Reduction Of Systematic Errors Research Articles

Reduction of systematic errors in structured light metrology at discontinuities in surface reflectivity

In measuring 3D shape with structured light techniques, systematic errors arise in the neighbourhood of discontinuities in reflectivity or geometry. A mechanism for this phenomenon is proposed, based on the finite size of the imaging system's point spread function. A theoretical analysis for the phase errors in a phase-shifting projected fringe system is given, from which a correction algorithm to minimise the systematic errors is presented. In this algorithm, a closed form expression for the errors based on the intensity values and the phase values in a neighbourhood excluding the affected region is used to remove the estimated error from the measured phase values within the affected region. Experiments on samples with both linear and circular discontinuities in reflectivity demonstrated respective reductions in systematic errors by factors of 2.5× and 3×.

On the determination of verticality and Eötvös effects in absolute gravimetry

We describe a new method for the accurate alignment of verticality in absolute gravimeters with macroscopic objects that allows simultaneous determination of the Eötvös effect. The method is based on measurements of lateral motion of freely falling objects by a position sensitive detector, and has been used experimentally for one FG5 and one FG5X gravimeter. As for the verticality effect, we show that the current method of verticality alignment by using the reflection off the geopotential surface placed outside the vacuum dropping chamber is insufficient, and that systematic errors exceeding 1 µGal might be expected—as demonstrated for FG5X-251. On the other hand, the new method of verticality alignment, based on minimizing the measured lateral accelerations, allows the reduction of systematic errors to about 0.1 µGal. Moreover, the measurements underlying the alignment can be used for determination of the Eötvös effect, which depends on the lateral velocity of the falling object in the east–west direction. The results for two FG5(X) gravimeters are presented, with Eötvös effects below 1 µGal that, however, cause biased gravity values so that relevant corrections should be applied. The method we are presenting does not allow determination of the verticality and Eötvös effects for particular drops. To do so, optical paths in the interferometer should have to be re-designed. Nevertheless, it is possible to determine both effects with a standard uncertainty better than 0.2 µGal using less than 50 drops carried out in a non-measurement mode.

Systematic Error Reduction in Geometric Measurements Based on Altimetric Enrichment of Geographical Features

In most GIS software, geometric measurements (length, area) computed from the geometry of vector objects are performed in two dimensions, which generates systematic underestimates. Several reasons can explain this critical situation: two of these include deficiencies in the geometric modelling of vector data and absence of correctly implemented methods for computing measurements using altitudes. To reduce the systematic error in geometric measurements caused by the omission of altitudes, methods are proposed to (1) enrich the geometry of geographical features using external altimetric data and (2) compute length and area using altitudes. These propositions are implemented in a model that allows any GIS user to take terrain into account in the computation of length and area and estimate the underestimation involved in two-dimensional measurements. Experiments are finally performed to illustrate the functioning of the model and test the impact of the quality of several altimetric data sources. Results demonstrate that freely available digital elevation models reduce measurement error. Based on comparisons with high-resolution databases, the results also show that omitting the terrain is not sufficient to assess the entire measurement error, which is also affected by other processes, such as digitizing error and cartographic projection.

A nonparametric statistical technique for combining global precipitation datasets: development and hydrological evaluation over the Iberian Peninsula

Abstract. This study investigates the use of a nonparametric, tree-based model, quantile regression forests (QRF), for combining multiple global precipitation datasets and characterizing the uncertainty of the combined product. We used the Iberian Peninsula as the study area, with a study period spanning 11 years (2000–2010). Inputs to the QRF model included three satellite precipitation products, CMORPH, PERSIANN, and 3B42 (V7); an atmospheric reanalysis precipitation and air temperature dataset; satellite-derived near-surface daily soil moisture data; and a terrain elevation dataset. We calibrated the QRF model for two seasons and two terrain elevation categories and used it to generate ensemble for these conditions. Evaluation of the combined product was based on a high-resolution, ground-reference precipitation dataset (SAFRAN) available at 5 km 1 h−1 resolution. Furthermore, to evaluate relative improvements and the overall impact of the combined product in hydrological response, we used the generated ensemble to force a distributed hydrological model (the SURFEX land surface model and the RAPID river routing scheme) and compared its streamflow simulation results with the corresponding simulations from the individual global precipitation and reference datasets. We concluded that the proposed technique could generate realizations that successfully encapsulate the reference precipitation and provide significant improvement in streamflow simulations, with reduction in systematic and random error on the order of 20–99 and 44–88 %, respectively, when considering the ensemble mean.

