One step geometrical calibration method for optical coherence tomography
NASA Astrophysics Data System (ADS)
Díaz Díaz, Jesús; Stritzel, Jenny; Rahlves, Maik; Majdani, Omid; Reithmeier, Eduard; Ortmaier, Tobias; Roth, Bernhard
2016-01-01
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.
A geometric calibration method for cone beam CT systems
Yang, Kai; Kwan, Alexander L. C.; Miller, DeWitt F.; Boone, John M.
2006-06-15
Cone beam CT systems are being deployed in large numbers for small animal imaging, dental imaging, and other specialty applications. A new high-precision method for cone beam CT system calibration is presented in this paper. It uses multiple projection images acquired from rotating point-like objects (metal ball bearings) and the angle information generated from the rotating gantry system is also used. It is assumed that the whole system has a mechanically stable rotation center and that the detector does not have severe out-of-plane rotation (<2 deg.). Simple geometrical relationships between the orbital paths of individual BBs and five system parameters were derived. Computer simulations were employed to validate the accuracy of this method in the presence of noise. Equal or higher accuracy was achieved compared with previous methods. This method was implemented for the geometrical calibration of both a micro CT scanner and a breast CT scanner. The reconstructed tomographic images demonstrated that the proposed method is robust and easy to implement with high precision.
Li Xinhua; Zhang Da; Liu, Bob
2011-01-15
Purpose: To study the sensitivity of a geometric calibration method using projection matrices for digital tomosynthesis systems. Methods: A generic geometric calibration method for tomographic imaging systems has been presented in our previous work. The method involves a scan of a calibration phantom with multiple markers. Their locations in projection images are detected and are associated with their 3D coordinates to compute 3x4 projection matrices, which can be used in subsequent image reconstruction. The accuracy of geometric calibration may be affected by errors in the input data of marker positions. The effects of errors may depend on the number of markers and the volume surrounded by them in 3D space. This work analyzed the sensitivity of the calibration method to the above factors. A 6 cm CIRS breast research phantom and a prototype breast tomosynthesis system were used for our tests. A high contrast ring and two small speck groups were reconstructed in various testing cases for comparison. To achieve quantitative assessment, a 15x15 point detection mask was adopted for detecting signals and for computing changes between testing cases and the regular geometric calibration. Results: When 3D coordinates and 2D projections of markers were accurate, all tested numbers of markers, 6-44, provided similar high quality reconstructions of the ring and the two speck groups. Errors in marker positions resulted in image degradations and signal changes, which increased with fewer markers and smaller volume surrounded by markers in the 3D object space. Signal changes of small specks were more significant than those of the ring. Errors in marker projections produced drastic image degradations. Coplanar marker placement caused a failure in projection matrix computation. Conclusions: For practical geometric calibration phantom design, ample markers are desired. They need to have a large volumetric coverage in the 3D space and be far from being coplanar. Precise
PLEIADES-HR 1A&1B image quality commissioning: innovative geometric calibration methods and results
NASA Astrophysics Data System (ADS)
Greslou, Daniel; de Lussy, Françoise; Amberg, Virginie; Dechoz, Cécile; Lenoir, Florie; Delvit, Jean-Marc; Lebègue, Laurent
2013-09-01
PLEIADES earth observing system consists of two satellites designed to provide optical 70cm resolution images to civilian and defense users. The first Pleiades satellite 1A was launched on December 2011 while the second satellite Pleiades 1B was placed on orbit, one year after, on December 2012. The calibration operations and the assessment of the image of the two satellites have been performed by CNES Image Quality team during the called commissioning phase which took place after each launch and lasted each time less than 6 months. The geometric commissioning activities consist in assessing and improving the geometric quality of the images in order to meet very demanding requirements. This paper deals with the means used and methods applied, mainly the innovative ones, in order to manage these activities. It describes both their accuracy and their operational interest. Finally it gives the main results for geometric image quality performances of the PHR system.
A geometric calibration method for inverse geometry computed tomography using P-matrices
NASA Astrophysics Data System (ADS)
Slagowski, Jordan M.; Dunkerley, David A. P.; Hatt, Charles R.; Speidel, Michael A.
2016-03-01
Accurate and artifact free reconstruction of tomographic images requires precise knowledge of the imaging system geometry. This work proposes a novel projection matrix (P-matrix) based calibration method to enable C-arm inverse geometry CT (IGCT). The method is evaluated for scanning-beam digital x-ray (SBDX), a C-arm mounted inverse geometry fluoroscopic technology. A helical configuration of fiducials is imaged at each gantry angle in a rotational acquisition. For each gantry angle, digital tomosynthesis is performed at multiple planes and a composite image analogous to a cone-beam projection is generated from the plane stack. The geometry of the C-arm, source array, and detector array is determined at each angle by constructing a parameterized 3D-to-2D projection matrix that minimizes the sum-of-squared deviations between measured and projected fiducial coordinates. Simulations were used to evaluate calibration performance with translations and rotations of the source and detector. In a geometry with 1 mm translation of the central ray relative to the axis-of-rotation and 1 degree yaw of the detector and source arrays, the maximum error in the recovered translational parameters was 0.4 mm and maximum error in the rotation parameter was 0.02 degrees. The relative rootmean- square error in a reconstruction of a numerical thorax phantom was 0.4% using the calibration method, versus 7.7% without calibration. Changes in source-detector-distance were the most challenging to estimate. Reconstruction of experimental SBDX data using the proposed method eliminated double contour artifacts present in a non-calibrated reconstruction. The proposed IGCT geometric calibration method reduces image artifacts when uncertainties exist in system geometry.
An optimization-based method for geometrical calibration in cone-beam CT without dedicated phantoms
NASA Astrophysics Data System (ADS)
Panetta, D.; Belcari, N.; DelGuerra, A.; Moehrs, S.
2008-07-01
In this paper we present a new method for the determination of geometrical misalignments in cone-beam CT scanners, from the analysis of the projection data of a generic object. No a priori knowledge of the object shape and positioning is required. We show that a cost function, which depends on the misalignment parameters, can be defined using the projection data and that such a cost function has a local minimum in correspondence to the actual parameters of the system. Hence, the calibration of the scanner can be carried out by minimizing the cost function using standard optimization techniques. The method is developed for a particular class of 3D object functions, for which the redundancy of the fan beam sinogram in the transaxial midplane can be extended to cone-beam projection data, even at wide cone angles. The method has an approximated validity for objects which do not belong to that class; in that case, a suitable subset of the projection data can be selected in order to compute the cost function. We show by numerical simulations that our method is capable to determine with high accuracy the most critical misalignment parameters of the scanner, i.e., the transversal shift and the skew of the detector. Additionally, the detector slant can be determined. Other parameters such as the detector tilt, the longitudinal shift and the error in the source-detector distance cannot be determined with our method, as the proposed cost function has a very weak dependence on them. However, due to the negligible influence of these latter parameters in the reconstructed image quality, they can be kept fixed at estimated values in both calibration and reconstruction processes without compromising the final result. A trade-off between computational cost and calibration accuracy must be considered when choosing the data subset used for the computation of the cost function. Results on real data of a mouse femur as obtained with a small animal micro-CT are shown as well, proving
Advanced geometric camera calibration for machine vision
NASA Astrophysics Data System (ADS)
Vo, Minh; Wang, Zhaoyang; Luu, Long; Ma, Jun
2011-11-01
In many machine vision applications, a crucial step is to accurately determine the relation between the image of the object and its physical dimension by performing a calibration process. Over time, various calibration techniques have been developed. Nevertheless, the existing methods cannot satisfy the ever-increasing demands for higher accuracy performance. In this letter, an advanced geometric camera calibration technique which employs a frontal image concept and a hyper-precise control point detection scheme with digital image correlation is presented. Simulation and real experimental results have successfully demonstrated the superior of the proposed technique.
Flexible geometrical calibration for fringe-reflection 3D measurement.
Xiao, Yong-Liang; Su, Xianyu; Chen, Wenjing
2012-02-15
System geometrical calibration is a challenging task in fringe-reflection 3D measurement because the fringe displayed on the LCD screen does not lie within the camera's field of view. Commonly, a flat mirror with markers can accomplish system geometrical calibration. However, the position of the markers must be precisely located by photogrammetry in advance. In this Letter, we introduce a calibration method by use of a markerless flat mirror. Experiments in phase measuring deflectometry demonstrate that the proposed method is simple and flexible. PMID:22344126
Geometric error detection and calibration in laser trackers
NASA Astrophysics Data System (ADS)
Zhang, Zili; Lao, Dabao; Dong, Dengfeng; Zhou, Weihu
2015-08-01
Geometric errors in laser trackers such as light offset and transit tilt have essential influence on the system measurement errors. Thus error detection and calibration are very important for producers and customers to execute error compensation. Different methods are developed to detect and calibrate errors. However, the commonly used methods such as length measurement and two-face measurement are sensitive to several misalignments which cannot calibrate errors directly and separately. In this paper a series of methods for detecting and calibrating geometric errors such as mirror tilt, beam tilt and transit tilt were presented which can calibrate geometric errors individually and precisely. The mirror tilt could be detected with the help of two autocollimators and one polygon. Then the beam tilt and offset errors were calibrated using a CCD camera and condenser lenses. Finally the transit tilt error was calibrated using a gradient and a vertical plane. Experiments and error assessment were executed to show that the accuracy of the calibration methods can meet the user's demand.
Geometrical calibration of photographic cameras against test objects
NASA Astrophysics Data System (ADS)
Bruchkouskaya, Sviatlana I.; Belajev, Boris I.; Katkovskij, Leonid V.
2013-04-01
In view of constantly growing application of aerospace remote research techniques of the Earth to study and monitor natural and technogenic objects, imaging systems are required to demonstrate high metric accuracy of the picture which can be provided through preliminary geometrical calibration of photographic cameras. Being defined as a result of the geometrical calibration, parameters of internal and external orientation of the cameras are needed while solving such problems of image processing, as orthotransformation, geometrical correction, geographical coordinate fixing, scale adjustment and image registration from various channels and cameras, creation of image mosaics of filmed territories, and determination of geometrical characteristics of objects in the images. The geometrical calibration also helps to eliminate image deformations arising due to manufacturing defects and errors in installation of camera elements and photo receiving matrices as well as those resulted from lens distortions. Designing calibration test objects and elaborating methods of the geometrical calibration is a necessary stage in the process of creating and operating systems of remote sounding of the Earth. In research institute of applied physical problems of Belarus State University, a complex of the geometrical calibration of aerospace remote sounding instrumentation with a three-dimensional calibration scene, having dimensions 3,2x2,0x1,5 m and containing more than 200 point markers in the scene volume, is currently devised. To determine space resolution and modulation transfer function of image systems, the corresponding test patterns, arranged within the scene, are being constructed. Furthermore, images of special test patterns will be formed by an optical collimator of the complex in the focal plane of a system undergoing calibration. The procedure of photogrammetric calibration is based on test object filming (the three-dimensional scene of the complex with markers location
MERTIS: using diffractive optical elements for geometrical calibration
NASA Astrophysics Data System (ADS)
Bauer, M.; Griessbach, D.; Säuberlich, T.; Scheele, M.; Schischmanow, A.
2010-09-01
Geometrical sensor calibration is essential for space applications based on high accuracy optical measurements, in this case for MERTIS. The goal is the determination of interiour sensor parameters. A conventional method is to measure the line of sight for a subset of pixels by single pixel illumination with collimated light. To adjust angles which define the line of sight of a pixel a manipulator construction is used. A new method for geometrical sensor calibration is presented using Diffractive Optical Elements (DOE) in connection with laser beam equipment. This method is especially used for 2D-sensor array systems but can also be applied to the thermal infrared push-broom imaging spectrometer MERTIS. Diffractive optical elements (DOE) are optical microstructures which are used to split an incoming laser beam with a dedicated wavelength into a number of beams with well-known propagation directions. As the virtual sources of the diffracted beams are points at infinity, the object to be imaged is similar to the starry sky which gives an image invariant against translation. This particular feature allows a complete geometrical sensor calibration with one image avoiding complex adjustment procedures which means a significant reduction of calibration effort.
X-ray CT geometrical calibration via locally linear embedding.
Chen, Mianyi; Xi, Yan; Cong, Wenxiang; Liu, Baodong; Wei, Biao; Wang, Ge
2016-03-14
For X-ray computed tomography (CT), geometric calibration and rigid patient motion compensation are inter-related issues for optimization of image reconstruction quality. Non-calibrated system geometry and patient movement during a CT scan will result in streak-like, blurring and other artifacts in reconstructed images. In this paper, we propose a locally linear embedding based calibration approach to address this challenge under a rigid 2D object assumption and a more general way than what has been reported before. In this method, projections are linearly represented by up-sampled neighbors via locally linear embedding, and CT system parameters are iteratively estimated from projection data themselves. Numerical and experimental studies show that images reconstructed with calibrated parameters are in excellent agreement with the counterparts reconstructed with the true parameters. PMID:27002904
D Catenary Curve Fitting for Geometric Calibration
NASA Astrophysics Data System (ADS)
Chan, T.-O.; Lichti, D. D.
2011-09-01
In modern road surveys, hanging power cables are among the most commonly-found geometric features. These cables are catenary curves that are conventionally modelled with three parameters in 2D Cartesian space. With the advent and popularity of the mobile mapping system (MMS), the 3D point clouds of hanging power cables can be captured within a short period of time. These point clouds, similarly to those of planar features, can be used for feature-based self-calibration of the system assembly errors of an MMS. However, to achieve this, a well-defined 3D equation for the catenary curve is needed. This paper proposes three 3D catenary curve models, each having different parameters. The models are examined by least squares fitting of simulated data and real data captured with an MMS. The outcome of the fitting is investigated in terms of the residuals and correlation matrices. Among the proposed models, one of them could estimate the parameters accurately and without any extreme correlation between the variables. This model can also be applied to those transmission lines captured by airborne laser scanning or any other hanging cable-like objects.
Linejitter and geometric calibration of CCD-cameras
NASA Astrophysics Data System (ADS)
Beyer, Horst A.
Precise radiometric and geometric transmission of images from CCD-sensor to memory is a fundamental aspect of CCD-camera calibration. Linejitter and other degradation occurring during transmission are major limiting factors of the precision attainable with most current CCD-cameras and framegrabbers. The video signal, synchronisation signals and principal electronic components involved in synchronisation and transmission are analysed and their influence on linejitter discussed. A method for signal transmission with the elimination of linejitter and other degradations is shown. Methods for the determination and correction of linejitter are discussed.
Four years of Landsat-7 on-orbit geometric calibration and performance
Lee, D.S.; Storey, J.C.; Choate, M.J.; Hayes, R.W.
2004-01-01
Unlike its predecessors, Landsat-7 has undergone regular geometric and radiometric performance monitoring and calibration since launch in April 1999. This ongoing activity, which includes issuing quarterly updates to calibration parameters, has generated a wealth of geometric performance data over the four-year on-orbit period of operations. A suite of geometric characterization (measurement and evaluation procedures) and calibration (procedures to derive improved estimates of instrument parameters) methods are employed by the Landsat-7 Image Assessment System to maintain the geometric calibration and to track specific aspects of geometric performance. These include geodetic accuracy, band-to-band registration accuracy, and image-to-image registration accuracy. These characterization and calibration activities maintain image product geometric accuracy at a high level - by monitoring performance to determine when calibration is necessary, generating new calibration parameters, and verifying that new parameters achieve desired improvements in accuracy. Landsat-7 continues to meet and exceed all geometric accuracy requirements, although aging components have begun to affect performance.
NASA Astrophysics Data System (ADS)
Wang, Mi; Fang, Chengcheng; Yang, Bo; Cheng, Yufeng
2016-06-01
The low frequency error is a key factor which has affected uncontrolled geometry processing accuracy of the high-resolution optical image. To guarantee the geometric quality of imagery, this paper presents an on-orbit calibration method for the low frequency error based on geometric calibration field. Firstly, we introduce the overall flow of low frequency error on-orbit analysis and calibration, which includes optical axis angle variation detection of star sensor, relative calibration among star sensors, multi-star sensor information fusion, low frequency error model construction and verification. Secondly, we use optical axis angle change detection method to analyze the law of low frequency error variation. Thirdly, we respectively use the method of relative calibration and information fusion among star sensors to realize the datum unity and high precision attitude output. Finally, we realize the low frequency error model construction and optimal estimation of model parameters based on DEM/DOM of geometric calibration field. To evaluate the performance of the proposed calibration method, a certain type satellite's real data is used. Test results demonstrate that the calibration model in this paper can well describe the law of the low frequency error variation. The uncontrolled geometric positioning accuracy of the high-resolution optical image in the WGS-84 Coordinate Systems is obviously improved after the step-wise calibration.
Calibration and verification of thermographic cameras for geometric measurements
NASA Astrophysics Data System (ADS)
Lagüela, S.; González-Jorge, H.; Armesto, J.; Arias, P.
2011-03-01
Infrared thermography is a technique with an increasing degree of development and applications. Quality assessment in the measurements performed with the thermal cameras should be achieved through metrology calibration and verification. Infrared cameras acquire temperature and geometric information, although calibration and verification procedures are only usual for thermal data. Black bodies are used for these purposes. Moreover, the geometric information is important for many fields as architecture, civil engineering and industry. This work presents a calibration procedure that allows the photogrammetric restitution and a portable artefact to verify the geometric accuracy, repeatability and drift of thermographic cameras. These results allow the incorporation of this information into the quality control processes of the companies. A grid based on burning lamps is used for the geometric calibration of thermographic cameras. The artefact designed for the geometric verification consists of five delrin spheres and seven cubes of different sizes. Metrology traceability for the artefact is obtained from a coordinate measuring machine. Two sets of targets with different reflectivity are fixed to the spheres and cubes to make data processing and photogrammetric restitution possible. Reflectivity was the chosen material propriety due to the thermographic and visual cameras ability to detect it. Two thermographic cameras from Flir and Nec manufacturers, and one visible camera from Jai are calibrated, verified and compared using calibration grids and the standard artefact. The calibration system based on burning lamps shows its capability to perform the internal orientation of the thermal cameras. Verification results show repeatability better than 1 mm for all cases, being better than 0.5 mm for the visible one. As it must be expected, also accuracy appears higher in the visible camera, and the geometric comparison between thermographic cameras shows slightly better
Landsat 8 thermal infrared sensor geometric characterization and calibration
Storey, James C.; Choate, Michael J.; Moe, Donald
2014-01-01
The Landsat 8 spacecraft was launched on 11 February 2013 carrying two imaging payloads: the Operational Land Imager (OLI) and the Thermal Infrared Sensor (TIRS). The TIRS instrument employs a refractive telescope design that is opaque to visible wavelengths making prelaunch geometric characterization challenging. TIRS geometric calibration thus relied heavily on on-orbit measurements. Since the two Landsat 8 payloads are complementary and generate combined Level 1 data products, the TIRS geometric performance requirements emphasize the co-alignment of the OLI and TIRS instrument fields of view and the registration of the OLI reflective bands to the TIRS long-wave infrared emissive bands. The TIRS on-orbit calibration procedures include measuring the TIRS-to-OLI alignment, refining the alignment of the three TIRS sensor chips, and ensuring the alignment of the two TIRS spectral bands. The two key TIRS performance metrics are the OLI reflective to TIRS emissive band registration accuracy, and the registration accuracy between the TIRS thermal bands. The on-orbit calibration campaign conducted during the commissioning period provided an accurate TIRS geometric model that enabled TIRS Level 1 data to meet all geometric accuracy requirements. Seasonal variations in TIRS-to-OLI alignment have led to several small calibration parameter adjustments since commissioning.
NASA Astrophysics Data System (ADS)
Bauer, M.; Baumbach, D.; Buder, M.; Börner, A.; Grießbach, D.; Peter, G.; Santier, E.; Säuberlich, T.; Schischmanow, A.; Schrader, S.; Walter, I.
2015-09-01
Geometrical sensor calibration is essential for space applications based on high accuracy optical measurements, in this case for the thermal infrared push-broom imaging spectrometer MERTIS. The goal is the determination of the interior sensor orientation. A conventional method is to measure the line of sight for a subset of pixels by single pixel illumination with collimated light. To adjust angles, which define the line of sight of a pixel, a manipulator construction is used. A new method for geometrical sensor calibration is using Diffractive Optical Elements (DOE) in connection with laser beam equipment. Diffractive optical elements (DOE) are optical microstructures, which are used to split an incoming laser beam with a dedicated wavelength into a number of beams with well-known propagation directions. As the virtual sources of the diffracted beams are points at infinity, the resulting image is invariant against translation. This particular characteristic allows a complete geometrical sensor calibration with only one taken image avoiding complex adjustment procedures, resulting in a significant reduction of calibration effort. We present a new method for geometrical calibration of a thermal infrared optical system, including an thermal infrared test optics and the MERTIS spectrometer bolometer detector. The fundamentals of this new approach for geometrical infrared optical systems calibration by applying diffractive optical elements and the test equipment are shown.
Data filtering with support vector machines in geometric camera calibration.
Ergun, B; Kavzoglu, T; Colkesen, I; Sahin, C
2010-02-01
The use of non-metric digital cameras in close-range photogrammetric applications and machine vision has become a popular research agenda. Being an essential component of photogrammetric evaluation, camera calibration is a crucial stage for non-metric cameras. Therefore, accurate camera calibration and orientation procedures have become prerequisites for the extraction of precise and reliable 3D metric information from images. The lack of accurate inner orientation parameters can lead to unreliable results in the photogrammetric process. A camera can be well defined with its principal distance, principal point offset and lens distortion parameters. Different camera models have been formulated and used in close-range photogrammetry, but generally sensor orientation and calibration is performed with a perspective geometrical model by means of the bundle adjustment. In this study, support vector machines (SVMs) using radial basis function kernel is employed to model the distortions measured for Olympus Aspherical Zoom lens Olympus E10 camera system that are later used in the geometric calibration process. It is intended to introduce an alternative approach for the on-the-job photogrammetric calibration stage. Experimental results for DSLR camera with three focal length settings (9, 18 and 36 mm) were estimated using bundle adjustment with additional parameters, and analyses were conducted based on object point discrepancies and standard errors. Results show the robustness of the SVMs approach on the correction of image coordinates by modelling total distortions on-the-job calibration process using limited number of images. PMID:20174021
Performance Assessment and Geometric Calibration of RESOURCESAT-2
NASA Astrophysics Data System (ADS)
Radhadevi, P. V.; Solanki, S. S.; Akilan, A.; Jyothi, M. V.; Nagasubramanian, V.
2016-06-01
Resourcesat-2 (RS-2) has successfully completed five years of operations in its orbit. This satellite has multi-resolution and multi-spectral capabilities in a single platform. A continuous and autonomous co-registration, geo-location and radiometric calibration of image data from different sensors with widely varying view angles and resolution was one of the challenges of RS-2 data processing. On-orbit geometric performance of RS-2 sensors has been widely assessed and calibrated during the initial phase operations. Since then, as an ongoing activity, various geometric performance data are being generated periodically. This is performed with sites of dense ground control points (GCPs). These parameters are correlated to the direct geo-location accuracy of the RS-2 sensors and are monitored and validated to maintain the performance. This paper brings out the geometric accuracy assessment, calibration and validation done for about 500 datasets of RS-2. The objectives of this study are to ensure the best absolute and relative location accuracy of different cameras, location performance with payload steering and co-registration of multiple bands. This is done using a viewing geometry model, given ephemeris and attitude data, precise camera geometry and datum transformation. In the model, the forward and reverse transformations between the coordinate systems associated with the focal plane, payload, body, orbit and ground are rigorously and explicitly defined. System level tests using comparisons to ground check points have validated the operational geo-location accuracy performance and the stability of the calibration parameters.
Leica Dmc III Calibration and Geometric Sensor Accuracy
NASA Astrophysics Data System (ADS)
Mueller, C.; Neumann, K.
2016-03-01
As an evolution of the successful DMC II digital camera series, Leica Geosystems has introduced the Leica DMC III digital aerial camera using, for the first time in the industry, a large-format CMOS sensor as a panchromatic high-resolution camera head. This paper describes the Leica DMC III calibration and its quality assurance and quality control (QA/QC) procedures. It will explain how calibration was implemented within the production process for the Leica DMC III camera. Based on many years of experience with the DMC and DMC II camera series, it is know that the sensor flatness has a huge influence on the final achievable results. The Leica DMC III panchromatic CMOS sensor with its 100.3mm x 56.9mm size shows remaining errors in a range of 0.1 to 0.2μm for the root mean square and shows maximum values not higher that 1.0μm. The Leica DMC III is calibrated based on a 5cm Ground Sample Distance (GSD) grid pattern flight and evaluated with three different flying heights at 5cm, 8cm and 11cm GSD. The geometric QA/QC has been performed using the calibration field area, as well as using an independent test field. The geometric performance and accuracy is unique and gives ground accuracies far better than the flown GSD.
Practical geometric calibration for helical cone-beam industrial computed tomography.
Zhang, Feng; Yan, Bin; Li, Lei; Xi, Xiaoqi; Jiang, Hua
2014-01-01
In helical cone-beam industrial computed tomography (ICT), the reconstructed images may be interfered by geometry artifacts due to the presence of mechanical misalignments. To obtain artifact-free reconstruction images, a practical geometric calibration method for helical scan is investigated based on Noo's analytic geometric calibration method for circular scan. The presented method is implemented by first dividing the whole ascending path of helical scan into several pieces, then acquiring the projections of a dedicated calibration phantom in circular scan at each section point, of which geometry parameters are calculated using Noo's analytic method. At last, the geometry parameters of each projection in a piece can be calculated by those of the two end points of the piece. We performed numerical simulations and real data experiments to study the performance of the presented method. The experimental results indicated that the method can obtain high-precision geometry parameters of helical scan and give satisfactory reconstruction images. PMID:24463383
Flexible geometrical calibration for fringe-reflection optical three-dimensional shape measurement.
Yuan, Ting; Zhang, Feng; Tao, Xiaoping; Zhang, Xuejun; Zhou, Run
2015-11-01
Accurate geometrical calibration is the basis of a fringe-reflection testing system, especially the calibration of reflection ray directions. However, such a calibration procedure is challenging because of two reasons: first of all, the common method of reflection ray directions calibration, which is based on the pinhole camera imaging model, fails in the presence of the pupil imaging aberration. What's more, although using a camera lens with an external stop in front can remove the pupil imaging aberration, it is difficult to achieve the exact geometrical measurement of the camera pinhole and the calibration of the reflection ray directions into the camera because of the low signal-to-noise ratio of images. In this paper, we introduce a new calibration method by finding the points on the liquid crystal display in front of the camera with different positions corresponding to the same camera pixels through correspondence matching. The calibration process and the results from the experiments on fringe-reflection testing demonstrate that the calibration method presented in this paper is simple, practical, and flexible. PMID:26560561
Accurate technique for complete geometric calibration of cone-beam computed tomography systems.
Cho, Youngbin; Moseley, Douglas J; Siewerdsen, Jeffrey H; Jaffray, David A
2005-04-01
Cone-beam computed tomography systems have been developed to provide in situ imaging for the purpose of guiding radiation therapy. Clinical systems have been constructed using this approach, a clinical linear accelerator (Elekta Synergy RP) and an iso-centric C-arm. Geometric calibration involves the estimation of a set of parameters that describes the geometry of such systems, and is essential for accurate image reconstruction. We have developed a general analytic algorithm and corresponding calibration phantom for estimating these geometric parameters in cone-beam computed tomography (CT) systems. The performance of the calibration algorithm is evaluated and its application is discussed. The algorithm makes use of a calibration phantom to estimate the geometric parameters of the system. The phantom consists of 24 steel ball bearings (BBs) in a known geometry. Twelve BBs are spaced evenly at 30 deg in two plane-parallel circles separated by a given distance along the tube axis. The detector (e.g., a flat panel detector) is assumed to have no spatial distortion. The method estimates geometric parameters including the position of the x-ray source, position, and rotation of the detector, and gantry angle, and can describe complex source-detector trajectories. The accuracy and sensitivity of the calibration algorithm was analyzed. The calibration algorithm estimates geometric parameters in a high level of accuracy such that the quality of CT reconstruction is not degraded by the error of estimation. Sensitivity analysis shows uncertainty of 0.01 degrees (around beam direction) to 0.3 degrees (normal to the beam direction) in rotation, and 0.2 mm (orthogonal to the beam direction) to 4.9 mm (beam direction) in position for the medical linear accelerator geometry. Experimental measurements using a laboratory bench Cone-beam CT system of known geometry demonstrate the sensitivity of the method in detecting small changes in the imaging geometry with an uncertainty of 0
Simulation on Measurement Method of Geometric Distortion of Telescopes
NASA Astrophysics Data System (ADS)
Li, F.; Ren, S. L.
2015-11-01
Measuring the geometric distortion is conducive to improve the astrometric accuracy of telescopes, which is meaningful for many disciplines of astronomy, such as stellar clusters, natural satellites, asteroids, comets, and the other celestial bodies in the solar system. For this reason, researchers have developed an iterative self-calibration method to measure the geometric distortion of telescopes by observing a dense star field in the dithering mode, and have achieved many good results. However, the previous work did not constrain the density of star field or the dithering number in the observing mode, but chose relative good conditions to observe, which took up much observing time. In order to explore the validity of self-calibration method, and optimize its observing conditions, it is necessary to carry out the corresponding simulation. Firstly, we introduce the self-calibration method in detail in the present work. By the simulation method, the effectiveness of self-calibration method to give the geometric distortion is proved, and the observing conditions, such as the density of star field and dithering number, are optimized to give the geometric distortion with a high accuracy. Considering the practical application for correcting the geometric distortion, we also analyze the relation between the number of reference stars in the field of view and the astrometric accuracy by virtue of the simulation method.
Geometric Calibration and Validation of Ultracam Aerial Sensors
NASA Astrophysics Data System (ADS)
Gruber, Michael; Schachinger, Bernhard; Muick, Marc; Neuner, Christian; Tschemmernegg, Helfried
2016-03-01
We present details of the calibration and validation procedure of UltraCam Aerial Camera systems. Results from the laboratory calibration and from validation flights are presented for both, the large format nadir cameras and the oblique cameras as well. Thus in this contribution we show results from the UltraCam Eagle and the UltraCam Falcon, both nadir mapping cameras, and the UltraCam Osprey, our oblique camera system. This sensor offers a mapping grade nadir component together with the four oblique camera heads. The geometric processing after the flight mission is being covered by the UltraMap software product. Thus we present details about the workflow as well. The first part consists of the initial post-processing which combines image information as well as camera parameters derived from the laboratory calibration. The second part, the traditional automated aerial triangulation (AAT) is the step from single images to blocks and enables an additional optimization process. We also present some special features of our software, which are designed to better support the operator to analyze large blocks of aerial images and to judge the quality of the photogrammetric set-up.
Iterative optimization calibration method for stereo deflectometry.
Ren, Hongyu; Gao, Feng; Jiang, Xiangqian
2015-08-24
An accurate system calibration method is presented in this paper to calibrate stereo deflectometry. A corresponding iterative optimization algorithm is also proposed to improve the system calibration accuracy. This merges CCD parameters and geometrical relation between CCDs and the LCD into one cost function. In this calibration technique, an optical flat acts as a reference mirror and simultaneously reflect sinusoidal fringe patterns into the two CCDs. The normal vector of the reference mirror is used as an intermediate variable to implement this iterative optimization algorithm until the root mean square of the reprojection errors converge to a minimum. The experiment demonstrates that this method can optimize all the calibration parameters and can effectively reduce reprojection error, which correspondingly improves the final reconstruction accuracy. PMID:26368180
Calibration method for an omnidirectional multicamera system
NASA Astrophysics Data System (ADS)
Ikeda, Sei; Sato, Tomokazu; Yokoya, Naokazu
2003-05-01
Telepresence systems using an omnidirectional image sensor enable us to experience remote site. A omnidirectional multi-camera system is more useful to acquire outdoor scenes than a monocular camera system, because the multi-camera system can easily capture high-resolution omnidirectional images. However, exact calibration of the camera system is necessary to virtualize the real world accurately. In this paper, we describe a geometric and photometric camera calibration and a panorama movie generation method for the omnidirectional multi-camera system. In the geometric calibration, intrinsic and extrinsic parameters of each camera are estimated using a calibration board and a laser measurement system called total station. In the photometric calibration, the limb darkening and color balances among the cameras are corrected. The result of the calibration is used in the panorama movie generation. In experiments, we have actually calibrated the multi-camera system and have generated spherical panorama movies by using the estimated camera parameters. A telepresence system was prototyped in order to confirm that the panorama movie can be used for telepresence well. In addition, we have evaluated the discontinuity in generated panoramic images.
Inspection system calibration methods
Deason, Vance A.; Telschow, Kenneth L.
2004-12-28
An inspection system calibration method includes producing two sideband signals of a first wavefront; interfering the two sideband signals in a photorefractive material, producing an output signal therefrom having a frequency and a magnitude; and producing a phase modulated operational signal having a frequency different from the output signal frequency, a magnitude, and a phase modulation amplitude. The method includes determining a ratio of the operational signal magnitude to the output signal magnitude, determining a ratio of a 1st order Bessel function of the operational signal phase modulation amplitude to a 0th order Bessel function of the operational signal phase modulation amplitude, and comparing the magnitude ratio to the Bessel function ratio.
View-dependent geometric calibration for offset flat-panel cone beam computed tomography systems
NASA Astrophysics Data System (ADS)
Nguyen, Van-Giang
2016-04-01
Geometric parameters that define the geometry of imaging systems are crucial for image reconstruction and image quality in x-ray computed tomography (CT). The problem of determining geometric parameters for an offset flat-panel cone beam CT (CBCT) system, a recently introduced modality with a large field of view, with the assumption of an unstable mechanism and geometric parameters that vary in each view, is considered. To accurately and rapidly find the geometric parameters for each projection view, we use the projection matrix method and design a dedicated phantom that is partially visible in all projection views. The phantom consists of balls distributed symmetrically in a cylinder to ensure the inclusion of the phantom in all views, and a large portion of the phantom is covered in the projection image. To efficiently use calibrated geometric information in the reconstruction process and get rid of approximation errors, instead of decomposing the projection matrix into actual geometric parameters that are manually corrected before being used in reconstruction, as in conventional methods, we directly use the projection matrix and its pseudo-inverse in projection and backprojection operations of reconstruction algorithms. The experiments illustrate the efficacy of the proposed method with a real offset flat-panel CBCT system in dental imaging.
On-Orbit Geometric Calibration Approach for High-Resolution Geostationary Optical Satellite GaoFen-4
NASA Astrophysics Data System (ADS)
Wang, Mi; Cheng, Yufeng; Long, Xiaoxiang; Yang, Bo
2016-06-01
The GaoFen-4 (GF-4) remote sensing satellite is China's first civilian high-resolution geostationary optical satellite, which has been launched at the end of December 2015. To guarantee the geometric quality of imagery, this paper presents an on-orbit geometric calibration method for the area-array camera of GF-4. Firstly, we introduce the imaging features of area-array camera of GF-4 and construct a rigorous imaging model based on the analysis of the major error sources from three aspects: attitude measurement error, orbit measurement error and camera distortion. Secondly, we construct an on-orbit geometric calibration model by selecting and optimizing parameters of the rigorous geometric imaging model. On this basis, the calibration parameters are divided into two groups: external and internal calibration parameters. The external parameters are installation angles between the area-array camera and the star tracker, and we propose a two-dimensional direction angle model as internal parameters to describe the distortion of the areaarray camera. Thirdly, we propose a stepwise parameters estimation method that external parameters are estimated firstly, then internal parameters are estimated based on the generalized camera frame determined by external parameters. Experiments based on the real data of GF-4 shows that after on-orbit geometric calibration, the geometric accuracy of the images without ground control points is significantly improved.
Habib, Ayman F.; Kersting, Ana P.; Shaker, Ahmed; Yan, Wai-Yeung
2011-01-01
LiDAR (Light Detection And Ranging) systems are capable of providing 3D positional and spectral information (in the utilized spectrum range) of the mapped surface. Due to systematic errors in the system parameters and measurements, LiDAR systems require geometric calibration and radiometric correction of the intensity data in order to maximize the benefit from the collected positional and spectral information. This paper presents a practical approach for the geometric calibration of LiDAR systems and radiometric correction of collected intensity data while investigating their impact on the quality of the derived products. The proposed approach includes the use of a quasi-rigorous geometric calibration and the radar equation for the radiometric correction of intensity data. The proposed quasi-rigorous calibration procedure requires time-tagged point cloud and trajectory position data, which are available to most of the data users. The paper presents a methodology for evaluating the impact of the geometric calibration on the relative and absolute accuracy of the LiDAR point cloud. Furthermore, the impact of the geometric calibration and radiometric correction on land cover classification accuracy is investigated. The feasibility of the proposed methods and their impact on the derived products are demonstrated through experimental results using real data. PMID:22164121
Habib, Ayman F; Kersting, Ana P; Shaker, Ahmed; Yan, Wai-Yeung
2011-01-01
LiDAR (Light Detection And Ranging) systems are capable of providing 3D positional and spectral information (in the utilized spectrum range) of the mapped surface. Due to systematic errors in the system parameters and measurements, LiDAR systems require geometric calibration and radiometric correction of the intensity data in order to maximize the benefit from the collected positional and spectral information. This paper presents a practical approach for the geometric calibration of LiDAR systems and radiometric correction of collected intensity data while investigating their impact on the quality of the derived products. The proposed approach includes the use of a quasi-rigorous geometric calibration and the radar equation for the radiometric correction of intensity data. The proposed quasi-rigorous calibration procedure requires time-tagged point cloud and trajectory position data, which are available to most of the data users. The paper presents a methodology for evaluating the impact of the geometric calibration on the relative and absolute accuracy of the LiDAR point cloud. Furthermore, the impact of the geometric calibration and radiometric correction on land cover classification accuracy is investigated. The feasibility of the proposed methods and their impact on the derived products are demonstrated through experimental results using real data. PMID:22164121
Rigorous geometric self-calibrating bundle adjustment for a dual fluoroscopic imaging system.
Lichti, Derek D; Sharma, Gulshan B; Kuntze, Gregor; Mund, Braden; Beveridge, Jillian E; Ronsky, Janet L
2015-02-01
High-speed dual fluoroscopy is a noninvasive imaging technology for three-dimensional skeletal kinematics analysis that finds numerous biomechanical applications. Accurate reconstruction of bone translations and rotations from dual-fluoroscopic data requires accurate calibration of the imaging geometry and the many imaging distortions that corrupt the data. Direct linear transformation methods are commonly applied for performing calibration using a two-step process that suffers from a number of potential shortcomings including that each X-ray source and corresponding camera must be calibrated separately. Consequently, the true imaging set-up and the constraints it presents are not incorporated during calibration. A method to overcome such drawbacks is the single-step self-calibrating bundle adjustment method. This procedure, based on the collinearity principle augmented with imaging distortion models and geometric constraints, has been developed and is reported herein. Its efficacy is shown with a carefully controlled experiment comprising 300 image pairs with 48 507 image points. Application of all geometric constraints and a 31 parameter distortion model resulted in up to 91% improvement in terms of precision (model fit) and up to 71% improvement in terms of 3-D point reconstruction accuracy (0.3-0.4 mm). The accuracy of distance reconstruction was improved from 0.3±2.0 mm to 0.2 ±1.1 mm and angle reconstruction accuracy was improved from -0.03±0.55(°) to 0.01±0.06(°). Such positioning accuracy will allow for the accurate quantification of in vivo arthrokinematics crucial for skeletal biomechanics investigations. PMID:25330483
Geometric in-flight calibration of the stereoscopic line-CCD scanner MOMS-2P
NASA Astrophysics Data System (ADS)
Kornus, Wolfgang; Lehner, Manfred; Schroeder, Manfred
This paper describes the geometric in-flight calibration of the Modular Optoelectronic Multispectral Scanner MOMS-2P, which has collected digital multispectral and threefold along-track stereoscopic imagery of the earth's surface from the PRIRODA module of the Russian space station MIR from October 1996 to August 1999. The goal is the verification and, if necessary, the update of the calibration data, which were estimated from the geometric laboratory calibration. The paper is subdivided into two parts, describing two different procedures of geometric in-flight calibration. The first method is based on DLR matching software and is restricted to nadir looking channels, which are read out simultaneously. From a high number of individual point matches between the images of the same area taken by the different CCD arrays, the most reliable ones are selected and used to calculate shifts with components in and across flight direction between the CCD arrays. These actual shifts are compared to the nominal shifts, derived from the results of the laboratory calibration, and parameters of the valid camera model are estimated from both data sets by least squares adjustment. A special case of band-to-band registration are the two optically combined CCD-arrays of the nadir high-resolution channel. They are read out simultaneously with a nominal 10 pixel overlap in stereoscopic imaging mode A. The DLR matching software is applied to calculate the displacement vector between the two CCD-arrays. The second method is based on combined photogrammetric bundle adjustment using an adapted functional model for the reconstruction of the interior orientation. It requires precise and reliable ground control information as well as navigation data of the navigation-package MOMS-NAV. Nine contiguous image scenes of MOMS-2P data-take T083C building an about 550-km-long strip over southern Germany and Austria taken in March 1997 were evaluated. From both procedures calibration data are
Geometric Parameters Estimation and Calibration in Cone-Beam Micro-CT.
Zhao, Jintao; Hu, Xiaodong; Zou, Jing; Hu, Xiaotang
2015-01-01
The quality of Computed Tomography (CT) images crucially depends on the precise knowledge of the scanner geometry. Therefore, it is necessary to estimate and calibrate the misalignments before image acquisition. In this paper, a Two-Piece-Ball (TPB) phantom is used to estimate a set of parameters that describe the geometry of a cone-beam CT system. Only multiple projections of the TPB phantom at one position are required, which can avoid the rotation errors when acquiring multi-angle projections. Also, a corresponding algorithm is derived. The performance of the method is evaluated through simulation and experimental data. The results demonstrated that the proposed method is valid and easy to implement. Furthermore, the experimental results from the Micro-CT system demonstrate the ability to reduce artifacts and improve image quality through geometric parameter calibration. PMID:26371008
Geometric Parameters Estimation and Calibration in Cone-Beam Micro-CT
Zhao, Jintao; Hu, Xiaodong; Zou, Jing; Hu, Xiaotang
2015-01-01
The quality of Computed Tomography (CT) images crucially depends on the precise knowledge of the scanner geometry. Therefore, it is necessary to estimate and calibrate the misalignments before image acquisition. In this paper, a Two-Piece-Ball (TPB) phantom is used to estimate a set of parameters that describe the geometry of a cone-beam CT system. Only multiple projections of the TPB phantom at one position are required, which can avoid the rotation errors when acquiring multi-angle projections. Also, a corresponding algorithm is derived. The performance of the method is evaluated through simulation and experimental data. The results demonstrated that the proposed method is valid and easy to implement. Furthermore, the experimental results from the Micro-CT system demonstrate the ability to reduce artifacts and improve image quality through geometric parameter calibration. PMID:26371008
Development and calibration of self-centring probes for assessing geometrical errors of machines
NASA Astrophysics Data System (ADS)
Yagüe, J. A.; Velázquez, J.; Albajez, J. A.; Aguilar, J. J.; Lope, M. A.; Santolaria, J.
2009-11-01
A new type of probe for calibration, verification or interim checking of machine tools as well as robots or parallel-kinematics machine tools is presented in this paper. This probe is part of a ball-artefact-based method to assess the geometrical errors of linear and angular axes in a quick and reliable way. The discussion about the best design concept for the self-centring probe, the mathematical modelling and design process of one of those concepts and the development of three different prototypes are shown. Different sensors and design options were developed to optimize the size and cost of the probe. The calibration of the probe prototypes by way of a kinematically coupled reference device to allow on-machine tests is shown. The uncertainties obtained were around 1 µm for one of the prototypes and below 5 µm for the other two. Finally, results of a geometrical verification of a machine tool are demonstrated, with values similar to the ones achieved using other methods, such as laser interferometry. Compared to those other methods, the new technique was shown to be less time consuming.
Geometric Calibration of ZIYUAN-3 Three-Line Cameras Combining Ground Control Points and Lines
NASA Astrophysics Data System (ADS)
Cao, Jinshan; Yuan, Xiuxiao; Gong, Jianya
2016-06-01
Due to the large biases between the laboratory-calibrated values of the orientation parameters and their in-orbit true values, the initial direct georeferencing accuracy of the Ziyuan-3 (ZY-3) three-line camera (TLC) images can only reach the kilometre level. In this paper, a point-based geometric calibration model of the ZY-3 TLCs is firstly established by using the collinearity constraint, and then a line-based geometric calibration model is established by using the coplanarity constraint. With the help of both the point-based and the line-based models, a feasible in-orbit geometric calibration approach for the ZY-3 TLCs combining ground control points (GCPs) and ground control lines (GCLs) is presented. Experimental results show that like GCPs, GCLs can also provide effective ground control information for the geometric calibration of the ZY-3 TLCs. The calibration accuracy of the look angles of charge-coupled device (CCD) detectors achieved by using the presented approach reached up to about 1.0''. After the geometric calibration, the direct georeferencing accuracy of the ZY-3 TLC images without ground controls was significantly improved from the kilometre level to better than 11 m in planimetry and 9 m in height. A more satisfactory georeferencing accuracy of better than 3.5 m in planimetry and 3.0 m in height was achieved after the block adjustment with four GCPs.
Landsat 8 operational land imager on-orbit geometric calibration and performance
Storey, James C.; Choate, Michael J.; Lee, Kenton
2014-01-01
The Landsat 8 spacecraft was launched on 11 February 2013 carrying the Operational Land Imager (OLI) payload for moderate resolution imaging in the visible, near infrared (NIR), and short-wave infrared (SWIR) spectral bands. During the 90-day commissioning period following launch, several on-orbit geometric calibration activities were performed to refine the prelaunch calibration parameters. The results of these calibration activities were subsequently used to measure geometric performance characteristics in order to verify the OLI geometric requirements. Three types of geometric calibrations were performed including: (1) updating the OLI-to-spacecraft alignment knowledge; (2) refining the alignment of the sub-images from the multiple OLI sensor chips; and (3) refining the alignment of the OLI spectral bands. The aspects of geometric performance that were measured and verified included: (1) geolocation accuracy with terrain correction, but without ground control (L1Gt); (2) Level 1 product accuracy with terrain correction and ground control (L1T); (3) band-to-band registration accuracy; and (4) multi-temporal image-to-image registration accuracy. Using the results of the on-orbit calibration update, all aspects of geometric performance were shown to meet or exceed system requirements.
Method for calibrating mass spectrometers
Anderson, Gordon A [Benton City, WA; Brands, Michael D [Richland, WA; Bruce, James E [Schwenksville, PA; Pasa-Tolic, Ljiljana [Richland, WA; Smith, Richard D [Richland, WA
2002-12-24
A method whereby a mass spectra generated by a mass spectrometer is calibrated by shifting the parameters used by the spectrometer to assign masses to the spectra in a manner which reconciles the signal of ions within the spectra having equal mass but differing charge states, or by reconciling ions having known differences in mass to relative values consistent with those known differences. In this manner, the mass spectrometer is calibrated without the need for standards while allowing the generation of a highly accurate mass spectra by the instrument.
Camera self-calibration method based on two vanishing points
NASA Astrophysics Data System (ADS)
Duan, Shaoli; Zang, Huaping; Xu, Mengmeng; Zhang, Xiaofang; Gong, Qiaoxia; Tian, Yongzhi; Liang, Erjun; Liu, Xiaomin
2015-10-01
Camera calibration is one of the indispensable processes to obtain 3D depth information from 2D images in the field of computer vision. Camera self-calibration is more convenient and flexible, especially in the application of large depth of fields, wide fields of view, and scene conversion, as well as other occasions like zooms. In this paper, a self-calibration method based on two vanishing points is proposed, the geometric characteristic of disappear points formed by two groups of orthogonal parallel lines is applied to camera self-calibration. By using the vectors' orthogonal properties of connection optical centers and the vanishing points, the constraint equations on the camera intrinsic parameters are established. By this method, four internal parameters of the camera can be solved though only four images taken from different viewpoints in a scene. Compared with the two other self-calibration methods with absolute quadric and calibration plate, the method based on two vanishing points does not require calibration objects, camera movement, the information on the size and location of parallel lines, without strict experimental equipment, and having convenient calibration process and simple algorithm. Compared with the experimental results of the method based on calibration plate, self-calibration method by using machine vision software Halcon, the practicability and effectiveness of the proposed method in this paper is verified.
NASA Astrophysics Data System (ADS)
Schneider, M.; Müller, R.; Krawzcyk, H.; Bachmann, M.; Storch, T.; Mogulsky, V.; Hofer, S.
2012-07-01
The German Aerospace Center DLR - namely the Earth Observation Center EOC and the German Space Operations Center GSOC - is responsible for the establishment of the ground segment of the future German hyperspectral satellite mission EnMAP (Environmental Mapping and Analysis Program). The Earth Observation Center has long lasting experiences with air- and spaceborne acquisition, processing, and analysis of hyperspectral image data. In the first part of this paper, an overview of the radiometric in-flight calibration concept including dark value measurements, deep space measurements, internal lamps measurements and sun measurements is presented. Complemented by pre-launch calibration and characterization these analyses will deliver a detailed and quantitative assessment of possible changes of spectral and radiometric characteristics of the hyperspectral instrument, e.g. due to degradation of single elements. A geometric accuracy of 100 m, which will be improved to 30 m with respect to a used reference image, if it exists, will be achieved by ground processing. Therfore, and for the required co-registration accuracy between SWIR and VNIR channels, additional to the radiometric calibration, also a geometric calibration is necessary. In the second part of this paper, the concept of the geometric calibration is presented in detail. The geometric processing of EnMAP scenes will be based on laboratory calibration results. During repeated passes over selected calibration areas images will be acquired. The update of geometric camera model parameters will be done by an adjustment using ground control points, which will be extracted by automatic image matching. In the adjustment, the improvements of the attitude angles (boresight angles), the improvements of the interior orientation (view vector) and the improvements of the position data are estimated. In this paper, the improvement of the boresight angles is presented in detail as an example. The other values and combinations
Calibration method for spectroscopic systems
Sandison, David R.
1998-01-01
Calibration spots of optically-characterized material placed in the field of view of a spectroscopic system allow calibration of the spectroscopic system. Response from the calibration spots is measured and used to calibrate for varying spectroscopic system operating parameters. The accurate calibration achieved allows quantitative spectroscopic analysis of responses taken at different times, different excitation conditions, and of different targets.
Calibration method for spectroscopic systems
Sandison, D.R.
1998-11-17
Calibration spots of optically-characterized material placed in the field of view of a spectroscopic system allow calibration of the spectroscopic system. Response from the calibration spots is measured and used to calibrate for varying spectroscopic system operating parameters. The accurate calibration achieved allows quantitative spectroscopic analysis of responses taken at different times, different excitation conditions, and of different targets. 3 figs.
Geometrical Calibration of the Photo-Spectral System and Digital Maps Retrieval
NASA Astrophysics Data System (ADS)
Bruchkouskaya, S.; Skachkova, A.; Katkovski, L.; Martinov, A.
2013-12-01
Imaging systems for remote sensing of the Earth are required to demonstrate high metric accuracy of the picture which can be provided through preliminary geometrical calibration of optical systems. Being defined as a result of the geometrical calibration, parameters of internal and external orientation of the cameras are needed while solving such problems of image processing, as orthotransformation, geometrical correction, geographical coordinate fixing, scale adjustment and image registration from various channels and cameras, creation of image mosaics of filmed territories, and determination of geometrical characteristics of objects in the images. The geometrical calibration also helps to eliminate image deformations arising due to manufacturing defects and errors in installation of camera elements and photo receiving matrices as well as those resulted from lens distortions. A Photo-Spectral System (PhSS), which is intended for registering reflected radiation spectra of underlying surfaces in a wavelength range from 350 nm to 1050 nm and recording images of high spatial resolution, has been developed at the A.N. Sevchenko Research Institute of Applied Physical Problems of the Belarusian State University. The PhSS has undergone flight tests over the territory of Belarus onboard the Antonov AN-2 aircraft with the aim to obtain visible range images of the underlying surface. Then we performed the geometrical calibration of the PhSS and carried out the correction of images obtained during the flight tests. Furthermore, we have plotted digital maps of the terrain using the stereo pairs of images acquired from the PhSS and evaluated the accuracy of the created maps. Having obtained the calibration parameters, we apply them for correction of the images from another identical PhSS device, which is located at the Russian Orbital Segment of the International Space Station (ROS ISS), aiming to retrieve digital maps of the terrain with higher accuracy.
Wang, Mi; Fan, Chengcheng; Yang, Bo; Jin, Shuying; Pan, Jun
2016-01-01
Satellite attitude accuracy is an important factor affecting the geometric processing accuracy of high-resolution optical satellite imagery. To address the problem whereby the accuracy of the Yaogan-24 remote sensing satellite's on-board attitude data processing is not high enough and thus cannot meet its image geometry processing requirements, we developed an approach involving on-ground attitude data processing and digital orthophoto (DOM) and the digital elevation model (DEM) verification of a geometric calibration field. The approach focuses on three modules: on-ground processing based on bidirectional filter, overall weighted smoothing and fitting, and evaluation in the geometric calibration field. Our experimental results demonstrate that the proposed on-ground processing method is both robust and feasible, which ensures the reliability of the observation data quality, convergence and stability of the parameter estimation model. In addition, both the Euler angle and quaternion could be used to build a mathematical fitting model, while the orthogonal polynomial fitting model is more suitable for modeling the attitude parameter. Furthermore, compared to the image geometric processing results based on on-board attitude data, the image uncontrolled and relative geometric positioning result accuracy can be increased by about 50%. PMID:27483287
A new phantom for image quality, geometric destortion, and HU calibration in MSCT and CBCT
NASA Astrophysics Data System (ADS)
Voigt, Johannes M.; Blendl, Christian; Selbach, Markus; Uphoff, Clemens; Fiebich, Martin
2012-03-01
Flat panel cone-beam computed tomography (CBCT) is developing to the state-of-the-art technique in several medical disciplines such as dental and otorhinolaryngological imaging. Dental and otorhinolaryngological CBCT systems offer a variety of different field-of-view sizes from 6.0 to 17.0 cm. Standard phantoms are only designed for the use in multi-slices CT (MSCT) and there is no phantom which provides detail structures for all common characteristic values and Hounsfield calibration. In this study we present a new phantom specially designed for use with MSCT and CBCT systems providing detail structures for MTF, 3D MTF, NPS, SNR, geometric distortion and HU calibration. With this phantom you'll only need one acquisition for image quality investigation and assurance. Materials and methods: The phantom design is shown in figure 1. To investigate the practicability, the phantom was scanned using dedicated MSCT-scanners, 3D C-arms und digital volume tomographs. The acquired axial image stacks were analyzed using a dedicated computer program, which is provided as an ImageJ plugin. The MTF was compared to other methodologies such as a thin wire, a sphere or noise response [10, 13, 14]. The HU values were also computed using other common methods. Results: These results are similar to the results of others studies [10, 13, 14]. The method has proven to be stable and delivers comparable results to other methodologies such as using a thin wire. The NPS was calculated for all materials. Furthermore, CT numbers for all materials were computed and compared to the desired values. The measurement of geometric deformation has proven to be accurate. Conclusion: A unique feature of this phantom is to compute the geometric deformation of the 3D-volume image. This offers the chance to improve accuracy, e.g. in dental implant planning. Another convenient feature is that the phantom needs to be scanned only once with otorhinolaryngological volume tomographs to be fully displayed. It is
Image Sensor Model Using Geometric Algebra: From Calibration to Motion Estimation
NASA Astrophysics Data System (ADS)
Debaecker, Thibaud; Benosman, Ryad; Ieng, Sio H.
