Simultaneous assessment of peak-locking and CCD readout errors through a multiple Δt strategy

Legrand, Mathieu; Nogueira, J.; Ventas, R.; Lecuona, A.

doi:10.1007/s00348-011-1248-2

Cited by 7 publications

(8 citation statements)

References 16 publications

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“…However, charge transfer efficiency is not identical for the first and for the second image capture readout, leading to a residual differential bias in the digitally registered particle displacement. This bias error has already been observed and its magnitude evaluated for particular cases by Nogueira et al (2009) and Legrand et al (2010Legrand et al ( , 2011.…”

Section: Readout Smearingsupporting

confidence: 55%

“…The conclusion leads to highlighting the importance of avoiding spurious sources of light and the use of interferometric filters as means to reduce measurement errors. Nogueira et al (2009) as well as Legrand et al (2011) have already discussed the feasibility of a multiple t strategy designed to evaluate the bias error, including the possibility of correcting it under certain circumstances. However, the present work sheds light on the physical phenomenon of particle image smearing, and predicts the magnitude and whether or not some readout displacement bias error would be present in the measurements.…”

Section: Displacement Bias Error In Real Piv Ccd Camerasmentioning

confidence: 99%

“…Among the many lines of study in the use of CCD cameras in PIV, Nogueira et al (2009) and Legrand et al (2011) recently reported that the double-frame CCD camera readout process present some relevant bias in the location of particle images, thus biasing the velocity measurement. Both works deal with the bias impact on the measurement error, and propose a way to evaluate its magnitude using a simple multiple t strategy, available for any usual PIV setup, in the image acquisition stage.…”

Section: Introductionmentioning

confidence: 99%

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CCD image sensor induced error in PIV applications

Legrand¹,

Nogueira²,

Vargas³

et al. 2014

Meas. Sci. Technol.

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The readout procedure of charge-coupled device (CCD) cameras is known to generate some image degradation in different scientific imaging fields, especially in astrophysics. In the particular field of particle image velocimetry (PIV), widely extended in the scientific community, the readout procedure of the interline CCD sensor induces a bias in the registered position of particle images. This work proposes simple procedures to predict the magnitude of the associated measurement error. Generally, there are differences in the position bias for the different images of a certain particle at each PIV frame. This leads to a substantial bias error in the PIV velocity measurement (∼0.1 pixels). This is the order of magnitude that other typical PIV errors such as peak-locking may reach. Based on modern CCD technology and architecture, this work offers a description of the readout phenomenon and proposes a modeling for the CCD readout bias error magnitude. This bias, in turn, generates a velocity measurement bias error when there is an illumination difference between two successive PIV exposures. The model predictions match the experiments performed with two 12-bit-depth interline CCD cameras (MegaPlus ES 4.0/E incorporating the Kodak KAI-4000M CCD sensor with 4 megapixels). For different cameras, only two constant values are needed to fit the proposed calibration model and predict the error from the readout procedure. Tests by different researchers using different cameras would allow verification of the model, that can be used to optimize acquisition setups. Simple procedures to obtain these two calibration values are also described.

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Section: Readout Smearingsupporting

confidence: 55%

Section: Displacement Bias Error In Real Piv Ccd Camerasmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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CCD image sensor induced error in PIV applications

Legrand¹,

Nogueira²,

Vargas³

et al. 2014

Meas. Sci. Technol.

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“…A number of methods have been proposed to exploit multiple images in the form of successive pairs of PIV images provided by current highspeed PIV cameras. These approaches improve the double-pulsed PIV measurements by using images at multiple times to optimize parameters (Legrand et al 2012), averaging over successive measurements assuming constant velocity (A. Sciacchitano, F. Scarano & B. Wieneke, private communication) or using adjustable time delays between double pulses (Hain & Kähler 2007). …”

Section: Time-resolved Pivmentioning

confidence: 99%

Particle Image Velocimetry for Complex and Turbulent Flows

Westerweel

Elsinga

Adrian

2013

Annu. Rev. Fluid Mech.

432

211

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Particle image velocimetry (PIV) has evolved to be the dominant method for velocimetry in experimental fluid mechanics and has contributed to many advances in our understanding of turbulent and complex flows. In this article we review the achievements of PIV and its latest implementations: time-resolved PIV for the rapid capture of sequences of vector fields; tomographic PIV for the capture of fully resolved volumetric data; and statistical PIV, designed to optimize measurements of mean statistical quantities rather than instantaneous fields. In each implementation, the accuracy and spatial resolution are limited. To advance the method to the next level, we need a completely new approach. We consider the fundamental limitations of twopulse PIV in terms of its dynamic ranges. We then discuss new paths and developments that hold the promise of achieving a fundamental reduction in uncertainty. 409

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“…The discussion above shows that the problem of peak locking errors due to small particle image diameters, especially in the case of CMOS cameras for high-speed PIV measurements, is still unsolved. In such a situation, a continuous development in the approaches based on multiple Δt image acquisition (Nogueira et al 2009, Nogueira et al 2011, Legrand et al 2012, Legrand et al 2018 has shown a high potential in peak-locking error quantification and correction, Δt being a time separation between two frames in PIV. Using a set of different Δt's for the same flow measurement allows for segregating the errors that scale with Δt (e.g.…”

Section: Introductionmentioning

confidence: 99%

Multi-Δt approach for peak-locking error correction and uncertainty quantification in PIV

Adatrao

Bertone

Sciacchitano

2021

Meas. Sci. Technol.

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A novel approach is devised for the quantification of the systematic uncertainty due to peak locking in particle image velocimetry (PIV), which also leads to correction of the peak-locking errors. The approach relies on a linear regression of the measured displacements from multiple Δt acquisitions (Δt being the time separation between two frames of an image pair). In presence of peak locking, the measured particle image displacement is not a linear function of Δt as the measurement error varies non-linearly with the sub-pixel particle image displacement. In the proposed approach, image acquisition is conducted with multiple Δt's, and then a linear regression is carried out among the measured time-averaged displacements at different Δt's, yielding a regression displacement. When the Δt's are selected properly, the latter represents a correction to the measured displacement where systematic errors due to peak locking are significantly diminished. The expression of the standard uncertainty in the regression displacement is provided. The regression displacement (and velocity) can also be used to quantify the systematic uncertainty due to peak locking in the measured time-averaged displacements (and velocities). The methodology is first assessed with synthetic data and then applied to planar PIV experiments on a uniform flow and an airfoil wake flow. Reference measurements with much larger Δt than the Δt's of the actual measurements (such that relative peak-locking errors are negligible for the former) are used to validate the proposed approach in both the experiments. Uncertainty coverages for the estimated uncertainties in the velocities measured in the experiments of the uniform flow and the wake flow are of 67% and 59%, respectively, which are comparable to 68% confidence level at which the uncertainties are computed. This proves the validity of the proposed multi-Δt approach for peak-locking uncertainty quantification.

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Simultaneous assessment of peak-locking and CCD readout errors through a multiple Δt strategy

Cited by 7 publications

References 16 publications

CCD image sensor induced error in PIV applications

CCD image sensor induced error in PIV applications

Particle Image Velocimetry for Complex and Turbulent Flows

Multi-Δt approach for peak-locking error correction and uncertainty quantification in PIV

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