Fluorescence decay data analysis correcting for detector pulse pile-up at very high count rates

Using Time-Correlated Single Photon Counting (TCSPC) for the purpose of fluorescence lifetime measurements is usually limited in speed due to pile-up. With modern instrumentation this limitation can be lifted significantly but some artefacts due to frequent merging of closely spaced detector pulses (detector pulse pile-up) remains an issue to be addressed. We propose here a data analysis method correcting for this type of artefact and the resulting systematic errors. It physically models the photon losses due to detector pulse pile-up and incorporates the loss in the decay fit model employed to obtain fluorescence lifetimes and relative amplitudes of the decay components. Comparison of results with and without this correction show a significant reduction of systematic errors at count rates approaching the excitation rate. This allows quantitatively accurate fluorescense lifetime imaging (FLIM) at very high frame rates.

Peak-locking error reduction by birefringent optical diffusers

The use of optical diffusers for the reduction of peak-locking errors in particle image velocimetry is investigated. The working principle of the optical diffusers is based on the concept of birefringence, where the incoming rays are subject to different deflections depending on the light direction and polarization. The performances of the diffusers are assessed via wind tunnel measurements in uniform flow and wall-bounded turbulence. Comparison with best-practice image defocusing is also conducted. It is found that the optical diffusers yield an increase of the particle image diameter up to 10 µm in the sensor plane. Comparison with reference measurements showed a reduction of both random and systematic errors by a factor of 3, even at low imaging signal-to-noise ratio.

Detection of applied and ambient forces with a matter-wave magnetic gradiometer

An atom interferometer using a Bose-Einstein condensate of $^{87}$Rb atoms is utilized for the measurement of magnetic field gradients. Composite optical pulses are used to construct a spatially symmetric Mach-Zehnder geometry. Using a biased interferometer we demonstrate the ability to measure small residual forces in our system at the position of the atoms. These are a residual magnetic field gradient of 15$\pm$2 mG/cm and and an inertial acceleration of 0.08$\pm$0.02 m/s$^2$. Our method has important applications in the calibration of precision measurement devices and the reduction of systematic errors.

Automatic graph based spatiotemporal extrinsic calibration of multiple Kinect V2 ToF cameras

Abstract This paper presents a novel technique for the automatic calibration of motion capture systems composed of multiple Time of Flight cameras (ToF) or any equivalent device able to provide 3D point clouds together with chromatic information. The calibration procedure is designed to be simple, fast and unsupervised: a colored sphere moved freely by hand is used as calibration tool. Three elements in particular distinguish the method we propose from other state of the art solutions: it takes into account and propagates measurement uncertainties, it allows the identification and recovery of systematic time delays in camera synchronization, it optimize the extrinsic parameters by means of a graph based approach. A widely used ToF, Microsoft Kinect V2, was used for the comparison with state of the art multi-ToF calibration techniques. Experimental results demonstrated that the proposed method is the most accurate both in terms of shape reconstruction and spatial consistency. Furthermore, the experimental results underlined that the application of the global graph optimization over a more standard couple-based unweighed matching achieves a higher accuracy in the assessment of the extrinsic parameters. Thus enabling the reduction of both systematic errors and data dispersion in 3D point clouds of reference shapes. The comparison among acquisition systems composed of 3 and 6 devices underlined that graph optimization becomes relevant when the number of devices grows. Taking into account several 3D configurations calibrated with the proposed method, it was assessed that the uncertainty of the extrinsic parameters is generally lower than 2 mm and 1 0 − 2 radiants, 0.6°. The resulting dense 3D reconstruction of objects, both static and in motion, achieved experimental errors lower than to 10 mm, approximately half of other state of the art methods, and, in first approximation, homogeneous for the entire monitored area. The software developed can be found at the site of the MIRo lab (Measurement Instrumentation and Robotics lab) at link 1 under the Creative Commons Attribution conditions.

Exploring the brown dwarf desert: new substellar companions from the SDSS-III MARVELS survey

Planet searches using the radial velocity technique show a paucity of companions to solar-type stars within ~5 AU in the mass range of ~10 - 80 M$_{\text{Jup}}$. This deficit, known as the brown dwarf desert, currently has no conclusive explanation. New substellar companions in this region help asses the reality of the desert and provide insight to the formation and evolution of these objects. Here we present 10 new brown dwarf and two low-mass stellar companion candidates around solar-type stars from the Multi-object APO Radial-Velocity Exoplanet Large-Area Survey (MARVELS) of the Sloan Digital Sky Survey III (SDSS-III). These companions were selected from processed MARVELS data using the latest University of Florida Two Dimensional (UF2D) pipeline, which shows significant improvement and reduction of systematic errors over previous pipelines. The 10 brown dwarf companions range in mass from ~13 to 76 M$_{\text{Jup}}$ and have orbital radii of less than 1 AU. The two stellar companions have minimum masses of ~98 and 100 M$_{\text{Jup}}$. The host stars of the MARVELS brown dwarf sample have a mean metallicity of [Fe/H] = 0.03 $\pm$ 0.08 dex. Given our stellar sample we estimate the brown dwarf occurrence rate around solar-type stars with periods less than ~300 days to be ~0.56%.