In computer vision image sensors have universally been defined as the nonparametric association of projection rays in the 3D world to pixels in the images. If the pixels' physical topology can be often neglected in the case of perspective cameras, this approximation is no longer valid in the case of variant scale sensors, which are now widely used in robotics. Neglecting the nonnull pixel area and then the pixel volumic field of view implies that geometric reconstruction problems are solved by minimizing a cost function that combines the reprojection errors in the 2D images. This paper provides a complete and realistic cone-pixel camera model that equally fits constant or variant scale resolution together with a protocol to calibrate such a sensor. The proposed model involves a new characterization of pixel correspondences with 3D-cone intersections computed using convex hull and twists in Conformal Geometric Algebra. Simulated experiments show that standard methods and especially Bundle Adjustment are sometimes unable to reach the correct motion, because of their ray-pixel approach and the choice of reprojection error as a cost function which does not particularly fit the physical reality. This problem can be solved using a nonprojective cone intersection cost function as introduced below.
Bothe, Thorsten; Li Wansong; Schulte, Michael; von Kopylow, Christoph; Bergmann, Ralf B.; Jueptner, Werner P. O.
2010-10-20
Exact geometric calibration of optical devices like projectors or cameras is the basis for utilizing them in quantitative metrological applications. The common state-of-the-art photogrammetric pinhole-imaging-based models with supplemental polynomial corrections fail in the presence of nonsymmetric or high-spatial-frequency distortions and in describing caustics efficiently. These problems are solved by our vision ray calibration (VRC), which is proposed in this paper. The VRC takes an optical mapping system modeled as a black box and directly delivers corresponding vision rays for each mapped pixel. The underlying model, the calibration process, and examples are visualized and reviewed, demonstrating the potential of the VRC.
A proposed standard method for polarimetric calibration and calibration verification
NASA Astrophysics Data System (ADS)
Persons, Christopher M.; Jones, Michael W.; Farlow, Craig A.; Morell, L. Denise; Gulley, Michael G.; Spradley, Kevin D.
2007-09-01
Accurate calibration of polarimetric sensors is critical to reducing and analyzing phenomenology data, producing uniform polarimetric imagery for deployable sensors, and ensuring predictable performance of polarimetric algorithms. It is desirable to develop a standard calibration method, including verification reporting, in order to increase credibility with customers and foster communication and understanding within the polarimetric community. This paper seeks to facilitate discussions within the community on arriving at such standards. Both the calibration and verification methods presented here are performed easily with common polarimetric equipment, and are applicable to visible and infrared systems with either partial Stokes or full Stokes sensitivity. The calibration procedure has been used on infrared and visible polarimetric imagers over a six year period, and resulting imagery has been presented previously at conferences and workshops. The proposed calibration method involves the familiar calculation of the polarimetric data reduction matrix by measuring the polarimeter's response to a set of input Stokes vectors. With this method, however, linear combinations of Stokes vectors are used to generate highly accurate input states. This allows the direct measurement of all system effects, in contrast with fitting modeled calibration parameters to measured data. This direct measurement of the data reduction matrix allows higher order effects that are difficult to model to be discovered and corrected for in calibration. This paper begins with a detailed tutorial on the proposed calibration and verification reporting methods. Example results are then presented for a LWIR rotating half-wave retarder polarimeter.
Geometrical calibration television measuring systems with solid state photodetectors
NASA Astrophysics Data System (ADS)
Matiouchenko, V. G.; Strakhov, V. V.; Zhirkov, A. O.
2000-11-01
The various optical measuring methods for deriving information about the size and form of objects are now used in difference branches- mechanical engineering, medicine, art, criminalistics. Measuring by means of the digital television systems is one of these methods. The development of this direction is promoted by occurrence on the market of various types and costs small-sized television cameras and frame grabbers. There are many television measuring systems using the expensive cameras, but accuracy performances of low cost cameras are also interested for the system developers. For this reason inexpensive mountingless camera SK1004CP (format 1/3', cost up to 40$) and frame grabber Aver2000 were used in experiments.
Pleiades HR in Flight Geometrical Calibration : Location and Mapping of the Focal Plane
NASA Astrophysics Data System (ADS)
de Lussy, F.; Greslou, D.; Dechoz, C.; Amberg, V.; Delvit, J. M.; Lebegue, L.; Blanchet, G.; Fourest, S.
2012-07-01
The Pleiades system, ORFEO system optical component (Optical and Radar Federated Earth Observation) consists of a constellation of two satellites for very High Resolution panchromatic and multispectral optical observation of the Earth. Its mission is to cover all European civilian needs (mapping, tracking floods and fires) and defence in the category of metric resolution: 0.7m Nadir. The first Pleiades satellite was launched at the end of last year. One of the key objectives of the Pleiades HR (PHR) project is to achieve a location accuracy that will allow the use of images in GIS (Geographical Information System) without geometrical model improvement by refining on ground control points. The image location without refined model was specified with the precision of the most commonly used tool ie the civil GPS. So the location accuracy has been specified at less than 12m for 90% of the images on a nominal satellite configuration. Very special care has been taken all along the PHR project realization to achieve this very good location accuracy. The final touch is given during the in-orbit commissioning phase which lasts until June 2012. The geometric quality implies to tune the parameters involved in the geolocation model (geometric calibration): besides attitude and orbit restitution tuning (not considered here), it consists in estimating the biases between the instrument orientation and the AOCS reference frame, and also the sight line of each detector in the focal plane. This is called static geometrical model. The analysis of dynamic perturbations outside of the model are the second most important image quality objective of in-flight commissioning, not described in this paper. Finally "image quality assessment" consists in evaluating the image quality obtained in the final products. For geolocation model, it is quantified by the absolute geolocation and the pointing accuracies, and it is a main contributor in length alteration and planimetric and altimetric
A practical method for sensor absolute calibration.
Meisenholder, G W
1966-04-01
This paper describes a method of performing sensor calibrations using an NBS standard of spectral irradiance. The method shown, among others, was used for calibration of the Mariner IV Canopus sensor. Agreement of inflight response to preflight calibrations performed by this technique has been found to be well within 10%. PMID:20048890
On-ground characterization of Rosetta/VIRTIS-M. I. Spectral and geometrical calibrations
Ammannito, E.; Filacchione, G.; Coradini, A.; Capaccioni, F.; Piccioni, G.; De Sanctis, M. C.; Dami, M.; Barbis, A.
2006-09-15
The complete characterization of complex imaging spectrometers, such as VIRTIS-M (visual infrared thermal imaging spectrometer) aboard the Rosetta mission, requires a detailed and prolonged activity starting with the instrument integration and continuing during the entire operational life of the experiment. In this article we report the main experimental activities realized during the on-ground characterizations to evaluate the spectral and geometric performances in order to check the conformance with the technical requirements derived from the scientific goals of the experiment. Spectral calibrations allow to confirm instrumental spectral range, resolution, and sampling; geometric calibrations are necessary to estimate the pixel and slit functions, field of view extension, and possible optical aberrations. Two separate sections are dedicated to each one of these subjects, including the strategy followed to prepare measurements, a basic description of the on-ground experimental setups, and the analysis of the collected data.
Geometric calibration and accuracy assessment of a multispectral imager on UAVs
NASA Astrophysics Data System (ADS)
Zheng, Fengjie; Yu, Tao; Chen, Xingfeng; Chen, Jiping; Yuan, Guoti
2012-11-01
The increasing developments in Unmanned Aerial Vehicles (UAVs) platforms and associated sensing technologies have widely promoted UAVs remote sensing application. UAVs, especially low-cost UAVs, limit the sensor payload in weight and dimension. Mostly, cameras on UAVs are panoramic, fisheye lens, small-format CCD planar array camera, unknown intrinsic parameters and lens optical distortion will cause serious image aberrations, even leading a few meters or tens of meters errors in ground per pixel. However, the characteristic of high spatial resolution make accurate geolocation more critical to UAV quantitative remote sensing research. A method for MCC4-12F Multispectral Imager designed to load on UAVs has been developed and implemented. Using multi-image space resection algorithm to assess geometric calibration parameters of random position and different photogrammetric altitudes in 3D test field, which is suitable for multispectral cameras. Both theoretical and practical accuracy assessments were selected. The results of theoretical strategy, resolving object space and image point coordinate differences by space intersection, showed that object space RMSE were 0.2 and 0.14 pixels in X direction and in Y direction, image space RMSE were superior to 0.5 pixels. In order to verify the accuracy and reliability of the calibration parameters，practical study was carried out in Tianjin UAV flight experiments, the corrected accuracy validated by ground checkpoints was less than 0.3m. Typical surface reflectance retrieved on the basis of geo-rectified data was compared with ground ASD measurement resulting 4% discrepancy. Hence, the approach presented here was suitable for UAV multispectral imager.
A depth estimation method based on geometric transformation for stereo light microscope.
Fan, Shengli; Yu, Mei; Wang, Yigang; Jiang, Gangyi
2014-01-01
Stereo light microscopes (SLM) with narrow vision and shallow depth of field are widely used in micro-domain research. In this paper, we propose a depth estimation method of micro objects based on geometric transformation. By analyzing the optical imaging geometry, the definition of geometric transformation distance is given and the depth-distance relation express is obtained. The parameters of geometric transformation and express are calibrated with calibration board images captured in aid of precise motorized stage. The depth of micro object can be estimated by calculating the geometric transformation distance. The proposed depth-distance relation express is verified using an experiment in which the depth map of an Olanzapine tablet surface is reconstructed. PMID:25226979
Geometric Calibration of the Orion Optical Navigation Camera using Star Field Images
NASA Astrophysics Data System (ADS)
Christian, John A.; Benhacine, Lylia; Hikes, Jacob; D'Souza, Christopher
2016-07-01
The Orion Multi Purpose Crew Vehicle will be capable of autonomously navigating in cislunar space using images of the Earth and Moon. Optical navigation systems, such as the one proposed for Orion, require the ability to precisely relate the observed location of an object in a 2D digital image with the true corresponding line-of-sight direction in the camera's sensor frame. This relationship is governed by the camera's geometric calibration parameters — typically described by a set of five intrinsic parameters and five lens distortion parameters. While pre-flight estimations of these parameters will exist, environmental conditions often necessitate on-orbit recalibration. This calibration will be performed for Orion using an ensemble of star field images. This manuscript provides a detailed treatment of the theory and mathematics that will form the foundation of Orion's on-orbit camera calibration. Numerical results and examples are also presented.
Geometric methods for the design of mechanisms
NASA Astrophysics Data System (ADS)
Stokes, Ann Westagard
1993-01-01
Challenges posed by the process of designing robotic mechanisms have provided a new impetus to research in the classical subjects of kinematics, elastic analysis, and multibody dynamics. Historically, mechanism designers have considered these areas of analysis to be generally separate and distinct sciences. However, there are significant classes of problems which require a combination of these methods to arrive at a satisfactory solution. For example, both the compliance and the inertia distribution strongly influence the performance of a robotic manipulator. In this thesis, geometric methods are applied to the analysis of mechanisms where kinematics, elasticity, and dynamics play fundamental and interactive roles. Tools for the mathematical analysis, design, and optimization of a class of holonomic and nonholonomic mechanisms are developed. Specific contributions of this thesis include a network theory for elasto-kinematic systems. The applicability of the network theory is demonstrated by employing it to calculate the optimal distribution of joint compliance in a serial manipulator. In addition, the advantage of applying Lie group theoretic approaches to mechanisms requiring specific dynamic properties is demonstrated by extending Brockett's product of exponentials formula to the domain of dynamics. Conditions for the design of manipulators having inertia matrices which are constant in joint angle coordinates are developed. Finally, analysis and design techniques are developed for a class of mechanisms which rectify oscillations into secular motions. These techniques are applied to the analysis of free-floating chains that can reorient themselves in zero angular momentum processes and to the analysis of rattleback tops.
Design Method and Calibration of Moulinet
NASA Astrophysics Data System (ADS)
Itoh, Hirokazu; Yamada, Hirokazu; Udagawa, Sinsuke
The formula for obtaining the absorption horsepower of a Moulinet was rewritten, and the physical meaning of the constant in the formula was clarified. Based on this study, the design method of the Moulinet and the calibration method of the Moulinet that was performed after manufacture were verified experimentally. Consequently, the following was clarified; (1) If the propeller power coefficient was taken to be the proportionality constant, the absorption horsepower of the Moulinet was proportional to the cube of the revolution speed, and the fifth power of the Moulinet diameter. (2) If the Moulinet design was geometrically similar to the standard dimensions of the Aviation Technical Research Center's type-6 Moulinet, the proportionality constant C1 given in the reference could be used, and the absorption horsepower of the Moulinet was proportional to the cube of the revolution speed, the cube of the Moulinet diameter, and the side projection area of the Moulinet. (3) The proportionality constant C1 was proportional to the propeller power coefficient CP.
An Incremental Target-Adapted Strategy for Active Geometric Calibration of Projector-Camera Systems
Chen, Chia-Yen; Chien, Hsiang-Jen
2013-01-01
The calibration of a projector-camera system is an essential step toward accurate 3-D measurement and environment-aware data projection applications, such as augmented reality. In this paper we present a two-stage easy-to-deploy strategy for robust calibration of both intrinsic and extrinsic parameters of a projector. Two key components of the system are the automatic generation of projected light patterns and the incremental calibration process. Based on the incremental strategy, the calibration process first establishes a set of initial parameters, and then it upgrades these parameters incrementally using the projection and captured images of dynamically-generated calibration patterns. The scene-driven light patterns allow the system to adapt itself to the pose of the calibration target, such that the difficulty in feature detection is greatly lowered. The strategy forms a closed-loop system that performs self-correction as more and more observations become available. Compared to the conventional method, which requires a time-consuming process for the acquisition of dense pixel correspondences, the proposed method deploys a homography-based coordinate computation, allowing the calibration time to be dramatically reduced. The experimental results indicate that an improvement of 70% in reprojection errors is achievable and 95% of the calibration time can be saved. PMID:23435056
An incremental target-adapted strategy for active geometric calibration of projector-camera systems.
Chen, Chia-Yen; Chien, Hsiang-Jen
2013-01-01
The calibration of a projector-camera system is an essential step toward accurate 3-D measurement and environment-aware data projection applications, such as augmented reality. In this paper we present a two-stage easy-to-deploy strategy for robust calibration of both intrinsic and extrinsic parameters of a projector. Two key components of the system are the automatic generation of projected light patterns and the incremental calibration process. Based on the incremental strategy, the calibration process first establishes a set of initial parameters, and then it upgrades these parameters incrementally using the projection and captured images of dynamically-generated calibration patterns. The scene-driven light patterns allow the system to adapt itself to the pose of the calibration target, such that the difficulty in feature detection is greatly lowered. The strategy forms a closed-loop system that performs self-correction as more and more observations become available. Compared to the conventional method, which requires a time-consuming process for the acquisition of dense pixel correspondences, the proposed method deploys a homography-based coordinate computation, allowing the calibration time to be dramatically reduced. The experimental results indicate that an improvement of 70% in reprojection errors is achievable and 95% of the calibration time can be saved. PMID:23435056
An Accurate Projector Calibration Method Based on Polynomial Distortion Representation
Liu, Miao; Sun, Changku; Huang, Shujun; Zhang, Zonghua
2015-01-01
In structure light measurement systems or 3D printing systems, the errors caused by optical distortion of a digital projector always affect the precision performance and cannot be ignored. Existing methods to calibrate the projection distortion rely on calibration plate and photogrammetry, so the calibration performance is largely affected by the quality of the plate and the imaging system. This paper proposes a new projector calibration approach that makes use of photodiodes to directly detect the light emitted from a digital projector. By analyzing the output sequence of the photoelectric module, the pixel coordinates can be accurately obtained by the curve fitting method. A polynomial distortion representation is employed to reduce the residuals of the traditional distortion representation model. Experimental results and performance evaluation show that the proposed calibration method is able to avoid most of the disadvantages in traditional methods and achieves a higher accuracy. This proposed method is also practically applicable to evaluate the geometric optical performance of other optical projection system. PMID:26492247
High-Precision Calibration of the WFC3/UVIS Geometric Distortion
NASA Astrophysics Data System (ADS)
Riess, Adam
2014-10-01
The geometric distortion solution for WFC3/UVIS is known in most filters to better than 0.01 pixels from the analysis of pointed data. Astrometric data taken with spatial scans suggest that residuals from this solution have typical magitudes of 0.003-0.005 pixels, and correlate on scales of 50-100 pixels. These deviations also appear to be stable in time, and therefore can be calibrated using apropriate data. This proposal aims at improving the calibration of local deviations from astrometric solution via spatial scans. The observations target two regions with high density of bright stars at several different large-scale dithers to obtain a dense coverage of high S/N trails over the majority of the detector. The data will be used to obtain a static correction to the distortion solution that can be used to improve the geometric distortion solution. The open clusters M 67 and M 48 have been selected to provide the highest density of stars of the right brightness for F606W (M 67) and F621M and F673N (M 48); these are the recommended filters for optimal extraction of astrometric information, depending on the brightness of the target.
Automatic alignment method for calibration of hydrometers
NASA Astrophysics Data System (ADS)
Lee, Y. J.; Chang, K. H.; Chon, J. C.; Oh, C. Y.
2004-04-01
This paper presents a new method to automatically align specific scale-marks for the calibration of hydrometers. A hydrometer calibration system adopting the new method consists of a vision system, a stepping motor, and software to control the system. The vision system is composed of a CCD camera and a frame grabber, and is used to acquire images. The stepping motor moves the camera, which is attached to the vessel containing a reference liquid, along the hydrometer. The operating program has two main functions: to process images from the camera to find the position of the horizontal plane and to control the stepping motor for the alignment of the horizontal plane with a particular scale-mark. Any system adopting this automatic alignment method is a convenient and precise means of calibrating a hydrometer. The performance of the proposed method is illustrated by comparing the calibration results using the automatic alignment method with those obtained using the manual method.
NASA Astrophysics Data System (ADS)
Lerma, J. L.; García-San-Miguel, D.
2014-05-01
Systematic errors are present in laser scanning system observations due to manufacturer imperfections, wearing over time, vibrations, changing environmental conditions and, last but not least, involuntary hits. To achieve maximum quality and rigorous measurements from terrestrial laser scanners, a least squares estimation of additional calibration parameters can be used to model the a priori unknown systematic errors and therefore improve output observations. The selection of the right set of additional parameters is not trivial and requires laborious statistical analysis. Based on this requirement, this article presents an approach to determine the best set of additional parameters which provides the best mathematical solution based on a dimensionless quality index. The best set of additional parameters is the one which provides the maximum quality index (i.e. minimum value) for the group of observables, exterior orientation parameters and reference points. Calibration performance is tested using both a phase shift continuous wave scanner, FARO PHOTON 880, and a pulse-based time-of-flight system, Leica HDS3000. The improvement achieved after the geometric calibration is 30% for the former and 70% for the latter.
Two highly accurate methods for pitch calibration
NASA Astrophysics Data System (ADS)
Kniel, K.; Härtig, F.; Osawa, S.; Sato, O.
2009-11-01
Among profiles, helix and tooth thickness pitch is one of the most important parameters of an involute gear measurement evaluation. In principle, coordinate measuring machines (CMM) and CNC-controlled gear measuring machines as a variant of a CMM are suited for these kinds of gear measurements. Now the Japan National Institute of Advanced Industrial Science and Technology (NMIJ/AIST) and the German national metrology institute the Physikalisch-Technische Bundesanstalt (PTB) have each developed independently highly accurate pitch calibration methods applicable to CMM or gear measuring machines. Both calibration methods are based on the so-called closure technique which allows the separation of the systematic errors of the measurement device and the errors of the gear. For the verification of both calibration methods, NMIJ/AIST and PTB performed measurements on a specially designed pitch artifact. The comparison of the results shows that both methods can be used for highly accurate calibrations of pitch standards.
Automatic camera calibration method based on dashed lines
NASA Astrophysics Data System (ADS)
Li, Xiuhua; Wang, Guoyou; Liu, Jianguo
2013-10-01
We present a new method for full-automatic calibration of traffic cameras using the end points on dashed lines. Our approach uses the improved RANSAC method with the help of pixels transverse projection to detect the dashed lines and end points on them. Then combining analysis of the geometric relationship between the camera and road coordinate systems, we construct a road model to fit the end points. Finally using two-dimension calibration method we can convert pixels in image to meters along the ground truth lane. On a large number of experiments exhibiting a variety of conditions, our approach performs well, achieving less than 5% error in measuring test lengths in all cases.
Accurate camera calibration method specialized for virtual studios
NASA Astrophysics Data System (ADS)
Okubo, Hidehiko; Yamanouchi, Yuko; Mitsumine, Hideki; Fukaya, Takashi; Inoue, Seiki
2008-02-01
Virtual studio is a popular technology for TV programs, that makes possible to synchronize computer graphics (CG) to realshot image in camera motion. Normally, the geometrical matching accuracy between CG and realshot image is not expected so much on real-time system, we sometimes compromise on directions, not to come out the problem. So we developed the hybrid camera calibration method and CG generating system to achieve the accurate geometrical matching of CG and realshot on virtual studio. Our calibration method is intended for the camera system on platform and tripod with rotary encoder, that can measure pan/tilt angles. To solve the camera model and initial pose, we enhanced the bundle adjustment algorithm to fit the camera model, using pan/tilt data as known parameters, and optimizing all other parameters invariant against pan/tilt value. This initialization yields high accurate camera position and orientation consistent with any pan/tilt values. Also we created CG generator implemented the lens distortion function with GPU programming. By applying the lens distortion parameters obtained by camera calibration process, we could get fair compositing results.
Method of Calibrating a Force Balance
NASA Technical Reports Server (NTRS)
Parker, Peter A. (Inventor); Rhew, Ray D. (Inventor); Johnson, Thomas H. (Inventor); Landman, Drew (Inventor)
2015-01-01
A calibration system and method utilizes acceleration of a mass to generate a force on the mass. An expected value of the force is calculated based on the magnitude and acceleration of the mass. A fixture is utilized to mount the mass to a force balance, and the force balance is calibrated to provide a reading consistent with the expected force determined for a given acceleration. The acceleration can be varied to provide different expected forces, and the force balance can be calibrated for different applied forces. The acceleration may result from linear acceleration of the mass or rotational movement of the mass.
Pre-flight and On-orbit Geometric Calibration of the Lunar Reconnaissance Orbiter Camera
NASA Astrophysics Data System (ADS)
Speyerer, E. J.; Wagner, R. V.; Robinson, M. S.; Licht, A.; Thomas, P. C.; Becker, K.; Anderson, J.; Brylow, S. M.; Humm, D. C.; Tschimmel, M.
2016-04-01
The Lunar Reconnaissance Orbiter Camera (LROC) consists of two imaging systems that provide multispectral and high resolution imaging of the lunar surface. The Wide Angle Camera (WAC) is a seven color push-frame imager with a 90∘ field of view in monochrome mode and 60∘ field of view in color mode. From the nominal 50 km polar orbit, the WAC acquires images with a nadir ground sampling distance of 75 m for each of the five visible bands and 384 m for the two ultraviolet bands. The Narrow Angle Camera (NAC) consists of two identical cameras capable of acquiring images with a ground sampling distance of 0.5 m from an altitude of 50 km. The LROC team geometrically calibrated each camera before launch at Malin Space Science Systems in San Diego, California and the resulting measurements enabled the generation of a detailed camera model for all three cameras. The cameras were mounted and subsequently launched on the Lunar Reconnaissance Orbiter (LRO) on 18 June 2009. Using a subset of the over 793000 NAC and 207000 WAC images of illuminated terrain collected between 30 June 2009 and 15 December 2013, we improved the interior and exterior orientation parameters for each camera, including the addition of a wavelength dependent radial distortion model for the multispectral WAC. These geometric refinements, along with refined ephemeris, enable seamless projections of NAC image pairs with a geodetic accuracy better than 20 meters and sub-pixel precision and accuracy when orthorectifying WAC images.
NASA Astrophysics Data System (ADS)
Haruyama, J.; Ohtake, M.; Matsunaga, T.; Morota, T.; Yokota, Y.; Honda, C.; Hirata, N.; Demura, H.; Iwasaki, A.; Nakamura, R.; Kodama, S.; LISM Working Group
2008-07-01
Surface relief maps have a significant role in the investigation of the solid planets. A 10 m resolution stereoscopic push-broom imager called the Terrain Camera (TC) will be installed on the Selenological and Engineering Explorer (SELENE), a Japanese lunar polar orbiter to be launched in 2007, to acquire lunar global topographic data from which lunar relief maps will be produced. Appropriate radiometric calibration and geometric correction (RGC) processing is required to construct reliable surface maps. An RGC processing system has already been installed in the SELENE Operation and Analysis Center (SOAC) of the Japanese Aerospace Exploration Agency (JAXA). The main tasks of the RGC processing system for TC data are dark-level correction, flat-field correction, photometric calibration, conversion of radiance to reflectance, and map projection. The several TC RGC-processed products in a scene size are superimposed, mosaicked, and stored in the SELENE level-2 database (L2DB) system as a relief map product. Relief maps of the entire Moon are scheduled for completion 1 year after the end of the SELENE nominal mission. Since a global 10 m resolution lunar relief map has never been produced before, the maps from the TC data will be valuable for lunar sciences and future exploration.
New Method for Calibration for Hyperspectral Pushbroom Imaging Systems
NASA Technical Reports Server (NTRS)
Ryan, Robert; Olive, Dan; ONeal, Duane; Schere, Chris; Nixon, Thomas; May, Chengye; Ryan, Jim; Stanley, Tom; Witcher, Kern
1999-01-01
A new, easy-to-implement approach for achieving highly accurate spectral and radiometric calibration of array-based, hyperspectral pushbroom imagers is presented in this paper. The equivalence of the plane of the exit port of an integrating sphere to a Lambertian surface is utilized to provide a field-filling radiance source for the imager. Several different continuous wave lasers of various wavelengths and a quartz-tungsten-halogen lamp internally illuminate the sphere. The imager is positioned to "stare" into the port, and the resultant data cube is analyzed to determine wavelength calibrations, spectral widths of channels, radiometric characteristics, and signal-to-noise ratio, as well as an estimate of signal-to-noise performance in the field. The "smile" (geometric distortion of spectra) of the system can be quickly ascertained using this method. As the price and availability of solid state laser sources improve, this technique could gain wide acceptance.
On-Orbit Geometric Calibration of the Lunar Reconnaissance Orbiter Wide Angle Camera
NASA Astrophysics Data System (ADS)
Speyerer, E. J.; Wagner, R.; Robinson, M. S.
2013-12-01
Lunar Reconnaissance Orbiter (LRO) is equipped with a single Wide Angle Camera (WAC) [1] designed to collect monochromatic and multispectral observations of the lunar surface. Cartographically accurate image mosaics and stereo image based terrain models requires the position of each pixel in a given image be known to a corresponding point on the lunar surface with a high degree of accuracy and precision. The Lunar Reconnaissance Orbiter Camera (LROC) team initially characterized the WAC geometry prior to launch at the Malin Space Science Systems calibration facility. After lunar orbit insertion, the LROC team recognized spatially varying geometric offsets between color bands. These misregistrations made analysis of the color data problematic and showed that refinements to the pre-launch geometric analysis were necessary. The geometric parameters that define the WAC optical system were characterized from statistics gathered from co-registering over 84,000 image pairs. For each pair, we registered all five visible WAC bands to a precisely rectified Narrow Angle Camera (NAC) image (accuracy <15 m) [2] to compute key geometric parameters. In total, we registered 2,896 monochrome and 1,079 color WAC observations to nearly 34,000 NAC observations and collected over 13.7 million data points across the visible portion of the WAC CCD. Using the collected statistics, we refined the relative pointing (yaw, pitch and roll), effective focal length, principal point coordinates, and radial distortion coefficients. This large dataset also revealed spatial offsets between bands after orthorectification due to chromatic aberrations in the optical system. As white light enters the optical system, the light bends at different magnitudes as a function of wavelength, causing a single incident ray to disperse in a spectral spread of color [3,4]. This lateral chromatic aberration effect, also known as 'chromatic difference in magnification' [5] introduces variation to the effective focal
MODIS Radiometric Calibration Program, Methods and Results
NASA Technical Reports Server (NTRS)
Xiong, Xiaoxiong; Guenther, Bruce; Angal, Amit; Barnes, William; Salomonson, Vincent; Sun, Junqiang; Wenny, Brian
2012-01-01
As a key instrument for NASA s Earth Observing System (EOS), the Moderate Resolution Imaging Spectroradiometer (MODIS) has made significant contributions to the remote sensing community with its unprecedented amount of data products continuously generated from its observations and freely distributed to users worldwide. MODIS observations, covering spectral regions from visible (VIS) to long-wave infrared (LWIR), have enabled a broad range of research activities and applications for studies of the earth s interactive system of land, oceans, and atmosphere. In addition to extensive pre-launch measurements, developed to characterize sensor performance, MODIS carries a set of on-board calibrators (OBC) that can be used to track on-orbit changes of various sensor characteristics. Most importantly, dedicated and continuous calibration efforts have been made to maintain sensor data quality. This paper provides an overview of the MODIS calibration program, on-orbit calibration activities, methods, and performance. Key calibration results and lessons learned from the MODIS calibration effort are also presented in this paper.
NASA Astrophysics Data System (ADS)
Archer, Cristina; Ghaisas, Niranjan
2015-04-01
The energy generation at a wind farm is controlled primarily by the average wind speed at hub height. However, two other factors impact wind farm performance: 1) the layout of the wind turbines, in terms of spacing between turbines along and across the prevailing wind direction; staggering or aligning consecutive rows; angles between rows, columns, and prevailing wind direction); and 2) atmospheric stability, which is a measure of whether vertical motion is enhanced (unstable), suppressed (stable), or neither (neutral). Studying both factors and their complex interplay with Large-Eddy Simulation (LES) is a valid approach because it produces high-resolution, 3D, turbulent fields, such as wind velocity, temperature, and momentum and heat fluxes, and it properly accounts for the interactions between wind turbine blades and the surrounding atmospheric and near-surface properties. However, LES are computationally expensive and simulating all the possible combinations of wind directions, atmospheric stabilities, and turbine layouts to identify the optimal wind farm configuration is practically unfeasible today. A new, geometry-based method is proposed that is computationally inexpensive and that combines simple geometric quantities with a minimal number of LES simulations to identify the optimal wind turbine layout, taking into account not only the actual frequency distribution of wind directions (i.e., wind rose) at the site of interest, but also atmospheric stability. The geometry-based method is calibrated with LES of the Lillgrund wind farm conducted with the Software for Offshore/onshore Wind Farm Applications (SOWFA), based on the open-access OpenFOAM libraries. The geometric quantities that offer the best correlations (>0.93) with the LES results are the blockage ratio, defined as the fraction of the swept area of a wind turbine that is blocked by an upstream turbine, and the blockage distance, the weighted distance from a given turbine to all upstream turbines
New Method of Calibrating IRT Models.
ERIC Educational Resources Information Center
Jiang, Hai; Tang, K. Linda
This discussion of new methods for calibrating item response theory (IRT) models looks into new optimization procedures, such as the Genetic Algorithm (GA) to improve on the use of the Newton-Raphson procedure. The advantages of using a global optimization procedure like GA is that this kind of procedure is not easily affected by local optima and…
Automatic calibration method for plenoptic camera
NASA Astrophysics Data System (ADS)
Luan, Yinsen; He, Xing; Xu, Bing; Yang, Ping; Tang, Guomao
2016-04-01
An automatic calibration method is proposed for a microlens-based plenoptic camera. First, all microlens images on the white image are searched and recognized automatically based on digital morphology. Then, the center points of microlens images are rearranged according to their relative position relationships. Consequently, the microlens images are located, i.e., the plenoptic camera is calibrated without the prior knowledge of camera parameters. Furthermore, this method is appropriate for all types of microlens-based plenoptic cameras, even the multifocus plenoptic camera, the plenoptic camera with arbitrarily arranged microlenses, or the plenoptic camera with different sizes of microlenses. Finally, we verify our method by the raw data of Lytro. The experiments show that our method has higher intelligence than the methods published before.
Calibration method for radiometric and wavelength calibration of a spectrometer
NASA Astrophysics Data System (ADS)
Granger, Edward M.
1998-12-01
A new calibration target or Certified Reference Material (CRM) has been designed that uses violet, orange, green and cyan dyes ont cotton paper. This paper type was chosen because it has a relatively flat spectral response from 400 nm to 700 nm and good keeping properties. These specific dyes were chosen because the difference signal between the orange, cyan, green and purple dyes have certain characteristics that then a low the calibration of an instrument. The ratio between the difference readings is a direct function of the center wavelength of a given spectral band. Therefore, the radiometric and spectral calibration can be determined simultaneously from the physical properties of the reference materials.
Image processing method for multicore fiber geometric parameters
NASA Astrophysics Data System (ADS)
Zhang, Chuanbiao; Ning, Tigang; Li, Jing; Li, Chao; Ma, Shaoshuo
2016-05-01
An image processing method has been developed to obtain multicore fiber geometric parameters. According to the characteristics of multicore fiber, we using MATLAB to processing the sectional view of the multicore fiber (MCF), and the algorithm mainly concludes the following steps: filter out image noise, edge detection, use an appropriate threshold for boundary extraction and an improved curve-fitting algorithm for reconstruction the cross section, then we get the relative geometric parameters of the MCF in pixels. We also compares different edge detection operator and analyzes each detection results, which can provide a meaningful reference for edge detection.
Camera calibration method for dimensional measurement of heavy forging in large scale
NASA Astrophysics Data System (ADS)
Liu, Bin; Hu, Chunhai; Song, Xiaoxue; Zhao, Zhenqing
2009-07-01
Camera calibration method plays an important role in the stereovision system to resolve the problems of dimensional measurement of heavy forging. Due to the intensive vibrating, the camera parameters must be calibrated every time after the action of the water press. This paper presents a method using the scene geometry to calibrate cameras. In the context of heavy machinery environments, the constraints which can be used are parallelism and orthogonality. These constraints lead to geometrically intuitive methods to calibrate the cameras. The huge forging equipment such as water press belongs to geometrically constrained object and insusceptible to vibrating, which gives natural prior knowledge and constraint conditions for 3-D reconstruction. The method focuses on the calibration of the extrinsic parameters which are subject to change since the effects of the workspace factors. The intrinsic parameters were calibrated in advance by an off-line method and were assumed as invariable. The results of simulation experiments demonstrate that the camera parameters could be calibrated effectively and achieve the real time need.
a Method for Self-Calibration in Satellite with High Precision of Space Linear Array Camera
NASA Astrophysics Data System (ADS)
Liu, Wei; Qian, Fangming; Miao, Yuzhe; Wang, Rongjian
2016-06-01
At present, the on-orbit calibration of the geometric parameters of a space surveying camera is usually processed by data from a ground calibration field after capturing the images. The entire process is very complicated and lengthy and cannot monitor and calibrate the geometric parameters in real time. On the basis of a large number of on-orbit calibrations, we found that owing to the influence of many factors, e.g., weather, it is often difficult to capture images of the ground calibration field. Thus, regular calibration using field data cannot be ensured. This article proposes a real time self-calibration method for a space linear array camera on a satellite using the optical auto collimation principle. A collimating light source and small matrix array CCD devices are installed inside the load system of the satellite; these use the same light path as the linear array camera. We can extract the location changes of the cross marks in the matrix array CCD to determine the real-time variations in the focal length and angle parameters of the linear array camera. The on-orbit status of the camera is rapidly obtained using this method. On one hand, the camera's change regulation can be mastered accurately and the camera's attitude can be adjusted in a timely manner to ensure optimal photography; in contrast, self-calibration of the camera aboard the satellite can be realized quickly, which improves the efficiency and reliability of photogrammetric processing.
Methods for manufacturing geometric multi-crystalline cast materials
Stoddard, Nathan G
2013-11-26
Methods are provided for casting one or more of a semi-conductor, an oxide, and an intermetallic material. With such methods, a cast body of a geometrically ordered multi-crystalline form of the one or more of a semiconductor, an oxide, and an intermetallic material may be formed that is free or substantially free of radially-distributed impurities and defects and having at least two dimensions that are each at least about 10 cm.
A geometric design method for side-stream distillation columns
Rooks, R.E.; Malone, M.F.; Doherty, M.F.
1996-10-01
A side-stream distillation column may replace two simple columns for some applications, sometimes at considerable savings in energy and investment. This paper describes a geometric method for the design of side-stream columns; the method provides rapid estimates of equipment size and utility requirements. Unlike previous approaches, the geometric method is applicable to nonideal and azeotropic mixtures. Several example problems for both ideal and nonideal mixtures, including azeotropic mixtures containing distillation boundaries, are given. The authors make use of the fact that azeotropes or pure components whose classification in the residue curve map is a saddle can be removed as side-stream products. Significant process simplifications are found among some alternatives in example problems, leading to flow sheets with fewer units and a substantial savings in vapor rate.
To develop a geometric matching method for precision mold alignment
NASA Astrophysics Data System (ADS)
Chen, Chun-Jen; Chang, Chun-Li; Jywe, Wenyuh
2014-09-01
In order to develop a high accuracy optical alignment system for precision molding machine, a geometric matching method was developed in this paper. The alignment system includes 4 high magnification lenses, 4 CCD cameras and 4 LED light sources. In the precision molding machine, a bottom metal mold and a top glass mold are used to produce a micro lens. The two molds combination does not use any pin or alignment part. They only use the optical alignment system to alignment. In this optical alignment system, the off-axis alignment method was used. The alignment accuracy of the alignment system is about 0.5 μm. There are 2 cross marks on the top glass mold and 2 cross marks on the bottom metal mod. In this paper did not use edge detection to recognize the mask center because the mask easy wears when the combination times increased. Therefore, this paper develops a geometric matching method to recognize mask center.
Research on calibration method of relative infrared radiometer
NASA Astrophysics Data System (ADS)
Yang, Sen; Li, Chengwei
2016-02-01
The Relative Infrared Radiometer (RIR) is commonly used to measure the irradiance of the Infrared Target Simulator (ITS), and the calibration of the RIR is central for the measurement accuracy. RIR calibration is conventionally performed using the Radiance Based (RB) calibration method or Irradiance Based (IB) calibration method, and the relationship between the radiation of standard source and the response of RIR is determined by curve fitting. One limitation existing in the calibration of RIR is the undesirable calibration voltage fluctuation in single measurement or in the reproducibility measurement, which reduces the calibration reproducibility and irradiance measurement accuracy. To address this limitation, the Equivalent Blackbody Temperature Based (EBTB) calibration method is proposed for the calibration of RIR. The purpose of this study is to compare the proposed EBTB calibration method with conventional RB and IB calibration methods. The comparison and experiment results have shown that the EBTB calibration method is not only able to provide comparable correlation between radiation and response to other calibration methods (IB and RB) in the irradiance measurement but also reduces the influence of calibration voltage fluctuation on the irradiance measurement result, which improves the calibration reproducibility and irradiance measurement accuracy.
Accurate wavelength calibration method for flat-field grating spectrometers.
Du, Xuewei; Li, Chaoyang; Xu, Zhe; Wang, Qiuping
2011-09-01
A portable spectrometer prototype is built to study wavelength calibration for flat-field grating spectrometers. An accurate calibration method called parameter fitting is presented. Both optical and structural parameters of the spectrometer are included in the wavelength calibration model, which accurately describes the relationship between wavelength and pixel position. Along with higher calibration accuracy, the proposed calibration method can provide information about errors in the installation of the optical components, which will be helpful for spectrometer alignment. PMID:21929865
A webcam photogrammetric method for robot calibration
NASA Astrophysics Data System (ADS)
Sargeant, Ben; Hosseininaveh, Ali A.; Erfani, Tohid; Robson, Stuart; Boehm, Jan
2013-04-01
This paper describes a strategy for accurate robot calibration using close range photogrammetry. A 5-DoF robot has been designed for placement of two web cameras relative to an object. To ensure correct camera positioning, the robot is calibrated using the following strategy. First, a Denavit-Hartenberg method is used to generate a general kinematic robot model. A set of reference frames are defined relative to each joint and each of the cameras, transformation matrices are then produced to represent change in position and orientation between frames in terms of joint positions and unknown parameters. The complete model is extracted by multiplying these matrices. Second, photogrammetry is used to estimate the postures of both cameras. A set of images are captured of a calibration fixture from different robot poses. The camera postures are then estimated using bundle adjustment. Third, the kinematic parameters are estimated using weighted least squares. For each pose a set of equations are extracted from the model and the unknown parameters are estimated in an iterative procedure. Finally these values are substituted back into the original model. This final model is tested using forward kinematics by comparing the model's predicted camera postures for given joint positions to the values obtained through photogrammetry. Inverse kinematics is performed using both least squares and particle swarm optimisation and these techniques are contrasted. Results demonstrate that this photogrammetry approach produces a reliable and accurate model of the robot that can be used with both least squares and particle swarm optimisation for robot control.
Geometric estimation method for x-ray digital intraoral tomosynthesis
NASA Astrophysics Data System (ADS)
Li, Liang; Yang, Yao; Chen, Zhiqiang
2016-06-01
It is essential for accurate image reconstruction to obtain a set of parameters that describes the x-ray scanning geometry. A geometric estimation method is presented for x-ray digital intraoral tomosynthesis (DIT) in which the detector remains stationary while the x-ray source rotates. The main idea is to estimate the three-dimensional (3-D) coordinates of each shot position using at least two small opaque balls adhering to the detector surface as the positioning markers. From the radiographs containing these balls, the position of each x-ray focal spot can be calculated independently relative to the detector center no matter what kind of scanning trajectory is used. A 3-D phantom which roughly simulates DIT was designed to evaluate the performance of this method both quantitatively and qualitatively in the sense of mean square error and structural similarity. Results are also presented for real data acquired with a DIT experimental system. These results prove the validity of this geometric estimation method.
A dynamic calibration method for the pressure transducer
NASA Astrophysics Data System (ADS)
Wang, Zhongyu; Wang, Zhuoran; Li, Qiang
2016-01-01
Pressure transducer is widely used in the field of industry. A calibrated pressure transducer can increase the performance of precision instruments in the closed mechanical relationship. Calibration is the key to ensure the pressure transducer with a high precision and dynamic characteristic. Unfortunately, the current calibration method can usually be used in the laboratory with a good condition and only one pressure transducer can be calibrated at each time. Therefore the calibration efficiency is hard to meet the requirement of modern industry with high efficiency. A dynamic and fast calibration technology with a calibration device and a corresponding data processing method is proposed in this paper. Firstly, the pressure transducer to be calibrated is placed in the small cavity chamber. The calibration process only contains a single loop. The outputs of each calibrated transducer are recorded automatically by the control terminal. Secondly, LabView programming is used for the information acquisition and data processing. The performance of the repeatability and nonlinear indicators can be figured out directly. At last the pressure transducers are calibrated simultaneously in the experiment to verify the suggested calibration technology. The experimental result shows this method can be used to calibrate the pressure transducer in the practical engineering measurement.
A detector response function design in pinhole SPECT including geometrical calibration
El Bitar, Z; Huesman, R H; Buchko, R; Bekaert, Virgile; Brasse, David; Gullberg, G T
2014-01-01
Clinical single photon emission computed tomography (SPECT) equipped with pinhole collimators have a magnification factor that results in high spatial resolution images for small animal imaging. Using Monte Carlo simulations to model the acquisition process and the propagation of the photons from their point of emission to their detection point then integrating the model into an iterative reconstruction algorithm improves the signal-to-noise ratio, the contrast and the spatial resolution in the reconstructed images. However, pinhole SPECT systems are known to be very sensitive to geometrical misalignments. Geometrical misalignments are defined as the radial or axial shift of the collimator pinhole and/or twist and tilt of the detector heads and are introduced in the system each time the collimation device is changed (pinhole to parallel holes or vice versa). In this work, we present a flexible detector response function table (DRFT) design that takes into account the geometrical misalignments and avoids performing new Monte Carlo simulations for each exam in order to calculate a geometrical study-dependent system matrix. The utilization of the DRFT for the calculation of the system matrix speeds up its computation time by two orders of magnitude making it acceptable for preclinical and clinical applications. PMID:23492938
Method for calibration of plutonium NDA
Lemming, J.F.; Campbell, A.R.; Rodenburg, W.W.
1980-01-01
Calibration materials characterized by calorimetric assay can be a practical alternative to synthetic standards for the calibration of plutonium nondestructive assay. Calorimetric assay is an effective measurement system for the characterization because: it can give an absolute assay from first principles when the isotopic composition is known, it is insensitive to most matrix effects, and its traceability to international measurement systems has been demonstrated.
Pulsed Electric Propulsion Thrust Stand Calibration Method
NASA Technical Reports Server (NTRS)
Wong, Andrea R.; Polzin, Kurt A.; Pearson, J. Boise
2011-01-01
The evaluation of the performance of any propulsion device requires the accurate measurement of thrust. While chemical rocket thrust is typically measured using a load cell, the low thrust levels associated with electric propulsion (EP) systems necessitate the use of much more sensitive measurement techniques. The design and development of electric propulsion thrust stands that employ a conventional hanging pendulum arm connected to a balance mechanism consisting of a secondary arm and variable linkage have been reported in recent publications by Polzin et al. These works focused on performing steady-state thrust measurements and employed a static analysis of the thrust stand response. In the present work, we present a calibration method and data that will permit pulsed thrust measurements using the Variable Amplitude Hanging Pendulum with Extended Range (VAHPER) thrust stand. Pulsed thrust measurements are challenging in general because the pulsed thrust (impulse bit) occurs over a short timescale (typically 1 micros to 1 millisecond) and cannot be resolved directly. Consequently, the imparted impulse bit must be inferred through observation of the change in thrust stand motion effected by the pulse. Pulsed thrust measurements have typically only consisted of single-shot operation. In the present work, we discuss repetition-rate pulsed thruster operation and describe a method to perform these measurements. The thrust stand response can be modeled as a spring-mass-damper system with a repetitive delta forcing function to represent the impulsive action of the thruster.
Methods for Geometric Data Validation of 3d City Models
NASA Astrophysics Data System (ADS)
Wagner, D.; Alam, N.; Wewetzer, M.; Pries, M.; Coors, V.
2015-12-01
Geometric quality of 3D city models is crucial for data analysis and simulation tasks, which are part of modern applications of the data (e.g. potential heating energy consumption of city quarters, solar potential, etc.). Geometric quality in these contexts is however a different concept as it is for 2D maps. In the latter case, aspects such as positional or temporal accuracy and correctness represent typical quality metrics of the data. They are defined in ISO 19157 and should be mentioned as part of the metadata. 3D data has a far wider range of aspects which influence their quality, plus the idea of quality itself is application dependent. Thus, concepts for definition of quality are needed, including methods to validate these definitions. Quality on this sense means internal validation and detection of inconsistent or wrong geometry according to a predefined set of rules. A useful starting point would be to have correct geometry in accordance with ISO 19107. A valid solid should consist of planar faces which touch their neighbours exclusively in defined corner points and edges. No gaps between them are allowed, and the whole feature must be 2-manifold. In this paper, we present methods to validate common geometric requirements for building geometry. Different checks based on several algorithms have been implemented to validate a set of rules derived from the solid definition mentioned above (e.g. water tightness of the solid or planarity of its polygons), as they were developed for the software tool CityDoctor. The method of each check is specified, with a special focus on the discussion of tolerance values where they are necessary. The checks include polygon level checks to validate the correctness of each polygon, i.e. closeness of the bounding linear ring and planarity. On the solid level, which is only validated if the polygons have passed validation, correct polygon orientation is checked, after self-intersections outside of defined corner points and edges
Geometrical distortions in two-dimensional gels: applicable correction methods.
Aittokallio, T; Salmi, J; Nyman, T A; Nevalainen, O S
2005-02-01
Two-dimensional electrophoresis (2-DE) provides a rapid means for separating thousands of proteins from cell and tissue samples in one run. Although this powerful research tool has been enthusiastically applied in many fields of biomedical research, accurate analysis and interpretation of the data have provided many challenges. Several analysis steps are needed to convert the large amount of noisy data obtained with 2-DE into reliable and interpretable biological information. The goals of such analysis steps include accurate protein detection and quantification, as well as the identification of differentially expressed proteins between samples run on different gels. To achieve these goals, systematic errors such as geometric distortions between the gels must be corrected by using computer-assisted methods. A wide range of computer software has been developed, but no general consensus exists as standard for 2-DE data analysis protocol. The choice of analysis approach is an important element depending both on the data and on the goals of the experiment. Therefore, basic understanding of the algorithms behind the software is required for optimal results. This review highlights some of the common themes in 2-DE data analysis, including protein spot detection and geometric image warping using both spot- and pixel-based approaches. Several computational strategies are overviewed and their relative merits and potential pitfalls discussed. Finally, we offer our own personal view of future trends and developments in large-scale proteome research. PMID:15652796
A Comparison of Two Balance Calibration Model Building Methods
NASA Technical Reports Server (NTRS)
DeLoach, Richard; Ulbrich, Norbert
2007-01-01
Simulated strain-gage balance calibration data is used to compare the accuracy of two balance calibration model building methods for different noise environments and calibration experiment designs. The first building method obtains a math model for the analysis of balance calibration data after applying a candidate math model search algorithm to the calibration data set. The second building method uses stepwise regression analysis in order to construct a model for the analysis. Four balance calibration data sets were simulated in order to compare the accuracy of the two math model building methods. The simulated data sets were prepared using the traditional One Factor At a Time (OFAT) technique and the Modern Design of Experiments (MDOE) approach. Random and systematic errors were introduced in the simulated calibration data sets in order to study their influence on the math model building methods. Residuals of the fitted calibration responses and other statistical metrics were compared in order to evaluate the calibration models developed with different combinations of noise environment, experiment design, and model building method. Overall, predicted math models and residuals of both math model building methods show very good agreement. Significant differences in model quality were attributable to noise environment, experiment design, and their interaction. Generally, the addition of systematic error significantly degraded the quality of calibration models developed from OFAT data by either method, but MDOE experiment designs were more robust with respect to the introduction of a systematic component of the unexplained variance.
NASA Astrophysics Data System (ADS)
Wilkening, Günter; Koenders, Ludger
2005-08-01
The quantitative determination of the properties of micro- and nanostructures is essential in research and development. It is also a prerequisite in process control and quality assurance in industry. The knowledge of the geometrical dimensions of structures in most cases is the base, to which other physical and chemical properties are linked. Quantitative measurements require reliable and stable instruments, suitable measurement procedures as well as appropriate calibration artefacts and methods. The seminar "NanoScale 2004" (6th Seminar on Quantitative Microscopy and 2nd Seminar on Nanoscale Calibration Standards and Methods) at the National Metrology Institute (Physikalisch-Technische Bundesanstalt PTB), Braunschweig, Germany, continues the series of seminars on Quantitative Microscopy. The series stimulates the exchange of information between manufacturers of relevant hard- and software and the users in science and industry. Topics addressed in these proceedings are a) the application of quantitative measurements and measurement problems in: microelectronics, microsystems technology, nano/quantum/molecular electronics, chemistry, biology, medicine, environmental technology, materials science, surface processing b) calibration & correction methods: calibration methods, calibration standards, calibration procedures, traceable measurements, standardization, uncertainty of measurements c) instrumentation and methods: novel/improved instruments and methods, reproducible probe/sample positioning, position-measuring systems, novel/improved probe/detector systems, linearization methods, image processing
A Study for Efficient Methods of System Calibration between Optical and Range Sensors
NASA Astrophysics Data System (ADS)
Choi, W.; Kim, C.; Kim, Y.
2015-06-01
Recently, interests in 3D indoor modeling and positioning have been growing. Data fusion by using different sensors data is one of the 3D model producing methods. For a data fusion between two kinds of sensors, precise system calibration is essential. If relative geometric location of each sensor can be accurately measured with a system-calibration, it is possible to locate a pixel that corresponds to the same object in two different images, and thus, produce a more precise data-fusion. Purpose of this study is finding more efficient method of system calibration between optical and range sensor. For this purpose, experiment was designed by considering following variables, i) system calibration method, ii) testbed type, iii) and distance data(whether use it or not). So, In this study, test-bed for system calibration was designed by considering the characteristics of sensors. Also, precise simulation was done to find efficient method of system calibration, and its results were reflected in real experiment. Results of simulation show that the bundle adjustment method is more efficient than single photo resection in system calibration between range and optical sensors. And the most efficient case was when using i) the bundle adjustment with ii) the simulated data set which were obtained between 2m to 4m away from the test-bed. These results of simulation were reflected in real system calibration. Finally, real system calibration were performed and its results were compared to results of simulation. And accuracy of system calibration was evaluated by producing fusion data between range and optical sensors.
Geometrical MTF computation method based on the irradiance model
NASA Astrophysics Data System (ADS)
Lin, P.-D.; Liu, C.-S.
2011-01-01
The Modulation Transfer Function (MTF) is a measure of an optical system's ability to transfer contrast from the specimen to the image plane at a specific resolution. It can be computed either numerically by geometrical optics or measured experimentally by imaging a knife edge or a bar-target pattern of varying spatial frequency. Previously, MTF accuracy was generally affected by the size of the mesh on the image plane. This paper presents a new MTF computation method based on the irradiance model, without counting the number of rays hitting each grid. To verify the method, the MTF in the sagittal and meridional directions of an axis-symmetrical optical system is computed by both the ray-counting and the proposed methods. It is found that the grid size meshed on the image plane significantly affects the MTF of the ray-counting method, sometimes with significantly negative results. The proposed irradiance method is immune to issues of grid size. The CPU computation time for the two methods is approximately the same.
A study of geometric phase topology using Fourier transform method
NASA Astrophysics Data System (ADS)
Samlan, C. T.; Naik, Dinesh N.; Viswanathan, Nirmal K.
2016-07-01
Topological aspect of the geometric phase (GP) due to pure polarization projection is studied using the 2D Fourier transform (2D-FT) method. Projection of orthogonal polarization state results in a phase singularity in the 2D parameter space of ellipticity and orientation of polarization ellipse. Projection of its surrounding states results in an accumulation of GP in different amount that form a spiral structure. A half wave plate–quarter wave plate combination is used to generate different polarization states which are projected using a polarizer. The accumulated phase for each orientation of the wave plate is extracted from 2D-FT of the interferogram, obtained by interfering it with a reference beam in a Mach–Zehnder like interferometer.
