scholarly journals Numerical Uncertainty in Density Estimation for Background Oriented Schlieren

2021 ◽  
Vol 1 (1) ◽  
Author(s):  
Jiacheng Zhang ◽  
Lalit Rajendran ◽  
Sally Bane ◽  
Pavlos Vlachos
Keyword(s):  
Density Gradient ◽  
Systematic Uncertainty ◽  
Density Measurement ◽  
Random Errors ◽  
Target Pattern ◽  
Density Estimates ◽  
Total Uncertainty ◽  
Spatially Resolved ◽  
Background Oriented Schlieren ◽  
Good Agreement

Background Oriented Schlieren (BOS) is an image-based density measurement technique. BOS estimates the density gradient from the apparent distortion of a target pattern viewed through a medium with varying density using cross-correlation, tracking, or optical flow algorithms. The density gradient can then be numerically integrated to yield a spatially resolved estimate of the density [1]. A method was recently proposed to estimate the a-posteriori instantaneous and spatially resolved density uncertainty for BOS [2] and showed good agreement between the propagated uncertainties and the random error. However, the density uncertainty quantification method could not account for the systematic uncertainty in the density field due to the discretization errors introduced during the numerical integration, which could be much larger than the displacement random errors [2]. In this work, we propose a method to estimate the numerical uncertainty introduced by the density integration in BOS measurements, using a Richardson extrapolation framework. A procedure is also introduced to combine this systematic uncertainty with the random uncertainty from the previous work to provide an instantaneous, spatially-resolved total uncertainty on the density  estimates. The method will be tested with synthetic fields and synthetic BOS images.

scholarly journals Spatially resolved measurements of the solar photospheric oxygen abundance

2020 ◽  
Vol 643 ◽  
pp. A142
Author(s):  
M. Cubas Armas ◽  
A. Asensio Ramos ◽  
H. Socas-Navarro
Keyword(s):  
Systematic Errors ◽  
Model Atmosphere ◽  
Nuisance Parameters ◽  
Hierarchical Bayesian Model ◽  
Random Errors ◽  
Vacuum Tower ◽  
Oxygen Abundance ◽  
Spatially Resolved ◽  
Good Agreement

Aims. We report the results of a novel determination of the solar oxygen abundance using spatially resolved observations and inversions. We seek to derive the photospheric solar oxygen abundance with a method that is robust against uncertainties in the model atmosphere. Methods. We use observations with spatial resolution obtained at the Vacuum Tower Telescope to derive the oxygen abundance at 40 different spatial positions in granules and intergranular lanes. We first obtain a model for each location by inverting the Fe I lines with the NICOLE inversion code. These models are then integrated into a hierarchical Bayesian model that is used to infer the most probable value for the oxygen abundance that is compatible with all the observations. The abundance is derived from the [O I] forbidden line at 6300 Å taking into consideration all possible nuisance parameters that can affect the abundance. Results. Our results show good agreement in the inferred oxygen abundance for all the pixels analyzed, demonstrating the robustness of the analysis against possible systematic errors in the model. We find a slightly higher oxygen abundance in granules than in intergranular lanes when treated separately (log(ϵO) = 8.83 ± 0.02 vs. log(ϵO) = 8.76 ± 0.02), which is a difference of approximately 2-σ. This tension suggests that some systematic errors in the model or the radiative transfer still exist but are small. When taking all pixels together, we obtain an oxygen abundance of log(ϵO) = 8.80 ± 0.03, which is compatible with both granules and lanes within 1-σ. The spread of results is due to both systematic and random errors.

scholarly journals Expansion of the Range of Refrigeration of the Surface Heat Flow Unit Under Conductive Energy Produce

2018 ◽  
pp. 27-32
Author(s):  
S. Kovtun
Keyword(s):  
Heat Flux ◽  
Heat Flow ◽  
Flux Density ◽  
Heat Flux Density ◽  
Dynamic Range ◽  
Density Measurement ◽  
Lower Boundary ◽  
Surface Heat ◽  
Total Uncertainty ◽  
Unit Of Measurement

The article presents the results of investigations of factors that influence the accuracy of reproduction of the unit of measurement of the surface density of the heat flow by conductivity. Components of the uncertainty of the surface heat flux density measurement were analyzed using the Ishikawa cause-and-effect diagram, as shown in Fig. 1 The mathematical model of the method of reproduction of the unit of measurement was obtained, which takes into account the influence of the sources of uncertainty by making the corresponding corrections. The possibility of extending the lower boundary of the dynamic range by the correction of the factors having the greatest influence is substantiated. The rationale is based on the estimation of the uncertainty of the individual components, which, in the course of the correction of their impact, should not exceed the values (achieved to date). As an example, the calculation of the total uncertainty in the reproduction of the heat flux density of 20 W·m-2 is given. Table 1 contains all data important for the uncertainty analysis such as input quantities, their estimated values as well as the associated sensitivity coefficients and the variances determined.