Liver Status Assessment by Spectrally and Time Resolved IR Detection of Drug Induced Breath Gas Changes

The actual metabolic capacity of the liver is crucial for disease identification, liver therapy, and liver tumor resection. By combining induced drug metabolism and high sensitivity IR spectroscopy of exhaled air, we provide a method for quantitative liver assessment at bedside within 20 to 60 min. Fast administration of 13C-labelled methacetin induces a fast response of liver metabolism and is tracked in real-time by the increase of 13CO2 in exhaled air. The 13CO2 concentration increase in exhaled air allows the determination of the metabolic liver capacity (LiMAx-test). Fluctuations in CO2 concentration, pressure and temperature are minimized by special gas handling, and tracking of several spectrally resolved CO2 absorption bands with a quantum cascade laser. Absorption measurement of different 12CO2 and 13CO2 rotation-vibration transitions in the same time window allows for multiple referencing and reduction of systematic errors. This FLIP (Fast liver investigation package) setup is being successfully used to plan operations and determine the liver status of patients.

Comparison of set-up errors by breast size on wing board by portal imaging

AimTo quantify and compare setup errors between small and large breast patients undergoing intact breast radiotherapy. Methods20 patients were inducted. 10 small/moderate size breast in arm I and 10 large breast in arm II. Two orthogonal and one lateral tangent portal images (PIs) were obtained and analyzed for systematic (Σ) and random (σ) errors. Effect of no action level (NAL) was also evaluated retrospectively. Results142 PIs were analyzed. Σ(mm) was 3.2 versus 6.7 (p=0.41) in the mediolateral (ML) direction, 2.1 versus 2.9 (p=0.06) in the craniocaudal (CC) and 2.2 versus 3.6 (p=0.08) in the anteroposterior (AP) direction in small and large breast, respectively. σ(mm) was 3.0, 3.3 and 3.3 for small breast and 4.1, 3.7 and 3.2 for large breast in the ML, CC and AP direction (p=0.07, 0.86, 0.37), respectively. 3 D Σ(mm) was 2.7 versus 4.2 (p=0.01) and σ(mm) was 2.5 versus 3.2 (p=0.14) in arm I and II, respectively. The standard deviation (SD) of variations (mm) in breast contour depicted by central lung distance (CLD) was 5.9 versus 7.4 (p<0.001), central flash distance (CFD) 6.6 versus 10.5 (p=0.002), inferior central margin (ICM) 4 versus 4.9 (p<0.001) in arm I and II, respectively. NAL showed a significant reduction of systematic error in large breast in the mediolateral direction only. ConclusionWing board can be used in a busy radiotherapy department for setting up breast patients with a margin of 1.1cm, 0.76cm and 0.71cm for small breasts and 1.96cm, 1.12cm and 0.98cm for large breast in the ML, AP and CC directions, respectively. The large PTV margin in the mediolateral direction in large breast can be reduced using NAL. Further research is needed to optimize positioning of large breasted women.

A.106 - NAL protocol implementation and reduction of systematic errors in patient setup during radiation therapy

A.106 - NAL protocol implementation and reduction of systematic errors in patient setup during radiation therapy

Study of single-spin asymmetries with polarized target at the SPASCHARM experiment at U70 accelerator

A new experiment SPASCHARM for systematic study of polarization phenomena in inclusive and exclusive hadronic reactions is currently under commissioning at IHEP. The universal experimental setup will detect dozens of various resonances and stable particles produced in collisions of unpolarized beams with the polarized target, and at the next stage, using polarized beams. At the first stage with polarized target, the final states composed of light quarks (u, d, s) will be reconstructed. Hyperon polarization and spin density matrix elements of the vector mesons will be measured along with the single-spin asymmetries. The 2π-acceptance in azimuth, which is extremely useful for reduction of systematic errors in measurements of spin observables, will be implemented in the experiment. The solid angle acceptance of the setup, Δθ≈250 mrad vertically and 350 mrad horizontally in the beam fragmentation region, covers a wide range of kinematic variables pT and xF. This provides the opportunity for separating dependences on these two variables which is usually not possible in the setups with a small solid angle acceptance. Unlike some previous polarization experiments, the SPASCHARM will be able to simultaneously accumulate and record data on the both, charged and neutral particle production.