Calibration methods for rotating shadowband irradiometers and evaluation of calibration duration
NASA Astrophysics Data System (ADS)
Jessen, W.; Wilbert, S.; Nouri, B.; Geuder, N.; Fritz, H.
2015-10-01
Resource assessment for Concentrated Solar Power (CSP) needs accurate Direct Normal Irradiance (DNI) measurements. An option for such measurement campaigns are Rotating Shadowband Irradiometers (RSIs) with a thorough calibration. Calibration of RSIs and Si-sensors in general is complex because of the inhomogeneous spectral response of such sensors and incorporates the use of several correction functions. A calibration for a given atmospheric condition and air mass might not work well for a different condition. This paper covers procedures and requirements for two calibration methods for the calibration of Rotating Shadowband Irradiometers. The necessary duration of acquisition of test measurements is examined in regard to the site specific conditions at Plataforma Solar de Almeria (PSA) in Spain. Data sets of several long-term calibration periods from PSA are used to evaluate the deviation of results from calibrations with varying duration from the long-term result. The findings show that seasonal changes of environmental conditions are causing small but noticeable fluctuation of calibration results. Certain periods (i.e. November to January and April to May) show a higher likelihood of particularly adverse calibration results. These effects can partially be compensated by increasing the inclusions of measurements from outside these periods. Consequently, the duration of calibrations at PSA can now be selected depending on the time of the year in which measurements are commenced.
Geometric multigrid for an implicit-time immersed boundary method
Guy, Robert D.; Philip, Bobby; Griffith, Boyce E.
2014-10-12
The immersed boundary (IB) method is an approach to fluid-structure interaction that uses Lagrangian variables to describe the deformations and resulting forces of the structure and Eulerian variables to describe the motion and forces of the fluid. Explicit time stepping schemes for the IB method require solvers only for Eulerian equations, for which fast Cartesian grid solution methods are available. Such methods are relatively straightforward to develop and are widely used in practice but often require very small time steps to maintain stability. Implicit-time IB methods permit the stable use of large time steps, but efficient implementations of such methods require significantly more complex solvers that effectively treat both Lagrangian and Eulerian variables simultaneously. Moreover, several different approaches to solving the coupled Lagrangian-Eulerian equations have been proposed, but a complete understanding of this problem is still emerging. This paper presents a geometric multigrid method for an implicit-time discretization of the IB equations. This multigrid scheme uses a generalization of box relaxation that is shown to handle problems in which the physical stiffness of the structure is very large. Numerical examples are provided to illustrate the effectiveness and efficiency of the algorithms described herein. Finally, these tests show that using multigrid as a preconditioner for a Krylov method yields improvements in both robustness and efficiency as compared to using multigrid as a solver. They also demonstrate that with a time step 100–1000 times larger than that permitted by an explicit IB method, the multigrid-preconditioned implicit IB method is approximately 50–200 times more efficient than the explicit method.
Stoddard, Nathan G
2015-02-10
Methods and apparatuses are provided for casting silicon for photovoltaic cells and other applications. With such methods and apparatuses, a cast body of geometrically ordered multi-crystalline silicon may be formed that is free or substantially free of radially-distributed impurities and defects and having at least two dimensions that are each at least about 10 cm is provided.
Geometric multigrid for an implicit-time immersed boundary method
Guy, Robert D.; Philip, Bobby; Griffith, Boyce E.
2014-10-12
The immersed boundary (IB) method is an approach to fluid-structure interaction that uses Lagrangian variables to describe the deformations and resulting forces of the structure and Eulerian variables to describe the motion and forces of the fluid. Explicit time stepping schemes for the IB method require solvers only for Eulerian equations, for which fast Cartesian grid solution methods are available. Such methods are relatively straightforward to develop and are widely used in practice but often require very small time steps to maintain stability. Implicit-time IB methods permit the stable use of large time steps, but efficient implementations of such methodsmore » require significantly more complex solvers that effectively treat both Lagrangian and Eulerian variables simultaneously. Moreover, several different approaches to solving the coupled Lagrangian-Eulerian equations have been proposed, but a complete understanding of this problem is still emerging. This paper presents a geometric multigrid method for an implicit-time discretization of the IB equations. This multigrid scheme uses a generalization of box relaxation that is shown to handle problems in which the physical stiffness of the structure is very large. Numerical examples are provided to illustrate the effectiveness and efficiency of the algorithms described herein. Finally, these tests show that using multigrid as a preconditioner for a Krylov method yields improvements in both robustness and efficiency as compared to using multigrid as a solver. They also demonstrate that with a time step 100–1000 times larger than that permitted by an explicit IB method, the multigrid-preconditioned implicit IB method is approximately 50–200 times more efficient than the explicit method.« less
Altazimuth mount based dynamic calibration method for GNSS attitude measurement
NASA Astrophysics Data System (ADS)
Jiang, Nan; He, Tao; Sun, Shaohua; Gu, Qing
2015-02-01
As the key process to ensure the test accuracy and quality, the dynamic calibration of the GNSS attitude measuring instrument is often embarrassed by the lack of the rigid enough test platform and an accurate enough calibration reference. To solve the problems, a novel dynamic calibration method for GNSS attitude measurement based on altazimuth mount is put forward in this paper. The principle and implementation of this method are presented, and then the feasibility and usability of the method are analyzed in detail involving the applicability of the mount, calibrating precision, calibrating range, base line rigidity and the satellite signal involved factors. Furthermore, to verify and test the method, a confirmatory experiment is carried out with the survey ship GPS attitude measuring instrument, and the experimental results prove that it is a feasible way to the dynamic calibration for GNSS attitude measurement.
Geometric optimization of helical tail designs to calibrate swimming velocities of microswimmers
NASA Astrophysics Data System (ADS)
Demir, Ebru; Yesilyurt, Serhat
2014-11-01
Artificial microswimmers present both a solution and a challenge as alternative tools to be used in medical applications, namely, drug delivery and minimally invasive surgeries. Achieving desired amount of controlled displacement of microswimmers at desired velocities plays an important role in determining the success of such applications. In this study, a non-dimensionalised CFD model is utilised to investigate the effects of various geometrical parameters on swimming velocities of microswimmers with helical tails in cylindrical confinements, such as helix wavelength, helical body thickness, and diameter. To this end, a ``one wavelength long'' helical tail is placed inside a cylindrical channel of the same length with periodic boundary conditions applied to both ends, constituting an infinite helix model. As the channel diameter is kept constant, a parametric study of abovementioned geometric identities is conducted to observe the change in the swimming velocities. Furthermore, effects of helix-channel eccentricity and helix rotation about the longitudinal axis on swimming velocity of a dimensionally optimized helix are investigated to reveal near wall effects. The results are found to be in good agreement with the theoretical models existing in the literature.
Chiu, Tsuicheng D; Yan, Yulong; Foster, Ryan; Mao, Weihua
2015-01-01
Geometric or mechanical accuracy of kV and MV imaging systems of two Varian TrueBeam linacs have been monitored by two geomertirc calibration systems, Varian IsoCal geometric calibration system and home-developed gQA system. Results of both systems are cross-checked and the long-term geometric stabilities of linacs are evaluated. Two geometric calibration methodologies have been used to assess kV and MV imaging systems and their coincidence periodically on two TrueBeam linacs for about one year. Both systems analyze kV or MV projection images of special designed phantoms to retrieve geometric parameters of the imaging systems. The isocenters — laser isocenter and centers of rotations of kV imager and EPID — are then calculated, based on results of multiple projections from different angles. Long-term calibration results from both systems are compared for cross-checking. There are 24 sessions of side-by-side calibrations performed by both systems on two TrueBeam linacs. All the disagreements of isocenters between two calibrations systems are less than 1 mm with ± 0.1 mm SD. Most of the large disagreements occurred in vertical direction (AP direction), with an averaged disagreement of 0.45 mm. The average disagreements of isocenters are 0.09 mm in other directions. Additional to long-term calibration monitoring, for the accuracy test, special tests were performed by misaligning QA phantoms on purpose (5 mm away from setup isocenter in AP, SI, and lateral directions) to test the liability performance of both systems with the known deviations. The errors are within 0.5 mm. Both geometric calibration systems, IsoCal and gQA, are capable of detecting geometric deviations of kV and MV imaging systems of linacs. The long-term evaluation also shows that the deviations of geometric parameters and the geometric accuracies of both linacs are small and very consistent during the one-year study period. PMID:26218992
Research radiometric calibration quantitative transfer methods between internal and external
NASA Astrophysics Data System (ADS)
Guo, Ju Guang; Ma, Yong hui; Zhang, Guang; Yang, Zhi hui
2015-10-01
This paper puts forward a method by realizing the internal and external radiation calibration transfer for infrared radiation characteristics quantitative measuring system. Through technological innovation and innovation application to establish a theoretical model of the corresponding radiated transfer method. This method can be well in engineering application for technology conversion process of radiometric calibration that with relatively simple and effective calibration in the half light path radiation instead of complex difficult whole optical path radiometric calibration. At the same time, it also will provide the basis of effective support to further carry out the target radiated characteristics quantitative measurement and application for ground type infrared radiated quantitative measuring system.
NASA Technical Reports Server (NTRS)
Chen, Fang-Jenq
1997-01-01
Flow visualization produces data in the form of two-dimensional images. If the optical components of a camera system are perfect, the transformation equations between the two-dimensional image and the three-dimensional object space are linear and easy to solve. However, real camera lenses introduce nonlinear distortions that affect the accuracy of transformation unless proper corrections are applied. An iterative least-squares adjustment algorithm is developed to solve the nonlinear transformation equations incorporated with distortion corrections. Experimental applications demonstrate that a relative precision on the order of 40,000 is achievable without tedious laboratory calibrations of the camera.
Calibration methods for rotating shadowband irradiometers and optimizing the calibration duration
NASA Astrophysics Data System (ADS)
Jessen, Wilko; Wilbert, Stefan; Nouri, Bijan; Geuder, Norbert; Fritz, Holger
2016-04-01
Resource assessment for concentrated solar power (CSP) needs accurate direct normal irradiance (DNI) measurements. An option for such measurement campaigns is the use of thoroughly calibrated rotating shadowband irradiometers (RSIs). Calibration of RSIs and Si-sensors is complex because of the inhomogeneous spectral response of these sensors and incorporates the use of several correction functions. One calibration for a given atmospheric condition and air mass might not be suitable under different conditions. This paper covers procedures and requirements of two calibration methods for the calibration of rotating shadowband irradiometers. The necessary duration of acquisition of test measurements is examined with regard to the site-specific conditions at Plataforma Solar de Almería (PSA) in Spain. Seven data sets of long-term test measurements were collected. For each data set, calibration results of varying durations were compared to its respective long-term result. Our findings show that seasonal changes of environmental conditions are causing small but noticeable fluctuation of calibration results. Calibration results within certain periods (i.e. November to January and April to May) show a higher likelihood of deviation. These effects can partially be attenuated by including more measurements from outside these periods. Consequently, the duration of calibrations at PSA can now be selected depending on the time of year in which measurements commence.
Simultaneous multi-headed imager geometry calibration method
Tran, Vi-Hoa; Meikle, Steven Richard; Smith, Mark Frederick
2008-02-19
A method for calibrating multi-headed high sensitivity and high spatial resolution dynamic imaging systems, especially those useful in the acquisition of tomographic images of small animals. The method of the present invention comprises: simultaneously calibrating two or more detectors to the same coordinate system; and functionally correcting for unwanted detector movement due to gantry flexing.
Improvements to and comparison of static terrestrial LiDAR self-calibration methods.
Chow, Jacky C K; Lichti, Derek D; Glennie, Craig; Hartzell, Preston
2013-01-01
Terrestrial laser scanners are sophisticated instruments that operate much like high-speed total stations. It has previously been shown that unmodelled systematic errors can exist in modern terrestrial laser scanners that deteriorate their geometric measurement precision and accuracy. Typically, signalised targets are used in point-based self-calibrations to identify and model the systematic errors. Although this method has proven its effectiveness, a large quantity of signalised targets is required and is therefore labour-intensive and limits its practicality. In recent years, feature-based self-calibration of aerial, mobile terrestrial, and static terrestrial laser scanning systems has been demonstrated. In this paper, the commonalities and differences between point-based and plane-based self-calibration (in terms of model identification and parameter correlation) are explored. The results of this research indicate that much of the knowledge from point-based self-calibration can be directly transferred to plane-based calibration and that the two calibration approaches are nearly equivalent. New network configurations, such as the inclusion of tilted scans, were also studied and prove to be an effective means for strengthening the self-calibration solution, and improved recoverability of the horizontal collimation axis error for hybrid scanners, which has always posed a challenge in the past. PMID:23727956
Improvements to and Comparison of Static Terrestrial LiDAR Self-Calibration Methods
Chow, Jacky C. K.; Lichti, Derek D.; Glennie, Craig; Hartzell, Preston
2013-01-01
Terrestrial laser scanners are sophisticated instruments that operate much like high-speed total stations. It has previously been shown that unmodelled systematic errors can exist in modern terrestrial laser scanners that deteriorate their geometric measurement precision and accuracy. Typically, signalised targets are used in point-based self-calibrations to identify and model the systematic errors. Although this method has proven its effectiveness, a large quantity of signalised targets is required and is therefore labour-intensive and limits its practicality. In recent years, feature-based self-calibration of aerial, mobile terrestrial, and static terrestrial laser scanning systems has been demonstrated. In this paper, the commonalities and differences between point-based and plane-based self-calibration (in terms of model identification and parameter correlation) are explored. The results of this research indicate that much of the knowledge from point-based self-calibration can be directly transferred to plane-based calibration and that the two calibration approaches are nearly equivalent. New network configurations, such as the inclusion of tilted scans, were also studied and prove to be an effective means for strengthening the self-calibration solution, and improved recoverability of the horizontal collimation axis error for hybrid scanners, which has always posed a challenge in the past. PMID:23727956
Study on self-calibration angle encoder using simulation method
NASA Astrophysics Data System (ADS)
Wang, Yan; Xue, Zi; Huang, Yao; Wang, Xiaona
2016-01-01
The angle measurement technology is very important in precision manufacture, optical industry, aerospace, aviation and navigation, etc. Further, the angle encoder, which uses concept `subdivision of full circle (2π rad=360°)' and transforms the angle into number of electronic pulse, is the most common instrument for angle measurement. To improve the accuracy of the angle encoder, a novel self-calibration method was proposed that enables the angle encoder to calibrate itself without angle reference. An angle deviation curve among 0° to 360° was simulated with equal weights Fourier components for the study of the self-calibration method. In addition, a self-calibration algorithm was used in the process of this deviation curve. The simulation result shows the relationship between the arrangement of multi-reading heads and the Fourier components distribution of angle encoder deviation curve. Besides, an actual self-calibration angle encoder was calibrated by polygon angle standard in national institute of metrology, China. The experiment result indicates the actual self-calibration effect on the Fourier components distribution of angle encoder deviation curve. In the end, the comparison, which is between the simulation self-calibration result and the experiment self-calibration result, reflects good consistency and proves the reliability of the self-calibration angle encoder.
Comparison of TLD calibration methods for 192Ir dosimetry.
Haworth, Annette; Butler, Duncan J; Wilfert, Lisa; Ebert, Martin A; Todd, Stephen P; Hayton, Anna J M; Kron, Tomas
2013-01-01
For the purpose of dose measurement using a high-dose rate (192)Ir source, four methods of thermoluminescent dosimeter (TLD) calibration were investigated. Three of the four calibration methods used the (192)Ir source. Dwell times were calculated to deliver 1 Gy to the TLDs irradiated either in air or water. Dwell time calculations were confirmed by direct measurement using an ionization chamber. The fourth method of calibration used 6 MV photons from a medical linear accelerator, and an energy correction factor was applied to account for the difference in sensitivity of the TLDs in (192)Ir and 6 MV. The results of the four TLD calibration methods are presented in terms of the results of a brachytherapy audit where seven Australian centers irradiated three sets of TLDs in a water phantom. The results were in agreement within estimated uncertainties when the TLDs were calibrated with the (192)Ir source. Calibrating TLDs in a phantom similar to that used for the audit proved to be the most practical method and provided the greatest confidence in measured dose. When calibrated using 6 MV photons, the TLD results were consistently higher than the (192)Ir-calibrated TLDs, suggesting this method does not fully correct for the response of the TLDs when irradiated in the audit phantom. PMID:23318392
NASA Technical Reports Server (NTRS)
Tripp, John S.; Tcheng, Ping
1999-01-01
Statistical tools, previously developed for nonlinear least-squares estimation of multivariate sensor calibration parameters and the associated calibration uncertainty analysis, have been applied to single- and multiple-axis inertial model attitude sensors used in wind tunnel testing to measure angle of attack and roll angle. The analysis provides confidence and prediction intervals of calibrated sensor measurement uncertainty as functions of applied input pitch and roll angles. A comparative performance study of various experimental designs for inertial sensor calibration is presented along with corroborating experimental data. The importance of replicated calibrations over extended time periods has been emphasized; replication provides independent estimates of calibration precision and bias uncertainties, statistical tests for calibration or modeling bias uncertainty, and statistical tests for sensor parameter drift over time. A set of recommendations for a new standardized model attitude sensor calibration method and usage procedures is included. The statistical information provided by these procedures is necessary for the uncertainty analysis of aerospace test results now required by users of industrial wind tunnel test facilities.
Calibration method for video and radiation imagers
Cunningham, Mark F.; Fabris, Lorenzo; Gee, Timothy F.; Goddard, Jr., James S.; Karnowski, Thomas P.; Ziock, Klaus-peter
2011-07-05
The relationship between the high energy radiation imager pixel (HERIP) coordinate and real-world x-coordinate is determined by a least square fit between the HERIP x-coordinate and the measured real-world x-coordinates of calibration markers that emit high energy radiation imager and reflect visible light. Upon calibration, a high energy radiation imager pixel position may be determined based on a real-world coordinate of a moving vehicle. Further, a scale parameter for said high energy radiation imager may be determined based on the real-world coordinate. The scale parameter depends on the y-coordinate of the moving vehicle as provided by a visible light camera. The high energy radiation imager may be employed to detect radiation from moving vehicles in multiple lanes, which correspondingly have different distances to the high energy radiation imager.
Landmark-free geometric methods in biological shape analysis.
Koehl, Patrice; Hass, Joel
2015-12-01
In this paper, we propose a new approach for computing a distance between two shapes embedded in three-dimensional space. We take as input a pair of triangulated genus zero surfaces that are topologically equivalent to spheres with no holes or handles, and construct a discrete conformal map f between the surfaces. The conformal map is chosen to minimize a symmetric deformation energy Esd(f) which we introduce. This measures the distance of f from an isometry, i.e. a non-distorting correspondence. We show that the energy of the minimizing map gives a well-behaved metric on the space of genus zero surfaces. In contrast to most methods in this field, our approach does not rely on any assignment of landmarks on the two surfaces. We illustrate applications of our approach to geometric morphometrics using three datasets representing the bones and teeth of primates. Experiments on these datasets show that our approach performs remarkably well both in shape recognition and in identifying evolutionary patterns, with success rates similar to, and in some cases better than, those obtained by expert observers. PMID:26631331
A geometric method for optimal design of color filter arrays.
Hao, Pengwei; Li, Yan; Lin, Zhouchen; Dubois, Eric
2011-03-01
A color filter array (CFA) used in a digital camera is a mosaic of spectrally selective filters, which allows only one color component to be sensed at each pixel. The missing two components of each pixel have to be estimated by methods known as demosaicking. The demosaicking algorithm and the CFA design are crucial for the quality of the output images. In this paper, we present a CFA design methodology in the frequency domain. The frequency structure, which is shown to be just the symbolic DFT of the CFA pattern (one period of the CFA), is introduced to represent images sampled with any rectangular CFAs in the frequency domain. Based on the frequency structure, the CFA design involves the solution of a constrained optimization problem that aims at minimizing the demosaicking error. To decrease the number of parameters and speed up the parameter searching, the optimization problem is reformulated as the selection of geometric points on the boundary of a convex polygon or the surface of a convex polyhedron. Using our methodology, several new CFA patterns are found, which outperform the currently commercialized and published ones. Experiments demonstrate the effectiveness of our CFA design methodology and the superiority of our new CFA patterns. PMID:20858581
NASA Astrophysics Data System (ADS)
Speyerer, E. J.; Wagner, R. V.; Robinson, M. S.
2016-06-01
The Clementine UVVIS camera returned over half a million images while in orbit around the Moon in 1994. Since the Clementine mission, our knowledge of lunar topography, gravity, and the location of features on the surface has vastly improved with the success of the Gravity Recovery and Interior Laboratory (GRAIL) mission and ongoing Lunar Reconnaissance Orbiter (LRO) mission. In particular, the Lunar Reconnaissance Orbiter Camera (LROC) has returned over a million images of the Moon since entering orbit in 2009. With the aid of improved ephemeris and on-orbit calibration, the LROC team created a series of precise and accurate global maps. With the updated reference frame, older lunar maps, such as those generated from Clementine UVVIS images, are misaligned making cross-mission analysis difficult. In this study, we use feature-based matching routines to refine and recalibrate the interior and exterior orientation parameters of the Clementine UVVIS camera. After applying these updates and rigorous orthorectification, we are able generate precise and accurate maps from UVVIS images to help support lunar science and future cross-mission investigations.
System and method for calibrating a rotary absolute position sensor
NASA Technical Reports Server (NTRS)
Davis, Donald R. (Inventor); Permenter, Frank Noble (Inventor); Radford, Nicolaus A (Inventor)
2012-01-01
A system includes a rotary device, a rotary absolute position (RAP) sensor generating encoded pairs of voltage signals describing positional data of the rotary device, a host machine, and an algorithm. The algorithm calculates calibration parameters usable to determine an absolute position of the rotary device using the encoded pairs, and is adapted for linearly-mapping an ellipse defined by the encoded pairs to thereby calculate the calibration parameters. A method of calibrating the RAP sensor includes measuring the rotary position as encoded pairs of voltage signals, linearly-mapping an ellipse defined by the encoded pairs to thereby calculate the calibration parameters, and calculating an absolute position of the rotary device using the calibration parameters. The calibration parameters include a positive definite matrix (A) and a center point (q) of the ellipse. The voltage signals may include an encoded sine and cosine of a rotary angle of the rotary device.
Method and apparatus for calibrating a particle emissions monitor
Flower, William L.; Renzi, Ronald F.
1998-07-07
The instant invention discloses method and apparatus for calibrating particulate emissions monitors, in particular, and sampling probes, in general, without removing the instrument from the system being monitored. A source of one or more specific metals in aerosol (either solid or liquid) or vapor form is housed in the instrument. The calibration operation is initiated by moving a focusing lens, used to focus a light beam onto an analysis location and collect the output light response, from an operating position to a calibration position such that the focal point of the focusing lens is now within a calibration stream issuing from a calibration source. The output light response from the calibration stream can be compared to that derived from an analysis location in the operating position to more accurately monitor emissions within the emissions flow stream.
Method and apparatus for calibrating a particle emissions monitor
Flower, W.L.; Renzi, R.F.
1998-07-07
The invention discloses a method and apparatus for calibrating particulate emissions monitors, in particular, sampling probes, and in general, without removing the instrument from the system being monitored. A source of one or more specific metals in aerosol (either solid or liquid) or vapor form is housed in the instrument. The calibration operation is initiated by moving a focusing lens, used to focus a light beam onto an analysis location and collect the output light response, from an operating position to a calibration position such that the focal point of the focusing lens is now within a calibration stream issuing from a calibration source. The output light response from the calibration stream can be compared to that derived from an analysis location in the operating position to more accurately monitor emissions within the emissions flow stream. 6 figs.
A novel calibration method of CCD camera for LAMOST
NASA Astrophysics Data System (ADS)
Gu, Yonggang; Jin, Yi; Zhai, Chao
2012-09-01
Large Sky Area Multi-object Fiber Spectroscopic Telescope - LAMOST, with a 1.75m-diameter focal plane on which 4000 optical fibers are arranged, is one of major scientific projects in China. During the surveying process of LAMOST, the optical imaging system makes the astrometric objects be imaged in the focal plane, and the optical fiber positioning system controls the 4000 fibers to be aligned with these objects and obtain their spectrum. In order to correct the positioning error of these optical fibers, the CCD camera is used to detect these fibers’ position in the way of close-range photogrammetry. As we all know, the calibration quality of the CCD camera is one of the most important factors for detection precision. However, the camera calibration has two following problems in the field work of LAMOST. First, the camera parameters are not stable due to the changes of on-site work environment and the vibration during movement. So, the CCD camera must be on-line calibrated. Second, a large-size high-precision calibration target is needed to calibrate the camera, for the focal plane is very big. Making such a calibration target, it is very difficult and costly. Meanwhile, the large calibration target is hard to be fixed on LAMOST because of the space constraint. In this paper, an improved bundle adjustment self-calibration method is proposed to solve the two problems above. The results of experiment indicate that this novel calibration method needs only a few control points while the traditional calibration methods need much more control points to get the same accuracy. So the method could realize the on-line high-precision calibration of CCD camera for LAMOST.
Method of Noncontact Calibration of the Robotic Ultrasonic Tomograph
NASA Astrophysics Data System (ADS)
Borikov, V. N.; Galtseva, O. V.; Filippov, G. A.
2016-01-01
The method of calibration of robotic ultrasonic tomograph with the construction of the trajectory of movement of the robot-manipulator on the object of control by using 3D- scanner is described. This method can significantly accelerate the process of calibration of tomograph and prevent possible displacement of the object during calibration. The algorithm of transition from use of a contact method of calibration of the tomograph to noncontact calibration is offered. Experimental data of application of this algorithm show a positive result: the time of research of object considerably decreases. Results of researches prove the practical relevance of the presented work and high efficiency of application of robotic ultrasonic tomography for nondestructive testing of objects of different forms.
A curve fitting method for extrinsic camera calibration from a single image of a cylindrical object
NASA Astrophysics Data System (ADS)
Winkler, A. W.; Zagar, B. G.
2013-08-01
An important step in the process of optical steel coil quality assurance is to measure the proportions of width and radius of steel coils as well as the relative position and orientation of the camera. This work attempts to estimate these extrinsic parameters from single images by using the cylindrical coil itself as the calibration target. Therefore, an adaptive least-squares algorithm is applied to fit parametrized curves to the detected true coil outline in the acquisition. The employed model allows for strictly separating the intrinsic and the extrinsic parameters. Thus, the intrinsic camera parameters can be calibrated beforehand using available calibration software. Furthermore, a way to segment the true coil outline in the acquired images is motivated. The proposed optimization method yields highly accurate results and can be generalized even to measure other solids which cannot be characterized by the identification of simple geometric primitives.
Suomi NPP VIIRS prelaunch and on-orbit geometric calibration and characterization
NASA Astrophysics Data System (ADS)
Wolfe, Robert E.; Lin, Guoqing; Nishihama, Masahiro; Tewari, Krishna P.; Tilton, James C.; Isaacman, Alice R.
2013-10-01
Visible Infrared Imaging Radiometer Suite (VIIRS) sensor was launched 28 October 2011 on the Suomi National Polar-orbiting Partnership (SNPP) satellite. VIIRS has 22 spectral bands covering the spectrum between 0.412 µm and 12.01 µm, including 16 moderate resolution bands (M-bands) with a nominal spatial resolution of 750 m at nadir, five imaging resolution bands (I-bands) with a nominal spatial resolution of 375 m at nadir, and a day-night band (DNB) with a near-constant nominal 750 m spatial resolution throughout the scan. These bands are located in a visible and near-infrared focal plane assembly (FPA), a shortwave and midwave infrared FPA, and a long-wave infrared FPA. All bands, except the DNB, are coregistered for proper environmental data records retrievals. Observations from VIIRS instrument provide long-term measurements of biogeophysical variables for climate research and polar satellite data stream for the operational community's use in weather forecasting and disaster relief and other applications. Well Earth-located (geolocated) instrument data are important to retrieving accurate biogeophysical variables. This paper describes prelaunch pointing and alignment measurements, and the two sets of on-orbit correction of geolocation errors, the first of which corrected error from 1300 m to within 75 m (20% I-band pixel size) and the second of which fine-tuned scan-angle dependent errors, bringing VIIRS geolocation products to high maturity in one and a half years of the SNPP VIIRS on-orbit operations. Prelaunch calibration and the on-orbit characterization of sensor spatial impulse responses and band-to-band coregistration are also described.
Suomi NPP VIIRS Prelaunch and On-orbit Geometric Calibration and Characterization
NASA Technical Reports Server (NTRS)
Wolfe, Robert E.; Lin, Guoqing; Nishihama, Masahiro; Tewari, Krishna P.; Tilton, James C.; Isaacman, Alice R.
2013-01-01
The Visible Infrared Imager Radiometer Suite (VIIRS) sensor was launched 28 October 2011 on the Suomi National Polarorbiting Partnership (SNPP) satellite. VIIRS has 22 spectral bands covering the spectrum between 0.412 m and 12.01 m, including 16 moderate resolution bands (M-bands) with a spatial resolution of 750 m at nadir, 5 imaging resolution bands (I-bands) with a spatial resolution of 375 m at nadir, and 1 day-night band (DNB) with a near-constant 750 m spatial resolution throughout the scan. These bands are located in a visible and near infrared (VisNIR) focal plane assembly (FPA), a short- and mid-wave infrared (SWMWIR) FPA and a long-wave infrared (LWIR) FPA. All bands, except the DNB, are co-registered for proper environmental data records (EDRs) retrievals. Observations from VIIRS instrument provide long-term measurements of biogeophysical variables for climate research and polar satellite data stream for the operational communitys use in weather forecasting and disaster relief and other applications. Well Earth-located (geolocated) instrument data is important to retrieving accurate biogeophysical variables. This paper describes prelaunch pointing and alignment measurements, and the two sets of on-orbit correction of geolocation errors, the first of which corrected error from 1,300 m to within 75 m (20 I-band pixel size), and the second of which fine tuned scan angle dependent errors, bringing VIIRS geolocation products to high maturity in one and a half years of the SNPP VIIRS on-orbit operations. Prelaunch calibration and the on-orbit characterization of sensor spatial impulse responses and band-to-band co-registration (BBR) are also described.
[High Precision Spectral Calibration Method of Fourier Interferometric Spectrometer].
Lin, Jun; Shao, Jun; Song, Chao-yu; Li, Yun-wei; Lei, Yu-fei
2015-12-01
The Fourier interferometric spectrometer (FIS) acquires the interference data information of the spectrum and during the spectrum data processing, a series of spectrum reconstruction will be performed on the interference information to obtain the final spectrum information data. The spectral calibration is the key step to spectrum reconstruction of FIS, which directly determines accuracy and availability of the spectrum results. This paper introduces the basic ideas and calibration accuracy about the spectral calibration for the FIS and puts forward a new spectral calibration method based on calculating the precise value of the total optical path difference (TOPD). The TOPD of FIS is difficult to be precisely measured, but it is the core and key to the spectral calibration. In order to calculate the precise TOPD, this paper proposes the idea how to traverse the TOPD and analyzes the spectrum drift. During the calibration, all the possible values of the TOPD participate in the spectrum reconstruction flow to carry out spectrum recovery and analysis. Ultimately the TOPD with the minimum spectrum drift will be achieved, namely solution value of the TOPD. This method can accurately resolve the TOPD of the FIS and then calibrate the spectrum with high accuracy. In addition, the paper introduces the detailed and complete spectral calibration flow and obtains the center wavelength value of every band and wavenumber resolution. Moreover, the paper designs the main parameters of the typical FIS and generates its simulation interference data. Using the above method to calibrate the simulation data, the analysis and verification of the spectral calibration results proves that the calibration precision of wavenumber resolution achieves 0.000 25 cm⁻¹ or above. PMID:26964245
New method for calibration of a computer controlled CRT: feedback calibration
NASA Astrophysics Data System (ADS)
Wang, Jingping; Zhu, Zhengfang; Zhao, Dazun
1994-08-01
There are many formulas to describe the input and output relationship of CRT. As the radiant output of CRT submits to the statistical distribution, the prediction of the colorimetry from these formulas is not good. Some deviation of the brightness are as high as 50%. There is a need to find a new method to calibrate CRT. We have set up an automatic measurement and calibration system with PHOTO 1980B, IEEE 4888 interface board, CRT and a computer.
Vanishing feature constraints calibration method for binocular vision sensor.
Wei, Zhenzhong; Liu, Xiaokun
2015-07-27
Based on analyzing the measurement model of binocular vision sensor, we proposed a new flexible calibration method for binocular vision sensor using a planar target with several parallel lines. It only requires the sensor to observe the planar target at a few (at least two) different orientations. Relying on vanishing feature constraints and spacing constraints of parallel lines, linear method and nonlinear optimization are combined to estimate the structure parameters of binocular vision sensor. Linear method achieves the separation of the rotation matrix and translation vector which reduces the complexity of computation; Nonlinear algorithm ensures the calibration results for the global optimization. Towards the factors that affect the accuracy of the calibration, theoretical analysis and computer simulation are carried out respectively consequence in qualitative analysis and quantitative result. Real data shows that the accuracy of the proposed calibration method is about 0.040mm with the working distance of 800mm and the view field of 300 × 300mm. The comparison with Bougust toolbox and the method based on known length indicates that the proposed calibration method is precise and is efficient and convenient as its simple calculation and easy operation, especially for onsite calibration and self-calibration. PMID:26367553
Geometric and Topological Methods for Quantum Field Theory
NASA Astrophysics Data System (ADS)
Cardona, Alexander; Contreras, Iván.; Reyes-Lega, Andrés. F.
2013-05-01
Introduction; 1. A brief introduction to Dirac manifolds Henrique Bursztyn; 2. Differential geometry of holomorphic vector bundles on a curve Florent Schaffhauser; 3. Paths towards an extension of Chern-Weil calculus to a class of infinite dimensional vector bundles Sylvie Paycha; 4. Introduction to Feynman integrals Stefan Weinzierl; 5. Iterated integrals in quantum field theory Francis Brown; 6. Geometric issues in quantum field theory and string theory Luis J. Boya; 7. Geometric aspects of the standard model and the mysteries of matter Florian Scheck; 8. Absence of singular continuous spectrum for some geometric Laplacians Leonardo A. Cano García; 9. Models for formal groupoids Iván Contreras; 10. Elliptic PDEs and smoothness of weakly Einstein metrics of Hölder regularity Andrés Vargas; 11. Regularized traces and the index formula for manifolds with boundary Alexander Cardona and César Del Corral; Index.
Scatterometer-Calibrated Stability Verification Method
NASA Technical Reports Server (NTRS)
McWatters, Dalia A.; Cheetham, Craig M.; Huang, Shouhua; Fischman, Mark A.; CHu, Anhua J.; Freedman, Adam P.
2011-01-01
The requirement for scatterometer-combined transmit-receive gain variation knowledge is typically addressed by sampling a portion of the transmit signal, attenuating it with a known-stable attenuation, and coupling it into the receiver chain. This way, the gain variations of the transmit and receive chains are represented by this loop-back calibration signal, and can be subtracted from the received remote radar echo. Certain challenges are presented by this process, such as transmit and receive components that are outside of this loop-back path and are not included in this calibration, as well as the impracticality for measuring the transmit and receive chains stability and post fabrication separately, without the resulting measurement errors from the test set up exceeding the requirement for the flight instrument. To cover the RF stability design challenge, the portions of the scatterometer that are not calibrated by the loop-back, (e.g., attenuators, switches, diplexers, couplers, and coaxial cables) are tightly thermally controlled, and have been characterized over temperature to contribute less than 0.05 dB of calibration error over worst-case thermal variation. To address the verification challenge, including the components that are not calibrated by the loop-back, a stable fiber optic delay line (FODL) was used to delay the transmitted pulse, and to route it into the receiver. In this way, the internal loopback signal amplitude variations can be compared to the full transmit/receive external path, while the flight hardware is in the worst-case thermal environment. The practical delay for implementing the FODL is 100 s. The scatterometer pulse width is 1 ms so a test mode was incorporated early in the design phase to scale the 1 ms pulse at 100-Hz pulse repetition interval (PRI), by a factor of 18, to be a 55 s pulse with 556 s PRI. This scaling maintains the duty cycle, thus maintaining a representative thermal state for the RF components. The FODL consists
Methods and apparatuses for signaling with geometric constellations
NASA Technical Reports Server (NTRS)
Barsoum, Maged F. (Inventor); Jones, Christopher R. (Inventor)
2012-01-01
Communication systems are described that use signal constellations, which have unequally spaced (i.e. geometrically shaped) points. In many embodiments, the communication systems use specific geometric constellations that are capacity optimized at a specific SNR. In addition, ranges within which the constellation points of a capacity optimized constellation can be perturbed and are still likely to achieve a given percentage of the optimal capacity increase compared to a constellation that maximizes d.sub.min, are also described. Capacity measures that are used in the selection of the location of constellation points include, but are not limited to, parallel decode (PD) capacity and joint capacity.
New methods of measuring and calibrating robots
NASA Astrophysics Data System (ADS)
Janocha, Hartmut; Diewald, Bernd
1995-10-01
ISO 9283 and RIA R15.05 define industrial robot parameters which are applied to compare the efficiency of different robots. Hitherto, however, no suitable measurement systems have been available. ICAROS is a system which combines photogrammetrical procedures with an inertial navigation system. For the first time, this combination allows the high-precision static and dynamic measurement of the position as well as of the orientation of the robot endeffector. Thus, not only the measuring data for the determination of all industrial robot parameters can be acquired. By integration of a new over-all-calibration procedure, ICAROS also allows the reduction of the absolute robot pose errors to the range of its repeatability. The integration of both system components as well as measurement and calibration results are presented in this paper, using a six-axes robot as example. A further approach also presented here takes into consideration not only the individual robot errors but also the tolerances of workpieces. This allows the adjustment of off-line programs of robots based on inexact or idealized CAD data in any pose. Thus the robot position which is defined relative to the workpiece to be processed, is achieved as required. This includes the possibility to transfer teached robot programs to other devices without additional expenditure. The adjustment is based on the measurement of the robot position using two miniaturized CCD cameras mounted near the endeffector which are carried along by the robot during the correction phase. In the area viewed by both cameras, the robot position is determined in relation to prominent geometry elements, e.g. lines or holes. The scheduled data to be compared therewith can either be calculated in modern off-line programming systems during robot programming, or they can be determined at the so-called master robot if a transfer of the robot program is desired.
Evaluation of two gas-dilution methods for instrument calibration
NASA Technical Reports Server (NTRS)
Evans, A., Jr.
1977-01-01
Two gas dilution methods were evaluated for use in the calibration of analytical instruments used in air pollution studies. A dual isotope fluorescence carbon monoxide analyzer was used as the transfer standard. The methods are not new but some modifications are described. The rotary injection gas dilution method was found to be more accurate than the closed loop method. Results by the two methods differed by 5 percent. This could not be accounted for by the random errors in the measurements. The methods avoid the problems associated with pressurized cylinders. Both methods have merit and have found a place in instrument calibration work.
Interferometric SAR phase difference calibration: Methods and results
Bickel, D.L.; Hensley, W.H.
1993-12-31
This paper addresses the steps necessary to determine and maintain the phase calibration of a two-channel interferometric synthetic aperture radar (IFSAR). The method, setup, and accuracy of four different calibration techniques are compared. The most novel technique involves pointing the interferometric baseline at nadir and imaging a lake surface. The other techniques include measuring various flat surfaces in traditional side-looking IFSAR maps, in-flight closed-loop calibration path measurements, and static laboratory measurements. Initial results indicate that, using combinations of these measurements, it is possible to maintain the interferometric phase calibration of Sandia National Laboratories` K{sub U} Band IFSAR to better than 3 degrees. The time variability of various parts of the calibration and requirements for recalibration are also discussed.
Method calibration of the model 13145 infrared target projectors
NASA Astrophysics Data System (ADS)
Huang, Jianxia; Gao, Yuan; Han, Ying
2014-11-01
The SBIR Model 13145 Infrared Target Projectors ( The following abbreviation Evaluation Unit ) used for characterizing the performances of infrared imaging system. Test items: SiTF, MTF, NETD, MRTD, MDTD, NPS. Infrared target projectors includes two area blackbodies, a 12 position target wheel, all reflective collimator. It provide high spatial frequency differential targets, Precision differential targets imaged by infrared imaging system. And by photoelectricity convert on simulate signal or digital signal. Applications software (IR Windows TM 2001) evaluate characterizing the performances of infrared imaging system. With regards to as a whole calibration, first differently calibration for distributed component , According to calibration specification for area blackbody to calibration area blackbody, by means of to amend error factor to calibration of all reflective collimator, radiance calibration of an infrared target projectors using the SR5000 spectral radiometer, and to analyze systematic error. With regards to as parameter of infrared imaging system, need to integrate evaluation method. According to regulation with -GJB2340-1995 General specification for military thermal imaging sets -testing parameters of infrared imaging system, the results compare with results from Optical Calibration Testing Laboratory . As a goal to real calibration performances of the Evaluation Unit.
Method for Accurately Calibrating a Spectrometer Using Broadband Light
NASA Technical Reports Server (NTRS)
Simmons, Stephen; Youngquist, Robert
2011-01-01
A novel method has been developed for performing very fine calibration of a spectrometer. This process is particularly useful for modern miniature charge-coupled device (CCD) spectrometers where a typical factory wavelength calibration has been performed and a finer, more accurate calibration is desired. Typically, the factory calibration is done with a spectral line source that generates light at known wavelengths, allowing specific pixels in the CCD array to be assigned wavelength values. This method is good to about 1 nm across the spectrometer s wavelength range. This new method appears to be accurate to about 0.1 nm, a factor of ten improvement. White light is passed through an unbalanced Michelson interferometer, producing an optical signal with significant spectral variation. A simple theory can be developed to describe this spectral pattern, so by comparing the actual spectrometer output against this predicted pattern, errors in the wavelength assignment made by the spectrometer can be determined.
Two laboratory methods for the calibration of GPS speed meters
NASA Astrophysics Data System (ADS)
Bai, Yin; Sun, Qiao; Du, Lei; Yu, Mei; Bai, Jie
2015-01-01
The set-ups of two calibration systems are presented to investigate calibration methods of GPS speed meters. The GPS speed meter calibrated is a special type of high accuracy speed meter for vehicles which uses Doppler demodulation of GPS signals to calculate the measured speed of a moving target. Three experiments are performed: including simulated calibration, field-test signal replay calibration, and in-field test comparison with an optical speed meter. The experiments are conducted at specific speeds in the range of 40-180 km h-1 with the same GPS speed meter as the device under calibration. The evaluation of measurement results validates both methods for calibrating GPS speed meters. The relative deviations between the measurement results of the GPS-based high accuracy speed meter and those of the optical speed meter are analyzed, and the equivalent uncertainty of the comparison is evaluated. The comparison results justify the utilization of GPS speed meters as reference equipment if no fewer than seven satellites are available. This study contributes to the widespread use of GPS-based high accuracy speed meters as legal reference equipment in traffic speed metrology.
A New Online Calibration Method for Multidimensional Computerized Adaptive Testing.
Chen, Ping; Wang, Chun
2016-09-01
Multidimensional-Method A (M-Method A) has been proposed as an efficient and effective online calibration method for multidimensional computerized adaptive testing (MCAT) (Chen & Xin, Paper presented at the 78th Meeting of the Psychometric Society, Arnhem, The Netherlands, 2013). However, a key assumption of M-Method A is that it treats person parameter estimates as their true values, thus this method might yield erroneous item calibration when person parameter estimates contain non-ignorable measurement errors. To improve the performance of M-Method A, this paper proposes a new MCAT online calibration method, namely, the full functional MLE-M-Method A (FFMLE-M-Method A). This new method combines the full functional MLE (Jones & Jin in Psychometrika 59:59-75, 1994; Stefanski & Carroll in Annals of Statistics 13:1335-1351, 1985) with the original M-Method A in an effort to correct for the estimation error of ability vector that might otherwise adversely affect the precision of item calibration. Two correction schemes are also proposed when implementing the new method. A simulation study was conducted to show that the new method generated more accurate item parameter estimation than the original M-Method A in almost all conditions. PMID:26608960
Method to calibrate fission chambers in Campbelling mode
Benoit Geslot; Troy C. Unruh; Philippe Filliatre; Christian Jammes; Jacques Di Salvo; Stéphane Bréaud; Jean-François Villard
2011-06-01
Fission chambers are neutron detectors which are widely used to instrument experimental reactors such as material testing reactors or zero power reactors. In the presence of a high level mixed gamma and neutron flux, fission chambers can be operated in Campbelling mode (also known as 'fluctuation mode' or 'mean square voltage mode') to provide reliable and precise neutron related measurements. Fission chamber calibration in Campbelling mode (in terms of neutron flux) is usually done empirically using a calibrated reference detector. A major drawback of this method is that calibration measurements have to be performed in a neutron environment very similar to the one in which the calibrated detector will be used afterwards. What we propose here is a different approach based on characterizing the fission chamber response in terms of fission rate. This way, the detector calibration coefficient is independent from the neutron spectrum and can be determined prior to the experiment. The fissile deposit response to the neutron spectrum can then be assessed independently by other means (experimental or numerical). In this paper, the response of CEA made miniature fission chambers in Campbelling mode is studied. We use a theoretical model of the signal to calculate the calibration coefficient. Input parameters of the model come from statistical distribution of individual pulses. Supporting measurements have been made in the CEA Cadarache zero power reactor MINERVE. Results are compared to an empirical Campbelling mode calibration.
Method of calibrating an interferometer and reducing its systematic noise
NASA Technical Reports Server (NTRS)
Hammer, Philip D. (Inventor)
1997-01-01
Methods of operation and data analysis for an interferometer so as to eliminate the errors contributed by non-responsive or unstable pixels, interpixel gain variations that drift over time, and spurious noise that would otherwise degrade the operation of the interferometer are disclosed. The methods provide for either online or post-processing calibration. The methods apply prescribed reversible transformations that exploit the physical properties of interferograms obtained from said interferometer to derive a calibration reference signal for subsequent treatment of said interferograms for interpixel gain variations. A self-consistent approach for treating bad pixels is incorporated into the methods.
Site characterization for calibration of radiometric sensors using vicarious method
NASA Astrophysics Data System (ADS)
Parihar, Shailesh; Rathore, L. S.; Mohapatra, M.; Sharma, A. K.; Mitra, A. K.; Bhatla, R.; Singh, R. S.; Desai, Yogdeep; Srivastava, Shailendra S.
2016-05-01
Radiometric performances of earth observation satellite/sensors vary from ground pre-launch calibration campaign to post launch period extended to lifetime of the satellite due to launching vibrations. Therefore calibration is carried out worldwide through various methods throughout satellite lifetime. In India Indian Space Research Organization (ISRO) calibrates the sensor of Resourcesat-2 satellite by vicarious method. One of these vicarious calibration methods is the reflectance-based approach that is applied in this study for radiometric calibration of sensors on-board Resouresat-2 satellite. The results of ground-based measurement of atmospheric conditions and surface reflectance are made at Bap, Rajasthan Calibration/Validation (Cal/Val) site. Cal/Val observations at site were carried out with hyper-spectral Spectroradiometer covering spectral range of 350nm- 2500nm for radiometric characterization of the site. The Sunphotometer/Ozonometer for measuring the atmospheric parameters has also been used. The calibrated radiance is converted to absolute at-sensor spectral reflectance and Top-Of-Atmosphere (TOA) radiance. TOA radiance was computed using radiative transfer model `Second simulation of the satellite signal in the solar spectrum' (6S), which can accurately simulate the problems introduced by the presence of the atmosphere along the path from Sun to target (surface) to Sensor. The methodology for band averaged reflectance retrieval and spectral reflectance fitting process are described. Then the spectral reflectance and atmospheric parameters are put into 6S code to predict TOA radiance which compare with Resourcesat-2 radiance. Spectral signature and its reflectance ratio indicate the uniformity of the site. Thus the study proves that the selected site is suitable for vicarious calibration of sensor of Resourcesat-2. Further the study demonstrates the procedure for similar exercise for site selection for Cal/Val analysis of other satellite over India
Coscia, Gianluca; Vaccara, Elena; Corvisiero, Roberta; Cavazzani, Paolo; Ruggieri, Filippo Grillo; Taccini, Gianni
2009-07-15
In the authors' hospital, stereotactic radiotherapy treatments are performed with a Varian Clinac 600C equipped with a BrainLAB m3 micro-multileaf-collimator generally using the dynamic conformal arc technique. Patient immobilization during the treatment is achieved with a fixation mask supplied by BrainLAB, made with two reinforced thermoplastic sheets fitting the patient's head. With this work the authors propose a method to evaluate treatment geometric accuracy and, consequently, to determine the amount of the margin to keep in the CTV-PTV expansion during the treatment planning. The reproducibility of the isocenter position was tested by simulating a complete treatment on the anthropomorphic phantom Alderson Rando, inserting in between two phantom slices a high sensitivity Gafchromic EBT film, properly prepared and calibrated, and repeating several treatment sessions, each time removing the fixing mask and replacing the film inside the phantom. The comparison between the dose distributions measured on films and computed by TPS, after a precise image registration procedure performed by a commercial piece of software (FILMQA, 3cognition LLC (Division of ISP), Wayne, NJ), allowed the authors to measure the repositioning errors, obtaining about 0.5 mm in case of central spherical PTV and about 1.5 mm in case of peripheral irregular PTV. Moreover, an evaluation of the errors in the registration procedure was performed, giving negligible values with respect to the quantities to be measured. The above intrinsic two-dimensional estimate of treatment accuracy has to be increased for the error in the third dimension, but the 2 mm margin the authors generally use for the CTV-PTV expansion seems adequate anyway. Using the same EBT films, a dosimetric verification of the treatment planning system was done. Measured dose values are larger or smaller than the nominal ones depending on geometric irradiation conditions, but, in the authors' experimental conditions, always
Coscia, Gianluca; Vaccara, Elena; Corvisiero, Roberta; Cavazzani, Paolo; Ruggieri, Filippo Grillo; Taccini, Gianni
2009-07-01
In the authors' hospital, stereotactic radiotherapy treatments are performed with a Varian Clinac 600C equipped with a BrainLAB m3 micro-multileaf-collimator generally using the dynamic conformal arc technique. Patient immobilization during the treatment is achieved with a fixation mask supplied by BrainLAB, made with two reinforced thermoplastic sheets fitting the patient's head. With this work the authors propose a method to evaluate treatment geometric accuracy and, consequently, to determine the amount of the margin to keep in the CTV-PTV expansion during the treatment planning. The reproducibility of the isocenter position was tested by simulating a complete treatment on the anthropomorphic phantom Alderson Rando, inserting in between two phantom slices a high sensitivity Gafchromic EBT film, properly prepared and calibrated, and repeating several treatment sessions, each time removing the fixing mask and replacing the film inside the phantom. The comparison between the dose distributions measured on films and computed by TPS, after a precise image registration procedure performed by a commercial piece of software (FILMQA, 3cognition LLC (Division of ISP), Wayne, NJ), allowed the authors to measure the repositioning errors, obtaining about 0.5 mm in case of central spherical PTV and about 1.5 mm in case of peripheral irregular PTV. Moreover, an evaluation of the errors in the registration procedure was performed, giving negligible values with respect to the quantities to be measured. The above intrinsic two-dimensional estimate of treatment accuracy has to be increased for the error in the third dimension, but the 2 mm margin the authors generally use for the CTV-PTV expansion seems adequate anyway. Using the same EBT films, a dosimetric verification of the treatment planning system was done. Measured dose values are larger or smaller than the nominal ones depending on geometric irradiation conditions, but, in the authors' experimental conditions, always
Method and apparatus for calibrating a linear variable differential transformer
Pokrywka, Robert J.
2005-01-18
A calibration apparatus for calibrating a linear variable differential transformer (LVDT) having an armature positioned in au LVDT armature orifice, and the armature able to move along an axis of movement. The calibration apparatus includes a heating mechanism with an internal chamber, a temperature measuring mechanism for measuring the temperature of the LVDT, a fixture mechanism with an internal chamber for at least partially accepting the LVDT and for securing the LVDT within the heating mechanism internal chamber, a moving mechanism for moving the armature, a position measurement mechanism for measuring the position of the armature, and an output voltage measurement mechanism. A method for calibrating an LVDT, including the steps of: powering the LVDT; heating the LVDT to a desired temperature; measuring the position of the armature with respect to the armature orifice; and measuring the output voltage of the LVDT.
Method and Appartus for Calibrating a Linear Variable Differential Transformer
Pokrywka, Robert J.
2005-01-18
A calibration apparatus for calibrating a linear variable differential transformer (LVDT) having an armature positioned in au LVDT armature orifice, and the armature able to move along an axis of movement. The calibration apparatus includes a heating mechanism with an internal chamber, a temperature measuring mechanism for measuring the temperature of the LVDT, a fixture mechanism with an internal chamber for at least partially accepting the LVDT and for securing the LVDT within the heating mechanism internal chamber, a moving mechanism for moving the armature, a position measurement mechanism for measuring the position of the armature, and an output voltage measurement mechanism. A method for calibrating an LVDT, including the steps of powering the LVDT; heating the LVDT to a desired temperature; measuring the position of the armature with respect to the armature orifice; and measuring the output voltage of the LVDT.
A new full pose measurement method for robot calibration.
Nguyen, Hoai-Nhan; Zhou, Jian; Kang, Hee-Jun
2013-01-01
Identification of robot kinematic errors during the calibration process often requires accurate full pose measurements (position and orientation) of robot end-effectors in Cartesian space. This paper proposes a new method of full pose measurement of robot end-effectors for calibration. This method is based on an analysis of the features of a set of target points (placed on a rotating end-effector) on a circular trajectory. The accurate measurement is validated by computational simulation results from the Puma robot. Moreover, experimental calibration and validation results for the Hyundai HA-06 robot prove the effectiveness, correctness, and reliability of the proposed method. This method can be applied to robots that have entirely revolute joints or to robots for which only the last joint is revolute. PMID:23863856
A Comparative Study of IRT Fixed Parameter Calibration Methods
ERIC Educational Resources Information Center
Kim, Seonghoon
2006-01-01
This article provides technical descriptions of five fixed parameter calibration (FPC) methods, which were based on marginal maximum likelihood estimation via the EM algorithm, and evaluates them through simulation. The five FPC methods described are distinguished from each other by how many times they update the prior ability distribution and by…
An improved method for determining force balance calibration accuracy
NASA Astrophysics Data System (ADS)
Ferris, Alice T.
The results of an improved statistical method used at Langley Research Center for determining and stating the accuracy of a force balance calibration are presented. The application of the method for initial loads, initial load determination, auxiliary loads, primary loads, and proof loads is described. The data analysis is briefly addressed.
Comparison of methods for calibrating AVIRIS data to ground reflectance
NASA Technical Reports Server (NTRS)
Clark, Roger N.; Swayze, Gregg; Heidebrecht, Kathy; Goetz, Alexander F. H.; Green, Robert O.
