Coastal Zone ◽  
Active Layer ◽  
Air Temperature ◽  
Field Measurements ◽  
Climatic Conditions ◽  
Surface Flow ◽  
The Arctic ◽  
Mean Annual Precipitation ◽  
Lake Area ◽  
Lake Basins

The lakes of the Arctic lowlands are both the unique indicator and the result of climatic and permafrost changes. Remote sensing methods and field measurements were used to consider the patterns and features of the morphometric indicators dynamics of the Anadyr lowland lakes over 65 years. We analyzed the parameters of 36 lakes with an area of 0.02–0.3 km2 located in the bottoms of drained lake basins, in river floodplains, on sea-shore terraces. Field studies were conducted on 22 typical lakes. The considered dynamics of seasonal thawing are based on the monitoring of the active layer for 1994–2020. Due to an increase of mean annual air temperature by 1.8 °C, as well as an increase and then a decrease in the mean annual precipitation by 135 mm, the average share of a lake area in the study area decreased by 24%. It is shown for the first time that cryogenic processes of the lacustrine coastal zone affect the change in the area of lakes simultaneously with the influence of precipitation and air temperature. Based on field observations, we considered two causes of natural drainage: discharge of the lakes through newly formed thermokarst and thermoerosional surface flow channels and decrease in suprapermafrost groundwater recharge as a result of changing depth of seasonally thawed active layer in the coastal zone.

scholarly journals Surface Flow Velocities From Space: Particle Image Velocimetry of Satellite Video of a Large, Sediment-Laden River

2021 ◽  
Vol 3 ◽  
Author(s):  
Carl J. Legleiter ◽  
Paul J. Kinzel
Keyword(s):  
Remote Sensing ◽  
Particle Image Velocimetry ◽  
River Discharge ◽  
Water Surface ◽  
Particle Image ◽  
Field Measurements ◽  
Surface Flow ◽  
Cross Sectional ◽  
Image Velocimetry ◽  
Flow Velocities

Conventional, field-based streamflow monitoring in remote, inaccessible locations such as Alaska poses logistical challenges. Safety concerns, financial considerations, and a desire to expand water-observing networks make remote sensing an appealing alternative means of collecting hydrologic data. In an ongoing effort to develop non-contact methods for measuring river discharge, we evaluated the potential to estimate surface flow velocities from satellite video of a large, sediment-laden river in Alaska via particle image velocimetry (PIV). In this setting, naturally occurring sediment boil vortices produced distinct water surface features that could be tracked from frame to frame as they were advected by the flow, obviating the need to introduce artificial tracer particles. In this study, we refined an end-to-end workflow that involved stabilization and geo-referencing, image preprocessing, PIV analysis with an ensemble correlation algorithm, and post-processing of PIV output to filter outliers and scale and geo-reference velocity vectors. Applying these procedures to image sequences extracted from satellite video allowed us to produce high resolution surface velocity fields; field measurements of depth-averaged flow velocity were used to assess accuracy. Our results confirmed the importance of preprocessing images to enhance contrast and indicated that lower frame rates (e.g., 0.25 Hz) lead to more reliable velocity estimates because longer capture intervals allow more time for water surface features to translate several pixels between frames, given the relatively coarse spatial resolution of the satellite data. Although agreement between PIV-derived velocity estimates and field measurements was weak (R2 = 0.39) on a point-by-point basis, correspondence improved when the PIV output was aggregated to the cross-sectional scale. For example, the correspondence between cross-sectional maximum velocities inferred via remote sensing and measured in the field was much stronger (R2 = 0.76), suggesting that satellite video could play a role in measuring river discharge. Examining correlation matrices produced as an intermediate output of the PIV algorithm yielded insight on the interactions between image frame rate and sensor spatial resolution, which must be considered in tandem. Although further research and technological development are needed, measuring surface flow velocities from satellite video could become a viable tool for streamflow monitoring in certain fluvial environments.

scholarly journals A Computational Fluid Dynamics Model for a Water Vortex Power Plant as Platform for Etho- and Ecohydraulic Research

Energies ◽  
2021 ◽  
Vol 14 (3) ◽  
pp. 639
Author(s):  
Dennis Powalla ◽  
Stefan Hoerner ◽  
Olivier Cleynen ◽  
Nadine Müller ◽  
Jürgen Stamm ◽  
...  
Keyword(s):  
Power Plant ◽  
Numerical Model ◽  
Large Scale ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Field Measurements ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Navier Stokes ◽  
Two Phase

The objective of the present paper is to develop a validated numerical model of a water vortex power plant that serves as a digital twin for further studies such as assessments of the ethohydraulic characteristics or the performance of such devices. The reference for the validation process is a large-scale hydraulic installation equipped with a full-scale water vortex power plant prototype installed in Dresden (Germany), where flow field measurements were carried out using three-dimensional Acoustic Doppler Velocimetry. The numerical model was implemented within the software package Star-CCM+. The unsteady, two-phase flow was solved with the Reynolds-Averaged Navier–Stokes equations in a Eulerian Multiphase approach, deploying a Volume of Fluid method to describe the free-surface flow. Water level and flow velocities were systematically compared in key areas of the device, demonstrating that the simulation is in good agreement with experimental observations. Relative differences are limited to at most 4% regarding water height in the system, and even the much more challenging velocity fields are reproduced with typical relative errors of roughly 10%. This validates the ability of the model to model the challenging flow conditions found in a water vortex power plant, enabling subsequent studies of the characteristics of this power plant concerning fish migration.

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