Systematic Study of Spin Effects at SPASCHARM Experiment at 70-GeV Accelerator in Protvino

A new experiment SPASCHARM for systematic study of polarization phenomena in the inclusive and exclusive hadronic reactions in the energy range of IHEP accelerator U-70 (12–50[Formula: see text]GeV) is currently under development. The universal experimental setup will detect dozens of various resonances and stable particles produced in collisions of unpolarized beams with the polarized target, and at the next stage, using polarized proton and antiproton beams. At the beginning, the final states consisting of light quarks ([Formula: see text], [Formula: see text], [Formula: see text]) will be reconstructed, and later on the charmonium states will be studied. Measurements are planned for a variety of beams: [Formula: see text], antiprotons. Hyperon polarization and spin density matrix elements of the vector mesons will be measured along with the single-spin asymmetry (SSA). The 2[Formula: see text]-acceptance in azimuth, which is extremely useful for reduction of systematic errors in measurements of spin observables, will be implemented in the experiment. The solid angle acceptance of the setup, [Formula: see text] mrad vertically and 350 mrad horizontally in the beam fragmentation region, covers a wide range of kinematic variables [Formula: see text] and [Formula: see text]. This provides the opportunity for separating dependences on these two variables which is usually not possible in the setups with a small solid angle acceptance. Unlike some previous polarization experiments, the SPASCHARM will be able to simultaneously accumulate and record data on the both, charged and neutral particle production.

One step geometrical calibration method for optical coherence tomography

We present a novel one-step calibration methodology for geometrical distortion correction for optical coherence tomography (OCT). A calibration standard especially designed for OCT is introduced, which consists of an array of inverse pyramidal structures. The use of multiple landmarks situated on four different height levels on the pyramids allow performing a 3D geometrical calibration. The calibration procedure itself is based on a parametric model of the OCT beam propagation. It is validated by experimental results and enables the reduction of systematic errors by more than one order of magnitude. In future, our results can improve OCT image reconstruction and interpretation for medical applications such as real time monitoring of surgery.

Dynamic intensity normalization using eigen flat fields in X-ray imaging.

In X-ray imaging, it is common practice to normalize the acquired projection data with averaged flat fields taken prior to the scan. Unfortunately, due to source instabilities, vibrating beamline components such as the monochromator, time varying detector properties, or other confounding factors, flat fields are often far from stationary, resulting in significant systematic errors in intensity normalization. In this work, a simple and efficient method is proposed to account for dynamically varying flat fields. Through principal component analysis of a set of flat fields, eigen flat fields are computed. A linear combination of the most important eigen flat fields is then used to individually normalize each X-ray projection. Experiments show that the proposed dynamic flat field correction leads to a substantial reduction of systematic errors in projection intensity normalization compared to conventional flat field correction.

Realization of mutually unbiased bases for a qubit with only one wave plate: theory and experiment.

We consider the problem of implementing mutually unbiased bases (MUB) for a polarization qubit with only one wave plate, the minimum number of wave plates. We show that one wave plate is sufficient to realize two MUB as long as its phase shift (modulo 360°) ranges between 45° and 315°. It can realize three MUB (a complete set of MUB for a qubit) if the phase shift of the wave plate is within [111.5°, 141.7°] or its symmetric range with respect to 180°. The systematic error of the realized MUB using a third-wave plate (TWP) with 120° phase is calculated to be a half of that using the combination of a quarter-wave plate (QWP) and a half-wave plate (HWP). As experimental applications, TWPs are used in single-qubit and two-qubit quantum state tomography experiments and the results show a systematic error reduction by 50%. This technique not only saves one wave plate but also reduces the systematic error, which can be applied to quantum state tomography and other applications involving MUB. The proposed TWP may become a useful instrument in optical experiments, replacing multiple elements like QWP and HWP.

Improved forcing scheme in pseudopotential lattice Boltzmann methods for multiphase flow at arbitrarily high density ratios.

The pseudopotential lattice Boltzmann method has been widely used to simulate many multiphase flow applications. However, there still exist problems with reproducing realistic values of density ratio and surface tension. In this study, a higher-order analysis of a general forcing term is derived. A forcing scheme is then constructed for the pseudopotential method that is able to accurately reproduce the full range of coexistence curves. As a result, multiphase flow of arbitrarily high density ratios independent of the surface tension can be simulated. Furthermore, the interface width can be tuned to allow for grid refinement and systematic error reduction. Numerical results confirm that the proposed scheme enables independent control of density ratio, surface tension, and interface width simultaneously.