1993-01-01
We are comparing three basic methods of calibrating AVIRIS data to ground reflectance: (1) atmospheric radiative transfer models with the solar flux can be used to calibrate AVIRIS radiance data (Specific methods include the University of Colorado CSES ARP and ATREM algorithms); (2) Robert Green's modified MODTRAN and AVIRIS radiance model (This method is similar to 1 but differs in that the solar radiance is bypassed, so any errors in the solar flux are canceled, too); and (3) ground calibration using known sites in the AVIRIS scene. We are using 1992AVIRIS data over Cuprite, Nevada, and Blackhawk Island, Wisconsin, as our test scenes. Both these sites have extensive field measurements. The Cuprite site had a very clear atmosphere, thus path radiance was dominated by Rayleigh scattering with little or no flux beyond 1 micron. The Blackhawk site has more aerosols, with significant path radiance flux beyond 2 micron.
Universal calculation formula and calibration method in Fourier transform profilometry
Wen Yongfu; Li Sikun; Cheng Haobo; Su Xianyu; Zhang Qican
2010-12-01
We propose a universal calculation formula of Fourier transform profilometry and give a strict theoretical analysis about the phase-height mapping relation. As the request on the experimental setup of the universal calculation formula is unconfined, the projector and the camera can be located arbitrarily to get better fringe information, which makes the operation flexible. The phase-height calibration method under the universal condition is proposed, which can avoid measuring the system parameters directly. It makes the system easy to manipulate and improves the measurement velocity. A computer simulation and experiment are conducted to verify its validity. The calculation formula and calibration method have been applied to measure an object of 22.00 mm maximal height. The relative error of the measurement result is only 0.59%. The experimental results prove that the three-dimensional shape of tested objects can be reconstructed exactly by using the calculation formula and calibration method, and the system has better universality.
NASA Technical Reports Server (NTRS)
Wolf, M. B.
1981-01-01
The determination and removal of instrument signature from Viking Lander camera geometric data are described. All tests conducted as well as a listing of the final database (calibration constants) used to remove instrument signature from Viking Lander flight images are included. The theory of the geometric aberrations inherent in the Viking Lander camera is explored.
Accurate projector calibration method by using an optical coaxial camera.
Huang, Shujun; Xie, Lili; Wang, Zhangying; Zhang, Zonghua; Gao, Feng; Jiang, Xiangqian
2015-02-01
Digital light processing (DLP) projectors have been widely utilized to project digital structured-light patterns in 3D imaging systems. In order to obtain accurate 3D shape data, it is important to calibrate DLP projectors to obtain the internal parameters. The existing projector calibration methods have complicated procedures or low accuracy of the obtained parameters. This paper presents a novel method to accurately calibrate a DLP projector by using an optical coaxial camera. The optical coaxial geometry is realized by a plate beam splitter, so the DLP projector can be treated as a true inverse camera. A plate having discrete markers on the surface is used to calibrate the projector. The corresponding projector pixel coordinate of each marker on the plate is determined by projecting vertical and horizontal sinusoidal fringe patterns on the plate surface and calculating the absolute phase. The internal parameters of the DLP projector are obtained by the corresponding point pair between the projector pixel coordinate and the world coordinate of discrete markers. Experimental results show that the proposed method can accurately calibrate the internal parameters of a DLP projector. PMID:25967789
An Automated Method for Ozonesonde Calibration: New Insights
NASA Technical Reports Server (NTRS)
Schmidlin, F. J.; Hoegger, Bruno A.; Levrat, Gilbert; Baldwin, Tony
2008-01-01
An automated method for preparation of the electrochemical concentration cell (ECC) ozonesonde is presented. Development of a computer-controlled system for preparation and calibration of the ECC is an improvement over the manual preparation method, and reduces subjectivity considerably. Preparation measurements in digital form aids analysis of the ECC before release and enhances post-flight data certification. Calibration of ozonesondes over a range of ozone concentrations between 0 mPA and 30 mPA is discussed. This presentation describes the automatic system, gives examples of calibrations. The automated system enables comparison of varying potassium iodide (KI) concentrations that should allow adjustment of earlier ozonesonde data obtained with different KT concentrations used since 1970, i.e., 2, 1.5, 1, and 0.5 percent. Preliminary results indicate ECC accuracy has a strong dependence on the electrolyte concentration and should not be considered linear with altitude.
An Expectation-Maximization Method for Calibrating Synchronous Machine Models
Meng, Da; Zhou, Ning; Lu, Shuai; Lin, Guang
2013-07-21
The accuracy of a power system dynamic model is essential to its secure and efficient operation. Lower confidence in model accuracy usually leads to conservative operation and lowers asset usage. To improve model accuracy, this paper proposes an expectation-maximization (EM) method to calibrate the synchronous machine model using phasor measurement unit (PMU) data. First, an extended Kalman filter (EKF) is applied to estimate the dynamic states using measurement data. Then, the parameters are calculated based on the estimated states using maximum likelihood estimation (MLE) method. The EM method iterates over the preceding two steps to improve estimation accuracy. The proposed EM method’s performance is evaluated using a single-machine infinite bus system and compared with a method where both state and parameters are estimated using an EKF method. Sensitivity studies of the parameter calibration using EM method are also presented to show the robustness of the proposed method for different levels of measurement noise and initial parameter uncertainty.
A stoichiometric calibration method for dual energy computed tomography.
Bourque, Alexandra E; Carrier, Jean-François; Bouchard, Hugo
2014-04-21
The accuracy of radiotherapy dose calculation relies crucially on patient composition data. The computed tomography (CT) calibration methods based on the stoichiometric calibration of Schneider et al (1996 Phys. Med. Biol. 41 111-24) are the most reliable to determine electron density (ED) with commercial single energy CT scanners. Along with the recent developments in dual energy CT (DECT) commercial scanners, several methods were published to determine ED and the effective atomic number (EAN) for polyenergetic beams without the need for CT calibration curves. This paper intends to show that with a rigorous definition of the EAN, the stoichiometric calibration method can be successfully adapted to DECT with significant accuracy improvements with respect to the literature without the need for spectrum measurements or empirical beam hardening corrections. Using a theoretical framework of ICRP human tissue compositions and the XCOM photon cross sections database, the revised stoichiometric calibration method yields Hounsfield unit (HU) predictions within less than ±1.3 HU of the theoretical HU calculated from XCOM data averaged over the spectra used (e.g., 80 kVp, 100 kVp, 140 kVp and 140/Sn kVp). A fit of mean excitation energy (I-value) data as a function of EAN is provided in order to determine the ion stopping power of human tissues from ED-EAN measurements. Analysis of the calibration phantom measurements with the Siemens SOMATOM Definition Flash dual source CT scanner shows that the present formalism yields mean absolute errors of (0.3 ± 0.4)% and (1.6 ± 2.0)% on ED and EAN, respectively. For ion therapy, the mean absolute errors for calibrated I-values and proton stopping powers (216 MeV) are (4.1 ± 2.7)% and (0.5 ± 0.4)%, respectively. In all clinical situations studied, the uncertainties in ion ranges in water for therapeutic energies are found to be less than 1.3 mm, 0.7 mm and 0.5 mm for protons, helium and carbon ions respectively, using a
A stoichiometric calibration method for dual energy computed tomography
NASA Astrophysics Data System (ADS)
Bourque, Alexandra E.; Carrier, Jean-François; Bouchard, Hugo
2014-04-01
The accuracy of radiotherapy dose calculation relies crucially on patient composition data. The computed tomography (CT) calibration methods based on the stoichiometric calibration of Schneider et al (1996 Phys. Med. Biol. 41 111-24) are the most reliable to determine electron density (ED) with commercial single energy CT scanners. Along with the recent developments in dual energy CT (DECT) commercial scanners, several methods were published to determine ED and the effective atomic number (EAN) for polyenergetic beams without the need for CT calibration curves. This paper intends to show that with a rigorous definition of the EAN, the stoichiometric calibration method can be successfully adapted to DECT with significant accuracy improvements with respect to the literature without the need for spectrum measurements or empirical beam hardening corrections. Using a theoretical framework of ICRP human tissue compositions and the XCOM photon cross sections database, the revised stoichiometric calibration method yields Hounsfield unit (HU) predictions within less than ±1.3 HU of the theoretical HU calculated from XCOM data averaged over the spectra used (e.g., 80 kVp, 100 kVp, 140 kVp and 140/Sn kVp). A fit of mean excitation energy (I-value) data as a function of EAN is provided in order to determine the ion stopping power of human tissues from ED-EAN measurements. Analysis of the calibration phantom measurements with the Siemens SOMATOM Definition Flash dual source CT scanner shows that the present formalism yields mean absolute errors of (0.3 ± 0.4)% and (1.6 ± 2.0)% on ED and EAN, respectively. For ion therapy, the mean absolute errors for calibrated I-values and proton stopping powers (216 MeV) are (4.1 ± 2.7)% and (0.5 ± 0.4)%, respectively. In all clinical situations studied, the uncertainties in ion ranges in water for therapeutic energies are found to be less than 1.3 mm, 0.7 mm and 0.5 mm for protons, helium and carbon ions respectively, using a generic
A new continuous calibration method for inductively coupled plasma spectrometry.
Paredes, E; Maestre, S E; Todolí, J L
2006-01-01
A new calibration method was developed and applied to inductively coupled plasma atomic emission spectrometry. External calibration was performed as follows. A container was filled with a given volume of deionized (V(p)) water. Then a concentrated standard was introduced at a controlled rate (Q(e)) into the tank by means of a peristaltic pump. The resulting solution was stirred throughout the experiment. Simultaneously, the solution inside the tank was pumped from the vessel to the plasma at a given rate (Q(s)). The signal was continuously recorded. The variation of the concentration of the solution leaving the tank with time was determined by applying a basic equation of stirred tanks. The representation of the emission intensity versus the time and the further conversion of the time scale into a concentration scale gave rise to the calibration line. The best results in terms of linearity were achieved for V(p)=15 cm3, Q(e)=0.6-0.75 ml min(-1) and Q(s)=1-1.2 ml min(-1). Graphs with more than 40 standards were obtained within about 10 min. The results found were not statistically different from those afforded by the conventional calibration method. In addition, the new method was faster and supplied better linearity and precision than the conventional one. Another advantage of the stirred tank was that procedures such as dynamic calibration and standard additions could be easily and quickly applied, thus shortening the analysis time. A complete analysis following these procedures based on the measurement of 30 standards took about 5 min. Several synthetic as well as certified samples (i.e., bovine liver, mussel tissue and powdered milk) were analyzed with the stirred tank by applying four different calibration methodologies (i.e., external calibration, internal calibration, standard additions and a combination of internal standardization and standard additions), with the combination of internal standardization and standard additions being the method that provided
A Calibration Method for Wide-Field Multicolor Photometric Systems
NASA Astrophysics Data System (ADS)
Zhou, Xu; Chen, Jiansheng; Xu, Wen; Zhang, Mei; Jiang, Zhaoji; Zheng, Zhongyuan; Zhu, Jin
1999-07-01
The purpose of this paper is to present a method to self-calibrate the spectral energy distribution (SED) of objects in a survey based on the fitting of a SED library to observed multicolor photometry. We adopt, for illustrative purposes, the Vilnius and Gunn & Stryker SED libraries. The self-calibration technique can improve the quality of observations which are not taken under perfectly photometric conditions. The more passbands used for the photometry, the better the results. This technique has been applied to the BATC 15 passband CCD survey.
Calibration method for angular measurement of moiré patterns
NASA Astrophysics Data System (ADS)
He, Fan; Bai, Jian; Wang, Kaiwei; Hou, Xiyun; Yao, Jiang
2014-09-01
In this paper, a high-accuracy calibration method for angular measurement of deformed and curved Moiré patterns, based on template matching algorithm, is presented. We report a feasible and accurate method, based on Talbot interferometry and Moiré deflectometry, to measure long focal-length lenses. Theoretical analysis indicates that the precision of this method is mainly influenced by the angle of Moiré patterns. However, it's difficult to obtain high-accuracy angle of Moiré patterns, since the Moiré patterns derived from experiment are constantly deformed or curved. We demonstrate a method, based on template matching algorithm, to calibrate deformed and curved Moiré patterns, thus their angle can be calculated fast and accurately in sub-pixel domain. Numerical analysis and simulation prove that the method mentioned above demonstrates high precision and stability, and experiment results show that the accuracy of the long focal lengths measurement is improved obviously.
A Novel Gaze Tracking Method Based on the Generation of Virtual Calibration Points
Lee, Ji Woo; Heo, Hwan; Park, Kang Ryoung
2013-01-01
Most conventional gaze-tracking systems require that users look at many points during the initial calibration stage, which is inconvenient for them. To avoid this requirement, we propose a new gaze-tracking method with four important characteristics. First, our gaze-tracking system uses a large screen located at a distance from the user, who wears a lightweight device. Second, our system requires that users look at only four calibration points during the initial calibration stage, during which four pupil centers are noted. Third, five additional points (virtual pupil centers) are generated with a multilayer perceptron using the four actual points (detected pupil centers) as inputs. Fourth, when a user gazes at a large screen, the shape defined by the positions of the four pupil centers is a distorted quadrangle because of the nonlinear movement of the human eyeball. The gaze-detection accuracy is reduced if we map the pupil movement area onto the screen area using a single transform function. We overcame this problem by calculating the gaze position based on multi-geometric transforms using the five virtual points and the four actual points. Experiment results show that the accuracy of the proposed method is better than that of other methods. PMID:23959241
Histogram-Based Calibration Method for Pipeline ADCs.
Son, Hyeonuk; Jang, Jaewon; Kim, Heetae; Kang, Sungho
2015-01-01
Measurement and calibration of an analog-to-digital converter (ADC) using a histogram-based method requires a large volume of data and a long test duration, especially for a high resolution ADC. A fast and accurate calibration method for pipelined ADCs is proposed in this research. The proposed calibration method composes histograms through the outputs of each stage and calculates error sources. The digitized outputs of a stage are influenced directly by the operation of the prior stage, so the results of the histogram provide the information of errors in the prior stage. The composed histograms reduce the required samples and thus calibration time being implemented by simple modules. For 14-bit resolution pipelined ADC, the measured maximum integral non-linearity (INL) is improved from 6.78 to 0.52 LSB, and the spurious-free dynamic range (SFDR) and signal-to-noise-and-distortion ratio (SNDR) are improved from 67.0 to 106.2dB and from 65.6 to 84.8dB, respectively. PMID:26070196
An MLC calibration method using a detector array
Simon, Thomas A.; Kahler, Darren; Simon, William E.; Fox, Christopher; Li, Jonathan; Palta, Jatinder; Liu, Chihray
2009-10-15
Purpose: The authors have developed a quantitative calibration method for a multileaf collimator (MLC) which measures individual leaf positions relative to the MLC backup jaw on an Elekta Synergy linear accelerator. Methods: The method utilizes a commercially available two-axis detector array (Profiler 2; Sun Nuclear Corporation, Melbourne, FL). To calibrate the MLC bank, its backup jaw is positioned at the central axis and the opposing jaw is retracted to create a half-beam configuration. The position of the backup jaws field edge is then measured with the array to obtain what is termed the radiation defined reference line. The positions of the individual leaf ends relative to this reference line are then inferred by the detector response in the leaf end penumbra. Iteratively adjusting and remeasuring the leaf end positions to within specifications completes the calibration. Using the backup jaw as a reference for the leaf end positions is based on three assumptions: (1) The leading edge of an MLC leaf bank is parallel to its backup jaw's leading edge, (2) the backup jaw position is reproducible, and (3) the measured radiation field edge created by each leaf end is representative of that leaf's position. Data from an electronic portal imaging device (EPID) were used in a similar analysis to check the results obtained with the array. Results: The relative leaf end positions measured with the array differed from those measured with the EPID by an average of 0.11 {+-}0.09 mm per leaf. The maximum leaf positional change measured with the Profiler 2 over a 3 month period was 0.51 mm. A leaf positional accuracy of {+-}0.4 mm is easily attainable through the iterative calibration process. The method requires an average of 40 min to measure both leaf banks. Conclusions: This work demonstrates that the Profiler 2 is an effective tool for efficient and quantitative MLC quality assurance and calibration.
Gravimetric method for in vitro calibration of skin hydration measurements.
Martinsen, Ørjan G; Grimnes, Sverre; Nilsen, Jon K; Tronstad, Christian; Jang, Wooyoung; Kim, Hongsig; Shin, Kunsoo; Naderi, Majid; Thielmann, Frank
2008-02-01
A novel method for in vitro calibration of skin hydration measurements is presented. The method combines gravimetric and electrical measurements and reveals an exponential dependency of measured electrical susceptance to absolute water content in the epidermal stratum corneum. The results also show that absorption of water into the stratum corneum exhibits three different phases with significant differences in absorption time constant. These phases probably correspond to bound, loosely bound, and bulk water. PMID:18270010
Airborne Linear Array Image Geometric Rectification Method Based on Unequal Segmentation
NASA Astrophysics Data System (ADS)
Li, J. M.; Li, C. R.; Zhou, M.; Hu, J.; Yang, C. M.
2016-06-01
As the linear array sensor such as multispectral and hyperspectral sensor has great potential in disaster monitoring and geological survey, the quality of the image geometric rectification should be guaranteed. Different from the geometric rectification of airborne planar array images or multi linear array images, exterior orientation elements need to be determined for each scan line of single linear array images. Internal distortion persists after applying GPS/IMU data directly to geometrical rectification. Straight lines may be curving and jagged. Straight line feature -based geometrical rectification algorithm was applied to solve this problem, whereby the exterior orientation elements were fitted by piecewise polynomial and evaluated with the straight line feature as constraint. However, atmospheric turbulence during the flight is unstable, equal piecewise can hardly provide good fitting, resulting in limited precision improvement of geometric rectification or, in a worse case, the iteration cannot converge. To solve this problem, drawing on dynamic programming ideas, unequal segmentation of line feature-based geometric rectification method is developed. The angle elements fitting error is minimized to determine the optimum boundary. Then the exterior orientation elements of each segment are fitted and evaluated with the straight line feature as constraint. The result indicates that the algorithm is effective in improving the precision of geometric rectification.
Efficient Calibration of Categorical Parameter Distributions using Subspace Methods
NASA Astrophysics Data System (ADS)
Khambhammettu, P.; Renard, P.; Doherty, J.
2014-12-01
Categorical parameter distributions are common-place in hydrogeological systems consisting of rock-types / aquifer materials with distinct properties, eg: sand channels in a clay matrix. Model calibration is difficult in such systems because the inverse problem is hindered by the discontinuities in the parameter space. In this paper, we present two approaches based on sub-space methods to generate categorical parameter distributions of aquifer parameters that meet calibration constraints (eg:- measured water level data, gradients) while honoring prior geological constraints. In the first approach, the prior geological information and acceptable parameter distributions are encapsulated in a simple object-based model. In the second approach, a Multiple-Point Statistics simulator is used to represent the prior geological information. Sub-space methods in conjunction with dynamic pilot points are then employed to explore the parameter space and determine the parameter combinations that optimally honor geologic and calibration constraints. Using a simple aquifer system, we demonstrate that the new approach is capable of quickly generating multiple multiple parameter distributions that honor both geological and calibration constraints. We also explore the underlying parameter and predictive uncertainty using Null Space Monte Carlo techniques.
NASA Astrophysics Data System (ADS)
Kunze, Hans-Joachim
Commercial spectrographic systems are usually supplied with some wave-length calibration, but it is essential that the experimenter performs his own calibration for reliable measurements. A number of sources emitting well-known emission lines are available, and the best values of their wavelengths may be taken from data banks accessible on the internet. Data have been critically evaluated for many decades by the National Institute of Standards and Technology (NIST) of the USA [13], see also p. 3. Special data bases have been established by the astronomy and fusion communities (Appendix B).
A method for small-animal PET/CT alignment calibration
NASA Astrophysics Data System (ADS)
Pascau, J.; Vaquero, J. J.; Chamorro-Servent, J.; Rodríguez-Ruano, A.; Desco, M.
2012-06-01
Small-animal positron-emission tomography/computed tomography (PET/CT) scanners provide anatomical and molecular imaging, which enables the joint visualization and analysis of both types of data. A proper alignment calibration procedure is essential for small-animal imaging since resolution is much higher than that in human devices. This work presents an alignment phantom and two different calibration methods that provide a reliable and repeatable measurement of the spatial geometrical alignment between the PET and the CT subsystems of a hybrid scanner. The phantom can be built using laboratory materials, and it is meant to estimate the rigid spatial transformation that aligns both modalities. It consists of three glass capillaries filled with a positron-emitter solution and positioned in a non-coplanar triangular geometry inside the system field of view. The calibration methods proposed are both based on automatic line detection, but with different approaches to calculate the transformation of the lines between both modalities. Our results show an average accuracy of the alignment estimation of 0.39 mm over the whole field of view.
A calibration method of the multi-channel imaging lidar
NASA Astrophysics Data System (ADS)
Xu, Weiming; Liu, Jun; Shu, Rong
2014-06-01
We design a kind of imaging LiDAR with sixteen channels, which consists of a fiber laser source, dual scanning galvanometers, range measurement circuits and information processing circuits etc. The image LiDAR provides sixteen range measurements for one laser shot and the distance accuracy of each channel is about 4cm. This paper provides a calibrate method to correct point cloud images captured with the multi-channel LiDAR. The method needs to construct different slanted planes to cover the imaging field, and establish precise plane equations in the known ground coordinates, then fit planes with point clouds data and calculate correction parameters of all channels through the error model. The image accuracy is better than 5cm processed by this calibration method.
a Modified Method for Polarimetric SAR Calibration Algorithm
NASA Astrophysics Data System (ADS)
Liao, L.; Li, P.; Yang, J.
2013-07-01
Present fully polarimetric synthetic aperture radar (SAR) systems often update calibration techniques to further enhance the accuracy to the polarimetric data. In this paper, we propose a modified method to estimate the value of crosstalk based on the corrected observed value. Since Ainsworth calibration algorithm firstly set the value of k to be one. And the value of k relates to the copolarization channel imbalance .We consider the effects of value of k and analyze it. Through comparison to crosstalk results between the stimulated parameters and the estimated parameters, we assume high co-polarization channel imbalance will be obviously to affect crosstalk results. Then, used covariance observation value of the initial value of k rewrites the model to solve related parameters. And crosstalk parameter is calculated by the same iterative method. To verify the effect of the modified calibration method, this letter compares the accuracy of the two methods using the simulated polarimetric SAR data and Chinese airborne X-band polarimetric SAR data. The results confirm that the modified method tends to get more accurate crosstalk results.
Liu, Bailing; Zhang, Fumin; Qu, Xinghua; Shi, Xiaojia
2016-01-01
Coordinate transformation plays an indispensable role in industrial measurements, including photogrammetry, geodesy, laser 3-D measurement and robotics. The widely applied methods of coordinate transformation are generally based on solving the equations of point clouds. Despite the high accuracy, this might result in no solution due to the use of ill conditioned matrices. In this paper, a novel coordinate transformation method is proposed, not based on the equation solution but based on the geometric transformation. We construct characteristic lines to represent the coordinate systems. According to the space geometry relation, the characteristic line scan is made to coincide by a series of rotations and translations. The transformation matrix can be obtained using matrix transformation theory. Experiments are designed to compare the proposed method with other methods. The results show that the proposed method has the same high accuracy, but the operation is more convenient and flexible. A multi-sensor combined measurement system is also presented to improve the position accuracy of a robot with the calibration of the robot kinematic parameters. Experimental verification shows that the position accuracy of robot manipulator is improved by 45.8% with the proposed method and robot calibration. PMID:26901203
Liu, Bailing; Zhang, Fumin; Qu, Xinghua; Shi, Xiaojia
2016-01-01
Coordinate transformation plays an indispensable role in industrial measurements, including photogrammetry, geodesy, laser 3-D measurement and robotics. The widely applied methods of coordinate transformation are generally based on solving the equations of point clouds. Despite the high accuracy, this might result in no solution due to the use of ill conditioned matrices. In this paper, a novel coordinate transformation method is proposed, not based on the equation solution but based on the geometric transformation. We construct characteristic lines to represent the coordinate systems. According to the space geometry relation, the characteristic line scan is made to coincide by a series of rotations and translations. The transformation matrix can be obtained using matrix transformation theory. Experiments are designed to compare the proposed method with other methods. The results show that the proposed method has the same high accuracy, but the operation is more convenient and flexible. A multi-sensor combined measurement system is also presented to improve the position accuracy of a robot with the calibration of the robot kinematic parameters. Experimental verification shows that the position accuracy of robot manipulator is improved by 45.8% with the proposed method and robot calibration. PMID:26901203
Geometric method for forming periodic orbits in the Lorenz system
NASA Astrophysics Data System (ADS)
Nicholson, S. B.; Kim, Eun-jin
2016-04-01
Many systems in nature are out of equilibrium and irreversible. The non-detailed balance observable representation (NOR) provides a useful methodology for understanding the evolution of such non-equilibrium complex systems, by mapping out the correlation between two states to a metric space where a small distance represents a strong correlation [1]. In this paper, we present the first application of the NOR to a continuous system and demonstrate its utility in controlling chaos. Specifically, we consider the evolution of a continuous system governed by the Lorenz equation and calculate the NOR by following a sufficient number of trajectories. We then show how to control chaos by converting chaotic orbits to periodic orbits by utilizing the NOR. We further discuss the implications of our method for potential applications given the key advantage that this method makes no assumptions of the underlying equations of motion and is thus extremely general.
Method of locating related items in a geometric space for data mining
Hendrickson, B.A.
1999-07-27
A method for locating related items in a geometric space transforms relationships among items to geometric locations. The method locates items in the geometric space so that the distance between items corresponds to the degree of relatedness. The method facilitates communication of the structure of the relationships among the items. The method is especially beneficial for communicating databases with many items, and with non-regular relationship patterns. Examples of such databases include databases containing items such as scientific papers or patents, related by citations or keywords. A computer system adapted for practice of the present invention can include a processor, a storage subsystem, a display device, and computer software to direct the location and display of the entities. The method comprises assigning numeric values as a measure of similarity between each pairing of items. A matrix is constructed, based on the numeric values. The eigenvectors and eigenvalues of the matrix are determined. Each item is located in the geometric space at coordinates determined from the eigenvectors and eigenvalues. Proper construction of the matrix and proper determination of coordinates from eigenvectors can ensure that distance between items in the geometric space is representative of the numeric value measure of the items' similarity. 12 figs.
Method of locating related items in a geometric space for data mining
Hendrickson, Bruce A.
1999-01-01
A method for locating related items in a geometric space transforms relationships among items to geometric locations. The method locates items in the geometric space so that the distance between items corresponds to the degree of relatedness. The method facilitates communication of the structure of the relationships among the items. The method is especially beneficial for communicating databases with many items, and with non-regular relationship patterns. Examples of such databases include databases containing items such as scientific papers or patents, related by citations or keywords. A computer system adapted for practice of the present invention can include a processor, a storage subsystem, a display device, and computer software to direct the location and display of the entities. The method comprises assigning numeric values as a measure of similarity between each pairing of items. A matrix is constructed, based on the numeric values. The eigenvectors and eigenvalues of the matrix are determined. Each item is located in the geometric space at coordinates determined from the eigenvectors and eigenvalues. Proper construction of the matrix and proper determination of coordinates from eigenvectors can ensure that distance between items in the geometric space is representative of the numeric value measure of the items' similarity.
A New Method for Geometric Quality Evaluation of Remote Sensing Image Based on Information Entropy
NASA Astrophysics Data System (ADS)
Jiao, W.; Long, T.; Yang, G.; He, G.
2014-11-01
Geometric accuracy of the remote sensing rectified image is usually evaluated by the root-mean-square errors (RMSEs) of the ground control points (GCPs) and check points (CPs). These discrete geometric accuracy index data represent only on a local quality of the image with statistical methods. In addition, the traditional methods only evaluate the difference between the rectified image and reference image, ignoring the degree of the original image distortion. A new method of geometric quality evaluation of remote sensing image based on the information entropy is proposed in this paper. The information entropy, the amount of information and the uncertainty interval of the image before and after rectification are deduced according to the information theory. Four kind of rectification model and seven situations of GCP distribution are applied on the remotely sensed imagery in the experiments. The effective factors of the geometrical accuracy are analysed and the geometric qualities of the image are evaluated in various situations. Results show that the proposed method can be used to evaluate the rectification model, the distribution model of GCPs and the uncertainty of the remotely sensed imagery, and is an effective and objective assessment method.
AVIRIS calibration using the cloud-shadow method
NASA Technical Reports Server (NTRS)
Carder, K. L.; Reinersman, P.; Chen, R. F.
1993-01-01
More than 90 percent of the signal at an ocean-viewing, satellite sensor is due to the atmosphere, so a 5 percent sensor-calibration error viewing a target that contributes but 10 percent of the signal received at the sensor may result in a target-reflectance error of more than 50 percent. Since prelaunch calibration accuracies of 5 percent are typical of space-sensor requirements, recalibration of the sensor using ground-base methods is required for low-signal target. Known target reflectance or water-leaving radiance spectra and atmospheric correction parameters are required. In this article we describe an atmospheric-correction method that uses cloud shadowed pixels in combination with pixels in a neighborhood region of similar optical properties to remove atmospheric effects from ocean scenes. These neighboring pixels can then be used as known reflectance targets for validation of the sensor calibration and atmospheric correction. The method uses the difference between water-leaving radiance values for these two regions. This allows nearly identical optical contributions to the two signals (e.g., path radiance and Fresnel-reflected skylight) to be removed, leaving mostly solar photons backscattered from beneath the sea to dominate the residual signal. Normalization by incident solar irradiance reaching the sea surface provides the remote-sensing reflectance of the ocean at the location of the neighbor region.
NASA Astrophysics Data System (ADS)
Pereira, Carlos Manuel
The contribution of this research work to the body of existing knowledge is a novel design (inverse) method to compute the distribution of fields when electromagnetic waves interact with surfaces. If given a desired distribution of electromagnetic fields (radiation pattern), the design (inverse) method developed will rapidly allow a designer to determine a unique geometric solution which will provide the desired radiation pattern, which is an inverse problem. The method developed can also be used as an analysis tool to analyze radiating or receiving structures with simple and complex non-linear geometric features. In the extensive literature search provided in this work, others have used analytical methods for computing the distribution of electromagnetic fields when waves propagate and interact with structures. This requires a mathematical framework to be developed using time-harmonic and magnetic fields to solve boundary value problems using closed-form mathematical relationships that only have closed-form solutions for a few simple geometrical shapes. When the geometrical features of a structure contain arbitrary shapes with irregular geometries, finite element methods can also be used as analysis tools to handle any type of geometrical features, however, both of these methods are used to perform analysis of these types of problems and are very time consuming and not suited as design tools to rapidly provide design information on the geometry features that provide a desired electric field distribution. This revolutionary methodology provides a design tool which currently does not exist in the reviewed published literature. It overcomes deficiencies presented by current analysis tools, such as theoretical, analytical and numerical methods which are capable of analyzing wave propagation and interaction problems, but are not suited to rapidly design geometrical features of radiating or receiving structures.
An alternative calibration method for counting P-32 reactor monitors
Quirk, T.J.; Vehar, D.W.
2011-07-01
Radioactivation of sulfur is a common technique used to measure fast neutron fluences in test and research reactors. Elemental sulfur can be pressed into pellets and used as monitors. The {sup 32}S(n, p) {sup 32}P reaction has a practical threshold of about 3 MeV and its cross section and associated uncertainties are well characterized [1]. The product {sup 32P} emits a beta particle with a maximum energy of 1710 keV [2]. This energetic beta particle allows pellets to be counted intact. ASTM Standard Test Method for Measuring Reaction Rates and Fast-Neutron Fluences by Radioactivation of Sulfur-32 (E265) [3] details a method of calibration for counting systems and subsequent analysis of results. This method requires irradiation of sulfur monitors in a fast-neutron field whose spectrum and intensity are well known. The resultant decay-corrected count rate is then correlated to the known fast neutron fluence. The Radiation Metrology Laboratory (RML) at Sandia has traditionally performed calibration irradiations of sulfur pellets using the {sup 252}Cf spontaneous fission neutron source at the National Inst. of Standards and Technology (NIST) [4] as a transfer standard. However, decay has reduced the intensity of NIST's source; thus lowering the practical upper limits of available fluence. As of May 2010, neutron emission rates have decayed to approximately 3 e8 n/s. In practice, this degradation of capabilities precludes calibrations at the highest fluence levels produced at test reactors and limits the useful range of count rates that can be measured. Furthermore, the reduced availability of replacement {sup 252}Cf threatens the long-term viability of the NIST {sup 252}Cf facility for sulfur pellet calibrations. In lieu of correlating count rate to neutron fluence in a reference field the total quantity of {sup 32}P produced in a pellet can be determined by absolute counting methods. This offers an attractive alternative to extended {sup 252}Cf exposures because it
Self-calibration method of two-dimensional grid plate
NASA Astrophysics Data System (ADS)
Ding, Guoqing; Chen, Xin; Wang, Lihua; Lei, Lihua; Li, Yuan
2011-12-01
A two-dimensional grid plate can offer an X-Y position standard where grids are aligned orthogonal to each other. It is important to ensure the positional accuracy of the grid plate when the grid plate is used to calibrate planar movement systems, such as vision measuring machines and scanning probe microscopes. Existing algorithms for self-calibration employ the discrete Fourier transform, which is complicated and has poor noise suppression capability. We have developed an algorithm that can achieve exact self-calibration for a two-dimensional grid plate using the least squares method when there is no random noise. In the presence of random noise, the algorithm still presents an excellent capability for noise suppression. As an extension of the classic three-location measurement, the algorithm can be applied to four- or five-location measurements, which reduce measurement uncertainties. The error propagation characteristic of the random errors has been investigated in the case of different measurement strategies. According to the simulation results, the mean error propagation ratios are less than 1 when the array size of the grid plate is less than 32×32. Finally, the influence of the scale errors of the planar movement system is discussed.
Method of Calibration for a Large Cathetometer System
NASA Technical Reports Server (NTRS)
Toland, Ronald
2004-01-01
A method of calibration has been devised for a pair of mutually orthogonal two-axis cathetometers that, when used together, yield measurements of three-dimensional positions of objects mounted on an optical bench. Each cathetometer has a horizontal travel of 1.8 m and a vertical travel of 1.2 m. The cathetometers are required to measure X, Y, and Z coordinates (see figure) to within plus or minus 0.005 in. (plus or minus 0.127 mm). Each cathetometer consists of an alignment telescope on a platform mounted on a two-dimensional translation stage. The knowledge required for calibration of each cathetometer is (1) the two-dimensional position of the cathetometer platform as a function of the electronic readouts of position encoders on the translation stage and (2) the amount of any angular misalignment (roll, pitch, and/or yaw) of the cathetometer platform as a function of the two-dimensional coordinates or the position-encoder readouts. By use of three equations derived from the applicable trigonometric relationships, the calibrated X, Y, and Z coordinates can be computed from the raw encoder readouts.
NASA Astrophysics Data System (ADS)
Lindlein, Norbert; Leuchs, Gerd
This chapter shall discuss the basics and the applications of geometrical optical methods in modern optics. Geometrical optics has a long tradition and some ideas are many centuries old. Nevertheless, the invention of modern personal computers which can perform several million floating-point operations in a second also revolutionized the methods of geometrical optics and so several analytical methods lost importance whereas numerical methods such as ray tracing became very important. Therefore, the emphasis in this chapter is also on modern numerical methods such as ray tracing and some other systematic methods such as the paraxial matrix theory.
Vogelmann, James E.; Helder, Dennis; Morfitt, Ron; Choate, Michael J.; Merchant, James W.; Bulley, Henry
2001-01-01
The Thematic Mapper (TM) instruments onboard Landsats 4 and 5 provide high-quality imagery appropriate for many different applications, including land cover mapping, landscape ecology, and change detection. Precise calibration was considered to be critical to the success of the Landsat 7 mission and, thus, issues of calibration were given high priority during the development of the Enhanced Thematic Mapper Plus (ETM+). Data sets from the Landsat 5 TM are not routinely corrected for a number of radiometric and geometric artifacts, including memory effect, gain/bias, and interfocal plane misalignment. In the current investigation, the effects of correcting vs. not correcting these factors were investigated for several applications. Gain/bias calibrations were found to have a greater impact on most applications than did memory effect calibrations. Correcting interfocal plane offsets was found to have a moderate effect on applications. On June 2, 1999, Landsats 5 and 7 data were acquired nearly simultaneously over a study site in the Niobrara, NE area. Field radiometer data acquired at that site were used to facilitate crosscalibrations of Landsats 5 and 7 data. Current findings and results from previous investigations indicate that the internal calibrator of Landsat 5 TM tracked instrument gain well until 1988. After this, the internal calibrator diverged from the data derived from vicarious calibrations. Results from this study also indicate very good agreement between prelaunch measurements and vicarious calibration data for all Landsat 7 reflective bands except Band 4. Values are within about 3.5% of each other, except for Band 4, which differs by 10%. Coefficient of variation (CV) values derived from selected targets in the imagery were also analyzed. The Niobrara Landsat 7 imagery was found to have lower CV values than Landsat 5 data, implying that lower levels of noise characterize Landsat 7 data than current Landsat 5 data. It was also found that following
The cryogenic balance design and balance calibration methods
NASA Astrophysics Data System (ADS)
Ewald, B.; Polanski, L.; Graewe, E.
1992-07-01
The current status of a program aimed at the development of a cryogenic balance for the European Transonic Wind Tunnel is reviewed. In particular, attention is given to the cryogenic balance design philosophy, mechanical balance design, reliability and accuracy, cryogenic balance calibration concept, and the concept of an automatic calibration machine. It is shown that the use of the automatic calibration machine will improve the accuracy of calibration while reducing the man power and time required for balance calibration.
NASA Astrophysics Data System (ADS)
Liu, Zhe; Zhang, Li; Jiang, Xiaolei
2012-10-01
Tomographic Gamma Scanning (TGS) is one of the non-destructive analysis technologies based on the principles of Emission Computed Tomography (ECT). Dedicated on imaging of the Gamma ray emission, TGS reveals radioactivity distributions for different radionuclides inside target objects such as nuclear waste barrels. Due to the special characteristics of TGS imaging geometry, namely, the relatively larger detector cell size and more remarkable view change in the imaging region, the line integral projection model widely used in ECT problems is no longer applicable for the radioactive intensity image reconstruction in TGS. The alternative Monte-Carlo based methods which calculate the detection efficiency at every detecting position for each voxel are effective and accurate, however time consuming. In this paper, we consider the geometrical detection efficiency of detector that is dependent on the detector-voxel relative position independently from the intrinsic detection efficiency. Further, a new geometrical correction method is proposed, where the voxel volume within the detector view is applied as the projection weight substituting the track length used in line integral model. And the geometrical detection efficiencies at different positions are analytically expressed by the volume integral on the voxel of geometrical point-source response function of the detector. Numerical simulations are taken and discussions are provided. The results show that the proposed method reduces the reconstruction errors compared to the line integral projection method while gaining better calculating efficiency and flexibility than former Monte-Carlo methods.
Various methods and developments for calibrating seismological sensors at EOST
NASA Astrophysics Data System (ADS)
JUND, H.; Bès de Berc, M.; Thore, J.
2013-12-01
Calibrating seismic sensors is crucial for knowing the quality of the sensor and generating precise dataless files. We present here three calibration methods that we have developed for the short period and broad band sensors included in the temporary and permanent seismic networks in France. First, in the case of a short-period sensor with no electronics and calibration coil, we inject a sine wave signal into the signal coil. After locking the sensor mass, we first connect a voltage generator of signal waves and a series resistor to the coil. Then, a sinusoidal signal is sent to the sensor signal coil output. Both the voltage at the terminal of the resistor, which gives an image of the intensity entering the signal coil, and the voltage at the terminal of the signal coil are measured. The frequency of the generator then varies in order to find a phase shift between both signals of π/2. The output frequency of the generator corresponds to the image of the natural frequency of the sensor. Second, in the case of all types of sensors provided with a calibration coil, we inject different signals into the calibration coil. We usually apply two signals: a step signal and a sweep (or wobble) signal. A step signal into the calibration coil is equivalent to a Dirac excitation in derived acceleration. The response to this Dirac gives the transfer function of the signal coil, derived two times and without absolute gain. We developed a field-module allowing us to always apply the same excitation to various models of seismometers, in order to compare the results from several instruments previously installed on field. A wobble signal is a signal whose frequency varies. By varying the frequency of the input signal around the sensor's natural frequency, we obtain an immediate response of the sensor in acceleration. This method is particularly suitable in order to avoid any disturbances which may modify the signal of a permanent station. Finally, for the determination of absolute
Anatomically Based Geometric Modelling Using Medical Image Data: Methods and Programs
Wang, Monan; Sun, Lei; Liu, Yuming
2015-01-01
The human organs geometric modeling software which can achieve two-dimensional medical image browsing, pretreatment and three dimensional (3D) reconstruction in this paper is designed. This software implements medical image segmentation using the method combining the region growing and the interactive segmentation. Also, the MC surface reconstruction algorithm is utilized to achieve the three-dimensional reconstruction. Furthermore, the software is projected by Visual C++. And then, to legitimately express the structural information of skeleton and muscle, the software is employed to obtain the geometric model using the segmentation and three-dimensional reconstruction for data of skeleton and muscle medical images of the object of study. PMID:26089991
NASA Astrophysics Data System (ADS)
Bieg, Bohdan; Chrzanowski, Janusz; Kravtsov, Yury A.; Orsitto, Francesco
Basic principles and recent findings of quasi-isotropic approximation (QIA) of a geometrical optics method are presented in a compact manner. QIA was developed in 1969 to describe electromagnetic waves in weakly anisotropic media. QIA represents the wave field as a power series in two small parameters, one of which is a traditional geometrical optics parameter, equal to wavelength ratio to plasma characteristic scale, and the other one is the largest component of anisotropy tensor. As a result, "" QIA ideally suits to tokamak polarimetry/interferometry systems in submillimeter range, where plasma manifests properties of weakly anisotropic medium.
Accurate, efficient, and (iso)geometrically flexible collocation methods for phase-field models
NASA Astrophysics Data System (ADS)
Gomez, Hector; Reali, Alessandro; Sangalli, Giancarlo
2014-04-01
We propose new collocation methods for phase-field models. Our algorithms are based on isogeometric analysis, a new technology that makes use of functions from computational geometry, such as, for example, Non-Uniform Rational B-Splines (NURBS). NURBS exhibit excellent approximability and controllable global smoothness, and can represent exactly most geometries encapsulated in Computer Aided Design (CAD) models. These attributes permitted us to derive accurate, efficient, and geometrically flexible collocation methods for phase-field models. The performance of our method is demonstrated by several numerical examples of phase separation modeled by the Cahn-Hilliard equation. We feel that our method successfully combines the geometrical flexibility of finite elements with the accuracy and simplicity of pseudo-spectral collocation methods, and is a viable alternative to classical collocation methods.
A quick telemanipulator calibration and repeatability method with applications
Jansen, J.F.; Haley, D.C.
1994-09-01
This paper will present a methodology that was used to calibrate and measure the repeatability of two telemanipulators at Oak Ridge National Laboratory. The global accuracy of the method was 0.05 in. ({approx_equal} 1.3 mm), and the orientation accuracy was approximately 6 min ({approx_equal} 0.002 rads). For most teleoperator systems, these accuracies are more than adequate because of the construction of the mechanism and sensor capabilities (e.g., typically 12 bits of resolution). Although industrial robots require accuracies of about 0.05 mm or better, telemanipulators do not.
Method of calibrating a fluid-level measurement system
NASA Technical Reports Server (NTRS)
Woodard, Stanley E. (Inventor); Taylor, Bryant D. (Inventor)
2010-01-01
A method of calibrating a fluid-level measurement system is provided. A first response of the system is recorded when the system's sensor(s) is (are) not in contact with a fluid of interest. A second response of the system is recorded when the system's sensor(s) is (are) fully immersed in the fluid of interest. Using the first and second responses, a plurality of expected responses of the system's sensor(s) is (are) generated for a corresponding plurality of levels of immersion of the sensor(s) in the fluid of interest.
Method of making self-calibrated displacement measurements
Pedersen, Herbert N.
1977-01-01
A method for monitoring the displacement of an object having an acoustically reflective surface at least partially submerged in an acoustically conductive medium. The reflective surface is designed to have a stepped interface responsive to an incident acoustic pulse to provide separate discrete reflected pulses to a receiving transducer. The difference in the time of flight of the reflected acoustic signals corresponds to the known step height and the time of travel of the signals to the receiving transducer provides a measure of the displacement of the object. Accordingly, the reference step length enables simultaneous calibration of each displacement measurement.
Spinning disk calibration method and apparatus for laser Doppler velocimeter
NASA Technical Reports Server (NTRS)
Snyder, P. K. (Inventor)
1986-01-01
A method and apparatus for calibrating laser Doppler velocimeters having one or more intersecting beam pairs are described. These velocimeters measure fluid velocity by observing the light scattered by particles in the fluid stream. Moving fluid particulates are simulated by fine taut wires that are radially mounted on a disk that is rotated at a known velocity. The laser beam intersection locus is first aimed at the very center of the disk and then the disk is translated so that the locus is swept by the rotating wires. The radial distance traversed is precisely measured so that the velocity of the wires (pseudo particles) may be calculated.
Novel method of calibration with restrictive constraints for stereo-vision system
NASA Astrophysics Data System (ADS)
Cui, Jiashan; Huo, Ju; Yang, Ming
2016-05-01
Regarding the calibration of a stereo vision measurement system, this paper puts forward a new bundle adjustment algorithm based on the stereo vision camera calibration method. Multiple-view geometric constraints and a bundle adjustment algorithm are used to optimize the inner and outer parameters of the camera accurately. A fixed relative constraint relationship between cameras is introduced. We have improved the normal equation construction process of the traditional bundle adjustment method, so that each iteration process occurs just outside the parameters of two images that are taken by a camera that has been optimized to better integrate two cameras bound together as one camera. The relationship between the fixed relative constraints can effectively increase the number of superfluous observations of the adjustment system and optimize higher accuracy while reducing the dimension of the normal matrix; it means that each iteration will reduce the time required. Simulation and actual experimental results show the superior performance of the proposed approach in terms of robustness and accuracy, and our approach also can be extended to stereo-vision system with more than two cameras.
A Bionic Polarization Navigation Sensor and Its Calibration Method.
Zhao, Huijie; Xu, Wujian
2016-01-01
The polarization patterns of skylight which arise due to the scattering of sunlight in the atmosphere can be used by many insects for deriving compass information. Inspired by insects' polarized light compass, scientists have developed a new kind of navigation method. One of the key techniques in this method is the polarimetric sensor which is used to acquire direction information from skylight. In this paper, a polarization navigation sensor is proposed which imitates the working principles of the polarization vision systems of insects. We introduce the optical design and mathematical model of the sensor. In addition, a calibration method based on variable substitution and non-linear curve fitting is proposed. The results obtained from the outdoor experiments provide support for the feasibility and precision of the sensor. The sensor's signal processing can be well described using our mathematical model. A relatively high degree of accuracy in polarization measurement can be obtained without any error compensation. PMID:27527171
Waveform correlation methods for identifying populations of calibration events
Harris, D.B.
1997-07-01
An approach for systematically screening large volumes of continuous data for repetitive events identified as mining explosions on basis of temporal and amplitude population characteristics. The method extends event clustering through waveform correlation with a new source-region-specific detector. The new signal subspace detector generalizes the matched filter and can be used to increase the number of events associated with a given cluster, thereby increasing the reliability of diagnostic cluster population characteristics. The method can be applied to obtain bootstrap ground truth explosion waveforms for testing discriminants, where actual ground truth is absent. The same events, if associated with to a particular mine, may help calibrate velocity models. The method may also assist earthquake hazard risk assessment by providing what amounts to blasting logs for identified mines. The cluster event lists can be reconciled against earthquake catalogs to screen explosions, otherwise hard to identify from the catalogs.
A method of calibrating wind velocity sensors with a modified gas flow calibrator
NASA Technical Reports Server (NTRS)
Stump, H. P.
1978-01-01
A procedure was described for calibrating air velocity sensors in the exhaust flow of a gas flow calibrator. The average velocity in the test section located at the calibrator exhaust was verified from the mass flow rate accurately measured by the calibrator's precision sonic nozzles. Air at elevated pressures flowed through a series of screens, diameter changes, and flow straighteners, resulting in a smooth flow through the open test section. The modified system generated air velocities of 2 to 90 meters per second with an uncertainty of about two percent for speeds below 15 meters per second and four percent for the higher speeds. Wind tunnel data correlated well with that taken in the flow calibrator.
Calibration Methods for a 3D Triangulation Based Camera
NASA Astrophysics Data System (ADS)
Schulz, Ulrike; Böhnke, Kay
A sensor in a camera takes a gray level image (1536 x 512 pixels), which is reflected by a reference body. The reference body is illuminated by a linear laser line. This gray level image can be used for a 3D calibration. The following paper describes how a calibration program calculates the calibration factors. The calibration factors serve to determine the size of an unknown reference body.
Optoacoustic imaging quality enhancement based on geometrical super-resolution method
NASA Astrophysics Data System (ADS)
He, Hailong; Mandal, Subhamoy; Buehler, Andreas; Deán-Ben, X. Luís.; Razansky, Daniel; Ntziachristos, Vasilis
2016-03-01
In optoacoustic imaging, the resolution and image quality in a certain imaging position usually cannot be enhanced without changing the imaging configuration. Post-reconstruction image processing methods offer a new possibility to improve image quality and resolution. We have developed a geometrical super-resolution (GSR) method which uses information from spatially separated frames to enhance resolution and contrast in optoacoustic images. The proposed method acquires several low resolution images from the same object located at different positions inside the imaging plane. Thereafter, it applies an iterative registration algorithm to integrate the information in the acquired set of images to generate a single high resolution image. Herein, we present the method and evaluate its performance in simulation and phantom experiments, and results show that geometrical super-resolution techniques can be a promising alternative to enhance resolution in optoacoustic imaging.
Calibration of the DRASTIC ground water vulnerability mapping method
Rupert, M.G.
2001-01-01
Ground water vulnerability maps developed using the DRASTIC method have been produced in many parts of the world. Comparisons of those maps with actual ground water quality data have shown that the DRASTIC method is typically a poor predictor of ground water contamination. This study significantly improved the effectiveness of a modified DRASTIC ground water vulnerability map by calibrating the point rating schemes to actual ground water quality data by using nonparametric statistical techniques and a geographic information system. Calibration was performed by comparing data on nitrite plus nitrate as nitrogen (NO2 + NO3-N) concentrations in ground water to land-use, soils, and depth to first-encountered ground water data. These comparisons showed clear statistical differences between NO2 + NO3-N concentrations and the various categories. Ground water probability point ratings for NO2 + NO3-N contamination were developed from the results of these comparisons, and a probability map was produced. This ground water probability map was then correlated with an independent set of NO2 + NO3-N data to demonstrate its effectiveness in predicting elevated NO2 + NO3-N concentrations in ground water. This correlation demonstrated that the probability map was effective, but a vulnerability map produced with the uncalibrated DRASTIC method in the same area and using the same data layers was not effective. Considerable time and expense have been outlaid to develop ground water vulnerability maps with the DRASTIC method. This study demonstrates a cost-effective method to improve and verify the effectiveness of ground water vulnerability maps.
Method for Ground-to-Satellite Laser Calibration System
NASA Technical Reports Server (NTRS)
Lukashin, Constantine (Inventor); Wielicki, Bruce A. (Inventor)
2015-01-01
The present invention comprises an approach for calibrating the sensitivity to polarization, optics degradation, spectral and stray light response functions of instruments on orbit. The concept is based on using an accurate ground-based laser system, Ground-to-Space Laser Calibration (GSLC), transmitting laser light to instrument on orbit during nighttime substantially clear-sky conditions. To minimize atmospheric contribution to the calibration uncertainty the calibration cycles should be performed in short time intervals, and all required measurements are designed to be relative. The calibration cycles involve ground operations with laser beam polarization and wavelength changes.
Method for Ground-to-Space Laser Calibration System
NASA Technical Reports Server (NTRS)
Lukashin, Constantine (Inventor); Wielicki, Bruce A. (Inventor)
2014-01-01
The present invention comprises an approach for calibrating the sensitivity to polarization, optics degradation, spectral and stray light response functions of instruments on orbit. The concept is based on using an accurate ground-based laser system, Ground-to-Space Laser Calibration (GSLC), transmitting laser light to instrument on orbit during nighttime substantially clear-sky conditions. To minimize atmospheric contribution to the calibration uncertainty the calibration cycles should be performed in short time intervals, and all required measurements are designed to be relative. The calibration cycles involve ground operations with laser beam polarization and wavelength changes.
A review of some radiometric calibration problems and methods
NASA Technical Reports Server (NTRS)
Slater, P. N.
1984-01-01
The in-flight radiometric calibration instrumentation and procedures of the Landsat Thematic Mapper and the high-resolution visible-range instruments of SPOT are illustrated with drawings and diagrams, characterized, and compared. Problems encountered in the laboratory calibration process, minimizing the temporal instability of the systems, identifying anomalies in the electronics in flight, and rechecking the calibration are examined, and it is pointed out that the stability of the calibration systems is less than that of the instruments themselves. The use of carefully measured ground-site data and atmospheric parameters in combination with radiative-transfer models for periodic calibration is recommended.
Advances in calibration methods for micro- and nanoscale surfaces
NASA Astrophysics Data System (ADS)
Leach, R. K.; Giusca, C. L.; Coupland, J. M.
2012-04-01
Optical surface topography measuring instrument manufacturers often quote accuracies of the order of nanometres and claim that the instruments can reliably measure a range of surfaces with structures on the micro- to nanoscale. However, for many years there has been debate about the interpretation of the data from optical surface topography measuring instruments. Optical artefacts in the output data and a lack of a calibration infrastructure mean that it can be difficult to get optical instruments to agree with contact stylus instruments. In this paper, the current situation with areal surface topography measurements is discussed along with the ISO specification standards that are in draft form. An infrastructure is discussed whereby the ISO-defined metrological characteristics of optical instruments can be determined, but these characteristics do not allow the instrument to measure complex surfaces. Current research into methods for determining the transfer function of optical instruments is reviewed, which will allow the calibration of optical instruments to measure complex surfaces, at least in the case of weak scattering. The ability of some optical instruments to measure outside the spatial bandwidth limitation of the numerical aperture is presented and some general outlook for future work given.
NASA Astrophysics Data System (ADS)
Zhang, Ming; Gong, Wei; Ma, Yingying; Wang, Lunche; Chen, Zhongyong
2016-03-01
Sun photometric measurements, which provide accurate and timely information on atmospheric components such as aerosols, clouds, and gases are important to climate research. For regions with heavy and variable aerosol loading, the traditional Langley plot method cannot be applied for Sun photometric instrument calibration, as almost no suitable prolonged periods with stable atmosphere and low-aerosol loading occurs. An improved calibration method, namely, the transmission and division of total optical depth method, is proposed in this study. Atmospheric total optical depth variation information obtained via other methods is transmitted, and period groups with similar atmospheric extinction effects are selected for Langley regression. This method is validated through calibration of a multifilter rotating shadowband radiometer under heavy aerosol-loading conditions. The obtained aerosol optical depth (AOD) compares well with the interpolated AOD from a Cimel Sun-sky radiometer.