Detecting Multiple Ground Contacts in Cloud-to-Ground Lightning Flashes

2009 ◽  
Vol 26 (11) ◽  
pp. 2392-2402 ◽  
Author(s):  
Christina A. Stall ◽  
Kenneth L. Cummins ◽  
E. Philip Krider ◽  
John A. Cramer
Keyword(s):  
Standard Deviation ◽  
Rise Time ◽  
Random Errors ◽  
Peak Current ◽  
Video Recordings ◽  
Lightning Detection ◽  
Cloud To Ground Lightning ◽  
The U.S ◽  
Good Agreement ◽  
Cg Lightning

Abstract Video recordings of cloud-to-ground (CG) lightning flashes have been analyzed in conjunction with correlated stroke reports from the U.S. National Lightning Detection Network (NLDN) to determine whether the NLDN is capable of identifying the different ground contacts in CG flashes. For 39 negative CG flashes that were recorded on video near Tucson, Arizona, the NLDN-based horizontal distances between the first stroke and the 62 subsequent strokes remaining in a preexisting channel had a mean and standard deviation of 0.9 ± 0.8 km and a median of 0.7 km. The horizontal distances between the first stroke and the 59 new ground contacts (NGCs) had a mean and standard deviation of 2.3 ± 1.7 km and a median of 2.1 km. These results are in good agreement with prior measurements of the random errors in NLDN positions in southern Arizona as well as video- and thunder-based measurements of the distances between all ground contacts in Florida. In cases where the distances between ground contacts are small and obscured by random errors in the NLDN locations, measurements of the stroke rise time, estimated peak current, and stroke order can be utilized to enhance the ability of the NLDN to identify strokes that produce new ground terminations.

scholarly journals Density measurements for rectangular free jets using background-oriented schlieren

2013 ◽  
Vol 117 (1194) ◽  
pp. 771-785 ◽  
Author(s):  
T. J. Tipnis ◽  
M. V. Finnis ◽  
K. Knowles ◽  
D. Bray
Keyword(s):  
Supersonic Jet ◽  
Digital Camera ◽  
Shock Cell ◽  
Axisymmetric Jets ◽  
Cell Spacing ◽  
Optical Alignment ◽  
Background Oriented Schlieren ◽  
Set Up ◽  
Axis Switching ◽  
Good Agreement

AbstractAn experimental study incorporating the use of the Background-Oriented Schlieren (BOS) technique was performed to measure the density field of a rectangular supersonic jet. This technique is easier to set up than conventional schlieren since the optical alignment involving the various mirrors, lenses and knife-edge is replaced by a background pattern and a single digital camera. The acquired images which contain information of density gradients in the flow are solved as a Poisson equation and further processed using deconvolution and tomographic algorithms to generate a 3D domain which contains information about the actual density. 2D slices can then be extracted to quantitatively visualise the density along any required planes. The results from supersonic axisymmetric jets are used for validation of the code; these show excellent agreement with pre-validated CFD data. The results for a rectangular supersonic jet are then obtained. These show good agreement with the CFD data, in terms of shock-cell spacing and overall structure of the jet. The technique has proved useful for investigating axis-switching, a phenomenon generally associated with non-axisymmetric jets.

Hydrogen Atmospheres in the Absence of Thermodynamic Equilibrium. IV. The Solar Chromosphere

1948 ◽  
Vol 1 (4) ◽  
pp. 360
Author(s):  
RG Giovanelli
Keyword(s):  
Observational Data ◽  
Density Gradient ◽  
Electron Concentration ◽  
Hydrostatic Equilibrium ◽  
Profile Measurement ◽  
Solar Chromosphere ◽  
Hydrogen Atoms ◽  
Lower Accuracy ◽  
Good Agreement ◽  
Lower Chromosphere

A discussion of the observational data shows that in the range 0<z<2.5 x 108 cm. the electron concentration in the lower chromosphere may be expressed as Ne=5x 1011 exp(-6 x 10-9z) per cc., where z cm. is the height measured from a level 500 km. above the base of the chromosphere. It is shown that above the 500-km. level hydrogen atoms are almost completely ionized, and that with hydrostatic equilibrium the observed density gradient corresponds to a temperature of 2.7 X 104 �K . This is in good agreement with the temperature derived by Redman from line profile measurement, so that the lower chromosphere appears to be effectively in thermal and hydrostatic equilibrium. Estimates of lower accuracy are given for the electron concentrations at some higher levels in the chromosphere. A discussion is given of the mechanism of absorption of Hα radiation by a chromosphere whose temperature is well above that of the photosphere.

scholarly journals Spatially-Resolved Electron Density Measurement in Hydrogen Pellet Ablation Cloud

Atoms ◽  
2018 ◽  
Vol 6 (2) ◽  
pp. 34 ◽  
Author(s):  
Guillaume Seguineaud ◽  
Gen Motojima ◽  
Yoshiro Narushima ◽  
Motoshi Goto
Keyword(s):  
Electron Density ◽  
Density Measurement ◽  
Spatially Resolved

Atomistic Simulation and Density Functional Analysis of Ni(111)-ZrO2(100)(Cubic) and NiO(111)-Ni(111)-ZrO2(100)(Cubic) Interfaces

2000 ◽  
Vol 654 ◽  
Author(s):  
Chang-Xin Guo ◽  
Donald E. Ellis ◽  
Vinayak P. Dravid ◽  
Luke Brewer
Keyword(s):  
First Principles ◽  
Atomistic Simulation ◽  
Density Functional ◽  
Depth Profiling ◽  
Interface Plane ◽  
Functional Theory ◽  
Spatially Resolved ◽  
Microscopy Data ◽  
Energy Profiling ◽  
Good Agreement

AbstractThe atomic arrangement and electronic structure in the vicinity of Ni(111)- ZrO2(100)(Cubic) and NiO(111)-Ni(111)-ZrO2(100)(Cubic) interfaces have been studied by atomistic simulation and by first-principles Density Functional theory. “Depth Profiling” is carred out in both methodologies, to determine modifications of cohesive energy and electron distribution of atomic layers from the interface plane. The energy profiling results show the interface consists of only a few atomic layers. Simulation results and electron density analyses are in good agreement with High Resolution Spatially Resolved Electron Microscopy data.

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