Многоволновая ИК-спектрометрия как способ оценки суммарного содержания углеводородов

Problem. To evaluate the total concentration (сΣ) of hydrocarbons (HСs) in natural or waste waters, it is possible to extract all HCs and to measure the generalized analytical signal in the certain IR spectral region. Then the total TPH index (с*) can be determined in terms of the certain standard substance Xst. The error of this estimation δс = (с* - сΣ) / сΣoften exceeds 50 % rel. Specialists believe that the transition to multiwavelength signal measurement using n analytical wavelength values (n > 1) improves the accuracy of сΣ estimations. No systematic investigations of this problem were conducted earlier. Experiment. The model mixtures of alkanes, cycloalkanes and arenes in CCl4 were prepared to simulate the composition of refined extracts. IR-spectra were registered with FT-801 Fourier-spectrometer. The absorbance of each mixture was measured by three methods: (1) – only with 2930 cm-1; (2) – with 2930, 2960 and 3030 cm-1; (3) – with 2855, 2930, 2960 and 3030 cm-1. The generalized signal was calculated for each mixture by summation of the measurands for different analytical wavelength values (AWV). Corresponding formulae with weighting factors were derived beforehand by the technique of least squares. The total index value (c*) was determined by the calibration curve АΣ= f(сx), and Simard mixture was used as Xst in all cases. Calculated δс values for standard methods (1) and (2) were compared with the data obtained using the new method (3). To interpret the results, the absorbance factors were compared for certain individual HCs. Results. The precision of generalized signals slightly decreases when the number of AWV grows. Simultaneous LODs are raised and the absorbance factors for individual HCs are leveled. The errors of сΣ evaluation via c* for all methods are statistically significant but they diminish when n grows. RMSEP parameter decreases with the methods line (1) > (2) > (3). Standard methods (1) and (2) do not provide the level of the result accuracy which is necessary according to Russian standards. The new multiwavelength method (3) provides the estimation accuracy which is required. For this method δс values do not exceed 15 % in modulo, even for mixtures with the high content of arenes.Discussion. Our experiment showed that the simultaneous use of some AWVs really provides more reliable сΣ estimations. The main reason for this effect is the leveling of the absorption coefficients for various HCs, particularly for alkanes and arenes. Subsequent reduction of systematic errors may be secured if we will not use the univariate calibration curves. The multivariate calibration, obtained from the training set of the spectral data (method 3a), leads to accurate сΣ estimations. In this case δс values do not exceed 8 %, and for the most part of model mixtures systematic errors are not statistically significant. In “Conclusion” the fundamental significances of obtained results and perspectives of their application in aqueous analysis are discussed. Key words: aqueous analysis, total indices, total content of hydrocarbons, multiwave IR spectrometry, systematic errors(Russian)DOI:http://dx.doi.org/10.15826/analitika.2015.19.1.011S.V. Usova, М.А. Fedorova, S.V. Petrov, V.I. VershininDostoevsky Omsk State University (OmGU), Omsk, Russian Federation

SU-E-T-642: Safety Procedures for Error Elimination in Cyberknife Stereotactic Radiosurgery (SRS) and Stereotactic Body Radiation Therapy (SBRT)

Purpose: Cyberknife system is used for providing stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT) hypofractionation scheme. The whole treatment delivery is based on live imaging of the patient. The minor error made at any stage may bring severe radiation injury to the patient or damage to the system itself. Several safety measures were taken to make the system safer. Methods: The radiation treatment provided thru a 6MV linac attached to Kuka robot (Cyberknife G4, Accuray Inc. Sunnyvale, CA, USA). Several possible errors were identified related to patient alignment, treatment planning, dose delivery and physics quality assurance. During dose delivery, manual and visual checks were introduced to confirm pre and intra-treatment imaging to reduce possible errors. One additional step was introduced to confirm that software tracking-tools had worked correctly with highest possible confidence level. Robotic head move in different orientations over and around the patient body, the rigidity of linac-head cover and other accessories was checked periodically. The vender was alerted when a tiny or bigger piece of equipment needed additional interlocked support. Results: As of our experience treating 525 patients on Cyberknife during the last four years, we saw on and off technical issues. During image acquisition, it was made essential to follow the site-specific imaging protocols. Adequate anatomy was contoured to document the respective doses. Followed by auto-segmentation, manual tweaking was performed on every structure. The calculation box was enclosing the whole image during the final calculation. Every plan was evaluated on slice-by slice basis. To review the whole process, a check list was maintained during the physics 2nd-check. Conclusion: The implementation of manual and visual additional checks introduced along with automated checks for confirmation was found promising in terms of reduction in systematic errors and making the system safer than before.