Geometrically Nonlinear Static Analysis of 3D Trusses Using the Arc-Length Method
NASA Technical Reports Server (NTRS)
Hrinda, Glenn A.
2006-01-01
Rigorous analysis of geometrically nonlinear structures demands creating mathematical models that accurately include loading and support conditions and, more importantly, model the stiffness and response of the structure. Nonlinear geometric structures often contain critical points with snap-through behavior during the response to large loads. Studying the post buckling behavior during a portion of a structure's unstable load history may be necessary. Primary structures made from ductile materials will stretch enough prior to failure for loads to redistribute producing sudden and often catastrophic collapses that are difficult to predict. The responses and redistribution of the internal loads during collapses and possible sharp snap-back of structures have frequently caused numerical difficulties in analysis procedures. The presence of critical stability points and unstable equilibrium paths are major difficulties that numerical solutions must pass to fully capture the nonlinear response. Some hurdles still exist in finding nonlinear responses of structures under large geometric changes. Predicting snap-through and snap-back of certain structures has been difficult and time consuming. Also difficult is finding how much load a structure may still carry safely. Highly geometrically nonlinear responses of structures exhibiting complex snap-back behavior are presented and analyzed with a finite element approach. The arc-length method will be reviewed and shown to predict the proper response and follow the nonlinear equilibrium path through limit points.
NASA Astrophysics Data System (ADS)
Riveiro, B.; DeJong, M.; Conde, B.
2016-06-01
Despite the tremendous advantages of the laser scanning technology for the geometric characterization of built constructions, there are important limitations preventing more widespread implementation in the structural engineering domain. Even though the technology provides extensive and accurate information to perform structural assessment and health monitoring, many people are resistant to the technology due to the processing times involved. Thus, new methods that can automatically process LiDAR data and subsequently provide an automatic and organized interpretation are required. This paper presents a new method for fully automated point cloud segmentation of masonry arch bridges. The method efficiently creates segmented, spatially related and organized point clouds, which each contain the relevant geometric data for a particular component (pier, arch, spandrel wall, etc.) of the structure. The segmentation procedure comprises a heuristic approach for the separation of different vertical walls, and later image processing tools adapted to voxel structures allows the efficient segmentation of the main structural elements of the bridge. The proposed methodology provides the essential processed data required for structural assessment of masonry arch bridges based on geometric anomalies. The method is validated using a representative sample of masonry arch bridges in Spain.
NASA Astrophysics Data System (ADS)
Nanda, Namita; Bandyopadhyay, J. N.
2009-08-01
The nonlinear transient response of composite shells with/without cutouts and initial geometric imperfection is investigated using the finite element method. The present formulation considers doubly curved shells incorporating von Kármán type nonlinear strains into the first order shear deformation theory. The analysis is carried out using quadratic C0 eight-noded isoparametric element. The governing nonlinear equations are solved by using the Newmark average acceleration method in the time integration in conjunction with modified Newton-Raphson iteration scheme. The validity of the model is demonstrated by comparing the present results with those available in the literature. Parametric studies are carried out varying the radius of curvature to width ratio and amplitude of initial geometric imperfection of laminated composite cylindrical, spherical and hyperbolic paraboloid shells with/without cutouts.
Geometric moire methods with enhanced sensitivity by optical/digital fringe multiplication
NASA Technical Reports Server (NTRS)
Han, B.; Ifju, P.; Post, D.
1993-01-01
A robust fringe-shifting and image processing scheme is applied to geometric moire experiments. High quality contour maps of U, V and W displacement fields are obtained with sensitivity enhanced by a factor of ten. The method is compatible with complicated intensity distributions, variable bar-to-space ratios of gratings, and optical noise. It is applicable to large fields for both in-plane moire and shadow moire measurements.
Method for in-situ calibration of electrophoretic analysis systems
Liu, Changsheng; Zhao, Hequan
2005-05-08
An electrophoretic system having a plurality of separation lanes is provided with an automatic calibration feature in which each lane is separately calibrated. For each lane, the calibration coefficients map a spectrum of received channel intensities onto values reflective of the relative likelihood of each of a plurality of dyes being present. Individual peaks, reflective of the influence of a single dye, are isolated from among the various sets of detected light intensity spectra, and these can be used to both detect the number of dye components present, and also to establish exemplary vectors for the calibration coefficients which may then be clustered and further processed to arrive at a calibration matrix for the system. The system of the present invention thus permits one to use different dye sets to tag DNA nucleotides in samples which migrate in separate lanes, and also allows for in-situ calibration with new, previously unused dye sets.
Simple method for calibrating omnidirectional stereo with multiple cameras
NASA Astrophysics Data System (ADS)
Ha, Jong-Eun; Choi, I.-Sak
2011-04-01
Cameras can give useful information for the autonomous navigation of a mobile robot. Typically, one or two cameras are used for this task. Recently, an omnidirectional stereo vision system that can cover the whole surrounding environment of a mobile robot is adopted. They usually adopt a mirror that cannot offer uniform spatial resolution. In this paper, we deal with an omnidirectional stereo system which consists of eight cameras where each two vertical cameras constitute one stereo system. Camera calibration is the first necessary step to obtain 3D information. Calibration using a planar pattern requires many images acquired under different poses so it is a tedious step to calibrate all eight cameras. In this paper, we present a simple calibration procedure using a cubic-type calibration structure that surrounds the omnidirectional stereo system. We can calibrate all the cameras on an omnidirectional stereo system in just one shot.
A novel plane method to the calibration of the thermal camera
NASA Astrophysics Data System (ADS)
Wang, Xunsi; Huang, Wei; Nie, Qiu-hua; Xu, Tiefeng; Dai, Shixun; Shen, Xiang; Cheng, Weihai
2009-07-01
This paper provides an up-to-date review of research efforts in thermal camera and target object recognition techniques based on two-dimensional (2D) images in the infrared (IR) spectra (8-12μm). From the geometric point of view, a special target plate was constructed with a radiation source of lamp excited that allows all of these devices to be calibrated geometrically along a radiance-based approach. The calibration theory and actual experimental procedures were described, then an automated measurement of the circle targets by image centroid algorithm. The key parameters of IR camera were calibrated out with 3 inner and 6 outer of Tsai model in thermal imaging. The subsequent data processing and analysis were then outlined. The 3D model from the successful calibration of a representative sample of the infrared array camera was presented and discussed. They provide much new and easy way to the geometric characteristics of these imagers that can be used in car-night-vision, medical, industrial, military, and environmental applications.
Combined non-contact coordinate measurement system and calibration method
NASA Astrophysics Data System (ADS)
Fan, Yiyan; Zhao, Bin
2015-07-01
A combined non-contact measurement system comprising attitude angle sensor, angle encoder, laser rangefinder, and total station is adopted to measure the spatial coordinate of the hidden zones in large-scale space. The laser from the total station is aimed at the optical system of the attitude angle sensor to obtain the spatial coordinate and the spatial attitude angles. Then, the angle encoder driven by a stepping motor is rotated to drive the laser rangefinder to direct at the measured point. This approach is used to obtain the distance from the rangefinder to the measured point and the angle of the angle encoder. Finally, the spatial coordinates of the measured point can be calculated by using these measured parameters. For the measurement system, we propose a weighted least squares (WLS) calibration method, in which weights are determined for the angular distribution density. Experimental results show that the measurement system could expand the scale and achieve reliable precision during combined measurement and the measurement error of the weighted least squares method is less than that of the ordinary least square (OLS) method.
Calibration Methods for Air Coupled Antennas - COST Action TU1208
NASA Astrophysics Data System (ADS)
Marecos, Vânia; Solla, Mercedes; Fontul, Simona; Pajewski, Lara
2016-04-01
This work focuses on the comparison of different methods for calibrating air coupled antennas: Coring, Surface Reflection Method (SRM) and Common Mid-Point (CMP) through the analysis of GPR data collected in a test site with different pavement solutions. Research activities have been carried out during a Short Term Scientific Mission (STSM) funded by the COST (European Cooperation in Science and Technology) Action TU1208 "Civil Engineering Applications of Ground Penetrating Radar" in December 2015. The use of GPR in transport infrastructures represents one of the most significant advances for obtaining continuous data along the road, with the advantage of operation at traffic speed and being a non-destructive technique. Its main application has been the evaluation of layer thickness. For the determination of layer thickness, it is necessary to know the velocity of the signal, which depends on the dielectric constant of the material, and the two-way travel time of the reflected signal that is recorded by the GPR system. The calculation of the dielectric value of the materials can be done using different approaches such as: using fixed values based on experience, laboratory determination of dielectric values, applying the SRM, performing back calculation from ground truth references such as cores and test pits, or using the CMP method. The problem with using ground truth is that it is time consuming, labour intensive and intrusive to traffic, in addition, a drill core is not necessarily representative of the whole surveyed area. Regarding the surface reflection technique, one of the problems is that it only measures the dielectric value from the layer surface and not from the whole layer. Recent works already started to address some of these challenges proposing new approaches for GPR layer thickness measurements using multiple antennas to calculate the average dielectric value of the asphalt layer, taking advantage of significant hardware improvements in GPR
Error analysis of the articulated flexible arm CMM based on geometric method
NASA Astrophysics Data System (ADS)
Wang, Xueying; Liu, Shugui; Zhang, Guoxiong; Wang, Bin
2006-11-01
In order to overcome the disadvantage of traditional CMM (Coordinate Measuring Machine), a new type of CMM with rotational joints and flexible arms named articulated arm flexible CMM is developed, in which linear measurements are substituted by angular ones. Firstly a quasi-spherical coordinate system is put forward, the ideal mathematical model of articulated arm flexible CMM is established. On the base of full analysis on the factors affecting the measurement accuracy, ideal mathematical model is modified to error model according to structural parameters and geometric errors. A geometric method is proposed to verify feasibility of error model, and the results convincingly show its validity. Position errors caused by different type of error sources are analyzed, and a theoretic base for introducing error compensation and improving the accuracy of articulated arm flexible CMM is established.
A note on geometric method-based procedures to calculate the Hurst exponent
NASA Astrophysics Data System (ADS)
Trinidad Segovia, J. E.; Fernández-Martínez, M.; Sánchez-Granero, M. A.
2012-03-01
Geometric method-based procedures, which we will call GM algorithms hereafter, were introduced in M.A. Sánchez-Granero, J.E. Trinidad Segovia, J. García Pérez, Some comments on Hurst exponent and the long memory processes on capital markets, Phys. A 387 (2008) 5543-5551, to calculate the Hurst exponent of a time series. The authors proved that GM algorithms, based on a geometrical approach, are more accurate than classical algorithms, especially with short length time series. The main contribution of this paper is to provide a mathematical background for the validity of these two algorithms to calculate the Hurst exponent H of random processes with stationary and self-affine increments. In particular, we show that these procedures are valid not only for exploring long memory in classical processes such as (fractional) Brownian motions, but also for estimating the Hurst exponent of (fractional) Lévy stable motions.
Canham, P B; Potter, R F; Woo, D
1984-01-01
The finer and more closely arrayed the capillaries are, the more efficiently oxygen will be transported to tissue because the same blood volume has greater contact area with the tissue and the diffusion distance for the oxygen is minimized. If these principles are actually governing microvascular structure, then the finest capillaries will be the narrowest channels which circulating erythrocytes can transit. Ascertaining the existence of this geometric limit requires quantitative data of demonstrated reliability on erythrocyte geometry and on capillary diameters. The study was done on Wistar rats. Constant flow perfusion of skeletal and cardiac muscle by a modified Batson's compound for anatomical casting made available rigid three-dimensional replicas of the microvasculature which shrank less than 1% when the tissue was digested with potassium hydroxide. Measurements of individual capillaries were made on high contrast scanning electron micrographs of the casts. Measurements on individual rat erythrocytes were done on photomicrographs of cells on edge. Reliability of these data was tested in three ways. First, repeatability of the tracing of the cell outline was tested by processing a duplicate set of photomicrographs. Secondly, correlations of the various parameters were found. Thirdly, results from other techniques of measuring erythrocytes were examined for areas of agreement and also for causes of possible error for areas in dispute. Because of known variability in erythrocyte sizes and shapes between species and between individuals within a species, we compared the data on erythrocyte geometry and capillary diameters for samples taken from the same individual rat. The data revealed a very positive indication that the lowest range of capillary diameters were at the limits of deformation of the circulating erythrocytes. Ninety-five per cent of the erythrocytes sampled could pass through a channel 2.9 micron in diameter. A small number of the capillaries
Optimal calibration method for water distribution water quality model.
Wu, Zheng Yi
2006-01-01
A water quality model is to predict water quality transport and fate throughout a water distribution system. The model is not only a promising alternative for analyzing disinfectant residuals in a cost-effective manner, but also a means of providing enormous engineering insights into the characteristics of water quality variation and constituent reactions. However, a water quality model is a reliable tool only if it predicts what a real system behaves. This paper presents a methodology that enables a modeler to efficiently calibrate a water quality model such that the field observed water quality values match with the model simulated values. The method is formulated to adjust the global water quality parameters and also the element-dependent water quality reaction rates for pipelines and tank storages. A genetic algorithm is applied to optimize the model parameters by minimizing the difference between the model-predicted values and the field-observed values. It is seamlessly integrated with a well-developed hydraulic and water quality modeling system. The approach has provided a generic tool and methodology for engineers to construct the sound water quality model in expedient manner. The method is applied to a real water system and demonstrated that a water quality model can be optimized for managing adequate water supply to public communities. PMID:16854809
Geometric correction method of rotary scanning hyperspectral image in agriculture application
NASA Astrophysics Data System (ADS)
Wan, Peng; Yang, Guijun; Xu, Bo; Feng, Haikuan; Yu, Haiyang
2015-04-01
In order to meet the demand of farmland plot experiments hyperspectral images acquisition, an equipment that incorporating an aerial lift vehicle with hyperspectral imager was proposed. In this manner, high spatial resolution (in millimeter) imageries were collected, which meets the need of spatial resolution on farm experiments, but also improves the efficiency of image acquisition. In allusion to the image circular geometric distortion which produced by telescopic arm rotation, an image rectification method that based on mounted position and orientation system was proposed. Experimental results shows that the image rectification method is effective.
Partially Strong Transparency Conditions and a Singular Localization Method In Geometric Optics
NASA Astrophysics Data System (ADS)
Lu, Yong; Zhang, Zhifei
2016-03-01
This paper focuses on the stability analysis of WKB approximate solutions in geometric optics with the absence of strong transparency conditions under the terminology of Joly, Métivier and Rauch. We introduce a compatible condition and a singular localization method which allows us to prove the stability of WKB solutions over long time intervals. This compatible condition is weaker than the strong transparency condition. The singular localization method allows us to do delicate analysis near resonances. As an application, we show the long time approximation of Klein-Gordon equations by Schrödinger equations in the non-relativistic limit regime.
Jia, Zhenyuan; Yang, Jinghao; Liu, Wei; Wang, Fuji; Liu, Yang; Wang, Lingli; Fan, Chaonan; Zhao, Kai
2015-06-15
High-precision calibration of binocular vision systems plays an important role in accurate dimensional measurements. In this paper, an improved camera calibration method is proposed. First, an accurate intrinsic parameters calibration method based on active vision with perpendicularity compensation is developed. Compared to the previous work, this method eliminates the effect of non-perpendicularity of the camera motion on calibration accuracy. The principal point, scale factors, and distortion factors are calculated independently in this method, thereby allowing the strong coupling of these parameters to be eliminated. Second, an accurate global optimization method with only 5 images is presented. The results of calibration experiments show that the accuracy of the calibration method can reach 99.91%. PMID:26193503
Gietzelt, Matthias; Wolf, Klaus-Hendrik; Marschollek, Michael; Haux, Reinhold
2013-07-01
Calibration of accelerometers can be reduced to 3D-ellipsoid fitting problems. Changing extrinsic factors like temperature, pressure or humidity, as well as intrinsic factors like the battery status, demand to calibrate the measurements permanently. Thus, there is a need for fast calibration algorithms, e.g. for online analyses. The primary aim of this paper is to propose a non-iterative calibration algorithm for accelerometers with the focus on minimal execution time and low memory consumption. The secondary aim is to benchmark existing calibration algorithms based on 3D-ellipsoid fitting methods. We compared the algorithms regarding the calibration quality and the execution time as well as the number of quasi-static measurements needed for a stable calibration. As evaluation criterion for the calibration, both the norm of calibrated real-life measurements during inactivity and simulation data was used. The algorithms showed a high calibration quality, but the execution time differed significantly. The calibration method proposed in this paper showed the shortest execution time and a very good performance regarding the number of measurements needed to produce stable results. Furthermore, this algorithm was successfully implemented on a sensor node and calibrates the measured data on-the-fly while continuously storing the measured data to a microSD-card. PMID:23566707
NASA Astrophysics Data System (ADS)
Hu, Zhan; Zheng, Gangtie
2016-08-01
A combined analysis method is developed in the present paper for studying the dynamic properties of a type of geometrically nonlinear vibration isolator, which is composed of push-pull configuration rings. This method combines the geometrically nonlinear theory of curved beams and the Harmonic Balance Method to overcome the difficulty in calculating the vibration and vibration transmissibility under large deformations of the ring structure. Using the proposed method, nonlinear dynamic behaviors of this isolator, such as the lock situation due to the coulomb damping and the usual jump resulting from the nonlinear stiffness, can be investigated. Numerical solutions based on the primary harmonic balance are first verified by direct integration results. Then, the whole procedure of this combined analysis method is demonstrated and validated by slowly sinusoidal sweeping experiments with different amplitudes of the base excitation. Both numerical and experimental results indicate that this type of isolator behaves as a hardening spring with increasing amplitude of the base excitation, which makes it suitable for isolating both steady-state vibrations and transient shocks.
NASA Astrophysics Data System (ADS)
Baatz, R.; Bogena, H. R.; Hendricks Franssen, H.-J.; Huisman, J. A.; Qu, W.; Montzka, C.; Vereecken, H.
2014-08-01
The objective of this work was to assess the accuracy of soil water content determination from neutron flux measured by cosmic-ray probes under humid climate conditions. Ten cosmic-ray probes were set up in the Rur catchment located in western Germany, and calibrated by gravimetric soil sampling campaigns. Aboveground biomass was estimated at the sites to investigate the role of vegetation cover on the neutron flux and the calibration procedure. Three parameterization methods were used to generate site-specific neutron flux - soil water content calibration curves: (i) the N0-method, (ii) the hydrogen molar fraction method (hmf-method), and (iii) the COSMIC-method. At five locations, calibration measurements were repeated to evaluate site-specific calibration parameters obtained in two different sampling campaigns. At two locations, soil water content determined by cosmic-ray probes was evaluated with horizontally and vertically weighted soil water content measurements of two distributed in situ soil water content sensor networks. All three methods were successfully calibrated to determine field scale soil water content continuously at the ten sites. The hmf-method and the COSMIC-method had more similar calibration curves than the N0-method. The three methods performed similarly well in the validation and errors were within the uncertainty of neutron flux measurements despite observed differences in the calibration curves and variable model complexity. In addition, we found that the obtained calibration parameters NCOSMIC, N0 and NS showed a strong correlation with aboveground biomass.
Real Time Calibration Method for Signal Conditioning Amplifiers
NASA Technical Reports Server (NTRS)
Medelius, Pedro J. (Inventor); Mata, Carlos T. (Inventor); Eckhoff, Anthony (Inventor); Perotti, Jose (Inventor); Lucena, Angel (Inventor)
2004-01-01
A signal conditioning amplifier receives an input signal from an input such as a transducer. The signal is amplified and processed through an analog to digital converter and sent to a processor. The processor estimates the input signal provided by the transducer to the amplifier via a multiplexer. The estimated input signal is provided as a calibration voltage to the amplifier immediately following the receipt of the amplified input signal. The calibration voltage is amplified by the amplifier and provided to the processor as an amplified calibration voltage. The amplified calibration voltage is compared to the amplified input signal, and if a significant error exists, the gain and/or offset of the amplifier may be adjusted as necessary.
Two-Step Camera Calibration Method Developed for Micro UAV'S
NASA Astrophysics Data System (ADS)
Gašparović, M.; Gajski, D.
2016-06-01
The development of unmanned aerial vehicles (UAVs) and continuous price reduction of unmanned systems attracted us to this research. Professional measuring systems are dozens of times more expensive and often heavier than "amateur", non-metric UAVs. For this reason, we tested the DJI Phantom 2 Vision Plus UAV. Phantom's smaller mass and velocity can develop less kinetic energy in relation to the professional measurement platforms, which makes it potentially less dangerous for use in populated areas. In this research, we wanted to investigate the ability of such non-metric UAV and find the procedures under which this kind of UAV may be used for the photogrammetric survey. It is important to emphasize that UAV is equipped with an ultra wide-angle camera with 14MP sensor. Calibration of such cameras is a complex process. In the research, a new two-step process is presented and developed, and the results are compared with standard one-step camera calibration procedure. Two-step process involves initially removed distortion on all images, and then uses these images in the phototriangulation with self-calibration. The paper presents statistical indicators which proved that the proposed two-step process is better and more accurate procedure for calibrating those types of cameras than standard one-step calibration. Also, we suggest two-step calibration process as the standard for ultra-wideangle cameras for unmanned aircraft.
A simple and flexible calibration method of non-overlapping camera rig
NASA Astrophysics Data System (ADS)
Guan, Banglei; Shang, Yang; Yu, Qifeng; Lei, Zhihui; Zhang, Xiaohu
2015-05-01
A simple and flexible method for non-overlapping camera rig calibration that includes camera calibration and relative poses calibration is presented. The proposed algorithm gives the solutions of the cameras parameters and the relative poses simultaneously by using nonlinear optimization. Firstly, the intrinsic and extrinsic parameters of each camera in the rig are estimated individually. Then, a linear solution derived from hand-eye calibration scheme is proposed to compute an initial estimate of the relative poses inside the camera rig. Finally, combined non-linear refinement of all parameters is performed, which optimizes the intrinsic parameters, the extrinsic parameters and relative poses of the coupled camera at the same time. We develop and test a novel approach for calibrating the parameters of non-overlapping camera rig using camera calibration and hand-eye calibration method. The method is designed inter alia for the purpose of deformation measurement using the calibrated rig. Compared the camera calibration with hand-eye calibration separately, our joint calibration is more convenient in practice application. Experimental data shows our algorithm is feasible and effective.
Optical geometry calibration method for free-form digital tomosynthesis
NASA Astrophysics Data System (ADS)
Chtcheprov, Pavel; Hartman, Allison; Shan, Jing; Lee, Yueh Z.; Zhou, Otto; Lu, Jianping
2016-03-01
Digital tomosynthesis is a type of limited angle tomography that allows 3D information to be reconstructed from a set of x-ray projection images taken at various angles using an x-ray tube, a mechanical arm to rotate the tube about the object, and a digital detector. Tomosynthesis reconstruction requires the precise location of the detector with respect to each x-ray source, forcing all current clinical tomosynthesis systems to use a physically coupled source and detector so the geometry is always known and is always the same. This limits the imaging geometries and its large size is impractical for mobile or field operations. To counter this, we have developed a free form tomosynthesis with a decoupled, free-moving source and detector that uses a novel optical method for accurate and real-time geometry calibration to allow for manual, hand-held tomosynthesis and even CT imaging. We accomplish this by using a camera, attached to the source, to track the motion of the source relative to the detector. Attached to the detector is an optical pattern and the image captured by the camera is then used to determine the relative camera/pattern position and orientation by analyzing the pattern distortion and calculating the source positions for each projection, necessary for 3D reconstruction. This allows for portable imaging in the field and also as an inexpensive upgrade to existing 2D systems, such as in developing countries, to provide 3D image data. Here we report the first feasibility demonstrations of free form digital tomosynthesis systems using the method.
Dong, Ren G.; Welcome, Daniel E.; McDowell, Thomas W.; Wu, John Z.
2015-01-01
While simulations of the measured biodynamic responses of the whole human body or body segments to vibration are conventionally interpreted as summaries of biodynamic measurements, and the resulting models are considered quantitative, this study looked at these simulations from a different angle: model calibration. The specific aims of this study are to review and clarify the theoretical basis for model calibration, to help formulate the criteria for calibration validation, and to help appropriately select and apply calibration methods. In addition to established vibration theory, a novel theorem of mechanical vibration is also used to enhance the understanding of the mathematical and physical principles of the calibration. Based on this enhanced understanding, a set of criteria was proposed and used to systematically examine the calibration methods. Besides theoretical analyses, a numerical testing method is also used in the examination. This study identified the basic requirements for each calibration method to obtain a unique calibration solution. This study also confirmed that the solution becomes more robust if more than sufficient calibration references are provided. Practically, however, as more references are used, more inconsistencies can arise among the measured data for representing the biodynamic properties. To help account for the relative reliabilities of the references, a baseline weighting scheme is proposed. The analyses suggest that the best choice of calibration method depends on the modeling purpose, the model structure, and the availability and reliability of representative reference data. PMID:26740726
NASA Astrophysics Data System (ADS)
Dong, Ren G.; Welcome, Daniel E.; McDowell, Thomas W.; Wu, John Z.
2015-11-01
While simulations of the measured biodynamic responses of the whole human body or body segments to vibration are conventionally interpreted as summaries of biodynamic measurements, and the resulting models are considered quantitative, this study looked at these simulations from a different angle: model calibration. The specific aims of this study are to review and clarify the theoretical basis for model calibration, to help formulate the criteria for calibration validation, and to help appropriately select and apply calibration methods. In addition to established vibration theory, a novel theorem of mechanical vibration is also used to enhance the understanding of the mathematical and physical principles of the calibration. Based on this enhanced understanding, a set of criteria was proposed and used to systematically examine the calibration methods. Besides theoretical analyses, a numerical testing method is also used in the examination. This study identified the basic requirements for each calibration method to obtain a unique calibration solution. This study also confirmed that the solution becomes more robust if more than sufficient calibration references are provided. Practically, however, as more references are used, more inconsistencies can arise among the measured data for representing the biodynamic properties. To help account for the relative reliabilities of the references, a baseline weighting scheme is proposed. The analyses suggest that the best choice of calibration method depends on the modeling purpose, the model structure, and the availability and reliability of representative reference data.
Research on method of geometry and spectral calibration of pushbroom dispersive hyperspectral imager
NASA Astrophysics Data System (ADS)
He, Zhiping; Shu, Rong; Wang, Jianyu
2012-11-01
Development and application of airborne and aerospace hyperspectral imager press for high precision geometry and spectral calibration of pixels of image cube. The research of geometry and spectral calibration of pushbroom hyperspectral imager, its target is giving the coordinate of angle field of view and center wavelength of each detect unit in focal plane detector of hyperspectral imager, and achieves the high precision, full field of view, full channel geometry and spectral calibration. It is importance for imaging quantitative and deep application of hyperspectal imager. The paper takes the geometry and spectral calibration of pushbroom dispersive hyperspectral imager as case study, and research on the constitution and analysis of imaging mathematical model. Aimed especially at grating-dispersive hyperspectral imaging, the specialty of the imaging mode and dispersive method has been concretely analyzed. Based on the analysis, the theory and feasible method of geometry and spectral calibration of dispersive hyperspectral imager is set up. The key technique has been solved is As follows: 1). the imaging mathematical model and feasible method of geometry and spectral calibration for full pixels of image cube has been set up, the feasibility of the calibration method has been analyzed. 2). the engineering model and method of the geometry and spectral calibration of pushbroom dispersive hyperspectral imager has been set up and the calibration equipment has been constructed, and the calibration precision has been analyzed.
NASA Astrophysics Data System (ADS)
Masuda, Kazuhiko; Ishimoto, Hiroshi; Sakai, Tetsu; Okamoto, Hajime
2016-06-01
Backscattering properties of ice crystal models (Voronoi aggregates (VA), hexagonal columns (COL), and six-branched bullet rosettes (BR6)) are calculated by using geometrical-opticsintegral-equation (GOIE) method. Characteristics of depolarization ratio (δ) and lidar ratio (L) of the crystal models are examined. δ (L) values are 0.2~0.3 (4~50), 0.3~0.4 (10~25), and 0.5~0.6 (50~100) for COL, BR6, and VA, respectively, at wavelength λ=0.532 μm. It is found that small deformation of COL model could produce significant changes in δ and L.
Hourdakis, Costas J; Büermann, Ludwig; Ciraj-Bjelac, Olivera; Csete, Istvan; Delis, Harry; Gomola, Igor; Persson, Linda; Novak, Leos; Petkov, Ivailo; Toroi, Paula
2016-01-01
A comparison of calibration results and procedures in terms of air kerma length product, PKL, and air kerma, K, was conducted between eight dosimetry laboratories. A pencil-type ionization chamber (IC), generally used for computed tomography dose measurements, was calibrated according to three calibration methods, while its residual signal and other characteristics (sensitivity profile, active length) were assessed. The results showed that the "partial irradiation method" is the preferred method for the pencil-type IC calibration in terms of PKL and it could be applied by the calibration laboratories successfully. Most of the participating laboratories achieved high level of agreement (>99%) for both dosimetry quantities (PKL and K). Estimated relative standard uncertainties of comparison results vary among laboratories from 0.34% to 2.32% depending on the quantity, beam quality and calibration method applied. Detailed analysis of the assigned uncertainties have been presented and discussed. PMID:26508013
Fast Geometric Method for Calculating Accurate Minimum Orbit Intersection Distances (MOIDs)
NASA Astrophysics Data System (ADS)
Wiźniowski, T.; Rickman, H.
2013-06-01
We present a new method to compute Minimum Orbit Intersection Distances (MOIDs) for arbitrary pairs of heliocentric orbits and compare it with Giovanni Gronchi's algebraic method. Our procedure is numerical and iterative, and the MOID configuration is found by geometric scanning and tuning. A basic element is the meridional plane, used for initial scanning, which contains one of the objects and is perpendicular to the orbital plane of the other. Our method also relies on an efficient tuning technique in order to zoom in on the MOID configuration, starting from the first approximation found by scanning. We work with high accuracy and take special care to avoid the risk of missing the MOID, which is inherent to our type of approach. We demonstrate that our method is both fast, reliable and flexible. It is freely available and its source Fortran code downloadable via our web page.
Geometrical force constraint method for vessel and x-ray angiogram simulation.
Song, Shuang; Yang, Jian; Fan, Jingfan; Cong, Weijian; Ai, Danni; Zhao, Yitian; Wang, Yongtian
2016-01-01
This study proposes a novel geometrical force constraint method for 3-D vasculature modeling and angiographic image simulation. For this method, space filling force, gravitational force, and topological preserving force are proposed and combined for the optimization of the topology of the vascular structure. The surface covering force and surface adhesion force are constructed to drive the growth of the vasculature on any surface. According to the combination effects of the topological and surface adhering forces, a realistic vasculature can be effectively simulated on any surface. The image projection of the generated 3-D vascular structures is simulated according to the perspective projection and energy attenuation principles of X-rays. Finally, the simulated projection vasculature is fused with a predefined angiographic mask image to generate a realistic angiogram. The proposed method is evaluated on a CT image and three generally utilized surfaces. The results fully demonstrate the effectiveness and robustness of the proposed method. PMID:26890908
Geometric methods in computer vision; Proceedings of the Meeting, San Diego, CA, July 25, 26, 1991
Vemuri, B.C.
1991-01-01
Various papers on geometric methods in computer vision are presented. Individual topics addressed include: mathematical theories of shape and the modeling of perception, free-form shape representation and deformable surfaces, new method for sensor data fusion in machine vision, spatial and temporal surface interpolation using wavelet bases, differential properties from adaptive thin-plate splines, shape metrics from curvature-scale spaced and curvature-tuned smoothing, energy functions for regularization algorithms, direct method for reconstructing shape from shading, coupled depth-slope model based on augmented Lagrangian techniques, physically based and probabilistic models for computer vision, probabilistic modeling of surfaces. Also discussed are: recognition and positioning of rigid objects using algebraic moment invariants, contour estimation using global shape constraints and local forces, recognizing human eyes, face recognition based on depth maps and surface curvature, model-based surface classification, hierarchical decomposition and axial representation of shape, direct computation of geometric features from motion disparities and shading, invariant feature matching in parameter space with application to line features, spatiotemporal curvature measures for flowfield analysis, primary set of characteristic views for 3D objects, image representation by integrating curvatures and Delaunay triangulations, 3D reconstruction using virtual planes and horopters.
NASA Astrophysics Data System (ADS)
Liao, Fei; Ye, Zhengyin
2015-12-01
Despite significant progress in recent computational techniques, the accurate numerical simulations, such as direct-numerical simulation and large-eddy simulation, are still challenging. For accurate calculations, the high-order finite difference method (FDM) is usually adopted with coordinate transformation from body-fitted grid to Cartesian grid. But this transformation might lead to failure in freestream preservation with the geometric conservation law (GCL) violated, particularly in high-order computations. GCL identities, including surface conservation law (SCL) and volume conservation law (VCL), are very important in discretization of high-order FDM. To satisfy GCL, various efforts have been made. An early and successful approach was developed by Thomas and Lombard [6] who used the conservative form of metrics to cancel out metric terms to further satisfy SCL. Visbal and Gaitonde [7] adopted this conservative form of metrics for SCL identities and satisfied VCL identity through invoking VCL equation to acquire the derivative of Jacobian in computation on moving and deforming grids with central compact schemes derived by Lele [5]. Later, using the metric technique from Visbal and Gaitonde [7], Nonomura et al. [8] investigated the freestream and vortex preservation properties of high-order WENO and WCNS on stationary curvilinear grids. A conservative metric method (CMM) was further developed by Deng et al. [9] with stationary grids, and detailed discussion about the innermost difference operator of CMM was shown with proof and corresponding numerical test cases. Noticing that metrics of CMM is asymmetrical without coordinate-invariant property, Deng et al. proposed a symmetrical CMM (SCMM) [12] by using the symmetric forms of metrics derived by Vinokur and Yee [10] to further eliminate asymmetric metric errors with stationary grids considered only. The research from Abe et al. [11] presented new asymmetric and symmetric conservative forms of time metrics and
NASA Technical Reports Server (NTRS)
Stoll, Frederick; Gurdal, Zafer; Starnes, James H., Jr.
1991-01-01
A method was developed for the geometrically nonlinear analysis of the static response of thin-walled stiffened composite structures loaded in uniaxial or biaxial compression. The method is applicable to arbitrary prismatic configurations composed of linked plate strips, such as stiffened panels and thin-walled columns. The longitudinal ends of the structure are assumed to be simply supported, and geometric shape imperfections can be modeled. The method can predict the nonlinear phenomena of postbuckling strength and imperfection sensitivity which are exhibited by some buckling-dominated structures. The method is computer-based and is semi-analytic in nature, making it computationally economical in comparison to finite element methods. The method uses a perturbation approach based on the use of a series of buckling mode shapes to represent displacement contributions associated with nonlinear response. Displacement contributions which are of second order in the model amplitudes are incorported in addition to the buckling mode shapes. The principle of virtual work is applied using a finite basis of buckling modes, and terms through the third order in the model amplitudes are retained. A set of cubic nonlinear algebraic equations are obtained, from which approximate equilibrium solutions are determined. Buckling mode shapes for the general class of structure are obtained using the VIPASA analysis code within the PASCO stiffened-panel design code. Thus, subject to some additional restrictions in loading and plate anisotropy, structures which can be modeled with respect to buckling behavior by VIPASA can be analyzed with respect to nonlinear response using the new method. Results obtained using the method are compared with both experimental and analytical results in the literature. The configurations investigated include several different unstiffened and blade-stiffening panel configurations, featuring both homogeneous, isotropic materials, and laminated composite
A robust method for determining calibration coefficients for VIIRS reflective solar bands
NASA Astrophysics Data System (ADS)
Ji, Qiang; McIntire, Jeffrey; Efremova, Boryana; Schwarting, Thomas; Oudrari, Hassan; Zeng, Jinan; Xiong, Xiaoxiong
2015-09-01
This paper presents a robust method for determining the calibration coefficients in polynomial calibration equations, and discusses the corresponding calibration uncertainties. An attenuator method that takes into account all measurements with and without an attenuator screen was used to restrict the impact of the absolute calibration of the light source. The originally proposed procedure attempts to simultaneously determine all unknowns nonlinearly using polynomial curve fitting. The newly proposed method divides the task into two simpler parts. For example, in the case of a quadratic calibration equation, the first part becomes a quadratic equation solely for the transmittance of attenuator, which has an analytical solution using three or four sets of measurements. Additionally, it is straightforward to determine the median value and the standard deviation of the transmittance from the solutions using all combinations of measured data points. In conjunction, the second part becomes a linear fit, with the ratio of the zeroth-order to first-order calibration coefficients as the intercept and the ratio of the second-order to first-order calibration coefficients as the slope. These ratios are unaffected by the absolute calibration of the light source and are then used in the calibration equation to calculate the first-order calibration coefficient. How the new method works is straightforward to visualize, which makes its results easier to verify. This is demonstrated using measurements from the Joint Polar Satellite System (JPSS) J1 Visible Infrared Imaging Radiometer Suite (VIIRS) reflective solar bands (RSB) pre-launch testing.
Model Robust Calibration: Method and Application to Electronically-Scanned Pressure Transducers
NASA Technical Reports Server (NTRS)
Walker, Eric L.; Starnes, B. Alden; Birch, Jeffery B.; Mays, James E.
2010-01-01
This article presents the application of a recently developed statistical regression method to the controlled instrument calibration problem. The statistical method of Model Robust Regression (MRR), developed by Mays, Birch, and Starnes, is shown to improve instrument calibration by reducing the reliance of the calibration on a predetermined parametric (e.g. polynomial, exponential, logarithmic) model. This is accomplished by allowing fits from the predetermined parametric model to be augmented by a certain portion of a fit to the residuals from the initial regression using a nonparametric (locally parametric) regression technique. The method is demonstrated for the absolute scale calibration of silicon-based pressure transducers.
Calibration of AVHRR sensors using the reflectance-based method
NASA Astrophysics Data System (ADS)
Czapla-Myers, Jeffrey S.; Thome, Kurtis J.; Leisso, Nathan P.
2007-09-01
The Remote Sensing Group at the University of Arizona has been active in the vicarious calibration of numerous sensors through the use of ground-based test sites. Recent efforts have included work to develop cross-calibration information between these sensors using the results from the reflectance-based approach. The current work extends the cross-calibration to the AVHRR series of sensors, specifically NOAA-17, and NOAA-18. The results include work done based on data collected by ground-based personnel nearly coincident with the sensor overpasses. The available number of calibrations for the AVHRR series is increased through a set of ground-based radiometers that are deployed without the need for on-site personnel and have been operating for more than three years at Railroad Valley Playa. The spectral, spatial, and temporal characteristics of the 1-km2 large-footprint site at Railroad Valley are well understood. It is therefore well suited for the radiometric calibration of AVHRR, which has a nadir-viewing footprint of 1.1 x 1.1 km. The at-sensor radiance is predicted via a radiative transfer code using atmospheric data from a fully-automated solar radiometer. The results for AVHRR show that errors are currently larger for the automated data sets, but results indicate that the AVHRR sensors studied in this work are consistent with the Aqua and Terra MODIS sensors to within the uncertainties of each sensor.
Indoor Calibration for Stereoscopic Camera STC, A New Method
NASA Astrophysics Data System (ADS)
Simioni, E.; Re, C.; Da Deppo, V.; Naletto, G.; Borrelli, D.; Dami, M.; Ficai Veltroni, I.; Cremonese, G.
2014-10-01
In the framework of the ESA-JAXA BepiColombo mission to Mercury, the global mapping of the planet will be performed by the on-board Stereo Camera (STC), part of the SIMBIO-SYS suite [1]. In this paper we propose a new technique for the validation of the 3D reconstruction of planetary surface from images acquired with a stereo camera. STC will provide a three-dimensional reconstruction of Mercury surface. The generation of a DTM of the observed features is based on the processing of the acquired images and on the knowledge of the intrinsic and extrinsic parameters of the optical system. The new stereo concept developed for STC needs a pre-flight verification of the actual capabilities to obtain elevation information from stereo couples: for this, a stereo validation setup to get an indoor reproduction of the flight observing condition of the instrument would give a much greater confidence to the developed instrument design. STC is the first stereo satellite camera with two optical channels converging in a unique sensor. Its optical model is based on a brand new concept to minimize mass and volume and to allow push-frame imaging. This model imposed to define a new calibration pipeline to test the reconstruction method in a controlled ambient. An ad-hoc indoor set-up has been realized for validating the instrument designed to operate in deep space, i.e. in-flight STC will have to deal with source/target essentially placed at infinity. This auxiliary indoor setup permits on one side to rescale the stereo reconstruction problem from the operative distance in-flight of 400 km to almost 1 meter in lab; on the other side it allows to replicate different viewing angles for the considered targets. Neglecting for sake of simplicity the Mercury curvature, the STC observing geometry of the same portion of the planet surface at periherm corresponds to a rotation of the spacecraft (SC) around the observed target by twice the 20Â° separation of each channel with respect to nadir
NASA Astrophysics Data System (ADS)
Naughton, Denis; Brunn, Andreas; Czapla-Myers, Jeff; Douglass, Scott; Thiele, Michael; Weichelt, Horst; Oxfort, Michael
2011-01-01
RapidEye AG is a commercial provider of geospatial information products and customized solutions derived from Earth observation image data. The source of the data is the RapidEye constellation consisting of five low-earth-orbit imaging satellites. We describe the rationale, methods, and results of a reflectance-based vicarious calibration campaign that was conducted between April 2009 and May 2010 at Railroad Valley Playa and Ivanpah Playa to determine the on-orbit radiometric accuracy of the RapidEye sensor. In situ surface spectral reflectance measurements of known ground targets and an assessment of the atmospheric conditions above the sites were taken during spacecraft overpasses. The ground data are used as input to a radiative transfer code to compute a band-specific top-of-atmosphere spectral radiance. A comparison of these predicted values based on absolute physical data to the measured at-sensor spectral radiance provide the absolute calibration of the sensor. Initial assessments show that the RapidEye sensor response is within 8% of the predicted values. Outcomes from this campaign are then used to update the calibration parameters in the ground segment processing system. Subsequent verification events confirmed that the measured RapidEye response improved to within 4% of the predictions based on the vicarious calibration method.
Calibration of three rainfall simulators with automatic measurement methods
NASA Astrophysics Data System (ADS)
Roldan, Margarita
2010-05-01
CALIBRATION OF THREE RAINFALL SIMULATORS WITH AUTOMATIC MEASUREMENT METHODS M. Roldán (1), I. Martín (2), F. Martín (2), S. de Alba(3), M. Alcázar(3), F.I. Cermeño(3) 1 Grupo de Investigación Ecología y Gestión Forestal Sostenible. ECOGESFOR-Universidad Politécnica de Madrid. E.U.I.T. Forestal. Avda. Ramiro de Maeztu s/n. Ciudad Universitaria. 28040 Madrid. margarita.roldan@upm.es 2 E.U.I.T. Forestal. Avda. Ramiro de Maeztu s/n. Ciudad Universitaria. 28040 Madrid. 3 Facultad de Ciencias Geológicas. Universidad Complutense de Madrid. Ciudad Universitaria s/n. 28040 Madrid The rainfall erosivity is the potential ability of rain to cause erosion. It is function of the physical characteristics of rainfall (Hudson, 1971). Most expressions describing erosivity are related to kinetic energy or momentum and so with drop mass or size and fall velocity. Therefore, research on factors determining erosivity leds to the necessity to study the relation between fall height and fall velocity for different drop sizes, generated in a rainfall simulator (Epema G.F.and Riezebos H.Th, 1983) Rainfall simulators are one of the most used tools for erosion studies and are used to determine fall velocity and drop size. Rainfall simulators allow repeated and multiple measurements The main reason for use of rainfall simulation as a research tool is to reproduce in a controlled way the behaviour expected in the natural environment. But in many occasions when simulated rain is used in order to compare it with natural rain, there is a lack of correspondence between natural and simulated rain and this can introduce some doubt about validity of data because the characteristics of natural rain are not adequately represented in rainfall simulation research (Dunkerley D., 2008). Many times the rainfall simulations have high rain rates and they do not resemble natural rain events and these measures are not comparables. And besides the intensity is related to the kinetic energy which
Methods to calibrate the absolute receive sensitivity of single-element, focused transducers
Rich, Kyle T.; Mast, T. Douglas
2015-01-01
Absolute pressure measurements of acoustic emissions by single-element, focused passive cavitation detectors would be facilitated by improved wideband receive calibration techniques. Here, calibration methods were developed to characterize the absolute, frequency-dependent receive sensitivity of a spherically focused, single-element transducer using pulse-echo and pitch-catch techniques. Validation of these calibration methods on a focused receiver were made by generating a pulse from a small diameter source at the focus of the transducer and comparing the absolute pressure measured by a calibrated hydrophone to that of the focused transducer using the receive sensitivities determined here. PMID:26428812
Methods to calibrate the absolute receive sensitivity of single-element, focused transducers.
Rich, Kyle T; Mast, T Douglas
2015-09-01
Absolute pressure measurements of acoustic emissions by single-element, focused passive cavitation detectors would be facilitated by improved wideband receive calibration techniques. Here, calibration methods were developed to characterize the absolute, frequency-dependent receive sensitivity of a spherically focused, single-element transducer using pulse-echo and pitch-catch techniques. Validation of these calibration methods on a focused receiver were made by generating a pulse from a small diameter source at the focus of the transducer and comparing the absolute pressure measured by a calibrated hydrophone to that of the focused transducer using the receive sensitivities determined here. PMID:26428812
A method for intensity calibration of an electron spectrometer with multi-angle detection
NASA Astrophysics Data System (ADS)
Ábrók, Levente; Buhr, Ticia; Kövér, Ákos; Balog, Róbert; Hatvani, Dávid; Herczku, Péter; Kovács, Sándor; Ricz, Sándor
2016-02-01
A special electrostatic electron spectrometer designed for precise and unique experiments and an intensity calibration method for universal application in electron spectroscopy are presented. The upgrade of the analyzer enables the intensity calibration at arbitrary electron energies using elastically scattered electrons. In order to test the calibration procedure the double differential (in energy and angle) ionization cross sections (DDCS) of electrons ejected from 300 keV proton-argon collisions were measured and compared with the data of Rudd et al. [1]. The good agreement between the two data sets verifies the applicability of the calibration method.
Analytical calculation of spectral phase of grism pairs by the geometrical ray tracing method
NASA Astrophysics Data System (ADS)
Rahimi, L.; Askari, A. A.; Saghafifar, H.
2016-07-01
The most optimum operation of a grism pair is practically approachable when an analytical expression of its spectral phase is in hand. In this paper, we have employed the accurate geometrical ray tracing method to calculate the analytical phase shift of a grism pair, at transmission and reflection configurations. As shown by the results, for a great variety of complicated configurations, the spectral phase of a grism pair is in the same form of that of a prism pair. The only exception is when the light enters into and exits from different facets of a reflection grism. The analytical result has been used to calculate the second-order dispersions of several examples of grism pairs in various possible configurations. All results are in complete agreement with those from ray tracing method. The result of this work can be very helpful in the optimal design and application of grism pairs at various configurations.
A method for the geometric and densitometric standardization of intraoral radiographs
Duckworth, J.E.; Judy, P.F.; Goodson, J.M.; Socransky, S.S.
1983-07-01
The interpretation of dental radiographs for the diagnosis of periodontal disease conditions poses several difficulties. These include the inability to adequately reproduce the projection geometry and optical density of the exposures. In order to improve the ability to extract accurate quantitative information from a radiographic survey of periodontal status, a method was developed which provided for consistent reproduction of both geometric and densitometric exposure parameters. This technique employed vertical bitewing projections in holders customized to individual segments of the dentition. A copper stepwedge was designed to provide densitometric standardization, and wire markers were included to permit measurement of angular variation. In a series of 53 paired radiographs, measurement of alveolar crest heights was found to be reproducible within approximately 0.1 mm. This method provided a full mouth radiographic survey using seven films, each complete with internal standards suitable for computer-based image processing.
NASA Astrophysics Data System (ADS)
Bernal, E. J.; Martinod, R. M.; Betancur, G. R.; Castañeda, L. F.
2016-05-01
The present work poses a method for the measurement of geometric parameters of rail wheels in a dynamic condition, by reconstructing the profilogram from a portion of the wheel surface wear with artificial vision. The suggested procedure can work with a two-dimensional laser displacement transducer or by processing a sole image from a single camera with a structured light source. These two procedures require fewer devices and simpler implementation processes and allow the use of mathematical algorithms that demand less information processing, thus generating more accurate results. Railway operators may implement this method to perform predictive maintenance to their rolling stock at a fraction of the regular cost; thus achieving better precision, availability, maintenance performance and improving safety. Results were compared to those given by commercial equipment, showing similar precision but a better cost-benefit relation.
A Method for Lung Boundary Correction Using Split Bregman Method and Geometric Active Contour Model.
Feng, Changli; Zhang, Jianxun; Liang, Rui
2015-01-01
In order to get the extracted lung region from CT images more accurately, a model that contains lung region extraction and edge boundary correction is proposed. Firstly, a new edge detection function is presented with the help of the classic structure tensor theory. Secondly, the initial lung mask is automatically extracted by an improved active contour model which combines the global intensity information, local intensity information, the new edge information, and an adaptive weight. It is worth noting that the objective function of the improved model is converted to a convex model, which makes the proposed model get the global minimum. Then, the central airway was excluded according to the spatial context messages and the position relationship between every segmented region and the rib. Thirdly, a mesh and the fractal theory are used to detect the boundary that surrounds the juxtapleural nodule. Finally, the geometric active contour model is employed to correct the detected boundary and reinclude juxtapleural nodules. We also evaluated the performance of the proposed segmentation and correction model by comparing with their popular counterparts. Efficient computing capability and robustness property prove that our model can correct the lung boundary reliably and reproducibly. PMID:26089976
NASA Astrophysics Data System (ADS)
Oliker, Vladimir
2005-08-01
Numerous optical and electromagnetic applications require numerical design of reflecting surfaces in 3D with capabilities to redirect the input energy flow and reshape the energy radiation intensity of a source into a prescribed output irradiance distribution over a specified target surface. In the geometrical optics approximation, a systematic application of the ray tracing equations and energy conservation law reduces the problem, in many cases, to finding numerical solutions to nonlinear, second order partial differential equations. If the severe limitation of rotational symmetry is not assumed then the resulting equations are very far from being standard and require significant efforts for their theoretical investigation and reliable numerical solution. In recent years a quite general approach combining geometric techniques with methods from calculus of variations has been developed and applied to a rigorous and unified investigation of several classes of such equations. Moreover, this approach allows implementations in provably convergent numerical algorithms. In this paper I outline this approach in the problem of designing a reflecting surface capable of redirecting the energy flow from a point source so that the reflected rays have directions specified in advance as a subset on the far-sphere and the output irradiance density is also pre-specified in advance as a function of the reflected direction. A numerical example illustrating the solution is also presented.
NASA Astrophysics Data System (ADS)
Wang, Quanzeng; Cheng, Wei-Chung; Suresh, Nitin; Hua, Hong
2016-05-01
With improved diagnostic capabilities and complex optical designs, endoscopic technologies are advancing. As one of the several important optical performance characteristics, geometric distortion can negatively affect size estimation and feature identification related diagnosis. Therefore, a quantitative and simple distortion evaluation method is imperative for both the endoscopic industry and the medical device regulatory agent. However, no such method is available yet. While the image correction techniques are rather mature, they heavily depend on computational power to process multidimensional image data based on complex mathematical model, i.e., difficult to understand. Some commonly used distortion evaluation methods, such as the picture height distortion (DPH) or radial distortion (DRAD), are either too simple to accurately describe the distortion or subject to the error of deriving a reference image. We developed the basic local magnification (ML) method to evaluate endoscope distortion. Based on the method, we also developed ways to calculate DPH and DRAD. The method overcomes the aforementioned limitations, has clear physical meaning in the whole field of view, and can facilitate lesion size estimation during diagnosis. Most importantly, the method can facilitate endoscopic technology to market and potentially be adopted in an international endoscope standard.
Comprehensive Evaluation of Protein Structure Alignment Methods: Scoring by Geometric Measures
Kolodny, Rachel; Koehl, Patrice; Levitt, Michael
2009-01-01
We report the largest and most comprehensive comparison of protein structural alignment methods. Specifically, we evaluate six publicly available structure alignment programs: SSAP, STRUCTAL, DALI, LSQMAN, CE and SSM by aligning all 8,581,970 protein structure pairs in a test set of 2930 protein domains specially selected from CATH v.2.4 to ensure sequence diversity. We consider an alignment good if it matches many residues, and the two substructures are geometrically similar. Even with this definition, evaluating structural alignment methods is not straightforward. At first, we compared the rates of true and false positives using receiver operating characteristic (ROC) curves with the CATH classification taken as a gold standard. This proved unsatisfactory in that the quality of the alignments is not taken into account: sometimes a method that finds less good alignments scores better than a method that finds better alignments. We correct this intrinsic limitation by using four different geometric match measures (SI, MI, SAS, and GSAS) to evaluate the quality of each structural alignment. With this improved analysis we show that there is a wide variation in the performance of different methods; the main reason for this is that it can be difficult to find a good structural alignment between two proteins even when such an alignment exists. We find that STRUCTAL and SSM perform best, followed by LSQMAN and CE. Our focus on the intrinsic quality of each alignment allows us to propose a new method, called “Best-of-All” that combines the best results of all methods. Many commonly used methods miss 10–50% of the good Best-of-All alignments. By putting existing structural alignments into proper perspective, our study allows better comparison of protein structures. By highlighting limitations of existing methods, it will spur the further development of better structural alignment methods. This will have significant biological implications now that structural
Method and apparatus for calibrating a tiled display
NASA Technical Reports Server (NTRS)
Johnson, Michael J. (Inventor); Chen, Chung-Jen (Inventor); Chandrasekhar, Rajesh (Inventor)
2001-01-01
A display system that can be calibrated and re-calibrated with a minimal amount of manual intervention. To accomplish this, one or more cameras are provided to capture an image of the display screen. The resulting captured image is processed to identify any non-desirable characteristics, including visible artifacts such as seams, bands, rings, etc. Once the non-desirable characteristics are identified, an appropriate transformation function is determined. The transformation function is used to pre-warp the input video signal that is provided to the display such that the non-desirable characteristics are reduced or eliminated from the display. The transformation function preferably compensates for spatial non-uniformity, color non-uniformity, luminance non-uniformity, and other visible artifacts.
Method and Apparatus for Accurately Calibrating a Spectrometer
NASA Technical Reports Server (NTRS)
Youngquist, Robert C. (Inventor); Simmons, Stephen M. (Inventor)
2013-01-01
A calibration assembly for a spectrometer is provided. The assembly includes a spectrometer having n detector elements, where each detector element is assigned a predetermined wavelength value. A first source emitting first radiation is used to calibrate the spectrometer. A device is placed in the path of the first radiation to split the first radiation into a first beam and a second beam. The assembly is configured so that one of the first and second beams travels a path-difference distance longer than the other of the first and second beams. An output signal is generated by the spectrometer when the first and second beams enter the spectrometer. The assembly includes a controller operable for processing the output signal and adapted to calculate correction factors for the respective predetermined wavelength values assigned to each detector element.
NASA Astrophysics Data System (ADS)
Sivaprakasam, Vasanthi; Killinger, Dennis K.
2003-09-01
A 266-nm laser-induced fluorescence system was used to study the effect of polarization of the excitation source and geometry of the collection optics on the ratio of the signal from a fluorescence standard, quinine sulfate, and the Raman scatter from water. Although the ratio is sometimes considered to be a constant and is used for intersystem comparisons, our studies showed that the Raman signal and, thus, the ratio can vary by a factor of up to 3.6. These experimental values agree with previous studies by others involving gas and flame Raman spectroscopy and suggest a new calibration method for intersystem comparison of different fluorescence systems.
A self-sufficient method for calibration of Varian electronic portal imaging device
NASA Astrophysics Data System (ADS)
Sun, Baozhou; Yaddanapudi, Sridhar; Goddu, Sreekrishna M.; Mutic, Sasa
2015-01-01
Electronic portal imaging device (EPID) is currently used for dosimetric verification of IMRT fields and linac quality assurance (QA). It is critical to understand the dosimetric response and perform an accurate and robust calibration of EPID. We present the implementation of an efficient method for the calibration and the validation of a Varian EPID, which relies only on data collected with that specific device. The calibration method is based on images obtained with five shifts of EPID panel. With this method, the relative gain (sensitivity) of each element of a detector matrix is calculated and applied on top of the calibration determined with the flood-field procedure. The calibration procedure was verified using a physical wedge inserted in the beam line and the corrected profile shows consistent results with the measurements using a calibrated 2D array. This method does not rely on the beam profile used in the flood-field calibration process, which allows EPID calibration in 10 minutes with no additional equipment compared to at least 2 hours to obtain beam profile and scanning beam equipment requirement with the conventional method.
A New Method for Common Calibration of Sun-Sky-Lunar Photometer
NASA Astrophysics Data System (ADS)
Li, Kaitao; Li, Zhengqiang; Li, Donghui; Xu, Hua; Xie, Yisong; Li, Li; Chen, Xingfeng; Ma, Yan
2016-04-01
A new calibration method is introduced to transfer extraterrestrial calibration coefficients to the moon measurements for a new sun-sky-lunar photometer, trade name CE318-T from CIMEL. The new transfer method has no relationship with lunar phase, therefore, the precision of the results is improved, and error analysis suggests that the uncertainty of the transferred method is about 2.2-2.6%, smaller than the lunar Langley calibrations. At the same time, the calibration time is also saved. The Sun-Sky-Lunar photometer numbered #1202 and located on the roof of Institute of remote sensing and digital earth (RADI) in Beijing was used in this study. The extraterrestrial calibration coefficients were got by using Langley calibration performed at Ali with a height of 5053 m above sea level in Tibet. The new lunar calibration coefficients were obtained with the new transfer method. And then the nocturnal AODs were calculated, which are well consistent with the daytime observations. The differences between two AODs obtained with transferred calibration coefficients and lunar Langley method were also compared in this paper. In this study, Lidar observation results was also presented to compare with the lunar observations, the results show that the nocturnal AODs have the same variation tendency with the Lidar observations.
A long-baseline method for HST gyro drift rate bias calibration
NASA Technical Reports Server (NTRS)
Boia, John J.; Welter, Gary L.; Gakenheimer, Martin F.
1994-01-01
The routine on-orbit calibration of the Hubble Space Telescope (HST) rate gyro assemblies (RGA's) has depended on several related algorithms for drift rate bias calibration. The gyros have exhibited time-varying biases, which must be regularly corrected to maintain pointing stability. Currently, gyro drift parameters are uplinked to the spacecraft every 1-2 days for low rate mode and every 7 days for high rate mode. In order to minimize the impact of frequent calibrations on the HST science schedule, we have refined the gyro calibration algorithms and data collection schemes to reduce the amounts of telemetry data and processing time required for accurate bias calibration. We present a review of the evolution of the gyro calibration algorithms, with particular attention to what we have called the long-baseline bias (LBBIAS) technique, and describe the relative success of these methods in maintaining spacecraft stability.
Camera calibration method of binocular stereo vision based on OpenCV
NASA Astrophysics Data System (ADS)
Zhong, Wanzhen; Dong, Xiaona
2015-10-01
Camera calibration, an important part of the binocular stereo vision research, is the essential foundation of 3D reconstruction of the spatial object. In this paper, the camera calibration method based on OpenCV (open source computer vision library) is submitted to make the process better as a result of obtaining higher precision and efficiency. First, the camera model in OpenCV and an algorithm of camera calibration are presented, especially considering the influence of camera lens radial distortion and decentering distortion. Then, camera calibration procedure is designed to compute those parameters of camera and calculate calibration errors. High-accurate profile extraction algorithm and a checkboard with 48 corners have also been used in this part. Finally, results of calibration program are presented, demonstrating the high efficiency and accuracy of the proposed approach. The results can reach the requirement of robot binocular stereo vision.
Axial Green’s function method for steady Stokes flow in geometrically complex domains
NASA Astrophysics Data System (ADS)
Jun, Sukky; Kim, Do Wan
2011-03-01
Axial Green's function method (AGM) is developed for the simulation of Stokes flow in geometrically complex solution domains. The AGM formulation systematically decomposes the multidimensional steady-state Stokes equations into 1D forms. The representation formula for the solution variables can then be derived using the 1D Green's functions only, from which a system of 1D integral equations is obtained. Furthermore, the explicit representation formula for the pressure variable enable the unique AGM approach to facilitating the stabilization issue caused by the saddle structure between velocity and pressure. The convergence of numerical solutions, the simple axial discretization of complex solution domains, and the nature of integral schemes are demonstrated through a variety of numerical examples.
An automated calibration method for non-see-through head mounted displays.
Gilson, Stuart J; Fitzgibbon, Andrew W; Glennerster, Andrew
2011-08-15
Accurate calibration of a head mounted display (HMD) is essential both for research on the visual system and for realistic interaction with virtual objects. Yet, existing calibration methods are time consuming and depend on human judgements, making them error prone, and are often limited to optical see-through HMDs. Building on our existing approach to HMD calibration Gilson et al. (2008), we show here how it is possible to calibrate a non-see-through HMD. A camera is placed inside a HMD displaying an image of a regular grid, which is captured by the camera. The HMD is then removed and the camera, which remains fixed in position, is used to capture images of a tracked calibration object in multiple positions. The centroids of the markers on the calibration object are recovered and their locations re-expressed in relation to the HMD grid. This allows established camera calibration techniques to be used to recover estimates of the HMD display's intrinsic parameters (width, height, focal length) and extrinsic parameters (optic centre and orientation of the principal ray). We calibrated a HMD in this manner and report the magnitude of the errors between real image features and reprojected features. Our calibration method produces low reprojection errors without the need for error-prone human judgements. PMID:21620891
Calibration to surface reflectance of terrestrial imaging spectrometry data: Comparison of methods
NASA Technical Reports Server (NTRS)
Clark, Roger N.; Swayze, Gregg A.; Heidebrecht, Kathy; Green, Robert O.; Goetz, F. H.
1995-01-01
Many algorithms for spectral analysis of imaging spectroscopy data of the Earth's surface require that the data be calibrated to surface reflectance. Calibration requires removing instrumental response, solar irradiance, atmospheric transmittance, and atmospheric scattering from the radiance detected at the sensor. Depending on the amount of support data, this can be a formidable task. This paper examines four methods of calibration: (1) a radiative transfer model from the University of Colorado (ATREM: Gao and Goetz, 1990; Gao et al., 1992), (2) a MODTRAN-based method developed at the Jet Propulsion Lab by Green et al., (1191), (3) a ground calibration using known sites as standards, and (4) a combined approach using radiative transfer methods and ground calibration. Data from the Airborne Visual and Infra-Red Imaging Spectrometer (AVIRIS) instrument were evaluated from data sets obtained over multiple years and multiple sites.
HosseiniAliabadi, S. J.; Hosseini Pooya, S. M.; Afarideh, H.; Mianji, F.
2015-01-01
Introduction The angular dependency of response for TLD cards may cause deviation from its true value on the results of environmental dosimetry, since TLDs may be exposed to radiation at different angles of incidence from the surrounding area. Objective A 3D setting of TLD cards has been calibrated isotropically in a standard radiation field to evaluate the improvement of the accuracy of measurement for environmental dosimetry. Method Three personal TLD cards were rectangularly placed in a cylindrical holder, and calibrated using 1D and 3D calibration methods. Then, the dosimeter has been used simultaneously with a reference instrument in a real radiation field measuring the accumulated dose within a time interval. Result The results show that the accuracy of measurement has been improved by 6.5% using 3D calibration factor in comparison with that of normal 1D calibration method. Conclusion This system can be utilized in large scale environmental monitoring with a higher accuracy. PMID:26157729
A New Method of Theodolite Calibration Based on Image Processing Technology
NASA Astrophysics Data System (ADS)
Zou, Hui-Hui; Wu, Hong-Bing; Chen, Di
Aiming at improving the theodolite calibration method for space tracking ship, a calibration device which consists of hardware and software is designed in this paper. Hereinto, the hardware part is a set of optical acquisition system that includes CCD, lens and 0.2" collimator, while the software part contains image acquisition module, image processing module, data processing module and interface display module. During the calibration process, the new methods of image denoising and image character extraction are applied to improve the precision of image measure. The result of the experiment shows that the calibration criteria of the theodolite errors was met by applying the image processing technology of the theodolite calibration device, it is more accurate than the manual reading method under the same situation in dock.
Fast wavelength calibration method for spectrometers based on waveguide comb optical filter
Yu, Zhengang; Huang, Meizhen Zou, Ye; Wang, Yang; Sun, Zhenhua; Cao, Zhuangqi
2015-04-15
A novel fast wavelength calibration method for spectrometers based on a standard spectrometer and a double metal-cladding waveguide comb optical filter (WCOF) is proposed and demonstrated. By using the WCOF device, a wide-spectrum beam is comb-filtered, which is very suitable for spectrometer wavelength calibration. The influence of waveguide filter’s structural parameters and the beam incident angle on the comb absorption peaks’ wavelength and its bandwidth are also discussed. The verification experiments were carried out in the wavelength range of 200–1100 nm with satisfactory results. Comparing with the traditional wavelength calibration method based on discrete sparse atomic emission or absorption lines, the new method has some advantages: sufficient calibration data, high accuracy, short calibration time, fit for produce process, stability, etc.
The molecular branching ratio method for calibration of optical systems in the vacuum ultraviolet
NASA Technical Reports Server (NTRS)
Mumma, M. J.
1972-01-01
The intensity distribution of bands belonging to six molecular band systems is discussed with special emphasis on their usefulness for intensity calibration of optical systems in the vacuum ultraviolet (1000A Lambda 3000A). The theory of molecular band intensities is outlined and the technique of measuring the spectral response curve is described. Several methods for establishing an absolute intensity calibration are discussed.
ERIC Educational Resources Information Center
Salazar, Douglas A.
2012-01-01
This study aimed to improve the van Hiele levels of geometric understanding, proof-construction performance and beliefs about proofs of the research respondents: future mathematics teachers exposed to the traditional (instructor-based) method and the enhanced-group Moore method. By using the quasi-experimental method of research, the study…
In Search of Easy-to-Use Methods for Calibrating ADCP's for Velocity and Discharge Measurements
Oberg, K.
2002-01-01
A cost-effective procedure for calibrating acoustic Doppler current profilers (ADCP) in the field was presented. The advantages and disadvantages of various methods which are used for calibrating ADCP were discussed. The proposed method requires the use of differential global positioning system (DGPS) with sub-meter accuracy and standard software for collecting ADCP data. The method involves traversing a long (400-800 meter) course at a constant compass heading and speed, while collecting simultaneous DGPS and ADCP data.
An Improved Calibration Method for Hydrazine Monitors for the United States Air Force
Korsah, K
2003-07-07
This report documents the results of Phase 1 of the ''Air Force Hydrazine Detector Characterization and Calibration Project''. A method for calibrating model MDA 7100 hydrazine detectors in the United States Air Force (AF) inventory has been developed. The calibration system consists of a Kintek 491 reference gas generation system, a humidifier/mixer system which combines the dry reference hydrazine gas with humidified diluent or carrier gas to generate the required humidified reference for calibrations, and a gas sampling interface. The Kintek reference gas generation system itself is periodically calibrated using an ORNL-constructed coulometric titration system to verify the hydrazine concentration of the sample atmosphere in the interface module. The Kintek reference gas is then used to calibrate the hydrazine monitors. Thus, coulometric titration is only used to periodically assess the performance of the Kintek reference gas generation system, and is not required for hydrazine monitor calibrations. One advantage of using coulometric titration for verifying the concentration of the reference gas is that it is a primary standard (if used for simple solutions), thereby guaranteeing, in principle, that measurements will be traceable to SI units (i.e., to the mole). The effect of humidity of the reference gas was characterized by using the results of concentrations determined by coulometric titration to develop a humidity correction graph for the Kintek 491 reference gas generation system. Using this calibration method, calibration uncertainty has been reduced by 50% compared to the current method used to calibrate hydrazine monitors in the Air Force inventory and calibration time has also been reduced by more than 20%. Significant findings from studies documented in this report are the following: (1) The Kintek 491 reference gas generation system (generator, humidifier and interface module) can be used to calibrate hydrazine detectors. (2) The Kintek system output
Wu, Jun; Yu, Zhijing; Zhuge, Jingchang
2016-04-01
A rotating laser positioning system (RLPS) is an efficient measurement method for large-scale metrology. Due to multiple transmitter stations, which consist of a measurement network, the position relationship of these stations must be first calibrated. However, with such auxiliary devices such as a laser tracker, scale bar, and complex calibration process, the traditional calibration methods greatly reduce the measurement efficiency. This paper proposes a self-calibration method for RLPS, which can automatically obtain the position relationship. The method is implemented through interscanning technology by using a calibration bar mounted on the transmitter station. Each bar is composed of three RLPS receivers and one ultrasonic sensor whose coordinates are known in advance. The calibration algorithm is mainly based on multiplane and distance constraints and is introduced in detail through a two-station mathematical model. The repeated experiments demonstrate that the coordinate measurement uncertainty of spatial points by using this method is about 0.1 mm, and the accuracy experiments show that the average coordinate measurement deviation is about 0.3 mm compared with a laser tracker. The accuracy can meet the requirements of most applications, while the calibration efficiency is significantly improved. PMID:27140762
NASA Astrophysics Data System (ADS)
Park, Soah; Kang, Sei-Kwon; Cheong, Kwang-Ho; Hwang, Taejin; Yoon, Jai-Woong; Koo, Taeryool; Han, Tae Jin; Kim, Haeyoung; Lee, Me Yeon; Bae, Hoonsik; Kim, Kyoung Ju
2016-07-01
EBT3 film is utilized as a dosimetry quality assurance tool for the verification of clinical radiotherapy treatments. In this work, we suggest a percentage-depth-dose (PDD) calibration method that can calibrate several EBT3 film pieces together at different dose levels because photon beams provide different dose levels at different depths along the axis of the beam. We investigated the feasibility of the film PDD calibration method based on PDD data and compared the results those from the traditional film calibration method. Photon beams at 6 MV were delivered to EBT3 film pieces for both calibration methods. For the PDD-based calibration, the film pieces were placed on solid phantoms at the depth of maximum dose (dmax) and at depths of 3, 5, 8, 12, 17, and 22 cm, and a photon beam was delivered twice, at 100 cGy and 400 cGy, to extend the calibration dose range under the same conditions. Fourteen film pieces, to maintain their consistency, were irradiated at doses ranging from approximately 30 to 400 cGy for both film calibrations. The film pieces were located at the center position on the scan bed of an Epson 1680 flatbed scanner in the parallel direction. Intensity-modulated radiation therapy (IMRT) plans were created, and their dose distributions were delivered to the film. The dose distributions for the traditional method and those for the PDD-based calibration method were evaluated using a Gamma analysis. The PDD dose values using a CC13 ion chamber and those obtained by using a FC65-G Farmer chamber and measured at the depth of interest produced very similar results. With the objective test criterion of a 1% dosage agreement at 1 mm, the passing rates for the four cases of the three IMRT plans were essentially identical. The traditional and the PDD-based calibrations provided similar plan verification results. We also describe another alternative for calibrating EBT3 films, i.e., a PDD-based calibration method that provides an easy and time-saving approach
Geometrically non-linear vibration of spinning structures by finite element method
NASA Astrophysics Data System (ADS)
Leung, A. Y. T.; Fung, T. C.
1990-05-01
The geometrically non-linear steady state vibration of spinning structures is studied. Full flap-lag-torsional gyroscopic coupling effects are considered. The non-linearity arises mainly from the non-linear axial strain-displacement relation. The equations of motion are derived from Lagrangian equations. Spatial discretization is achieved by the finite element method and steady state nodal displacements are expanded into Fourier series. The harmonic balance method gives a set of non-linear algebraic equations with the Fourier coefficients of the nodal displacements as unknowns. The non-linear algebraic equations are solved by a Newtonian algorithm iteratively. The importance of the conditions of completeness and balanceability in choosing the number of harmonic terms to be used is discussed. General frame structures with arbitrary orientation in a rotating frame can be investigated by the present method. Rotating blades and shafts are treated as special cases. Examples of a rotating ring with different orientations are given. The non-linear amplitude-frequency relation can be constructed parametrically.
A new method for automated dynamic calibration of tipping-bucket rain gauges
Humphrey, M.D.; Istok, J.D.; Lee, J.Y.; Hevesi, J.A.; Flint, A.L.
1997-01-01
Existing methods for dynamic calibration of tipping-bucket rain gauges (TBRs) can be time consuming and labor intensive. A new automated dynamic calibration system has been developed to calibrate TBRs with minimal effort. The system consists of a programmable pump, datalogger, digital balance, and computer. Calibration is performed in two steps: 1) pump calibration and 2) rain gauge calibration. Pump calibration ensures precise control of water flow rates delivered to the rain gauge funnel; rain gauge calibration ensures precise conversion of bucket tip times to actual rainfall rates. Calibration of the pump and one rain gauge for 10 selected pump rates typically requires about 8 h. Data files generated during rain gauge calibration are used to compute rainfall intensities and amounts from a record of bucket tip times collected in the field. The system was tested using 5 types of commercial TBRs (15.2-, 20.3-, and 30.5-cm diameters; 0.1-, 0.2-, and 1.0-mm resolutions) and using 14 TBRs of a single type (20.3-cm diameter; 0.1-mm resolution). Ten pump rates ranging from 3 to 154 mL min-1 were used to calibrate the TBRs and represented rainfall rates between 6 and 254 mm h-1 depending on the rain gauge diameter. All pump calibration results were very linear with R2 values greater than 0.99. All rain gauges exhibited large nonlinear underestimation errors (between 5% and 29%) that decreased with increasing rain gauge resolution and increased with increasing rainfall rate, especially for rates greater than 50 mm h-1. Calibration curves of bucket tip time against the reciprocal of the true pump rate for all rain gauges also were linear with R2 values of 0.99. Calibration data for the 14 rain gauges of the same type were very similar, as indicated by slope values that were within 14% of each other and ranged from about 367 to 417 s mm h-1. The developed system can calibrate TBRs efficiently, accurately, and virtually unattended and could be modified for use with other
A new method for internal calibration of nuclear track detectors
NASA Technical Reports Server (NTRS)
Oda, K.; Csige, I.; Henke, R. P.; Benton, E. V.
1992-01-01
A new technique is proposed for an internal calibration of a two-layer detector assembly. Spatially coincident pairs of conical tracks on one surface and overetched tracks on the adjacent surface are selected for measurement. Both the etch rate ratio and the particle range can be obtained from the minor and major diameters of the elliptical track and the radii of the circular tracks for two etching steps. This technique was applied to CR-39 detectors exposed to fast neutrons and those flown on a high altitude balloon in order to evaluate the proton response. An improvement by using multi-step etching was also carried out. It was found that not only a single set of the etch rate ratio and the range but also the response curve could be estimated in an extended region by analyzing combined growth curves.
Calibration methods and tools for KM3NeT
NASA Astrophysics Data System (ADS)
Kulikovskiy, Vladimir
2016-04-01
The KM3NeT detectors, ARCA and ORCA, composed of several thousands digital optical modules, are in the process of their realization in the Mediterranean Sea. Each optical module contains 31 3-inch photomultipliers. Readout of the optical modules and other detector components is synchronized at the level of sub-nanoseconds. The position of the module is measured by acoustic piezo detectors inside the module and external acoustic emitters installed on the bottom of the sea. The orientation of the module is obtained with an internal attitude and heading reference system chip. Detector calibration, i.e. timing, positioning and sea-water properties, is overviewed in this talk and discussed in detail in this conference. Results of the procedure applied to the first detector unit ready for installation in the deep sea will be shown.
Kalivas, John H; Héberger, Károly; Andries, Erik
2015-04-15
Most multivariate calibration methods require selection of tuning parameters, such as partial least squares (PLS) or the Tikhonov regularization variant ridge regression (RR). Tuning parameter values determine the direction and magnitude of respective model vectors thereby setting the resultant predication abilities of the model vectors. Simultaneously, tuning parameter values establish the corresponding bias/variance and the underlying selectivity/sensitivity tradeoffs. Selection of the final tuning parameter is often accomplished through some form of cross-validation and the resultant root mean square error of cross-validation (RMSECV) values are evaluated. However, selection of a "good" tuning parameter with this one model evaluation merit is almost impossible. Including additional model merits assists tuning parameter selection to provide better balanced models as well as allowing for a reasonable comparison between calibration methods. Using multiple merits requires decisions to be made on how to combine and weight the merits into an information criterion. An abundance of options are possible. Presented in this paper is the sum of ranking differences (SRD) to ensemble a collection of model evaluation merits varying across tuning parameters. It is shown that the SRD consensus ranking of model tuning parameters allows automatic selection of the final model, or a collection of models if so desired. Essentially, the user's preference for the degree of balance between bias and variance ultimately decides the merits used in SRD and hence, the tuning parameter values ranked lowest by SRD for automatic selection. The SRD process is also shown to allow simultaneous comparison of different calibration methods for a particular data set in conjunction with tuning parameter selection. Because SRD evaluates consistency across multiple merits, decisions on how to combine and weight merits are avoided. To demonstrate the utility of SRD, a near infrared spectral data set and a
A direct micropipette-based calibration method for atomic force microscope cantilevers
Liu, Baoyu; Yu, Yan; Yao, Da-Kang; Shao, Jin-Yu
2009-01-01
In this report, we describe a direct method for calibrating atomic force microscope (AFM) cantilevers with the micropipette aspiration technique (MAT). A closely fitting polystyrene bead inside a micropipette is driven by precisely controlled hydrostatic pressures to apply known loads on the sharp tip of AFM cantilevers, thus providing a calibration at the most functionally relevant position. The new method is capable of calibrating cantilevers with spring constants ranging from 0.01 to hundreds of newtons per meter. Under appropriate loading conditions, this new method yields measurement accuracy and precision both within 10%, with higher performance for softer cantilevers. Furthermore, this method may greatly enhance the accuracy and precision of calibration for colloidal probes. PMID:19566228
Emery, K.A.; Waddington, D.; Rummel, S.; Myers, D.R.; Stoffel, T.L.; Osterwald, C.R.
1989-03-01
The SERI results for the Photovoltaic Solar Energy Project (PEP) 1987 summit round robin are presented and the proposed International Electrotechnical Commission (IEC) technical committee TC82 global calibration method is evaluated in this report. The global calibration method has a +-4% uncertainty in the short-circuit current (I/sub sc/) including random and nonrandom error sources. This uncertainty can be reduced +-3% if the global normal method is used and the direct component of the total irradiance is measured with a primary absolute cavity radiometer. Nearly half of the uncertainty for various primary and secondary PV calibration methods is nonrandom. If a +-4% uncertainty in I/sub sc/ under standard reporting conditions is acceptable, then the global calibration method with spectral corrections is suitable for cells or modules. If a primary reference device with an uncertainty less than +-3% is required, then the global method is unsuitable. The SERI primary direct normal calibration method has a +-1% uncertainty in I/sub sc/ as verified by comparison with primary AMO cells. If a +-1% primary reference cell is used for secondary calibrations, then a +-2% uncertainty could be achieved for reference cells or modules. 37 refs., 29 figs., 42 tabs.
Pan, Congyuan; Du, Xuewei; An, Ning; Zeng, Qiang; Wang, Shengbo; Wang, Qiuping
2016-04-01
A multi-line internal standard calibration method is proposed for the quantitative analysis of carbon steel using laser-induced breakdown spectroscopy (LIBS). A procedure based on the method was adopted to select the best calibration curves and the corresponding emission lines pairs automatically. Laser-induced breakdown spectroscopy experiments with carbon steel samples were performed, and C, Cr, and Mn were analyzed via the proposed method. Calibration curves of these elements were constructed via a traditional single line internal standard calibration method and a multi-line internal standard calibration method. The calibration curves obtained were evaluated with the determination coefficient, the root mean square error of cross-validation, and the average relative error of cross-validation. All of the parameters were improved significantly with the proposed method. The results show that accurate and stable calibration curves can be obtained efficiently via the multi-line internal standard calibration method. PMID:26872822
Calibration Methods Used in Cancer Simulation Models and Suggested Reporting Guidelines
Stout, Natasha K.; Knudsen, Amy B.; Kong, Chung Yin (Joey); McMahon, Pamela M.; Gazelle, G. Scott
2009-01-01
Background Increasingly, computer simulation models are used for economic and policy evaluation in cancer prevention and control. A model’s predictions of key outcomes such as screening effectiveness depends on the values of unobservable natural history parameters. Calibration is the process of determining the values of unobservable parameters by constraining model output to replicate observed data. Because there are many approaches for model calibration and little consensus on best practices, we surveyed the literature to catalogue the use and reporting of these methods in cancer simulation models. Methods We conducted a MEDLINE search (1980 through 2006) for articles on cancer screening models and supplemented search results with articles from our personal reference databases. For each article, two authors independently abstracted pre-determined items using a standard form. Data items included cancer site, model type, methods used for determination of unobservable parameter values, and description of any calibration protocol. All authors reached consensus on items of disagreement. Reviews and non-cancer models were excluded. Articles describing analytical models which estimate parameters with statistical approaches (e.g., maximum likelihood) were catalogued separately. Models that included unobservable parameters were analyzed and classified by whether calibration methods were reported and if so, the methods used. Results The review process yielded 154 articles that met our inclusion criteria and of these, we concluded that 131 may have used calibration methods to determine model parameters. Although the term “calibration” was not always used, descriptions of calibration or “model fitting” were found in 50% (n=66) of the articles with an additional 16% (n=21) providing a reference to methods. Calibration target data were identified in nearly all of these articles. Other methodologic details such as the goodness-of-fit metric were discussed in 54% (n=47
Novel Method for Processing the Dynamic Calibration Signal of Pressure Sensor
Wang, Zhongyu; Li, Qiang; Wang, Zhuoran; Yan, Hu
2015-01-01
Dynamic calibration is one of the important ways to acquire the dynamic performance parameters of a pressure sensor. This research focuses on the processing method for the output of calibrated pressure sensor, and mainly attempts to solve the problem of extracting the true information of step response under strong interference noise. A dynamic calibration system based on a shock tube is established to excite the time-domain response signal of a calibrated pressure sensor. A key processing on difference modeling is applied for the obtained signal, and several generating sequences are established. A fusion process for the generating sequences is then undertaken, and the true information of the step response of the calibrated pressure sensor can be obtained. Finally, by implementing the common QR decomposition method to deal with the true information, a dynamic model characterizing the dynamic performance of the calibrated pressure sensor is established. A typical pressure sensor was used to perform calibration tests and a frequency-domain experiment for the sensor was also conducted. Results show that the proposed method could effectively filter strong interference noise in the output of the sensor and the corresponding dynamic model could effectively characterize the dynamic performance of the pressure sensor. PMID:26197324
Automatic Calibration Method for Driver’s Head Orientation in Natural Driving Environment
Fu, Xianping; Guan, Xiao; Peli, Eli; Liu, Hongbo; Luo, Gang
2013-01-01
Gaze tracking is crucial for studying driver’s attention, detecting fatigue, and improving driver assistance systems, but it is difficult in natural driving environments due to nonuniform and highly variable illumination and large head movements. Traditional calibrations that require subjects to follow calibrators are very cumbersome to be implemented in daily driving situations. A new automatic calibration method, based on a single camera for determining the head orientation and which utilizes the side mirrors, the rear-view mirror, the instrument board, and different zones in the windshield as calibration points, is presented in this paper. Supported by a self-learning algorithm, the system tracks the head and categorizes the head pose in 12 gaze zones based on facial features. The particle filter is used to estimate the head pose to obtain an accurate gaze zone by updating the calibration parameters. Experimental results show that, after several hours of driving, the automatic calibration method without driver’s corporation can achieve the same accuracy as a manual calibration method. The mean error of estimated eye gazes was less than 5°in day and night driving. PMID:24639620
Novel Method for Processing the Dynamic Calibration Signal of Pressure Sensor.
Wang, Zhongyu; Li, Qiang; Wang, Zhuoran; Yan, Hu
2015-01-01
Dynamic calibration is one of the important ways to acquire the dynamic performance parameters of a pressure sensor. This research focuses on the processing method for the output of calibrated pressure sensor, and mainly attempts to solve the problem of extracting the true information of step response under strong interference noise. A dynamic calibration system based on a shock tube is established to excite the time-domain response signal of a calibrated pressure sensor. A key processing on difference modeling is applied for the obtained signal, and several generating sequences are established. A fusion process for the generating sequences is then undertaken, and the true information of the step response of the calibrated pressure sensor can be obtained. Finally, by implementing the common QR decomposition method to deal with the true information, a dynamic model characterizing the dynamic performance of the calibrated pressure sensor is established. A typical pressure sensor was used to perform calibration tests and a frequency-domain experiment for the sensor was also conducted. Results show that the proposed method could effectively filter strong interference noise in the output of the sensor and the corresponding dynamic model could effectively characterize the dynamic performance of the pressure sensor. PMID:26197324
Lambertian nature of tissue phantoms for use as calibrators in near infrared fluorescence imaging
NASA Astrophysics Data System (ADS)
Litorja, Maritoni; Lorenzo, Simón; Zhu, Banghe; Sevick Muraca, Eva
2016-03-01
The use of tissue phantoms as calibrators to transfer SI-referenced scale to an imager offers convenience, compared to other methods of calibration. The tissue phantoms are calibrated separately for radiance at emission wavelength per irradiance at excitation wavelength. This calibration is only performed at a single geometric configuration, typically with the detector normal to the sample. In the clinic however, the imager can be moved around, resulting in a geometric configuration different from the calibration configuration. In this study, radiometric measurements are made at different sample-imager angles to test whether the tissue phantoms are Lambertian and the angular limits to which the calibration values hold true.
Benazzi, Stefano; Stansfield, Ekaterina; Kullmer, Ottmar; Fiorenza, Luca; Gruppioni, Giorgio
2009-08-01
The issue of reconstructing lost or deformed bone presents an equal challenge in the fields of paleoanthropology, bioarchaeology, forensics, and medicine. Particularly, within the disciplines of orthodontics and surgery, the main goal of reconstruction is to restore or create ex novo the proper form and function. The reconstruction of the mandibular condyle requires restoration of articulation, occlusion, and mastication from the functional side as well as the correct shape of the mandible from the esthetic point of view. Meeting all these demands is still problematic for surgeons. It is unfortunate that the collaboration between anthropologists and medical professionals is still limited. Nowadays, geometric morphometric methods (GMM) are routinely applied in shape analysis and increasingly in the reconstruction of missing data in skeletal material in paleoanthropology. Together with methods for three-dimensional (3D) digital model construction and reverse engineering, these methods could prove to be useful in surgical fields for virtual planning of operations and the production of customized biocompatible scaffolds. In this contribution, we have reconstructed the missing left condylar process of the mandible belonging to a famous Italian humanist of the 15th century, Pico della Mirandola (1463-1494) by means of 3D digital models and GMM, having first compared two methods (a simple reflection of the opposite side and the mathematical-statistical GMM approach) in a complete human mandible on which loss of the left condyle was virtually simulated. Finally, stereolithographic models of Pico's skull were prototyped providing the physical assembly of the bony skull structures with a high fitting accuracy. PMID:19645014
A Tool-Free Calibration Method for Turntable-Based 3D Scanning Systems.
Pang, Xufang; Lau, Rynson W H; Song, Zhan; Li, Yangyan; He, Shengfeng
2016-01-01
Turntable-based 3D scanners are popular but require calibration of the turntable axis. Existing methods for turntable calibration typically make use of specially designed tools, such as a chessboard or criterion sphere, which users must manually install and dismount. In this article, the authors propose an automatic method to calibrate the turntable axis without any calibration tools. Given a scan sequence of the input object, they first recover the initial rotation axis from an automatic registration step. Then they apply an iterative procedure to obtain the optimized turntable axis. This iterative procedure alternates between two steps: refining the initial pose of the input scans and approximating the rotation matrix. The performance of the proposed method was evaluated on a structured light-based scanning system. PMID:25137724
Automated calibration methods for robotic multisensor landmine detection
NASA Astrophysics Data System (ADS)
Keranen, Joe G.; Miller, Jonathan; Schultz, Gregory; Topolosky, Zeke
2007-04-01
Both force protection and humanitarian demining missions require efficient and reliable detection and discrimination of buried anti-tank and anti-personnel landmines. Widely varying surface and subsurface conditions, mine types and placement, as well as environmental regimes challenge the robustness of the automatic target recognition process. In this paper we present applications created for the U.S. Army Nemesis detection platform. Nemesis is an unmanned rubber-tracked vehicle-based system designed to eradicate a wide variety of anti-tank and anti-personnel landmines for humanitarian demining missions. The detection system integrates advanced ground penetrating synthetic aperture radar (GPSAR) and electromagnetic induction (EMI) arrays, highly accurate global and local positioning, and on-board target detection/classification software on the front loader of a semi-autonomous UGV. An automated procedure is developed to estimate the soil's dielectric constant using surface reflections from the ground penetrating radar. The results have implications not only for calibration of system data acquisition parameters, but also for user awareness and tuning of automatic target recognition detection and discrimination algorithms.
GMI Instrument Spin Balance Method, Optimization, Calibration and Test
NASA Technical Reports Server (NTRS)
Ayari, Laoucet; Kubitschek, Michael; Ashton, Gunnar; Johnston, Steve; Debevec, Dave; Newell, David; Pellicciotti, Joseph
2014-01-01
The Global Microwave Imager (GMI) instrument must spin at a constant rate of 32 rpm continuously for the 3-year mission life. Therefore, GMI must be very precisely balanced about the spin axis and center of gravity (CG) to maintain stable scan pointing and to minimize disturbances imparted to the spacecraft and attitude control on-orbit. The GMI instrument is part of the core Global Precipitation Measurement (GPM) spacecraft and is used to make calibrated radiometric measurements at multiple microwave frequencies and polarizations. The GPM mission is an international effort managed by the National Aeronautics and Space Administration (NASA) to improve climate, weather, and hydro-meteorological predictions through more accurate and frequent precipitation measurements. Ball Aerospace and Technologies Corporation (BATC) was selected by NASA Goddard Space Flight Center to design, build, and test the GMI instrument. The GMI design has to meet a challenging set of spin balance requirements and had to be brought into simultaneous static and dynamic spin balance after the entire instrument was already assembled and before environmental tests began. The focus of this contribution is on the analytical and test activities undertaken to meet the challenging spin balance requirements of the GMI instrument. The novel process of measuring the residual static and dynamic imbalances with a very high level of accuracy and precision is presented together with the prediction of the optimal balance masses and their locations.
GMI Instrument Spin Balance Method, Optimization, Calibration, and Test
NASA Technical Reports Server (NTRS)
Ayari, Laoucet; Kubitschek, Michael; Ashton, Gunnar; Johnston, Steve; Debevec, Dave; Newell, David; Pellicciotti, Joseph
2014-01-01
The Global Microwave Imager (GMI) instrument must spin at a constant rate of 32 rpm continuously for the 3 year mission life. Therefore, GMI must be very precisely balanced about the spin axis and CG to maintain stable scan pointing and to minimize disturbances imparted to the spacecraft and attitude control on-orbit. The GMI instrument is part of the core Global Precipitation Measurement (GPM) spacecraft and is used to make calibrated radiometric measurements at multiple microwave frequencies and polarizations. The GPM mission is an international effort managed by the National Aeronautics and Space Administration (NASA) to improve climate, weather, and hydro-meteorological predictions through more accurate and frequent precipitation measurements. Ball Aerospace and Technologies Corporation (BATC) was selected by NASA Goddard Space Flight Center to design, build, and test the GMI instrument. The GMI design has to meet a challenging set of spin balance requirements and had to be brought into simultaneous static and dynamic spin balance after the entire instrument was already assembled and before environmental tests began. The focus of this contribution is on the analytical and test activities undertaken to meet the challenging spin balance requirements of the GMI instrument. The novel process of measuring the residual static and dynamic imbalances with a very high level of accuracy and precision is presented together with the prediction of the optimal balance masses and their locations.
NASA Technical Reports Server (NTRS)
Parker, Peter A. (Inventor)
2003-01-01
A single vector calibration system is provided which facilitates the calibration of multi-axis load cells, including wind tunnel force balances. The single vector system provides the capability to calibrate a multi-axis load cell using a single directional load, for example loading solely in the gravitational direction. The system manipulates the load cell in three-dimensional space, while keeping the uni-directional calibration load aligned. The use of a single vector calibration load reduces the set-up time for the multi-axis load combinations needed to generate a complete calibration mathematical model. The system also reduces load application inaccuracies caused by the conventional requirement to generate multiple force vectors. The simplicity of the system reduces calibration time and cost, while simultaneously increasing calibration accuracy.
Radiometric calibration method for large aperture infrared system with broad dynamic range.
Sun, Zhiyuan; Chang, Songtao; Zhu, Wei
2015-05-20
Infrared radiometric measurements can acquire important data for missile defense systems. When observation is carried out by ground-based infrared systems, a missile is characterized by long distance, small size, and large variation of radiance. Therefore, the infrared systems should be manufactured with a larger aperture to enhance detection ability and calibrated at a broader dynamic range to extend measurable radiance. Nevertheless, the frequently used calibration methods demand an extended-area blackbody with broad dynamic range or a huge collimator for filling the system's field stop, which would greatly increase manufacturing costs and difficulties. To overcome this restriction, a calibration method based on amendment of inner and outer calibration is proposed. First, the principles and procedures of this method are introduced. Then, a shifting strategy of infrared systems for measuring targets with large fluctuations of infrared radiance is put forward. Finally, several experiments are performed on a shortwave infrared system with Φ400 mm aperture. The results indicate that the proposed method cannot only ensure accuracy of calibration but have the advantage of low cost, low power, and high motility. Hence, it is an effective radiometric calibration method in the outfield. PMID:26192499
A flexile and high precision calibration method for binocular structured light scanning system.
Yuan, Jianying; Wang, Qiong; Li, Bailin
2014-01-01
3D (three-dimensional) structured light scanning system is widely used in the field of reverse engineering, quality inspection, and so forth. Camera calibration is the key for scanning precision. Currently, 2D (two-dimensional) or 3D fine processed calibration reference object is usually applied for high calibration precision, which is difficult to operate and the cost is high. In this paper, a novel calibration method is proposed with a scale bar and some artificial coded targets placed randomly in the measuring volume. The principle of the proposed method is based on hierarchical self-calibration and bundle adjustment. We get initial intrinsic parameters from images. Initial extrinsic parameters in projective space are estimated with the method of factorization and then upgraded to Euclidean space with orthogonality of rotation matrix and rank 3 of the absolute quadric as constraint. Last, all camera parameters are refined through bundle adjustment. Real experiments show that the proposed method is robust, and has the same precision level as the result using delicate artificial reference object, but the hardware cost is very low compared with the current calibration method used in 3D structured light scanning system. PMID:25202736
NASA Astrophysics Data System (ADS)
Rosu, Mihaela
The aim of any radiotherapy is to tailor the tumoricidal radiation dose to the target volume and to deliver as little radiation dose as possible to all other normal tissues. However, the motion and deformation induced in human tissue by ventilatory motion is a major issue, as standard practice usually uses only one computed tomography (CT) scan (and hence one instance of the patient's anatomy) for treatment planning. The interfraction movement that occurs due to physiological processes over time scales shorter than the delivery of one treatment fraction leads to differences between the planned and delivered dose distributions. Due to the influence of these differences on tumors and normal tissues, the tumor control probabilities and normal tissue complication probabilities are likely to be impacted upon in the face of organ motion. In this thesis we apply several methods to compute dose distributions that include the effects of the treatment geometric uncertainties by using the time-varying anatomical information as an alternative to the conventional Planning Target Volume (PTV) approach. The proposed methods depend on the model used to describe the patient's anatomy. The dose and fluence convolution approaches for rigid organ motion are discussed first, with application to liver tumors and the rigid component of the lung tumor movements. For non-rigid behavior a dose reconstruction method that allows the accumulation of the dose to the deforming anatomy is introduced, and applied for lung tumor treatments. Furthermore, we apply the cumulative dose approach to investigate how much information regarding the deforming patient anatomy is needed at the time of treatment planning for tumors located in thorax. The results are evaluated from a clinical perspective. All dose calculations are performed using a Monte Carlo based algorithm to ensure more realistic and more accurate handling of tissue heterogeneities---of particular importance in lung cancer treatment planning.
Vicarious calibration of the Ocean PHILLS hyperspectral sensor using a coastal tree-shadow method
NASA Astrophysics Data System (ADS)
Filippi, Anthony M.; Carder, Kendall L.; Davis, Curtiss O.
2006-11-01
Ocean color remote-sensing systems require highly accurate calibration (<0.5%) for accurate retrieval of water properties. This accuracy is typically achieved by vicarious calibration which is done by comparing the atmospherically corrected remote-sensing data to accurate estimates of the water-leaving radiance. Here we present a new method for vicarious calibration of a hyperspectral sensor that exploits shadows cast by trees and cliffs along coastlines. Hyperspectral Ocean PHILLS imagery was acquired over East Sound and adjacent waters around Orcas Island, Washington, USA, in August, 1998, in concert with field data collection. To vicariously calibrate the PHILLS data, a method was developed employing pixel pairs in tree-shaded and adjacent unshadowed waters, which utilizes the sky radiance dominating the shaded pixel as a known calibration target. Transects extracted from East Sound imagery were calibrated and validated with field data (RMSE = 0.00033 sr-1), providing validation of this approach for acquiring calibration-adjustment data from the image itself.
A new automated and precise calibration method for gamma level gauges with rod detector arrangement.
Peyvandi, Reza Gholipour; Taheri, Ali; Olfateh, Ali; Islami, Seyyedeh Zahra
2016-06-01
Gamma-ray liquid level gauging is of particular importance in several industries. Industrial vessels, tanks, and reactors, which work at high temperatures and pressures, usually have thick metal walls up to 20cm. These factors make it impossible to know the exact level of liquid or fluid while the system is operating. For this reason, the calibration process of the gamma level gauges is difficult as it is impossible to gain access to the inside of the vessels, which is important during the calibration process. In this study, a new auto-calibration method was proposed for the aforementioned situations. PMID:26974485
Balance Calibration – A Method for Assigning a Direct-Reading Uncertainty to an Electronic Balance.
Mike Stears
2010-07-01
Paper Title: Balance Calibration – A method for assigning a direct-reading uncertainty to an electronic balance. Intended Audience: Those who calibrate or use electronic balances. Abstract: As a calibration facility, we provide on-site (at the customer’s location) calibrations of electronic balances for customers within our company. In our experience, most of our customers are not using their balance as a comparator, but simply putting an unknown quantity on the balance and reading the displayed mass value. Manufacturer’s specifications for balances typically include specifications such as readability, repeatability, linearity, and sensitivity temperature drift, but what does this all mean when the balance user simply reads the displayed mass value and accepts the reading as the true value? This paper discusses a method for assigning a direct-reading uncertainty to a balance based upon the observed calibration data and the environment where the balance is being used. The method requires input from the customer regarding the environment where the balance is used and encourages discussion with the customer regarding sources of uncertainty and possible means for improvement; the calibration process becomes an educational opportunity for the balance user as well as calibration personnel. This paper will cover the uncertainty analysis applied to the calibration weights used for the field calibration of balances; the uncertainty is calculated over the range of environmental conditions typically encountered in the field and the resulting range of air density. The temperature stability in the area of the balance is discussed with the customer and the temperature range over which the balance calibration is valid is decided upon; the decision is based upon the uncertainty needs of the customer and the desired rigor in monitoring by the customer. Once the environmental limitations are decided, the calibration is performed and the measurement data is entered into a
A flexible method for calibrating external parameters of two cameras with no-overlapping FOV
NASA Astrophysics Data System (ADS)
Shao, Mingwei; Wei, Zhenzhong; Hu, Mengjie
2016-01-01
A new flexible method to calibrate the external parameters of two cameras with no-overlapping field of view (FOV) is proposed in our paper. A flexible target with four spheres and a 1D bar is designed. All spheres can move freely along the bar to make sure that each camera can capture the image of two spheres clearly. As the radius of each sphere is known exactly, the center of each sphere under its corresponding camera coordinate system can be confirmed from each sphere projection. The centers of the four spheres are collinear in the process of calibration, so we can express the relationship of the four centers only by external parameters of the two cameras. When the expressions in different positions are obtained, the external parameters of two cameras can be determined. In our proposed calibration method, the center of the sphere can be determined accurately as the sphere projection is not concerned with the sphere orientation, meanwhile, the freely movement of the spheres can ensure the image of spheres clearly. Experiment results show that the proposed calibration method can obtain an acceptable accuracy, the calibrated vision system reaches 0.105 mm when measuring a distance section of 1040 mm. Moreover, the calibration method is efficient, convenient and with an easy operation.
NASA Astrophysics Data System (ADS)
Zhang, Yanshun; Guo, Yajing; Yang, Tao; Li, Chunyu; Wang, Zhanqing
2016-06-01
The scale factor error δ C of the Doppler velocity log (DVL) and the heading angle error δ \\psi of a compass are so integrated in dead reckoning (DR) navigation systems that it is difficult to separate them. This paper aims to solve this problem by putting forward an online separation and calibration method for δ C and δ \\psi based on an ‘arc and linear’ trajectory. This method introduces the high-accuracy location information of a long base line (LBL) acoustic positioning system. At first, the relationship between the displacements on the ‘arc’ trajectory in directions of east and north, output by the LBL and DR systems, serves to judge the carrier direction and calibrate δ C . And then by compensating δ C , the displacement on the ‘linear’ trajectory is used to calibrate δ \\psi . Finally, a semi-physical simulation experiment is conducted to test and verify this calibration method to see how effective and accurate it is. Experimental results show that after calibration the residual error ratios of δ C and δ \\psi are 8.24% and 3.70% respectively. Therefore, online calibration of δ C and δ \\psi is realized effectively. What’s more, when the DR system is working alone in 400 s, this method reduces position error by up to 93.39%, from 18.91 m to 1.25 m.
A new method for the absolute radiance calibration for UV-vis measurements of scattered sunlight
NASA Astrophysics Data System (ADS)
Wagner, T.; Beirle, S.; Dörner, S.; Penning de Vries, M.; Remmers, J.; Rozanov, A.; Shaiganfar, R.
2015-10-01
Absolute radiometric calibrations are important for measurements of the atmospheric spectral radiance. Such measurements can be used to determine actinic fluxes, the properties of aerosols and clouds, and the shortwave energy budget. Conventional calibration methods in the laboratory are based on calibrated light sources and reflectors and are expensive, time consuming and subject to relatively large uncertainties. Also, the calibrated instruments might change during transport from the laboratory to the measurement sites. Here we present a new calibration method for UV-vis instruments that measure the spectrally resolved sky radiance, for example zenith sky differential optical absorption spectroscopy (DOAS) instruments or multi-axis (MAX)-DOAS instruments. Our method is based on the comparison of the solar zenith angle dependence of the measured zenith sky radiance with radiative transfer simulations. For the application of our method, clear-sky measurements during periods with almost constant aerosol optical depth are needed. The radiative transfer simulations have to take polarisation into account. We show that the calibration results are almost independent from the knowledge of the aerosol optical properties and surface albedo, which causes a rather small uncertainty of about < 7 %. For wavelengths below about 330 nm it is essential that the ozone column density during the measurements be constant and known.
A Radial Self-Calibrated (RASCAL) GRAPPA method using Weight Interpolation
Codella, Noel C. F.; Spincemaille, Pascal; Prince, Martin; Wang, Yi
2011-01-01
A generalized autocalibrating partially parallel acquisition (GRAPPA) method for radial k-space sampling is presented that calculates GRAPPA weights without synthesized or acquired calibration data. Instead, GRAPPA weights are fit to the undersampled data as if it were the calibration data itself. Because the relative k-space shifts associated with these GRAPPA weights are varying for a radial trajectory, new GRAPPA weights can be resampled for arbitrary shifts through interpolation, which is then used to generate missing projections between the acquired projections. The method is demonstrated in phantoms and in abdominal and brain imaging. Image quality is similar to radial GRAPPA using fully sampled calibration data, and improved compared to a previously described self-calibrated radial GRAPPA technique. PMID:21834008
A new and simple calibration-independent method for measuring the beam energy of a cyclotron.
Gagnon, Katherine; Jensen, Mikael; Thisgaard, Helge; Publicover, Julia; Lapi, Suzanne; McQuarrie, Steve A; Ruth, Thomas J
2011-01-01
This work recommends a new and simple-to-perform method for measuring the beam energy of an accelerator. The proposed method requires the irradiation of two monitor foils interspaced by an energy degrader. The primary advantage of the proposed method, which makes this method unique from previous energy evaluation strategies that employ the use of monitor foils, is that this method is independent of the detector efficiency calibration. This method was evaluated by performing proton activation of (nat)Cu foils using both a cyclotron and a tandem Van de Graaff accelerator. The monitor foil activities were read using a dose calibrator set to an arbitrary calibration setting. Excellent agreement was noted between the nominal and measured proton energies. PMID:20926304
NASA Astrophysics Data System (ADS)
Ahn, SeungKyu; Ahn, SeJin; Yun, Jae Ho; Lee, Dong-Hoon; Winter, Stefan; Igari, Sanekazu; Yoon, KyungHoon
2014-06-01
A primary reference solar cell calibration technique recently established at the Korea Institute of Energy Research in Korea is introduced. This calibration technique is an indoor method that uses a highly collimated continuous-type solar simulator and absolute cavity radiometer traceable to the World Radiometric Reference. The results obtained using this calibration technique are shown with a precise uncertainty analysis, and the system configuration and calibration procedures are introduced. The calibration technique avoids overestimating the short-circuit current of a reference solar cell due to multiple reflections of incident simulator light using a novel method. In addition, the uncertainty analysis indicates that the calibration technique has an expanded uncertainty of approximately 0.7% with a coverage factor of k = 2 for a c-Si reference cell calibration. In addition, the developed primary reference solar cell calibration technique was compared with other techniques established in the World Photovoltaic Scale (WPVS) qualified calibration laboratories to verify its validity and reliability.
Calibration of the analogue method for precipitation forecasting by means of genetic algorithms
NASA Astrophysics Data System (ADS)
Horton, P.; Jaboyedoff, M.; Obled, C.
2012-04-01
The analogue downscaling technique allows precipitation forecasting on the basis of the synoptic circulation and humidity variables resulting from a global circulation model (GCM). The method identifies analog days in a long archive of past situations and uses their observed precipitation amount to build the empirical conditional distribution considered as the probabilistic forecast for the target day. The Atmoswing model (Analog Technique MOdel for Statistical Weather forecastING) was developed to calibrate the method and to process real-time forecasting in the Swiss Alps. It is part of the MINERVE project, which aims at reducing the flood peaks of the Rhône River by means of water retention in dams. Such a method is highly non-linear, works with both discrete and continuous variables and has a complex cost surface. Calibration with linear methods such as a simplex concept has been tried, but has led to unsatisfying results. The complexity of the analogue technique gives the user no choice but to use either a step-by-step manual calibration or a global optimizer. While the first option is the commonly used approach, a global optimizer has never been used to fulfill that goal. The classic calibration's main issue is that parameters are not independent and the choices made in the beginning of the calibration procedure have an impact on the final set. We decided to implement the genetic algorithms to achieve the model calibration, and so to avoid subjective choices of initial parameters. Genetic algorithms exist with multiple operators (natural selection, mating selection, chromosomes crossover, and mutation) variations and specific parameterizations. Most used implementations were compared to choose the version resulting in the best calibration with the minimum processing time. Afterwards, the optimizer is used to explore new variable spaces and even to choose the best atmospheric variables, what was not possible in the traditional calibration procedure.
Richardson, R Tyler; Nicholson, Kristen F; Rapp, Elizabeth A; Johnston, Therese E; Richards, James G
2016-05-01
Accurate measurement of joint kinematics is required to understand the musculoskeletal effects of a therapeutic intervention such as upper extremity (UE) ergometry. Traditional surface-based motion capture is effective for quantifying humerothoracic motion, but scapular kinematics are challenging to obtain. Methods for estimating scapular kinematics include the widely-reported acromion marker cluster (AMC) which utilizes a static calibration between the scapula and the AMC to estimate the orientation of the scapula during motion. Previous literature demonstrates that including additional calibration positions throughout the motion improves AMC accuracy for single plane motions; however this approach has not been assessed for the non-planar shoulder complex motion occurring during UE ergometry. The purpose of this study was to evaluate the accuracy of single, dual, and multiple AMC calibration methods during UE ergometry. The orientations of the UE segments of 13 healthy subjects were recorded with motion capture. Scapular landmarks were palpated at eight evenly-spaced static positions around the 360° cycle. The single AMC method utilized one static calibration position to estimate scapular kinematics for the entire cycle, while the dual and multiple AMC methods used two and four static calibration positions, respectively. Scapulothoracic angles estimated by the three AMC methods were compared with scapulothoracic angles determined by palpation. The multiple AMC method produced the smallest RMS errors and was not significantly different from palpation about any axis. We recommend the multiple AMC method as a practical and accurate way to estimate scapular kinematics during UE ergometry. PMID:26976228
Local Strategy Combined with a Wavelength Selection Method for Multivariate Calibration.
Chang, Haitao; Zhu, Lianqing; Lou, Xiaoping; Meng, Xiaochen; Guo, Yangkuan; Wang, Zhongyu
2016-01-01
One of the essential factors influencing the prediction accuracy of multivariate calibration models is the quality of the calibration data. A local regression strategy, together with a wavelength selection approach, is proposed to build the multivariate calibration models based on partial least squares regression. The local algorithm is applied to create a calibration set of spectra similar to the spectrum of an unknown sample; the synthetic degree of grey relation coefficient is used to evaluate the similarity. A wavelength selection method based on simple-to-use interactive self-modeling mixture analysis minimizes the influence of noisy variables, and the most informative variables of the most similar samples are selected to build the multivariate calibration model based on partial least squares regression. To validate the performance of the proposed method, ultraviolet-visible absorbance spectra of mixed solutions of food coloring analytes in a concentration range of 20-200 µg/mL is measured. Experimental results show that the proposed method can not only enhance the prediction accuracy of the calibration model, but also greatly reduce its complexity. PMID:27271636
NASA Astrophysics Data System (ADS)
Li, Yafeng; Zhang, Ning; Zhou, Yueming; Wang, Jianing; Zhang, Yiming; Wang, Jiyun; Xiong, Caiqiao; Chen, Suming; Nie, Zongxiu
2013-09-01
Accurate mass information is of great importance in the determination of unknown compounds. An effective and easy-to-control internal mass calibration method will dramatically benefit accurate mass measurement. Here we reported a simple induced dual-nanospray internal calibration device which has the following three advantages: (1) the two sprayers are in the same alternating current field; thus both reference ions and sample ions can be simultaneously generated and recorded. (2) It is very simple and can be easily assembled. Just two metal tubes, two nanosprayers, and an alternating current power supply are included. (3) With the low-flow-rate character and the versatility of nanoESI, this calibration method is capable of calibrating various samples, even untreated complex samples such as urine and other biological samples with small sample volumes. The calibration errors are around 1 ppm in positive ion mode and 3 ppm in negative ion mode with good repeatability. This new internal calibration method opens up new possibilities in the determination of unknown compounds, and it has great potential for the broad applications in biological and chemical analysis.
A Visual Servoing-Based Method for ProCam Systems Calibration
Berry, Francois; Aider, Omar Ait; Mosnier, Jeremie
2013-01-01
Projector-camera systems are currently used in a wide field of applications, such as 3D reconstruction and augmented reality, and can provide accurate measurements, depending on the configuration and calibration. Frequently, the calibration task is divided into two steps: camera calibration followed by projector calibration. The latter still poses certain problems that are not easy to solve, such as the difficulty in obtaining a set of 2D–3D points to compute the projection matrix between the projector and the world. Existing methods are either not sufficiently accurate or not flexible. We propose an easy and automatic method to calibrate such systems that consists in projecting a calibration pattern and superimposing it automatically on a known printed pattern. The projected pattern is provided by a virtual camera observing a virtual pattern in an OpenGL model. The projector displays what the virtual camera visualizes. Thus, the projected pattern can be controlled and superimposed on the printed one with the aid of visual servoing. Our experimental results compare favorably with those of other methods considering both usability and accuracy. PMID:24084121
Local Strategy Combined with a Wavelength Selection Method for Multivariate Calibration
Chang, Haitao; Zhu, Lianqing; Lou, Xiaoping; Meng, Xiaochen; Guo, Yangkuan; Wang, Zhongyu
2016-01-01
One of the essential factors influencing the prediction accuracy of multivariate calibration models is the quality of the calibration data. A local regression strategy, together with a wavelength selection approach, is proposed to build the multivariate calibration models based on partial least squares regression. The local algorithm is applied to create a calibration set of spectra similar to the spectrum of an unknown sample; the synthetic degree of grey relation coefficient is used to evaluate the similarity. A wavelength selection method based on simple-to-use interactive self-modeling mixture analysis minimizes the influence of noisy variables, and the most informative variables of the most similar samples are selected to build the multivariate calibration model based on partial least squares regression. To validate the performance of the proposed method, ultraviolet-visible absorbance spectra of mixed solutions of food coloring analytes in a concentration range of 20–200 µg/mL is measured. Experimental results show that the proposed method can not only enhance the prediction accuracy of the calibration model, but also greatly reduce its complexity. PMID:27271636
Data Sparseness and On-Line Pretest Item Calibration-Scaling Methods in CAT.
ERIC Educational Resources Information Center
Ban, Jae-Chun; Hanson, Bradley A.; Yi, Qing; Harris, Deborah J.
2002-01-01
Compared three online pretest calibration scaling methods through simulation: (1) marginal maximum likelihood with one expectation maximization (EM) cycle (OEM) method; (2) marginal maximum likelihood with multiple EM cycles (MEM); and (3) M. Stocking's method B. MEM produced the smallest average total error in parameter estimation; OEM yielded…
ERIC Educational Resources Information Center
Ban, Jae-Chun; Hanson, Bradley A.; Yi, Qing; Harris, Deborah J.
The purpose of this study was to compare and evaluate three online pretest item calibration/scaling methods in terms of item parameter recovery when the item responses to the pretest items in the pool would be sparse. The three methods considered were the marginal maximum likelihood estimate with one EM cycle (OEM) method, the marginal maximum…
Gafchromic EBT2 film dosimetry in reflection mode with a novel plan-based calibration method
Mendez, I.; Hartman, V.; Hudej, R.; Strojnik, A.; Casar, B.
2013-01-15
Purpose:A dosimetric system formed by Gafchromic EBT2 radiochromic film and Epson Expression 10000XL flatbed scanner was commissioned for dosimetry. In this paper, several open questions concerning the commissioning of radiochromic films for dosimetry were addressed: (a) is it possible to employ this dosimetric system in reflection mode; (b) if so, can the methods used in transmission mode also be used in reflection mode; (c) is it possible to obtain accurate absolute dose measurements with Gafchromic EBT2 films; (d) which calibration method should be followed; (e) which calibration models should be used; and (f) does three-color channel dosimetry offer a significant improvement over single channel dosimetry. The purpose of this paper is to help clarify these questions. Methods: In this study, films were scanned in reflection mode, the effect of surrounding film was evaluated and the feasibility of EBT2 film dosimetry in reflection mode was studied. EBT2's response homogeneity has been reported to lead to excessive dose uncertainties. To overcome this problem, a new plan-based calibration method was implemented. Plan-based calibration can use every pixel and each of the three color channels of the scanned film to obtain the parameters of the calibration model. A model selection analysis was conducted to select lateral correction and sensitometric curve models. The commonly used calibration with fragments was compared with red-channel plan-based calibration and with three-channel plan-based calibration. Results: No effect of surrounding film was found in this study. The film response inhomogeneity in EBT2 films was found to be important not only due to differences in the fog but also due to differences in sensitivity. The best results for lateral corrections were obtained using absolute corrections independent of the dose. With respect to the sensitometric curves, an empirical polynomial fit of order 4 was found to obtain results equivalent to a gamma
Rukke, E O; Olsen, E F; Devold, T; Vegarud, G; Isaksson, T
2010-07-01
A rapid spectroscopic method to determine total protein in bovine and buffalo milk using UV spectra of guanidine-hydrochloride mixed milk has previously been reported and validated. The method was based on mixed calibration samples and univariate calibrations of fourth derivative (4D) spectra. In this study the same method was compared and tested for determination of total protein in goat milk. Calculations based on multivariate calibration (partial least squares regression) on full spectra of goat milk were used. The method was tested on 2 UV instruments. The comparison resulted in a significantly more robust (i.e., better) transferability between UV instruments for the partial least squares regression method on full spectra compared with previous univariate calibration of 4D spectra. Local (1 instrument) calibrations gave similar, significantly not different (chi-squared test) cross-validated prediction error results for the 2 methods. It can be concluded that there is no need for fourth derivation. Partial least squares regression on full spectra was equal or superior to using the 4D spectra. PMID:20630209
A parallel geometric multigrid method for finite elements on octree meshes
Sampath, Rahul S; Biros, George
2010-01-01
In this article, we present a parallel geometric multigrid algorithm for solving variable-coefficient elliptic partial differential equations on the unit box (with Dirichlet or Neumann boundary conditions) using highly nonuniform, octree-based, conforming finite element discretizations. Our octrees are 2:1 balanced, that is, we allow no more than one octree-level difference between octants that share a face, edge, or vertex. We describe a parallel algorithm whose input is an arbitrary 2:1 balanced fine-grid octree and whose output is a set of coarser 2:1 balanced octrees that are used in the multigrid scheme. Also, we derive matrix-free schemes for the discretized finite element operators and the intergrid transfer operations. The overall scheme is second-order accurate for sufficiently smooth right-hand sides and material properties; its complexity for nearly uniform trees is {Omicron}(N/n{sub p} log N/n{sub p}) + {Omicron}(n{sub p} log n{sub p}), where N is the number of octree nodes and n{sub p} is the number of processors. Our implementation uses the Message Passing Interface standard. We present numerical experiments for the Laplace and Navier (linear elasticity) operators that demonstrate the scalability of our method. Our largest run was a highly nonuniform, 8-billion-unknown, elasticity calculation using 32,000 processors on the Teragrid system, 'Ranger,' at the Texas Advanced Computing Center. Our implementation is publically available in the Dendro library, which is built on top of the PETSc library from Argonne National Laboratory.
NASA Astrophysics Data System (ADS)
Kelson, J.; Huntington, K. W.; Schauer, A. J.; Saenger, C.; Lechler, A. R.
2015-12-01
An accurate empirical calibration is necessary to confidently apply the carbonate clumped isotope (Δ47) thermometer. Previous synthetic carbonate calibrations disagree in temperature sensitivity, with one group of calibrations displaying a shallow Δ47-temperature slope (e.g., Dennis & Schrag, GCA, 2010), and the other a steep slope (e.g., Zaarur et al., EPSL, 2013). These calibrations differ in both the method of mineral precipitation and the temperature of the phosphoric acid used to digest carbonates for analysis, making it difficult to isolate the cause of the discrepancy. Here, we precipitate synthetic carbonates at temperatures of 6-80ºC using 4 different precipitation methods, and analyze the samples using both 90 and 25°C acid digestion. Precipitation experiments varied the use of salts (NaHCO3 and CaCl2) vs. dissolved CaCO3 as a starting solution, the use of carbonic anhydrase to promote isotopic equilibrium among dissolved inorganic carbon species in solution, and the method by which CO2 degasses to force carbonate precipitation. Carbonates precipitated by using salts and allowing CO2 to passively degas produce a shallow calibration slope that we hypothesize to approach isotopic equilibrium. Precipitation methods that bubble CO2 into solution then degas that CO2 (either passively or actively by bubbling N2) produce carbonates with consistently lower Δ47 and higher δ18O values for a given growth temperature. We infer that these carbonates grew in disequilibrium during rapid CO2 degassing. Varying acid digestion temperature does not change the results; acid fractionation factor is not correlated with grain size, Δ47, or d47 values. No precipitation method produces a steep calibration slope. Our large sample set of >60 carbonates lend confidence to a shallow slope calibration, and inform interpretations of Δ47 and δ18O values of natural carbonates that grow under conditions of isotopic disequilibrium.
Method of rotation angle measurement in machine vision based on calibration pattern with spot array
Li Weimin; Jin Jing; Li Xiaofeng; Li Bin
2010-02-20
We propose a method of rotation angle measurement with high precision in machine vision. An area scan CCD camera, imaging lens, and calibration pattern with a spot array make up the measurement device for measuring the rotation angle. The calibration pattern with a spot array is installed at the rotation part, and the CCD camera is set at a certain distance from the rotation components. The coordinates of the spots on the calibration pattern is acquired through the vision image of the calibration pattern captured by the CCD camera. At the initial position of the calibration pattern, the camera is calibrated with the spot array; the mathematical model of distortion error of the CCD camera is built. With the equation of coordinate rotation measurement, the rotation angle of the spot array is detected. In the theoretic simulation, noise of different levels is added to the coordinates of the spot array. The experiment results show that the measurement device can measure the rotation angle precisely with a noncontact method. The standard deviation of rotation angle measurement is smaller than 3 arc sec. The measurement device can measure both microangles and large angles.
Method of rotation angle measurement in machine vision based on calibration pattern with spot array.
Li, Weimin; Jin, Jing; Li, Xiaofeng; Li, Bin
2010-02-20
We propose a method of rotation angle measurement with high precision in machine vision. An area scan CCD camera, imaging lens, and calibration pattern with a spot array make up the measurement device for measuring the rotation angle. The calibration pattern with a spot array is installed at the rotation part, and the CCD camera is set at a certain distance from the rotation components. The coordinates of the spots on the calibration pattern is acquired through the vision image of the calibration pattern captured by the CCD camera. At the initial position of the calibration pattern, the camera is calibrated with the spot array; the mathematical model of distortion error of the CCD camera is built. With the equation of coordinate rotation measurement, the rotation angle of the spot array is detected. In the theoretic simulation, noise of different levels is added to the coordinates of the spot array. The experiment results show that the measurement device can measure the rotation angle precisely with a noncontact method. The standard deviation of rotation angle measurement is smaller than 3 arc sec. The measurement device can measure both microangles and large angles. PMID:20174168
An efficient calibration method for SQUID measurement system using three orthogonal Helmholtz coils
NASA Astrophysics Data System (ADS)
Hua, Li; Shu-Lin, Zhang; Chao-Xiang, Zhang; Xiang-Yan, Kong; Xiao-Ming, Xie
2016-06-01
For a practical superconducting quantum interference device (SQUID) based measurement system, the Tesla/volt coefficient must be accurately calibrated. In this paper, we propose a highly efficient method of calibrating a SQUID magnetometer system using three orthogonal Helmholtz coils. The Tesla/volt coefficient is regarded as the magnitude of a vector pointing to the normal direction of the pickup coil. By applying magnetic fields through a three-dimensional Helmholtz coil, the Tesla/volt coefficient can be directly calculated from magnetometer responses to the three orthogonally applied magnetic fields. Calibration with alternating current (AC) field is normally used for better signal-to-noise ratio in noisy urban environments and the results are compared with the direct current (DC) calibration to avoid possible effects due to eddy current. In our experiment, a calibration relative error of about 6.89 × 10‑4 is obtained, and the error is mainly caused by the non-orthogonality of three axes of the Helmholtz coils. The method does not need precise alignment of the magnetometer inside the Helmholtz coil. It can be used for the multichannel magnetometer system calibration effectively and accurately. Project supported by the “Strategic Priority Research Program (B)” of the Chinese Academy of Sciences (Grant No. XDB04020200) and the Shanghai Municipal Science and Technology Commission Project, China (Grant No. 15DZ1940902).
Crystal timing offset calibration method for time of flight PET scanners
NASA Astrophysics Data System (ADS)
Ye, Jinghan; Song, Xiyun
2016-03-01
In time-of-flight (TOF) positron emission tomography (PET), precise calibration of the timing offset of each crystal of a PET scanner is essential. Conventionally this calibration requires a specially designed tool just for this purpose. In this study a method that uses a planar source to measure the crystal timing offsets (CTO) is developed. The method uses list mode acquisitions of a planar source placed at multiple orientations inside the PET scanner field-of-view (FOV). The placement of the planar source in each acquisition is automatically figured out from the measured data, so that a fixture for exactly placing the source is not required. The expected coincidence time difference for each detected list mode event can be found from the planar source placement and the detector geometry. A deviation of the measured time difference from the expected one is due to CTO of the two crystals. The least squared solution of the CTO is found iteratively using the list mode events. The effectiveness of the crystal timing calibration method is evidenced using phantom images generated by placing back each list mode event into the image space with the timing offset applied to each event. The zigzagged outlines of the phantoms in the images become smooth after the crystal timing calibration is applied. In conclusion, a crystal timing calibration method is developed. The method uses multiple list mode acquisitions of a planar source to find the least squared solution of crystal timing offsets.
Evaluation of Linking Methods for Multidimensional IRT Calibrations
ERIC Educational Resources Information Center
Min, Kyung-Seok
2007-01-01
Most researchers agree that psychological/educational tests are sensitive to multiple traits, implying the need for a multidimensional item response theory (MIRT). One limitation of applying a MIRT in practice is the difficulty in establishing equivalent scales of multiple traits. In this study, a new MIRT linking method was proposed and evaluated…
A GPS-Based Pitot-Static Calibration Method Using Global Output-Error Optimization
NASA Technical Reports Server (NTRS)
Foster, John V.; Cunningham, Kevin
2010-01-01
Pressure-based airspeed and altitude measurements for aircraft typically require calibration of the installed system to account for pressure sensing errors such as those due to local flow field effects. In some cases, calibration is used to meet requirements such as those specified in Federal Aviation Regulation Part 25. Several methods are used for in-flight pitot-static calibration including tower fly-by, pacer aircraft, and trailing cone methods. In the 1990 s, the introduction of satellite-based positioning systems to the civilian market enabled new inflight calibration methods based on accurate ground speed measurements provided by Global Positioning Systems (GPS). Use of GPS for airspeed calibration has many advantages such as accuracy, ease of portability (e.g. hand-held) and the flexibility of operating in airspace without the limitations of test range boundaries or ground telemetry support. The current research was motivated by the need for a rapid and statistically accurate method for in-flight calibration of pitot-static systems for remotely piloted, dynamically-scaled research aircraft. Current calibration methods were deemed not practical for this application because of confined test range size and limited flight time available for each sortie. A method was developed that uses high data rate measurements of static and total pressure, and GPSbased ground speed measurements to compute the pressure errors over a range of airspeed. The novel application of this approach is the use of system identification methods that rapidly compute optimal pressure error models with defined confidence intervals in nearreal time. This method has been demonstrated in flight tests and has shown 2- bounds of approximately 0.2 kts with an order of magnitude reduction in test time over other methods. As part of this experiment, a unique database of wind measurements was acquired concurrently with the flight experiments, for the purpose of experimental validation of the
Research on calibration method of axis-shift multi-camera for aerial photogrammetry
NASA Astrophysics Data System (ADS)
Wang, Xiao; Fang, Junyong; Ma, Jingyu; Zhang, Xiaohong; Zhao, Dong; Liu, Xue
2015-12-01
Axis-shift multi-camera has been gradually applied in the aerial photogrammetry because of its advantages on structure design. In this paper, the basic axis-shift theory is analyzed, and an improved calibration method is described. A prototype system, including two axis-shift cameras, is developed to validate the feasibility and correctness of the proposed method. With the help of a high-precision indoor control field, the parameters of single camera and the relative orientation parameters of the dual camera system are calculated respectively. Experiment result indicates that this calibration method is suitable for the axis-shift multi camera system.
Calibrated propensity score method for survey nonresponse in cluster sampling
Kim, Jae Kwang; Kwon, Yongchan; Paik, Myunghee Cho
2016-01-01
Weighting adjustment is commonly used in survey sampling to correct for unit nonresponse. In cluster sampling, the missingness indicators are often correlated within clusters and the response mechanism is subject to cluster-specific nonignorable missingness. Based on a parametric working model for the response mechanism that incorporates cluster-specific nonignorable missingness, we propose a method of weighting adjustment. We provide a consistent estimator of the mean or totals in cases where the study variable follows a generalized linear mixed-effects model. The proposed method is robust in the sense that the consistency of the estimator does not require correct specification of the functional forms of the response and outcome models. A consistent variance estimator based on Taylor linearization is also proposed. Numerical results, including a simulation and a real-data application, are presented.
A robust method for online stereo camera self-calibration in unmanned vehicle system
NASA Astrophysics Data System (ADS)
Zhao, Yu; Chihara, Nobuhiro; Guo, Tao; Kimura, Nobutaka
2014-06-01
Self-calibration is a fundamental technology used to estimate the relative posture of the cameras for environment recognition in unmanned system. We focused on the issue of recognition accuracy decrease caused by the vibration of platform and conducted this research to achieve on-line self-calibration using feature point's registration and robust estimation of fundamental matrix. Three key factors in this respect are needed to be improved. Firstly, the feature mismatching exists resulting in the decrease of estimation accuracy of relative posture. The second, the conventional estimation method cannot satisfy both the estimation speed and calibration accuracy at the same tame. The third, some system intrinsic noises also lead greatly to the deviation of estimation results. In order to improve the calibration accuracy, estimation speed and system robustness for the practical implementation, we discuss and analyze the algorithms to make improvements on the stereo camera system to achieve on-line self-calibration. Based on the epipolar geometry and 3D images parallax, two geometry constraints are proposed to make the corresponding feature points search performed in a small search-range resulting in the improvement of matching accuracy and searching speed. Then, two conventional estimation algorithms are analyzed and evaluated for estimation accuracy and robustness. The third, Rigorous posture calculation method is proposed with consideration of the relative posture deviation of each separated parts in the stereo camera system. Validation experiments were performed with the stereo camera mounted on the Pen-Tilt Unit for accurate rotation control and the evaluation shows that our proposed method is fast and of high accuracy with high robustness for on-line self-calibration algorithm. Thus, as the main contribution, we proposed methods to solve the on-line self-calibration fast and accurately, envision the possibility for practical implementation on unmanned system as
A new time calibration method for switched-capacitor-array-based waveform samplers
Kim, H.; Chen, C. -T.; Eclov, N.; Ronzhin, A.; Murat, P.; Ramberg, E.; Los, S.; Moses, W.; Choong, W. -S.; Kao, C. -M.
2014-08-24
Here we have developed a new time calibration method for the DRS4 waveform sampler that enables us to precisely measure the non-uniform sampling interval inherent in the switched-capacitor cells of the DRS4. The method uses the proportionality between the differential amplitude and sampling interval of adjacent switched-capacitor cells responding to a sawtooth-shape pulse. In the experiment, a sawtooth-shape pulse with a 40 ns period generated by a Tektronix AWG7102 is fed to a DRS4 evaluation board for calibrating the sampling intervals of all 1024 cells individually. The electronic time resolution of the DRS4 evaluation board with the new time calibration is measured to be ~2.4 ps RMS by using two simultaneous Gaussian pulses with 2.35 ns full-width at half-maximum and applying a Gaussian fit. The time resolution dependencies on the time difference with the new time calibration are measured and compared to results obtained by another method. Ultimately, the new method could be applicable for other switched-capacitor-array technology-based waveform samplers for precise time calibration.
Enhanced Calibration Method of Silver Detector to Use in a Plasma Focus Device of Low Yield
Moreno, Jose; Soto, Leopoldo; Tarifeno-Saldivia, Ariel
2010-08-04
In this work, a calibration method based only in the use of a continuous neutron source as reference is presented. After the silver foil reached activation steady state, the neutron source was removed. The accumulated were analyzed by the method of linear least squares.
Matsumoto, Tetsuro; Harano, Hideki; Masuda, Akihiko; Nishiyama, Jun; Matsue, Hideaki; Uritani, Akira; Nunomiya, Tomoya
2013-08-01
A new thermal neutron calibration method to experimentally determine the energy response function of a neutron detector using a pulse parallel beam and the time-of-flight (TOF) technique is developed. The calibration method was experimentally demonstrated for a (3)He proportional counter and an electric personal dosemeter using a pulsed thermal neutron beam from the research reactor JRR-3M. The responses of the detectors were successfully obtained as a function of neutron energy. However, detailed information on the detector structure is required to obtain the spatial response distribution for the detector. The authors further propose an improved calibration method obtaining the spatial response distribution using a pulsed narrow beam, the TOF technique and a beam scanning technique. PMID:23509397
A simple method for wind tunnel balance calibration including non-linear interaction terms
NASA Astrophysics Data System (ADS)
Ramaswamy, M. A.; Srinivas, T.; Holla, V. S.
The conventional method for calibrating wind tunnel balances to obtain the coupled linear and nonlinear interaction terms requires the application of combinations of pure components of the loads on the calibration body compensating the deflection of the balance. For a six-component balance, this calls for a complex loading system and an arrangement to translate and tilt the balance support about all three axes. A simple method called the least-square method is illustrated for a three-component balance. The simplicity arises from the fact that application of the pure components of the loads or reorientation of the balance is not required. A single load is applied that has various components whose magnitudes can be easily found knowing the orientation of the calibration body under load and the point of application of the load. The coefficients are obtained by using the least-square-fit approach to match the outputs obtained for various combinations of load.
NASA Astrophysics Data System (ADS)
Gonçalves, Hernâni; Teodoro, Ana C.; Gonçalves, José A.; Corte Real, Luís
2011-11-01
The geometric correction of images under the scope of remote sensing applications is still mostly a manual work. This is a time and effort consuming task associated with an intra- and inter-operator subjectivity. One of the main reasons may be the lack of a proper evaluation of the different available automatic image registration (AIR) methods, since some of them are only adequate for certain types of applications/data. In order to fulfill a gap in this context, a first reference dataset of pairs of images comprising some types of geometric distortions was created, different spatial and spectral resolutions, and divided according to the Level 1 of CORINE Land Cover nomenclature (European Environment Agency). This dataset will allow for gaining perception of the abilities and limitations of some AIR methods. Some AIR methods were evaluated in this work, including the traditional correlation-based method and the SIFT approach, for which a set of measures for an objective evaluation of the geometric correction process quality was computed for every combination of pair of images/AIR method. The reference dataset is available from an internet address, being expected that it becomes a channel of interaction among the remote sensing community interested in this field.
Optical System Error Analysis and Calibration Method of High-Accuracy Star Trackers
Sun, Ting; Xing, Fei; You, Zheng
2013-01-01
The star tracker is a high-accuracy attitude measurement device widely used in spacecraft. Its performance depends largely on the precision of the optical system parameters. Therefore, the analysis of the optical system parameter errors and a precise calibration model are crucial to the accuracy of the star tracker. Research in this field is relatively lacking a systematic and universal analysis up to now. This paper proposes in detail an approach for the synthetic error analysis of the star tracker, without the complicated theoretical derivation. This approach can determine the error propagation relationship of the star tracker, and can build intuitively and systematically an error model. The analysis results can be used as a foundation and a guide for the optical design, calibration, and compensation of the star tracker. A calibration experiment is designed and conducted. Excellent calibration results are achieved based on the calibration model. To summarize, the error analysis approach and the calibration method are proved to be adequate and precise, and could provide an important guarantee for the design, manufacture, and measurement of high-accuracy star trackers. PMID:23567527
Optical system error analysis and calibration method of high-accuracy star trackers.
Sun, Ting; Xing, Fei; You, Zheng
2013-01-01
The star tracker is a high-accuracy attitude measurement device widely used in spacecraft. Its performance depends largely on the precision of the optical system parameters. Therefore, the analysis of the optical system parameter errors and a precise calibration model are crucial to the accuracy of the star tracker. Research in this field is relatively lacking a systematic and universal analysis up to now. This paper proposes in detail an approach for the synthetic error analysis of the star tracker, without the complicated theoretical derivation. This approach can determine the error propagation relationship of the star tracker, and can build intuitively and systematically an error model. The analysis results can be used as a foundation and a guide for the optical design, calibration, and compensation of the star tracker. A calibration experiment is designed and conducted. Excellent calibration results are achieved based on the calibration model. To summarize, the error analysis approach and the calibration method are proved to be adequate and precise, and could provide an important guarantee for the design, manufacture, and measurement of high-accuracy star trackers. PMID:23567527
Standardization of Laser Methods and Techniques for Vibration Measurements and Calibrations
Martens, Hans-Juergen von
2010-05-28
The realization and dissemination of the SI units of motion quantities (vibration and shock) have been based on laser interferometer methods specified in international documentary standards. New and refined laser methods and techniques developed by national metrology institutes and by leading manufacturers in the past two decades have been swiftly specified as standard methods for inclusion into in the series ISO 16063 of international documentary standards. A survey of ISO Standards for the calibration of vibration and shock transducers demonstrates the extended ranges and improved accuracy (measurement uncertainty) of laser methods and techniques for vibration and shock measurements and calibrations. The first standard for the calibration of laser vibrometers by laser interferometry or by a reference accelerometer calibrated by laser interferometry (ISO 16063-41) is on the stage of a Draft International Standard (DIS) and may be issued by the end of 2010. The standard methods with refined techniques proved to achieve wider measurement ranges and smaller measurement uncertainties than that specified in the ISO Standards. The applicability of different standardized interferometer methods to vibrations at high frequencies was recently demonstrated up to 347 kHz (acceleration amplitudes up to 350 km/s{sup 2}). The relative deviations between the amplitude measurement results of the different interferometer methods that were applied simultaneously, differed by less than 1% in all cases.
Application of the MCMC Method for the Calibration of DSMC Parameters
Strand, James S.; Goldstein, David B.
2011-05-20
A Markov Chain Monte Carlo (MCMC) algorithm was employed to obtain a calibrated distribution for the hard sphere diameter, the VHS reference diameter, and the temperature viscosity exponent of argon, for use in the Direct Simulation Monte Carlo (DSMC) method. Shock-tube experiments from Alsmeyer [1] were used to provide the necessary calibration data for use in the MCMC method. The DSMC method used in this work employs the algorithm of Bird [2], with modifications to allow for the efficient simulation of a 1D shock. When calibrating for the hard sphere diameter (the temperature viscosity exponent is set to 0.5 for the hard sphere method), the results of the MCMC method agree with a simple brute-force method, and a single value for the hard-sphere diameter is obtained. For the VHS method, however, when simultaneously calibrating the VHS reference diameter and the temperature viscosity exponent, we find that normalized density data alone does not provide sufficient information to obtain a single solution for both parameters. Instead we find a band in parameter space where acceptable solutions are obtained.
Kann, Frank van; Winterflood, John
2005-03-01
A simple but powerful method is presented for calibrating geophones, seismometers, and other inertial vibration sensors, including passive accelerometers. The method requires no cumbersome or expensive fixtures such as shaker platforms and can be performed using a standard instrument commonly available in the field. An absolute calibration is obtained using the reciprocity property of the device, based on the standard mathematical model for such inertial sensors. It requires only simple electrical measurement of the impedance of the sensor as a function of frequency to determine the parameters of the model and hence the sensitivity function. The method is particularly convenient if one of these parameters, namely the suspended mass is known. In this case, no additional mechanical apparatus is required and only a single set of impedance measurements yields the desired calibration function. Moreover, this measurement can be made with the device in situ. However, the novel and most powerful aspect of the method is its ability to accurately determine the effective suspended mass. For this, the impedance measurement is made with the device hanging from a simple spring or flexible cord (depending on the orientation of its sensitive axis). To complete the calibration, the device is weighed to determine its total mass. All the required calibration parameters, including the suspended mass, are then determined from a least-squares fit to the impedance as a function of frequency. A demonstration using both a 4.5 Hz geophone and a 1 Hz seismometer shows that the method can yield accurate absolute calibrations with an error of 0.1% or better, assuming no a priori knowledge of any parameters.
Calibration method for a vision guiding-based laser-tracking measurement system
NASA Astrophysics Data System (ADS)
Shao, Mingwei; Wei, Zhenzhong; Hu, Mengjie; Zhang, Guangjun
2015-08-01
Laser-tracking measurement systems (laser trackers) based on a vision-guiding device are widely used in industrial fields, and their calibration is important. As conventional methods typically have many disadvantages, such as difficult machining of the target and overdependence on the retroreflector, a novel calibration method is presented in this paper. The retroreflector, which is necessary in the normal calibration method, is unnecessary in our approach. As the laser beam is linear, points on the beam can be obtained with the help of a normal planar target. In this way, we can determine the function of a laser beam under the camera coordinate system, while its corresponding function under the laser-tracker coordinate system can be obtained from the encoder of the laser tracker. Clearly, when several groups of functions are confirmed, the rotation matrix can be solved from the direction vectors of the laser beams in different coordinate systems. As the intersection of the laser beams is the origin of the laser-tracker coordinate system, the translation matrix can also be determined. Our proposed method not only achieves the calibration of a single laser-tracking measurement system but also provides a reference for the calibration of a multistation system. Simulations to evaluate the effects of some critical factors were conducted. These simulations show the robustness and accuracy of our method. In real experiments, the root mean square error of the calibration result reached 1.46 mm within a range of 10 m, even though the vision-guiding device focuses on a point approximately 5 m away from the origin of its coordinate system, with a field of view of approximately 200 mm × 200 mm.
Methods and Apparatuses for Signaling with Geometric Constellations in a Raleigh Fading Channel
NASA Technical Reports Server (NTRS)
Barsoum, Maged F. (Inventor); Jones, Christopher R. (Inventor)
2015-01-01
Communication systems are described that use signal constellations, which have unequally spaced (i.e., `geometrically` shaped) points. In many embodiments, the communication systems use specific geometric constellations that are capacity optimized at a specific SNR (signal to noise ratio). In addition, ranges within which the constellation points of a capacity optimized constellation can be perturbed and are still likely to achieve a given percentage of the optimal capacity increase compared to a constellation that maximizes d (sub min) (i.e. minimum distance between constellations) are also described. Capacity measures that are used in the selection of the location of constellation points include, but are not limited to, parallel decode (PD) capacity and joint capacity.
CEILINEX 2015: Validation of calibration methods during the ceilometer inter-comparison
NASA Astrophysics Data System (ADS)
Hervo, Maxime
2016-04-01
In Europe, more than 700 ceilometers are measuring continuously. These instruments can be used for many applications such as detection of cloud base and aerosol layers height, aerosol profiling or for fog now-casting. However, from different manufacturers exist and the results can vary extensively from one type to another. During the CeiLinEx2015 campaign (Ceilometer Performance Experiment at Lindenberg 2015), 6 types of ceilometers (CL31, CL51, CHM15k, CHM15kx CS135 and LD40) were measuring simultaneously at Lindenberg (Germany) from June to September 2015. Each type was represented by two instruments in order to assess the instrument-to-instrument variability. A companion contribution by Mattis et al. presents an overview of the campaign. The monitoring of the temporal and spatial evolution of aerosol layers like the volcanic ash, is crucial to compare measurements from different sites. Therefore, all instruments need to be calibrated in order to provide consistent results. This contribution will focus on the validation and the comparison of state-of-the-art calibration methods. The calibration methods tested were are the cloud calibration (O'Connor et al., 2004) and the Rayleigh calibration Method (Wiegner and Geiß, 2012). Both methods can be applied without on-site intervention and are thus suitable for automatic networks. Operational automated algorithms based on these methods were developed in the framework of the TOPROF project (ESSEM COST Action ES1303)..The Cloud calibration was found more appropriate for analog instruments with analog signal detection measuring at around 905nm (Vaisala CL51 and CL31 and Campbell Scientific CS135). The Rayleigh was more suitable for photon-counting systems measuring at 1064nm (CHM15k, CHM15kx). For the first time, these methods were tested simultaneously on different instrument types and compared amongst each other. For a dust event occurred on the 13/08/2015, the attenuated backscatter coefficient difference amongst all
Haaland, D.M.; Jones, H.D.T.
1997-09-01
Multivariate calibration methods have been applied extensively to the quantitative analysis of Fourier transform infrared (FT-IR) spectral data. Partial least squares (PLS) methods have become the most widely used multivariate method for quantitative spectroscopic analyses. Most often these methods are limited by model error or the accuracy or precision of the reference methods. However, in some cases, the precision of the quantitative analysis is limited by the noise in the spectroscopic signal. In these situations, the precision of the PLS calibrations and predictions can be improved by the incorporation of weighting in the PLS algorithm. If the spectral noise of the system is known (e.g., in the case of detector-noise-limited cases), then appropriate weighting can be incorporated into the multivariate spectral calibrations and predictions. A weighted PLS (WPLS) algorithm was developed to improve the precision of the analysis in the case of spectral-noise-limited data. This new PLS algorithm was then tested with real and simulated data, and the results compared with the unweighted PLS algorithm. Using near-infrared (NIR) calibration precision when the WPLS algorithm was applied. The best WPLS method improved prediction precision for the analysis of one of the minor components by a factor of nearly 9 relative to the unweighted PLS algorithm.
Ballyns, Jeffrey J; Cohen, Daniel L; Malone, Evan; Maher, Suzanne A; Potter, Hollis G; Wright, Timothy; Lipson, Hod; Bonassar, Lawrence J
2010-08-01
Quantification of shape fidelity of complex geometries for tissue-engineered constructs has not been thoroughly investigated. The objective of this study was to quantitatively describe geometric fidelities of various approaches to the fabrication of anatomically shaped meniscal constructs. Ovine menisci (n = 4) were imaged using magnetic resonance imaging (MRI) and microcomputed tomography (microCT). Acrylonitrile butadiene styrene plastic molds were designed from each imaging modality and three-dimensional printed on a Stratasys FDM 3000. Silastic impression molds were fabricated directly from ovine menisci. These molds were used to generate shaped constructs using 2% alginate with 2% CaSO(4). Solid freeform fabrication was conducted on a custom open-architecture three-dimensional printing platform. Printed samples were made using 2% alginate with 0.75% CaSO(4). Hydrogel constructs were scanned via laser triangulation distance sensor. The point cloud images were analyzed to acquire computational measurements for key points of interest (e.g., height, width, and volume). Silastic molds were within + or - 10% error with respect to the native tissue for seven key measurements, microCT molds for six of seven, microCT prints for four of seven, MRI molds for five of seven, and MRI prints for four of seven. This work shows the ability to generate and quantify anatomically shaped meniscal constructs of high geometric fidelity and lends insight into the relative geometric fidelities of several tissue engineering techniques. PMID:19788346
An improved method for calibrating the gantry angles of linear accelerators.
Higgins, Kyle; Treas, Jared; Jones, Andrew; Fallahian, Naz Afarin; Simpson, David
2013-11-01
Linear particle accelerators (linacs) are widely used in radiotherapy procedures; therefore, accurate calibrations of gantry angles must be performed to prevent the exposure of healthy tissue to excessive radiation. One of the common methods for calibrating these angles is the spirit level method. In this study, a new technique for calibrating the gantry angle of a linear accelerator was examined. A cubic phantom was constructed of Styrofoam with small lead balls, embedded at specific locations in this foam block. Several x-ray images were taken of this phantom at various gantry angles using an electronic portal imaging device on the linac. The deviation of the gantry angles were determined by analyzing the images using a customized computer program written in ImageJ (National Institutes of Health). Gantry angles of 0, 90, 180, and 270 degrees were chosen and the results of both calibration methods were compared for each of these angles. The results revealed that the image method was more precise than the spirit level method. For the image method, the average of the measured values for the selected angles of 0, 90, 180, and 270 degrees were found to be -0.086 ± 0.011, 90.018 ± 0.011, 180.178 ± 0.015, and 269.972 ± 0.006 degrees, respectively. The corresponding average values using the spirit level method were 0.2 ± 0.03, 90.2 ± 0.04, 180.1 ± 0.01, and 269.9 ± 0.05 degrees, respectively. Based on these findings, the new method was shown to be a reliable technique for calibrating the gantry angle. PMID:24077078
Hinker, P.; Hansen, C.
1993-09-01
An algorithm is presented which describes an application independent method for reducing the number of polygonal primitives required to faithfully represent an object. Reducing polygon count without a corresponding reduction in object detail is important for: achieving interactive frame rates in scientific visualization, reducing mass storage requirements, and facilitating the transmission of large, multi-timestep geometric data sets. This paper shows how coplanar and nearly coplanar polygons can be merged into larger complex polygons and re-triangulated into fewer simple polygons than originally required. The notable contributions of this paper are: (1) a method for quickly grouping polygons into nearly coplanar sets, (2) a fast approach for merging coplanar polygon sets and, (3) a simple, robust triangulation method for polygons created by 1 and 2. The central idea of the algorithm is the notion of treating polygonal data as a collection of segments and removing redundant segments to quickly form polygon hulls which represent the merged coplanar sets.
Calibrating CAT Pools and Online Pretest Items Using Marginal Maximum Likelihood Methods.
ERIC Educational Resources Information Center
Pommerich, Mary; Segall, Daniel O.
Research discussed in this paper was conducted as part of an ongoing large-scale simulation study to evaluate methods of calibrating pretest items for computerized adaptive testing (CAT) pools. The simulation was designed to mimic the operational CAT Armed Services Vocational Aptitude Battery (ASVAB) testing program, in which a single pretest item…
Calibration method for line-structured light vision sensor based on a single ball target
NASA Astrophysics Data System (ADS)
Liu, Zhen; Li, Xiaojing; Li, Fengjiao; Zhang, Guangjun
2015-06-01
Profile feature imaging for ball targets is unaffected by the position of the target. On this basis, this study proposes a method for the rapid calibration of a line-structured light system based on a single ball target. The calibration process is as follows: the ball target is placed at least once and is illuminated by the light stripe from the laser projector. The vision sensor captures an image of this target. The laser stripe and profile images of the ball target are then extracted. Based on these extracted features and the optical centre of the camera, the spatial equations of the ball target and a cone profile are calculated. The plane on which the intersection line of the two equations lies is the light plane. Finally, the optimal solution for the light plane equation is obtained through nonlinear optimization under a maximum likelihood criterion. The validity of the proposed method is demonstrated through simulation and physical experiments. In the physical experiment, the field of view of the structured light vision sensor measures 300 mm×250 mm. A calibration accuracy of 0.04 mm can be achieved using the proposed method. This accuracy is comparable to that of the calibration method which utilizes planar targets.
A method for atomic force microscopy cantilever stiffness calibration under heavy fluid loading
Kennedy, Scott J.; Cole, Daniel G.; Clark, Robert L.
2009-12-15
This work presents a method for force calibration of rectangular atomic force microscopy (AFM) microcantilevers under heavy fluid loading. Theoretical modeling of the thermal response of microcantilevers is discussed including a fluid-structure interaction model of the cantilever-fluid system that incorporates the results of the fluctuation-dissipation theorem. This model is curve fit to the measured thermal response of a cantilever in de-ionized water and a cost function is used to quantify the difference between the theoretical model and measured data. The curve fit is performed in a way that restricts the search space to parameters that reflect heavy fluid loading conditions. The resulting fitting parameters are used to calibrate the cantilever. For comparison, cantilevers are calibrated using Sader's method in air and the thermal noise method in both air and water. For a set of eight cantilevers ranging in stiffness from 0.050 to 5.8 N/m, the maximum difference between Sader's calibration performed in air and the new method performed in water was 9.4%. A set of three cantilevers that violate the aspect ratio assumption associated with the fluid loading model (length-to-width ratios less than 3.5) ranged in stiffness from 0.85 to 4.7 N/m and yielded differences as high as 17.8%.
ERIC Educational Resources Information Center
Zhang, Mo; Williamson, David M.; Breyer, F. Jay; Trapani, Catherine
2012-01-01
This article describes two separate, related studies that provide insight into the effectiveness of "e-rater" score calibration methods based on different distributional targets. In the first study, we developed and evaluated a new type of "e-rater" scoring model that was cost-effective and applicable under conditions of absent human rating and…
A new time calibration method for switched-capacitor-array-based waveform samplers
Kim, H.; Chen, C. -T.; Eclov, N.; Ronzhin, A.; Murat, P.; Ramberg, E.; Los, S.; Moses, W.; Choong, W. -S.; Kao, C. -M.
2014-08-24
Here we have developed a new time calibration method for the DRS4 waveform sampler that enables us to precisely measure the non-uniform sampling interval inherent in the switched-capacitor cells of the DRS4. The method uses the proportionality between the differential amplitude and sampling interval of adjacent switched-capacitor cells responding to a sawtooth-shape pulse. In the experiment, a sawtooth-shape pulse with a 40 ns period generated by a Tektronix AWG7102 is fed to a DRS4 evaluation board for calibrating the sampling intervals of all 1024 cells individually. The electronic time resolution of the DRS4 evaluation board with the new time calibrationmore » is measured to be ~2.4 ps RMS by using two simultaneous Gaussian pulses with 2.35 ns full-width at half-maximum and applying a Gaussian fit. The time resolution dependencies on the time difference with the new time calibration are measured and compared to results obtained by another method. Ultimately, the new method could be applicable for other switched-capacitor-array technology-based waveform samplers for precise time calibration.« less
NASA Astrophysics Data System (ADS)
He, Qian; Wang, Guangping; Wu, Jingli; Li, Junwei
2014-11-01
As the impact of the instrument internal error, external interference and other factors, the interferogram measured by Fourier transform spectrometer is asymmetric, result in the complex outcome after Fourier transform. Currently, most radiometric calibration method used for Fourier transform spectrometer is usually based on real spectrums, which is converted from the above complex spectrum by calculating magnitude value or make the phase correction first. Proceed from error sources and mechanisms of the Fourier transform spectrometer, we propose a multi-point radiometric calibration method based on complex spectral data to improve the processing efficiency and accuracy, which is obtained by the original interferogram via Fourier transform. We solving the instrument response function include linear gain and offset by complex spectrum above to calculate complex spectral radiance. Compared with the traditional method based on real spectrum, the present efficient method does not limited to real spectrum and the phase correction is not required. In this paper, we use BOMEM's MR304 Fourier transform infrared spectrometer and the DCN1000N3 blackbody made by HGH Infrared Systems to carry out the radiation calibration experiment in laboratory. The results show that, the amplitude of complex radiance spectrum obtained by this method has a high consistency with the theoretical value, while the extra imaginary spectrum is similar with the difference between results and theoretical value in absolute value and trends. It proved that, this multi-point radiometric calibration method by using the amplitude of complex spectral data is highly reliable; meanwhile, the imaginary spectrum can reflect the calibration error very well and offer a new technical approach for accuracy evaluation research.
Energy Calibration of the BaBar EMC Using the Pi0 Invariant Mass Method
Tanner, David J.; /Manchester U.
2007-04-06
The BaBar electromagnetic calorimeter energy calibration method was compared with the local and global peak iteration procedures, of Crystal Barrel and CLEO-II. An investigation was made of the possibility of {Upsilon}(4S) background reduction which could lead to increased statistics over a shorter time interval, for efficient calibration runs. The BaBar software package was used with unreconstructed data to study the energy response of the calorimeter, by utilizing the {pi}{sup 0} mass constraint on pairs of photon clusters.
Method and system for calibrating acquired spectra for use in spectral analysis
Reber, Edward L.; Rohde, Kenneth W.; Blackwood, Larry G.
2010-09-14
A method for calibrating acquired spectra for use in spectral analysis includes performing Gaussian peak fitting to spectra acquired by a plurality of NaI detectors to define peak regions. A Na and annihilation doublet may be located among the peak regions. A predetermined energy level may be applied to one of the peaks in the doublet and a location of a hydrogen peak may be predicted based on the location of at least one of the peaks of the doublet. Control systems for calibrating spectra are also disclosed.
NASA Astrophysics Data System (ADS)
Benamou, J.-D.; Lafitte, O.; Solliec, I.; Sentis, R.
2004-05-01
We present the computation of the amplitudes needed to evaluate the energy deposited by the laser wave in a plasma when a fold caustic forms. We first recall the Eulerian method designed in Benamou et al. (J. Comput. Appl. Math. 156 (2003) 93) to compute the caustic location and the phases associated to the two ray branches on its illuminated side. We then turn to the computation of the amplitudes needed to evaluate the energy. We use the classical geometrical form of the amplitudes to avoid the blow up problem at the caustic. As our proposed method is Eulerian we have to consider transport equations for these geometrical quantities where the advection field depends on the ray flow. The associated vector field structurally vanishes like the square root of the distance to the caustic when approaching the caustic. This introduces an additional difficulty as traditional finite difference scheme do not retain their accuracy for such advection fields. We propose a new scheme which remains of order 1 at the caustic and present a partial theoretical analysis as well as a numerical validation. We also test the capability of our Eulerian geometrical algorithm to produce numerical solution of the Helmholtz equation and attempt to check their frequency asymptotic accuracy.
A least squares method for CVT calibration in a RLC capacitor discharge circuit.
Yao, Stephen E.; Dickey, Fred McCartney; Pecak, Sara North
2003-11-01
In many applications, the ability to monitor the output of a capacitive discharge circuit is imperative to ensuring the reliability and accuracy of the unit. This monitoring is commonly accomplished with the use of a Current Viewing Transformer (CVT). In order to calibrate the CVT, the circuit is assembled with a Current Viewing Transformer (CVR) in addition to the CVT and the peak outputs compared. However, difficulties encountered with the use of CVRs make it desirable to eliminate the use of the CVR from the calibration process. This report describes a method for determining the calibration factor between the current throughput and the CVT voltage output in a capacitive discharge unit from the CVT ringdown data and values of initial voltage and capacitance of the circuit. Previous linear RLC fitting work for determining R, L, and C is adapted to return values of R, L, and the calibration factor, k. Separate solutions for underdamped and overdamped cases are presented and implemented on real circuit data using MathCad software with positive results. This technique may also offer a unique approach to self calibration of current measuring devices.
Cosmological models and gamma-ray bursts calibrated by using Padé method
NASA Astrophysics Data System (ADS)
Liu, Jing; Wei, Hao
2015-11-01
Gamma-ray bursts (GRBs) are among the most powerful sources in the universe. In the recent years, GRBs have been proposed as a complementary probe to type Ia supernovae. However, as is well known, there is a circularity problem in the use of GRBs to study cosmology. In this work, based on the Padé approximant, we propose a new cosmology-independent method to calibrate GRBs. We consider a sample consisting of 138 long Swift GRBs and obtain 79 calibrated long GRBs at high-redshift z>1.4 (named Mayflower sample) which can be used to constrain cosmological models without the circularity problem. Then, we consider the constraints on several cosmological models with these 79 calibrated GRBs and other observational data. We show that GRBs are competent to be a complementary probe to the other well-established cosmological observations.
Investigation of factors affecting the heater wire method of calibrating fine wire thermocouples
NASA Technical Reports Server (NTRS)
Keshock, E. G.
1972-01-01
An analytical investigation was made of a transient method of calibrating fine wire thermocouples. The system consisted of a 10 mil diameter standard thermocouple (Pt, Pt-13% Rh) and an 0.8 mil diameter chromel-alumel thermocouple attached to a 20 mil diameter electrically heated platinum wire. The calibration procedure consisted of electrically heating the wire to approximately 2500 F within about a seven-second period in an environment approximating atmospheric conditions at 120,000 feet. Rapid periodic readout of the standard and fine wire thermocouple signals permitted a comparison of the two temperature indications. An analysis was performed which indicated that the temperature distortion at the heater wire produced by the thermocouple junctions appears to be of negligible magnitude. Consequently, the calibration technique appears to be basically sound, although several practical changes which appear desirable are presented and discussed. Additional investigation is warranted to evaluate radiation effects and transient response characteristics.
Kaczmarczyk, B; Morejko-Buz, B; Stolarzewicz, A
2001-08-01
Infrared spectroscopy has been used to monitor the polymerization of methyl methacrylate. Concentrations of methyl methacrylate in the reaction mixture were determined by use of three calibration methods. Classical quantitative analysis was used to measure the height of the stretching vibration bands of the vinyl group at 1639 cm(-1). A calibration procedure using the considerably higher intensity of the C = O stretching vibration band of the carbonyl ester group at 1725 cm(-1) seemed useful only for high concentrations of methyl methacrylate, i.e. at the beginning of reaction, because this band overlaps that of poly(methyl methacrylate). Use of second-derivative spectra and measuring their values at 1725 cm(-1) enabled estimation of ten times lower concentrations of methyl methacrylate the calibration using the band from the vinyl group. PMID:11569872
Dong, Zhichao; Cheng, Haobo; Feng, Yunpeng; Su, Jingshi; Wu, Hengyu; Tam, Hon-Yuen
2015-07-01
This study presents a subaperture stitching method to calibrate system errors of several ∼2 m large scale 3D profile measurement instruments (PMIs). The calibration process was carried out by measuring a Φ460 mm standard flat sample multiple times at different sites of the PMI with a length gauge; then the subaperture data were stitched together using a sequential or simultaneous stitching algorithm that minimizes the inconsistency (i.e., difference) of the discrete data in the overlapped areas. The system error can be used to compensate the measurement results of not only large flats, but also spheres and aspheres. The feasibility of the calibration was validated by measuring a Φ1070 mm aspheric mirror, which can raise the measurement accuracy of PMIs and provide more reliable 3D surface profiles for guiding grinding, lapping, and even initial polishing processes. PMID:26193139
Method and apparatus for calibrating multi-axis load cells in a dexterous robot
NASA Technical Reports Server (NTRS)
Wampler, II, Charles W. (Inventor); Platt, Jr., Robert J. (Inventor)
2012-01-01
A robotic system includes a dexterous robot having robotic joints, angle sensors adapted for measuring joint angles at a corresponding one of the joints, load cells for measuring a set of strain values imparted to a corresponding one of the load cells during a predetermined pose of the robot, and a host machine. The host machine is electrically connected to the load cells and angle sensors, and receives the joint angle values and strain values during the predetermined pose. The robot presses together mating pairs of load cells to form the poses. The host machine executes an algorithm to process the joint angles and strain values, and from the set of all calibration matrices that minimize error in force balance equations, selects the set of calibration matrices that is closest in a value to a pre-specified value. A method for calibrating the load cells via the algorithm is also provided.
A novel implementation of homodyne time interval analysis method for primary vibration calibration
NASA Astrophysics Data System (ADS)
Sun, Qiao; Zhou, Ling; Cai, Chenguang; Hu, Hongbo
2011-12-01
In this paper, the shortcomings and their causes of the conventional homodyne time interval analysis (TIA) method is described with respect to its software algorithm and hardware implementation, based on which a simplified TIA method is proposed with the help of virtual instrument technology. Equipped with an ordinary Michelson interferometer and dual channel synchronous data acquisition card, the primary vibration calibration system using the simplified method can perform measurements of complex sensitivity of accelerometers accurately, meeting the uncertainty requirements laid down in pertaining ISO standard. The validity and accuracy of the simplified TIA method is verified by simulation and comparison experiments with its performance analyzed. This simplified method is recommended to apply in national metrology institute of developing countries and industrial primary vibration calibration labs for its simplified algorithm and low requirements on hardware.
NASA Astrophysics Data System (ADS)
Han, Buzhang; Wang, Mingying; Johnson, G. I.; Widmark, S.
1992-06-01
This investigation was started in order to obtain preliminary experience on the concept of a reference balance planned to be used in the T1500 calibration rig. The reference balance was simulated by using an available half model balance in the MK5 calibration rig at FFA. First the reference balance was calibrated and then the result was used for calibration of an ordinary six component sting balance attached with its model end to the half model balance. Both balances had been previously calibrated by the reposition method. Evaluation of the reference balance nonrepositioning concept was obtained by comparison of results.
Optics-Only Calibration of a Neural-Net Based Optical NDE Method for Structural Health Monitoring
NASA Technical Reports Server (NTRS)
Decker, Arthur J.
2004-01-01
A calibration process is presented that uses optical measurements alone to calibrate a neural-net based NDE method. The method itself detects small changes in the vibration mode shapes of structures. The optics-only calibration process confirms previous work that the sensitivity to vibration-amplitude changes can be as small as 10 nanometers. A more practical value in an NDE service laboratory is shown to be 50 nanometers. Both model-generated and experimental calibrations are demonstrated using two implementations of the calibration technique. The implementations are based on previously published demonstrations of the NDE method and an alternative calibration procedure that depends on comparing neural-net and point sensor measurements. The optics-only calibration method, unlike the alternative method, does not require modifications of the structure being tested or the creation of calibration objects. The calibration process can be used to test improvements in the NDE process and to develop a vibration-mode-independence of damagedetection sensitivity. The calibration effort was intended to support NASA s objective to promote safety in the operations of ground test facilities or aviation safety, in general, by allowing the detection of the gradual onset of structural changes and damage.
VIIRS Day-Night Band (DNB) calibration methods for improved uniformity
NASA Astrophysics Data System (ADS)
Mills, Stephen; Miller, Steven D.
2014-10-01
The Suomi-NPP VIIRS Day-Night Band (DNB) offers quantitative measurements of visible and near-infrared light over a dynamic range from full daylight to the dimmest nighttime scenes. This range presents a challenge to radiometric calibration, but the instrument has exceeded all of its absolute radiometric requirements. Nevertheless, striping and banding are still visible, day or night, but especially in low-light scenes. The causes may be cross talk, stray light or hysteresis in the data used for calibration. These issues combine to reduce the utility of these unique observations for gaining new insight on the nocturnal environment. This paper presents methods for improving gain and offset uniformity for both day and night scenes while maintaining absolute radiometric accuracy. We evaluate removal of fixed-pattern non-uniformity in dark scenes on a per orbit basis using three different techniques: i) tracking the darkest 25th percentile calibration sector signal; ii) taking the mean of filtered dark Earth-view scenes to determine offset; iii) minimizing correlated error for dark scenes within an aggregation zone. For gain uniformity we discuss some problems with the current calibration methods, and demonstrate a technique to minimize the correlated error between detectors and aggregation zones using the moment matching technique for moonlit scenes. A similar technique can be used for daytime and twilight scenes. An alternative cross-calibration technique between gain stages uses indirect illumination of solar diffuser view. The use of the space view and blackbody view for cross-calibration is also discussed. Histogram equalization is discussed for minimizing striping and banding. In all cases, data with stray light is filtered out to prevent contamination of the destriping process.
Johnston, Mark D.; Oliver, Bryan V.; Droemer, Darryl W.; Frogget, Brent; Crain, Marlon D.; Maron, Yitzhak
2012-08-15
This paper describes a convenient and accurate method to calibrate fast (<1 ns resolution) streaked, fiber optic light collection, spectroscopy systems. Such systems are inherently difficult to calibrate due to the lack of sufficiently intense, calibrated light sources. Such a system is used to collect spectral data on plasmas generated in electron beam diodes fielded on the RITS-6 accelerator (8-12MV, 140-200kA) at Sandia National Laboratories. On RITS, plasma light is collected through a small diameter (200 {mu}m) optical fiber and recorded on a fast streak camera at the output of a 1 meter Czerny-Turner monochromator. For this paper, a 300 W xenon short arc lamp (Oriel Model 6258) was used as the calibration source. Since the radiance of the xenon arc varies from cathode to anode, just the area around the tip of the cathode ('hotspot') was imaged onto the fiber, to produce the highest intensity output. To compensate for chromatic aberrations, the signal was optimized at each wavelength measured. Output power was measured using 10 nm bandpass interference filters and a calibrated photodetector. These measurements give power at discrete wavelengths across the spectrum, and when linearly interpolated, provide a calibration curve for the lamp. The shape of the spectrum is determined by the collective response of the optics, monochromator, and streak tube across the spectral region of interest. The ratio of the spectral curve to the measured bandpass filter curve at each wavelength produces a correction factor (Q) curve. This curve is then applied to the experimental data and the resultant spectra are given in absolute intensity units (photons/sec/cm{sup 2}/steradian/nm). Error analysis shows this method to be accurate to within +/- 20%, which represents a high level of accuracy for this type of measurement.
NASA Astrophysics Data System (ADS)
Johnston, Mark D.; Oliver, Bryan V.; Droemer, Darryl W.; Frogget, Brent; Crain, Marlon D.; Maron, Yitzhak
2012-08-01
This paper describes a convenient and accurate method to calibrate fast (<1 ns resolution) streaked, fiber optic light collection, spectroscopy systems. Such systems are inherently difficult to calibrate due to the lack of sufficiently intense, calibrated light sources. Such a system is used to collect spectral data on plasmas generated in electron beam diodes fielded on the RITS-6 accelerator (8-12MV, 140-200kA) at Sandia National Laboratories. On RITS, plasma light is collected through a small diameter (200 μm) optical fiber and recorded on a fast streak camera at the output of a 1 meter Czerny-Turner monochromator. For this paper, a 300 W xenon short arc lamp (Oriel Model 6258) was used as the calibration source. Since the radiance of the xenon arc varies from cathode to anode, just the area around the tip of the cathode ("hotspot") was imaged onto the fiber, to produce the highest intensity output. To compensate for chromatic aberrations, the signal was optimized at each wavelength measured. Output power was measured using 10 nm bandpass interference filters and a calibrated photodetector. These measurements give power at discrete wavelengths across the spectrum, and when linearly interpolated, provide a calibration curve for the lamp. The shape of the spectrum is determined by the collective response of the optics, monochromator, and streak tube across the spectral region of interest. The ratio of the spectral curve to the measured bandpass filter curve at each wavelength produces a correction factor (Q) curve. This curve is then applied to the experimental data and the resultant spectra are given in absolute intensity units (photons/sec/cm2/steradian/nm). Error analysis shows this method to be accurate to within +/- 20%, which represents a high level of accuracy for this type of measurement.
NASA Astrophysics Data System (ADS)
Berglund, M.; Baxter, D. C.
1992-12-01
One of the major problems involved in the direct analysis of solid samples by electrothermal atomic absorption spectrometry (ETAAS) lies in the calibration step because non-spectral interference effects are often pronounced. Three standardization techniques have been described and used in solid sampling-ETAAS: (i) standard additions method; (ii) calibration relative to a certified reference material; and (iii) calibration curve technique. However, an adequate statistical evaluation of the uncertainty in the analyte concentration in the solid sample is most frequently neglected, and reported errors may be seriously underestimated. This can be attributed directly to the complexity of the statistical expressions required to accurately account for errors in each of the calibration techniques mentioned above, and the general lack of relevant reference literature. The object of this work has been to develop a computer package which will perform the necessary statistical analyses of solid sampling-ETAAS data; the result is the program "SOLIDS" described here in the form of an electronic publication in Spectrochimica Acta Electronica, the electronic section of Spectrochimica Acta Part B. The program could also be useful in other analytical fields where similar calibration methods are used. The hard copy text, outlining the calibration models and their associated errors, is accompanied by a diskette containing the program, some data files, and a manual. Use of the program is exemplified in the text, with some of the data files discussed included on the diskette which, together with the manual, should enable the reader to become familiarized with the operation of the program, and the results generated.
von Bartheld, C
2002-04-01
Investigators must choose between counting methods to quantify microscopic particles in tissues. The conventional profile-based ("model-based" or "2D-") counting methods have been criticized for their potential biases due to assumptions about shapes, sizes, and orientation of particles when converting profile counts into cell numbers. New stereological methods ("design-based" or "3D-") methods such as the optical disector or physical disector were initially introduced as being inherently unbiased. Recent calibration analyses and comparisons of results from different investigators have revealed the potential for significant biases in the most efficient and most frequently used design-based method, the optical disector. This review aims to objectively assess the strengths and limitations of current profile- and disector-based cell counting methods by examination of studies in which these methods have been calibrated against the "gold-standard", counts obtained by 3-dimensional reconstruction of serial sections. Advantages and disadvantages of each counting method and the associated embedding and sectioning techniques are compared and frequent mistakes and pitfalls of each technique are discussed. The importance of a calibration step for each technique is emphasized, and a protocol is provided for a quick and simple calibration by a "sampling" 3-D reconstruction of limited serial sections. Trends in the usage of counting methods are analyzed in four major journals. It is hoped that this review will be helpful, for both investigators and manuscript reviewers, in clarifying some of the contentious issues in the choice and implementation of appropriate methods for particle counting in tissue sections. PMID:11962763
New methods for treatment effect calibration, with applications to non-inferiority trials.
Zhang, Zhiwei; Nie, Lei; Soon, Guoxing; Hu, Zonghui
2016-03-01
In comparative effectiveness research, it is often of interest to calibrate treatment effect estimates from a clinical trial to a target population that differs from the study population. One important application is an indirect comparison of a new treatment with a placebo control on the basis of two separate randomized clinical trials: a non-inferiority trial comparing the new treatment with an active control and a historical trial comparing the active control with placebo. The available methods for treatment effect calibration include an outcome regression (OR) method based on a regression model for the outcome and a weighting method based on a propensity score (PS) model. This article proposes new methods for treatment effect calibration: one based on a conditional effect (CE) model and two doubly robust (DR) methods. The first DR method involves a PS model and an OR model, is asymptotically valid if either model is correct, and attains the semiparametric information bound if both models are correct. The second DR method involves a PS model, a CE model, and possibly an OR model, is asymptotically valid under the union of the PS and CE models, and attains the semiparametric information bound if all three models are correct. The various methods are compared in a simulation study and applied to recent clinical trials for treating human immunodeficiency virus infection. PMID:26363775
Self-referencing calibration method for transmission spheres in Fizeau interferometry
NASA Astrophysics Data System (ADS)
Burke, Jan; Wu, David S.
2010-08-01
The calibration of reference surfaces becomes important in interferometry whenever the tolerances for the tested component are comparable to the imperfections of the reference surface itself. To achieve measurement accuracy better than the reference surface, its errors must be characterised and subtracted from the measurement result. We propose a rapid and simple technique utilising a flat mirror in the focus of the converging test wavefront and a partial occlusion of the test beam, to implement a double-pass self-calibration of the reference surface. Stitching together three or more measurements, with the beam stop appropriately rotated, yields the full-aperture calibration data. The method cannot detect point-antisymmetric errors, but common errors in reference spheres, such as spherical aberration and astigmatism, are point-symmetric and should still be adequately captured. For calibrating spherical surfaces in Fizeau interferometry, a ball of good sphericity can be measured against the reference surface in a number of random orientations. This averages out the errors of the ball and converges toward the stationary error in the reference sphere. Depending on the quality of the ball and the desired uncertainty, the number of orientations required can be large (50-100), which is laborious and time-consuming. We compare the performance of the new technique with the ball-averaging method and the so-called "cat's eye" method to assess the practical trade-offs involved.
A velocity dependent effective angle method for calibration of X-probes at low velocities
NASA Astrophysics Data System (ADS)
Bakken, Ole Martin; Krogstad, Per-Åge
A velocity dependent effective angle (VDEA) method for the calibration of yaw response of hot-wire X-probes at low flow velocities (0.5-6 m/s) is presented. Comparisons with a full velocity vs. yaw-angle method (Österlund 1999) in a smooth wall channel flow indicate that there is only moderate advantage in using the latter method, which is considerably more laborious. Comparisons with direct numerical simulations (DNS) (Moser et al. 1999) and the more common fixed effective angle method (FEA) show that the VDEA method significantly improves estimates of Reynolds stresses compared to the FEA method.
Comparison of different methods for liquid level adjustment in tank prover calibration
NASA Astrophysics Data System (ADS)
Garcia, D. A.; Farias, E. C.; Gabriel, P. C.; Aquino, M. H.; Gomes, R. S. E.; Y Aibe, V.
2015-01-01
The adjustment of the liquid level during the calibration of tank provers with fixed volume is normally done by overfill but it can be done in different ways. In this article four level adjustment techniques are compared: plate, pipette, ruler and overfill adjustment. The adjustment methods using plate and pipette presented good agreement with the tank's nominal volume and lower uncertainty among the tested methods.
A fully Bayesian method for jointly fitting instrumental calibration and X-ray spectral models
Xu, Jin; Yu, Yaming; Van Dyk, David A.; Kashyap, Vinay L.; Siemiginowska, Aneta; Drake, Jeremy; Ratzlaff, Pete; Connors, Alanna; Meng, Xiao-Li E-mail: yamingy@ics.uci.edu E-mail: vkashyap@cfa.harvard.edu E-mail: jdrake@cfa.harvard.edu E-mail: meng@stat.harvard.edu
2014-10-20
Owing to a lack of robust principled methods, systematic instrumental uncertainties have generally been ignored in astrophysical data analysis despite wide recognition of the importance of including them. Ignoring calibration uncertainty can cause bias in the estimation of source model parameters and can lead to underestimation of the variance of these estimates. We previously introduced a pragmatic Bayesian method to address this problem. The method is 'pragmatic' in that it introduced an ad hoc technique that simplified computation by neglecting the potential information in the data for narrowing the uncertainty for the calibration product. Following that work, we use a principal component analysis to efficiently represent the uncertainty of the effective area of an X-ray (or γ-ray) telescope. Here, however, we leverage this representation to enable a principled, fully Bayesian method that coherently accounts for the calibration uncertainty in high-energy spectral analysis. In this setting, the method is compared with standard analysis techniques and the pragmatic Bayesian method. The advantage of the fully Bayesian method is that it allows the data to provide information not only for estimation of the source parameters but also for the calibration product—here the effective area, conditional on the adopted spectral model. In this way, it can yield more accurate and efficient estimates of the source parameters along with valid estimates of their uncertainty. Provided that the source spectrum can be accurately described by a parameterized model, this method allows rigorous inference about the effective area by quantifying which possible curves are most consistent with the data.
Development and evaluation of a method of calibrating medical displays based on fixed adaptation
Sund, Patrik Månsson, Lars Gunnar; Båth, Magnus
2015-04-15
Purpose: The purpose of this work was to develop and evaluate a new method for calibration of medical displays that includes the effect of fixed adaptation and by using equipment and luminance levels typical for a modern radiology department. Methods: Low contrast sinusoidal test patterns were derived at nine luminance levels from 2 to 600 cd/m{sup 2} and used in a two alternative forced choice observer study, where the adaptation level was fixed at the logarithmic average of 35 cd/m{sup 2}. The contrast sensitivity at each luminance level was derived by establishing a linear relationship between the ten pattern contrast levels used at every luminance level and a detectability index (d′) calculated from the fraction of correct responses. A Gaussian function was fitted to the data and normalized to the adaptation level. The corresponding equation was used in a display calibration method that included the grayscale standard display function (GSDF) but compensated for fixed adaptation. In the evaluation study, the contrast of circular objects with a fixed pixel contrast was displayed using both calibration methods and was rated on a five-grade scale. Results were calculated using a visual grading characteristics method. Error estimations in both observer studies were derived using a bootstrap method. Results: The contrast sensitivities for the darkest and brightest patterns compared to the contrast sensitivity at the adaptation luminance were 37% and 56%, respectively. The obtained Gaussian fit corresponded well with similar studies. The evaluation study showed a higher degree of equally distributed contrast throughout the luminance range with the calibration method compensated for fixed adaptation than for the GSDF. The two lowest scores for the GSDF were obtained for the darkest and brightest patterns. These scores were significantly lower than the lowest score obtained for the compensated GSDF. For the GSDF, the scores for all luminance levels were statistically
A calibration method for proposed XRF measurements of arsenic and selenium in nail clippings.
Gherase, Mihai R; Fleming, David E B
2011-10-21
A calibration method for proposed x-ray fluorescence (XRF) measurements of arsenic and selenium in nail clippings is demonstrated. Phantom nail clippings were produced from a whole nail phantom (0.7 mm thickness, 25 × 25 mm(2) area) and contained equal concentrations of arsenic and selenium ranging from 0 to 20 µg g(-1) in increments of 5 µg g(-1). The phantom nail clippings were then grouped in samples of five different masses: 20, 40, 60, 80 and 100 mg for each concentration. Experimental x-ray spectra were acquired for each of the sample masses using a portable x-ray tube and a detector unit. Calibration lines (XRF signal in a number of counts versus stoichiometric elemental concentration) were produced for each of the two elements. A semi-empirical relationship between the mass of the nail phantoms (m) and the slope of the calibration line (s) was determined separately for arsenic and selenium. Using this calibration method, one can estimate elemental concentrations and their uncertainties from the XRF spectra of human nail clippings. PMID:21937772
Noo, F; Clackdoyle, R; Mennessier, C; White, T A; Roney, T J
2000-11-01
This paper is about calibration of cone-beam (CB) scanners for both x-ray computed tomography and single-photon emission computed tomography. Scanner calibration refers here to the estimation of a set of parameters which fully describe the geometry of data acquisition. Such parameters are needed for the tomographic reconstruction step. The discussion is limited to the usual case where the cone vertex and planar detector move along a circular path relative to the object. It is also assumed that the detector does not have spatial distortions. We propose a new method which requires a small set of measurements of a simple calibration object consisting of two spherical objects, that can be considered as 'point' objects. This object traces two ellipses on the detector and from the parametric description of these ellipses, the calibration geometry can be determined analytically using explicit formulae. The method is robust and easy to implement. However, it is not fully general as it is assumed that the detector is parallel to the rotation axis of the scanner. Implementation details are given for an experimental x-ray CB scanner. PMID:11098919
A calibration method for proposed XRF measurements of arsenic and selenium in nail clippings
NASA Astrophysics Data System (ADS)
Gherase, Mihai R.; Fleming, David E. B.
2011-10-01
A calibration method for proposed x-ray fluorescence (XRF) measurements of arsenic and selenium in nail clippings is demonstrated. Phantom nail clippings were produced from a whole nail phantom (0.7 mm thickness, 25 × 25 mm2 area) and contained equal concentrations of arsenic and selenium ranging from 0 to 20 µg g-1 in increments of 5 µg g-1. The phantom nail clippings were then grouped in samples of five different masses: 20, 40, 60, 80 and 100 mg for each concentration. Experimental x-ray spectra were acquired for each of the sample masses using a portable x-ray tube and a detector unit. Calibration lines (XRF signal in a number of counts versus stoichiometric elemental concentration) were produced for each of the two elements. A semi-empirical relationship between the mass of the nail phantoms (m) and the slope of the calibration line (s) was determined separately for arsenic and selenium. Using this calibration method, one can estimate elemental concentrations and their uncertainties from the XRF spectra of human nail clippings.
Xu, Wen-Bin; Li, Jian-Jun; Zheng, Xiao-Bing
2013-01-01
In the present paper, a new calibration method of absolute spectral irradiance responsivity of sun channel of sun photometer was developed. A tunable laser was used as source and a standard tranfer detector, calibrated against cryogenic absolute radiometer, was used to measure laser beam power. By raster scanning of a single collimated laser beam to generate the uniform irradiance field at the plane of effective aperture stop of sun photometer, the absolute irradiance responsivity of center wavelength of the 870 nm unpolarized sun channels of sun photometer was obtained accurately. The relative spectral irradiance responsivity of corresponding channel was obtained by using lamp-monochromator system and then used to acquire the absolute spectral irradiance responsivity in the laboratory. On the basis of the above results, the top-of-the-atmosphere responsive constant V0 was obtained by integration with extraterrestrial solar spectral irradiance data. Comparing the calibration result with that from GSFC, NASA in 2009, the difference is only 3.75%. In the last, the uncertainties of calibration were evaluated and reached to 2.06%. The principle feasibility of the new method was validated. PMID:23586268
Hybrid PSO-ASVR-based method for data fitting in the calibration of infrared radiometer
NASA Astrophysics Data System (ADS)
Yang, Sen; Li, Chengwei
2016-06-01
The present paper describes a hybrid particle swarm optimization-adaptive support vector regression (PSO-ASVR)-based method for data fitting in the calibration of infrared radiometer. The proposed hybrid PSO-ASVR-based method is based on PSO in combination with Adaptive Processing and Support Vector Regression (SVR). The optimization technique involves setting parameters in the ASVR fitting procedure, which significantly improves the fitting accuracy. However, its use in the calibration of infrared radiometer has not yet been widely explored. Bearing this in mind, the PSO-ASVR-based method, which is based on the statistical learning theory, is successfully used here to get the relationship between the radiation of a standard source and the response of an infrared radiometer. Main advantages of this method are the flexible adjustment mechanism in data processing and the optimization mechanism in a kernel parameter setting of SVR. Numerical examples and applications to the calibration of infrared radiometer are performed to verify the performance of PSO-ASVR-based method compared to conventional data fitting methods.
Hybrid PSO-ASVR-based method for data fitting in the calibration of infrared radiometer.
Yang, Sen; Li, Chengwei
2016-06-01
The present paper describes a hybrid particle swarm optimization-adaptive support vector regression (PSO-ASVR)-based method for data fitting in the calibration of infrared radiometer. The proposed hybrid PSO-ASVR-based method is based on PSO in combination with Adaptive Processing and Support Vector Regression (SVR). The optimization technique involves setting parameters in the ASVR fitting procedure, which significantly improves the fitting accuracy. However, its use in the calibration of infrared radiometer has not yet been widely explored. Bearing this in mind, the PSO-ASVR-based method, which is based on the statistical learning theory, is successfully used here to get the relationship between the radiation of a standard source and the response of an infrared radiometer. Main advantages of this method are the flexible adjustment mechanism in data processing and the optimization mechanism in a kernel parameter setting of SVR. Numerical examples and applications to the calibration of infrared radiometer are performed to verify the performance of PSO-ASVR-based method compared to conventional data fitting methods. PMID:27370427
NASA Astrophysics Data System (ADS)
Lu, Zenghai; Kasaragod, Deepa K.; Matcher, Stephen J.
2011-06-01
A phase fluctuation calibration method is presented for polarization-sensitive swept-source optical coherence tomography (PS-SS-OCT) using continuous polarization modulation. The method consists of the generation of a continuous triggered tone-burst waveform rather than an asynchronous waveform by use of a function generator and the removal of the global phases of the measured Jones matrices by use of matrix normalization. This could remove the use of auxiliary optical components for the phase fluctuation compensation in the system, which reduces the system complexity. Phase fluctuation calibration is necessary to obtain the reference Jones matrix by averaging the measured Jones matrices at sample surfaces. Measurements on an equine tendon sample were made by the PS-SS-OCT system to validate the proposed method.
A Focusing Method in the Calibration Process of Image Sensors Based on IOFBs
Fernández, Pedro R.; Lázaro, José L.; Gardel, Alfredo; Cano, Ángel E.; Bravo, Ignacio
2010-01-01
A focusing procedure in the calibration process of image sensors based on Incoherent Optical Fiber Bundles (IOFBs) is described using the information extracted from fibers. These procedures differ from any other currently known focusing method due to the non spatial in-out correspondence between fibers, which produces a natural codification of the image to transmit. Focus measuring is essential prior to carrying out calibration in order to guarantee accurate processing and decoding. Four algorithms have been developed to estimate the focus measure; two methods based on mean grey level, and the other two based on variance. In this paper, a few simple focus measures are defined and compared. Some experimental results referred to the focus measure and the accuracy of the developed methods are discussed in order to demonstrate its effectiveness. PMID:22315526
CHAMBERS,WILLIAM B.; HAALAND,DAVID M.; KEENAN,MICHAEL R.; MELGAARD,DAVID K.
1999-10-01
The advent of inductively coupled plasma-atomic emission spectrometers (ICP-AES) equipped with charge-coupled-device (CCD) detector arrays allows the application of multivariate calibration methods to the quantitative analysis of spectral data. We have applied classical least squares (CLS) methods to the analysis of a variety of samples containing up to 12 elements plus an internal standard. The elements included in the calibration models were Ag, Al, As, Au, Cd, Cr, Cu, Fe, Ni, Pb, Pd, and Se. By performing the CLS analysis separately in each of 46 spectral windows and by pooling the CLS concentration results for each element in all windows in a statistically efficient manner, we have been able to significantly improve the accuracy and precision of the ICP-AES analyses relative to the univariate and single-window multivariate methods supplied with the spectrometer. This new multi-window CLS (MWCLS) approach simplifies the analyses by providing a single concentration determination for each element from all spectral windows. Thus, the analyst does not have to perform the tedious task of reviewing the results from each window in an attempt to decide the correct value among discrepant analyses in one or more windows for each element. Furthermore, it is not necessary to construct a spectral correction model for each window prior to calibration and analysis: When one or more interfering elements was present, the new MWCLS method was able to reduce prediction errors for a selected analyte by more than 2 orders of magnitude compared to the worst case single-window multivariate and univariate predictions. The MWCLS detection limits in the presence of multiple interferences are 15 rig/g (i.e., 15 ppb) or better for each element. In addition, errors with the new method are only slightly inflated when only a single target element is included in the calibration (i.e., knowledge of all other elements is excluded during calibration). The MWCLS method is found to be vastly
An improved method of energy calibration for position-sensitive silicon detectors
NASA Astrophysics Data System (ADS)
Sun, Ming-Dao; Huang, Tian-Heng; Liu, Zhong; Ding, Bing; Yang, Hua-Bin; Zhang, Zhi-Yuan; Wang, Jian-Guo; Ma, Long; Yu, Lin; Wang, Yong-Sheng; Gan, Zai-Guo; Xiao-Hong, Zhou
2016-04-01
Energy calibration of resistive charge division-based position-sensitive silicon detectors is achieved by parabolic fitting in the traditional method, where the systematic variations of vertex and curvature of the parabola with energy must be considered. In this paper we extend the traditional method in order to correct the fitting function, simplify the procedure of calibration and improve the experimental data quality. Instead of a parabolic function as used in the traditional method, a new function describing the relation of position and energy is introduced. The energy resolution of the 8.088 MeV α decay of 213Rn is determined to be about 87 keV (FWHM), which is better than the result of the traditional method, 104 keV (FWHM). The improved method can be applied to the energy calibration of resistive charge division-based position-sensitive silicon detectors with various performances. Supported by ‘100 Person Project’ of the Chinese Academy of Sciences and the National Natural Science Foundation of China (11405224 and 11435014)
A Global Calibration Method for Widely Distributed Cameras Based on Vanishing Features
Wu, Xiaolong; Wu, Sentang; Xing, Zhihui; Jia, Xiang
2016-01-01
This paper presents a global calibration method for widely distributed vision sensors in ring-topologies. Planar target with two mutually orthogonal groups of parallel lines is needed for each camera. Firstly, the relative pose of each camera and its corresponding target is found from the vanishing points and lines. Next, an auxiliary camera is used to find the relative poses between neighboring pairs of calibration targets. Then the relative pose from each target to the reference target is initialized by the chain of transformations, followed by nonlinear optimization based on the constraint of ring-topologies. Lastly, the relative poses between the cameras are found from the relative poses of calibration targets. Synthetic data, simulation images and real experiments all demonstrate that the proposed method is reliable and accurate. The accumulated error due to multiple coordinate transformations can be adjusted effectively by the proposed method. In real experiment, eight targets are located in an area about 1200 mm × 1200 mm. The accuracy of the proposed method is about 0.465 mm when the times of coordinate transformations reach a maximum. The proposed method is simple and can be applied to different camera configurations. PMID:27338386
A shearing-based method for the simultaneous calibration of angle measuring devices
NASA Astrophysics Data System (ADS)
Geckeler, Ralf D.; Just, Andreas
2014-10-01
In this paper, we present a novel adaptation of the shearing method to the simultaneous calibration of angle measuring devices which is based on multiple comparisons of their angle readings in different relative angular orientations. Without recourse to an external standard, the errors of the two devices can be recovered, up to their linear components, from a set of three comparisons. We demonstrate the method by the use of an autocollimator and an angle encoder. It proved to be ideally suited for the calibration of interpolation errors of the devices at small angular scales which are difficult to characterize with other methods. In the case that the linear components of the errors are needed, too, only two angle differences, which correspond to the changes in the relative angular orientations of the devices, need to be traced back to an external standard. A comprehensive overview, both theoretical and experimental, of the capabilities and limitations of the method is presented, including experimental data obtained with the high-precision primary angle standard of PTB. We demonstrate error-separation with a standard measurement uncertainty at a level of 1 milliarcsecond (5 nrad) which, when compared to uncertainties reachable by conventional calibration methods for autocollimators, represents an improvement by a factor of 2-3.
NASA Astrophysics Data System (ADS)
Roehrig, Hans; Hashmi, Syed F.; Dallas, William J.; Krupinski, Elizabeth A.; Rehm, Kelly; Fan, Jiahua
2010-08-01
Our laboratory has investigated the efficacy of a suite of color calibration and monitor profiling packages which employ a variety of color measurement sensors. Each of the methods computes gamma correction tables for the red, green and blue color channels of a monitor that attempt to: a) match a desired luminance range and tone reproduction curve; and b) maintain a target neutral point across the range of grey values. All of the methods examined here produce International Color Consortium (ICC) profiles that describe the color rendering capabilities of the monitor after calibration. Color profiles incorporate a transfer matrix that establishes the relationship between RGB driving levels and the International Commission on Illumination (CIE) XYZ (tristimulus) values of the resulting on-screen color; the matrix is developed by displaying color patches of known RGB values on the monitor and measuring the tristimulus values with a sensor. The number and chromatic distribution of color patches varies across methods and is usually not under user control. In this work we examine the effect of employing differing calibration and profiling methods on rendition of color images. A series of color patches encoded in sRGB color space were presented on the monitor using color-management software that utilized the ICC profile produced by each method. The patches were displayed on the calibrated monitor and measured with a Minolta CS200 colorimeter. Differences in intended and achieved luminance and chromaticity were computed using the CIE DE2000 color-difference metric, in which a value of ΔE = 1 is generally considered to be approximately one just noticeable difference (JND) in color. We observed between one and 17 JND's for individual colors, depending on calibration method and target. As an extension of this fundamental work1, we further improved our calibration method by defining concrete calibration parameters for the display, using the NEC wide gamut puck, and making sure
NASA Astrophysics Data System (ADS)
Summers, Jason E.; Takahashi, Kengo; Shimizu, Yasushi; Yamakawa, Takashi
2001-05-01
When based on geometrical acoustics, computational models used for auralization of auditorium sound fields are physically inaccurate at low frequencies. To increase accuracy while keeping computation tractable, hybrid methods using computational wave acoustics at low frequencies have been proposed and implemented in small enclosures such as simplified models of car cabins [Granier et al., J. Audio Eng. Soc. 44, 835-849 (1996)]. The present work extends such an approach to an actual 2400-m3 auditorium using the boundary-element method for frequencies below 100 Hz. The effect of including wave-acoustics at low frequencies is assessed by comparing the predictions of the hybrid model with those of the geometrical-acoustics model and comparing both with measurements. Conventional room-acoustical metrics are used together with new methods based on two-dimensional distance measures applied to time-frequency representations of impulse responses. Despite in situ measurements of boundary impedance, uncertainties in input parameters limit the accuracy of the computed results at low frequencies. However, aural perception ultimately defines the required accuracy of computational models. An algorithmic method for making such evaluations is proposed based on correlating listening-test results with distance measures between time-frequency representations derived from auditory models of the ear-brain system. Preliminary results are presented.
Roux, A; Laporte, S; Lecompte, J; Gras, L-L; Iordanoff, I
2016-01-25
The muscle-tendon complex (MTC) is a multi-scale, anisotropic, non-homogeneous structure. It is composed of fascicles, gathered together in a conjunctive aponeurosis. Fibers are oriented into the MTC with a pennation angle. Many MTC models use the Finite Element Method (FEM) to simulate the behavior of the MTC as a hyper-viscoelastic material. The Discrete Element Method (DEM) could be adapted to model fibrous materials, such as the MTC. DEM could capture the complex behavior of a material with a simple discretization scheme and help in understanding the influence of the orientation of fibers on the MTC׳s behavior. The aims of this study were to model the MTC in DEM at the macroscopic scale and to obtain the force/displacement curve during a non-destructive passive tensile test. Another aim was to highlight the influence of the geometrical parameters of the MTC on the global mechanical behavior. A geometrical construction of the MTC was done using discrete element linked by springs. Young׳s modulus values of the MTC׳s components were retrieved from the literature to model the microscopic stiffness of each spring. Alignment and re-orientation of all of the muscle׳s fibers with the tensile axis were observed numerically. The hyper-elastic behavior of the MTC was pointed out. The structure׳s effects, added to the geometrical parameters, highlight the MTC׳s mechanical behavior. It is also highlighted by the heterogeneity of the strain of the MTC׳s components. DEM seems to be a promising method to model the hyper-elastic macroscopic behavior of the MTC with simple elastic microscopic elements. PMID:26708963
Engel, Karsten; Hartmann, Ulrich; Potthast, Wolfgang; Brüggemann, Gert-Peter
2016-06-01
Biomechanical analyses of the stress distribution and the force transfer in the human knee are essential to better understand the aetiology of joint diseases. Accuracy studies of commonly used capacitive or resistive-based stress distribution measurement systems have led to severe problems caused by an inaccurate experimental setup. For instance, in one study, overestimations of the measured forces in the sensor's centre were reported. Therefore, the primary aim of this study was to investigate the ability of capacitive and resistive-based sensors to measure forces in a homogenous pressure environment and the secondary goal was to analyse the influence of different calibration materials on the measurement accuracy. A Novel pressure vessel and metal indenters covered with different rubber materials were used in combination with a material testing machine to load the sensors. Four different linearly increasing nominal forces (925-3670 N) were applied and the deviations between the nominal and the measured forces were calculated. The capacitive measurement system showed errors between 1% and 7% in the homogenous pressure environment, whereas the errors of the resistive system were found to vary between 4% and 17%. The influence of the calibration material was observed to be greater for the resistive sensors (1-179%) than for the capacitive sensors (0.5-25%). In conclusion, it can be stated that - for the pressure measurement systems compared in this article - the capacitive one is less sensitive to the calibration method and the calibration material than the resistive system. PMID:26146092
Study for external calibration method for cloud profiling radar on EarthCARE
NASA Astrophysics Data System (ADS)
Horie, Hiroaki; Kimura, Toshiyoshi; Okada, Kazuyuki; Ohno, Yuichi; Sato, Kenji; Kumagai, Hiroshi
2008-10-01
EarthCARE mission has objectives to reveal aerosol and cloud interaction and to reveal relationships with radiation budget. For this purpose, the EarthCARE satellite has four instruments, which are Atmospheric LIDAR (ATLID), Multi Spectral Imager (MSI) and Broad Band Radiometer (BBR) in addition to Cloud Profiling Radar (CPR). CPR is developed under cooperation of Japanese Aerospace Exploration Agency (JAXA) and National Institute of Information and Communications Technology (NICT) in Japan. The requirement of sensitivity is -35dBZ, therefore CPR uses W-band frequency and needs a large (2.5m) antenna reflector. The large antenna has small footprint and is to give up antenna scanning. From this, some difficulty of external calibration using active radar calibrator (ARC) is recognized. One solution of external calibration is using scattering from natural distributed target, such as sea surface. Then the measurement of sea surface scattering using airborne cloud radar was performed. The sea surface scattering property is being prepared. Second solution is that ARC puts on exact location of sub-satellite track. Precise sub-satellite track prediction is necessary. We focus second solution in this paper. The test experiment was demonstrated using CloudSat of NASA/JPL, which is provided CPR using W-band frequency. The feasibility of this calibration method is discussed.
NASA Technical Reports Server (NTRS)
Decker, Arthur J.
2004-01-01
A completely optical calibration process has been developed at Glenn for calibrating a neural-network-based nondestructive evaluation (NDE) method. The NDE method itself detects very small changes in the characteristic patterns or vibration mode shapes of vibrating structures as discussed in many references. The mode shapes or characteristic patterns are recorded using television or electronic holography and change when a structure experiences, for example, cracking, debonds, or variations in fastener properties. An artificial neural network can be trained to be very sensitive to changes in the mode shapes, but quantifying or calibrating that sensitivity in a consistent, meaningful, and deliverable manner has been challenging. The standard calibration approach has been difficult to implement, where the response to damage of the trained neural network is compared with the responses of vibration-measurement sensors. In particular, the vibration-measurement sensors are intrusive, insufficiently sensitive, and not numerous enough. In response to these difficulties, a completely optical alternative to the standard calibration approach was proposed and tested successfully. Specifically, the vibration mode to be monitored for structural damage was intentionally contaminated with known amounts of another mode, and the response of the trained neural network was measured as a function of the peak-to-peak amplitude of the contaminating mode. The neural network calibration technique essentially uses the vibration mode shapes of the undamaged structure as standards against which the changed mode shapes are compared. The published response of the network can be made nearly independent of the contaminating mode, if enough vibration modes are used to train the net. The sensitivity of the neural network can be adjusted for the environment in which the test is to be conducted. The response of a neural network trained with measured vibration patterns for use on a vibration isolation
NASA Technical Reports Server (NTRS)
Hrinda, Glenn A.; Nguyen, Duc T.
2008-01-01
A technique for the optimization of stability constrained geometrically nonlinear shallow trusses with snap through behavior is demonstrated using the arc length method and a strain energy density approach within a discrete finite element formulation. The optimization method uses an iterative scheme that evaluates the design variables' performance and then updates them according to a recursive formula controlled by the arc length method. A minimum weight design is achieved when a uniform nonlinear strain energy density is found in all members. This minimal condition places the design load just below the critical limit load causing snap through of the structure. The optimization scheme is programmed into a nonlinear finite element algorithm to find the large strain energy at critical limit loads. Examples of highly nonlinear trusses found in literature are presented to verify the method.
Ozone Correction for AM0 Calibrated Solar Cells for the Aircraft Method
NASA Technical Reports Server (NTRS)
Snyder, David B.; Scheiman, David A.; Jenkins, Phillip P.; Lyons, Valerie J. (Technical Monitor)
2002-01-01
The aircraft solar cell calibration method has provided cells calibrated to space conditions for 37 years. However, it is susceptible to systematic errors due to ozone concentration in the stratosphere. The present correction procedure applies a 1% increase to the measured Isc values. High band-gap cells are more sensitive to ozone adsorbed wavelengths so it has become important to reassess the correction technique. This paper evaluates the ozone correction to be 1+{O3}sup Fo, where Fo is 29.5x10(exp-6)/d.u. for a Silicon solar cell and 42.2xl0(exp -6)/d.u. for a GaAs cell. Results will be presented for high band-gap cells. A comparison with flight data indicates that this method of correcting for the ozone density improves the uncertainty of AM0 Isc to 0.5%.
A High Speed Calibration Method for Laser Positioner by Constant Velocity Scanning
NASA Astrophysics Data System (ADS)
Ono, Hiroyuki
This paper describes a high speed calibration method for laser positioner by scanning work area under constant velocity. Laser positioner consists of sinusoidal laser encoder, DC motor and the controller. The encoder has diffraction grating scale and laser optics. It generates sine and cosine outputs according to the travel distance. Qualities of the scale and the optics contribute to the fluctuation of output signal amplitude, DC offset and relative phase. First, the controller collects the output data under constant velocity of 4 samples per 1 sine wave length. The parameter can be estimated by simplified discrete Fourier transform method. Calibration data are collected every quarter sine wave length over all positioner work area. The result is stored in the table then referred by the controller in real time operation. Experiment results are also reported for HDD servo track writer application.
Effects of sensor calibration, balancing and parametrization on the signal space separation method
NASA Astrophysics Data System (ADS)
Nurminen, J.; Taulu, S.; Okada, Y.
2008-04-01
Signal space separation (SSS) is a novel method for processing multichannel biomagnetic data. It is useful for a variety of applications including interference suppression, movement compensation and conversion of measurements between sensor arrays. The performance of SSS has been examined mainly on a 306-channel whole-head magnetoencephalography system. To facilitate the adaptation of the method to other biomagnetometer systems, the effect of various properties of the sensor array on its performance needs to be studied. To this end, we examined the effects of gradiometer imbalance, sensor calibration errors and erroneous sensor geometry information on SSS using simulations. The results indicate that depending on the application, gradiometer balance on the level of 0.1% to 0.5% may be needed for satisfactory SSS performance. For wire-wound gradiometers, this requires very careful attention in manufacturing. Errors in calibration coefficients and geometry information were found to have less significance.
Effects of sensor calibration, balancing and parametrization on the signal space separation method.
Nurminen, J; Taulu, S; Okada, Y
2008-04-01
Signal space separation (SSS) is a novel method for processing multichannel biomagnetic data. It is useful for a variety of applications including interference suppression, movement compensation and conversion of measurements between sensor arrays. The performance of SSS has been examined mainly on a 306-channel whole-head magnetoencephalography system. To facilitate the adaptation of the method to other biomagnetometer systems, the effect of various properties of the sensor array on its performance needs to be studied. To this end, we examined the effects of gradiometer imbalance, sensor calibration errors and erroneous sensor geometry information on SSS using simulations. The results indicate that depending on the application, gradiometer balance on the level of 0.1% to 0.5% may be needed for satisfactory SSS performance. For wire-wound gradiometers, this requires very careful attention in manufacturing. Errors in calibration coefficients and geometry information were found to have less significance. PMID:18354243
Method for in-situ restoration of platinum resistance thermometer calibration
Carroll, R.M.
1989-01-03
A method is described for the in situ restoration of a platinum resistance thermometer, which has become decalibrated due to oxide surface film formation and/or strain-related damage, to a stress-free calibration condition wherein the thermometer includes a platinum resistor sensing element whose resistance varies with the temperature of the element in accordance with a known relationship. The method consists of: passing a controlled dc current through the platinum resistor sensing element, the current having a magnitude sufficient to raise the temperature of the element to its oxide decomposition and annealing temperature. The current is maintained for a heating period sufficient to restore the element to an oxide free surface and stress-free calibration condition.
NASA Astrophysics Data System (ADS)
Chung, Kun-Jen
2012-08-01
Cardenas-Barron [Cardenas-Barron, L.E. (2010) 'A Simple Method to Compute Economic order Quantities: Some Observations', Applied Mathematical Modelling, 34, 1684-1688] indicates that there are several functions in which the arithmetic-geometric mean method (AGM) does not give the minimum. This article presents another situation to reveal that the AGM inequality to locate the optimal solution may be invalid for Teng, Chen, and Goyal [Teng, J.T., Chen, J., and Goyal S.K. (2009), 'A Comprehensive Note on: An Inventory Model under Two Levels of Trade Credit and Limited Storage Space Derived without Derivatives', Applied Mathematical Modelling, 33, 4388-4396], Teng and Goyal [Teng, J.T., and Goyal S.K. (2009), 'Comment on 'Optimal Inventory Replenishment Policy for the EPQ Model under Trade Credit Derived without Derivatives', International Journal of Systems Science, 40, 1095-1098] and Hsieh, Chang, Weng, and Dye [Hsieh, T.P., Chang, H.J., Weng, M.W., and Dye, C.Y. (2008), 'A Simple Approach to an Integrated Single-vendor Single-buyer Inventory System with Shortage', Production Planning and Control, 19, 601-604]. So, the main purpose of this article is to adopt the calculus approach not only to overcome shortcomings of the arithmetic-geometric mean method of Teng et al. (2009), Teng and Goyal (2009) and Hsieh et al. (2008), but also to develop the complete solution procedures for them.
NASA Astrophysics Data System (ADS)
Kovalyshyn, Stepan J.; Dadak, Viktor O.; Sokolyk, Vitalij V.; Grundas, Stanisław; Stasiak, Mateusz; Tys, Jerzy
2015-04-01
Many seed mixtures of herbs are difficult to separate. This is confirmed by studies determining the basic geometrical and friction properties of the seeds of perennial grasses and seeds of their weeds. The results show that in most cases the value of their geometrical parameters (length, thickness, and width) and friction properties (friction coefficients for different external surfaces of internal friction coefficients) are substantially similar and differ slightly among each other. This is the evidence that these properties are impractical to use in the process of separation as signs of divisibility. In the paper, a method for electro-separation of seed mixtures of herbs based on the use of complex physical, mechanical properties and electrical components in the separation are presented. The electric field that acts as an additional working body allows considering the surface conditions and biological status of seed mixtures of particles and significantly expands the functionality of the separators. Confirmation of the effectiveness of the proposed method for separation can be seen in the example of purification of red clover and sorrel seeds. By imposition of an electric field on an inclined moving separating plane, we can completely separate weed seeds from the main crop. The results confirm the effectiveness of the electro-separating method.
Kelkar, K.M.; Choudhury, D.; Minkowycz, W.J.
1997-01-01
Flows in many engineering applications occur in devices that exhibit geometric periodicity, giving rise to flow characteristics that are spatially periodic. This periodicity can be of two types, translational and rotational. Since the geometries encountered in practice are often complex, periodic boundary-fitted grids are used over a typical module to predict such flows. Nonstaggered grids are frequently used for discretizing the equations governing the flow. These methods employ Cartesian velocities as the primary unknowns. In rotationally periodic geometries, these components themselves are not periodic, necessitating special considerations in incorporating the periodicity conditions over the periodic modules. The aim of the present study is to propose modifications to the conventional nonstaggered grid methods for computations of spatially periodic flows, so that geometric periodicities can be treated in a unified manner. The proposed formulation represents a generalization of the existing formulations for nonstaggered grids and can be applied for the discretization of the governing equations in domains with or without periodicity. The proposed formulation is first validated by comparing the computed solutions with the exact solutions for Couette flows in a parallel-plate channel and a cylindrical annulus. The method is then applied to three physical situations to illustrate its utility.
Calibration method and apparatus for measuring the concentration of components in a fluid
Durham, Michael D.; Sagan, Francis J.; Burkhardt, Mark R.
1993-01-01
A calibration method and apparatus for use in measuring the concentrations of components of a fluid is provided. The measurements are determined from the intensity of radiation over a selected range of radiation wavelengths using peak-to-trough calculations. The peak-to-trough calculations are simplified by compensating for radiation absorption by the apparatus. The invention also allows absorption characteristics of an interfering fluid component to be accurately determined and negated thereby facilitating analysis of the fluid.
Calibration method and apparatus for measuring the concentration of components in a fluid
Durham, M.D.; Sagan, F.J.; Burkhardt, M.R.
1993-12-21
A calibration method and apparatus for use in measuring the concentrations of components of a fluid is provided. The measurements are determined from the intensity of radiation over a selected range of radiation wavelengths using peak-to-trough calculations. The peak-to-trough calculations are simplified by compensating for radiation absorption by the apparatus. The invention also allows absorption characteristics of an interfering fluid component to be accurately determined and negated thereby facilitating analysis of the fluid. 7 figures.
Geometrical Optimization Of Clinch Forming Process Using The Response Surface Method
Oudjene, M.; Ben-Ayed, L.; Batoz, J.-L.
2007-05-17
The determination of optimum tool shapes in clinch forming process is needed to achieve the required high quality of clinch joints. The design of the tools (punch and die) is crucial since the strength of the clinch joints is closely correlated to the tools geometry. To increase the strength of clinch joints, an automatic optimization procedure is developed. The objective function is defined in terms of the maximum value of the tensile force, obtained by separation of the sheets. Feasibility constraints on the geometrical parameters are also taken into account. First, a Python Script is used to generate the ABAQUS finite element model, to run the computations and post-process results, which are exported in an ASCII file. Then, this ASCII file is read by a FORTRAN program, in which the response surface approximation and SQP algorithm are implemented. The results show the potential interest of the developed optimization procedure towards the improvement of the strength of the clinch forming joints to tensile loading.
NASA Technical Reports Server (NTRS)
Stoll, Frederick
1993-01-01
The NLPAN computer code uses a finite-strip approach to the analysis of thin-walled prismatic composite structures such as stiffened panels. The code can model in-plane axial loading, transverse pressure loading, and constant through-the-thickness thermal loading, and can account for shape imperfections. The NLPAN code represents an attempt to extend the buckling analysis of the VIPASA computer code into the geometrically nonlinear regime. Buckling mode shapes generated using VIPASA are used in NLPAN as global functions for representing displacements in the nonlinear regime. While the NLPAN analysis is approximate in nature, it is computationally economical in comparison with finite-element analysis, and is thus suitable for use in preliminary design and design optimization. A comprehensive description of the theoretical approach of NLPAN is provided. A discussion of some operational considerations for the NLPAN code is included. NLPAN is applied to several test problems in order to demonstrate new program capabilities, and to assess the accuracy of the code in modeling various types of loading and response. User instructions for the NLPAN computer program are provided, including a detailed description of the input requirements and example input files for two stiffened-panel configurations.
Lu, B.; Smallwood, A. M.; Sellers, T. A.; Drukteinis, J. S.; Heine, J. J.
2015-01-01
Purpose: The authors are developing a system for calibrated breast density measurements using full field digital mammography (FFDM). Breast tissue equivalent (BTE) phantom images are used to establish baseline (BL) calibration curves at time zero. For a given FFDM unit, the full BL dataset is comprised of approximately 160 phantom images, acquired prior to calibrating prospective patient mammograms. BL curves are monitored serially to ensure they produce accurate calibration and require updating when calibration accuracy degrades beyond an acceptable tolerance, rather than acquiring full BL datasets repeatedly. BL updating is a special case of generalizing calibration datasets across FFDM units, referred to as cross-calibration. Serial monitoring, BL updating, and cross-calibration techniques were developed and evaluated. Methods: BL curves were established for three Hologic Selenia FFDM units at time zero. In addition, one set of serial phantom images, comprised of equal proportions of adipose and fibroglandular BTE materials (50/50 compositions) of a fixed height, was acquired biweekly and monitored with the cumulative sum (Cusum) technique. These 50/50 composition images were used to update the BL curves when the calibration accuracy degraded beyond a preset tolerance of ±4 standardized units. A second set of serial images, comprised of a wide-range of BTE compositions, was acquired biweekly to evaluate serial monitoring, BL updating, and cross-calibration techniques. Results: Calibration accuracy can degrade serially and is a function of acquisition technique and phantom height. The authors demonstrated that all heights could be monitored simultaneously while acquiring images of a 50/50 phantom with a fixed height for each acquisition technique biweekly, translating into approximately 16 image acquisitions biweekly per FFDM unit. The same serial images are sufficient for serial monitoring, BL updating, and cross-calibration. Serial calibration accuracy was
Regression calibration method for correcting measurement-error bias in nutritional epidemiology.
Spiegelman, D; McDermott, A; Rosner, B
1997-04-01
Regression calibration is a statistical method for adjusting point and interval estimates of effect obtained from regression models commonly used in epidemiology for bias due to measurement error in assessing nutrients or other variables. Previous work developed regression calibration for use in estimating odds ratios from logistic regression. We extend this here to estimating incidence rate ratios from Cox proportional hazards models and regression slopes from linear-regression models. Regression calibration is appropriate when a gold standard is available in a validation study and a linear measurement error with constant variance applies or when replicate measurements are available in a reliability study and linear random within-person error can be assumed. In this paper, the method is illustrated by correction of rate ratios describing the relations between the incidence of breast cancer and dietary intakes of vitamin A, alcohol, and total energy in the Nurses' Health Study. An example using linear regression is based on estimation of the relation between ultradistal radius bone density and dietary intakes of caffeine, calcium, and total energy in the Massachusetts Women's Health Study. Software implementing these methods uses SAS macros. PMID:9094918
A vision-based self-calibration method for robotic visual inspection systems.
Yin, Shibin; Ren, Yongjie; Zhu, Jigui; Yang, Shourui; Ye, Shenghua
2013-01-01
A vision-based robot self-calibration method is proposed in this paper to evaluate the kinematic parameter errors of a robot using a visual sensor mounted on its end-effector. This approach could be performed in the industrial field without external, expensive apparatus or an elaborate setup. A robot Tool Center Point (TCP) is defined in the structural model of a line-structured laser sensor, and aligned to a reference point fixed in the robot workspace. A mathematical model is established to formulate the misalignment errors with kinematic parameter errors and TCP position errors. Based on the fixed point constraints, the kinematic parameter errors and TCP position errors are identified with an iterative algorithm. Compared to the conventional methods, this proposed method eliminates the need for a robot-based-frame and hand-to-eye calibrations, shortens the error propagation chain, and makes the calibration process more accurate and convenient. A validation experiment is performed on an ABB IRB2400 robot. An optimal configuration on the number and distribution of fixed points in the robot workspace is obtained based on the experimental results. Comparative experiments reveal that there is a significant improvement of the measuring accuracy of the robotic visual inspection system. PMID:24300597
A Vision-Based Self-Calibration Method for Robotic Visual Inspection Systems
Yin, Shibin; Ren, Yongjie; Zhu, Jigui; Yang, Shourui; Ye, Shenghua
2013-01-01
A vision-based robot self-calibration method is proposed in this paper to evaluate the kinematic parameter errors of a robot using a visual sensor mounted on its end-effector. This approach could be performed in the industrial field without external, expensive apparatus or an elaborate setup. A robot Tool Center Point (TCP) is defined in the structural model of a line-structured laser sensor, and aligned to a reference point fixed in the robot workspace. A mathematical model is established to formulate the misalignment errors with kinematic parameter errors and TCP position errors. Based on the fixed point constraints, the kinematic parameter errors and TCP position errors are identified with an iterative algorithm. Compared to the conventional methods, this proposed method eliminates the need for a robot-based-frame and hand-to-eye calibrations, shortens the error propagation chain, and makes the calibration process more accurate and convenient. A validation experiment is performed on an ABB IRB2400 robot. An optimal configuration on the number and distribution of fixed points in the robot workspace is obtained based on the experimental results. Comparative experiments reveal that there is a significant improvement of the measuring accuracy of the robotic visual inspection system. PMID:24300597
THE EURADOS-KIT TRAINING COURSE ON MONTE CARLO METHODS FOR THE CALIBRATION OF BODY COUNTERS.
Breustedt, B; Broggio, D; Gomez-Ros, J M; Leone, D; Marzocchi, O; Poelz, S; Shutt, A; Lopez, M A
2016-09-01
Monte Carlo (MC) methods are numerical simulation techniques that can be used to extend the scope of calibrations performed in in vivo monitoring laboratories. These methods allow calibrations to be carried out for a much wider range of body shapes and sizes than would be feasible using physical phantoms. Unfortunately, nowadays, this powerful technique is still used mainly in research institutions only. In 2013, EURADOS and the in vivo monitoring laboratory of Karlsruhe Institute of Technology (KIT) organized a 3-d training course to disseminate knowledge on the application of MC methods for in vivo monitoring. It was intended as a hands-on course centered around an exercise which guided the participants step by step through the calibration process using a simplified version of KIT's equipment. Only introductory lectures on in vivo monitoring and voxel models were given. The course was based on MC codes of the MCNP family, widespread in the community. The strong involvement of the participants and the working atmosphere in the classroom as well as the formal evaluation of the course showed that the approach chosen was appropriate. Participants liked the hands-on approach and the extensive course materials on the exercise. PMID:27103642
A calibration-independent method for accurate complex permittivity determination of liquid materials
Hasar, U. C.
2008-08-15
This note presents a calibration-independent method for accurate complex permittivity determination of liquid materials. There are two main advantages of the proposed method over those in the literature, which require measurements of two cells with different lengths loaded by the same liquid material. First, it eliminates any inhomogeneity or impurity present in the second sample and decreases the uncertainty in sample thickness. Second, it removes the undesired impacts of measurement plane deterioration on measurements of liquid materials. For validation of the proposed method, we measure the complex permittivity of distilled water and compare its extracted permittivity with the theoretical datum obtained from the Debye equation.
NASA Astrophysics Data System (ADS)
He, Wantao; Li, Zhongwei; Zhong, Kai; Shi, Yusheng; Zhao, Can; Cheng, Xu
2014-11-01
Fast and precise 3D inspection system is in great demand in modern manufacturing processes. At present, the available sensors have their own pros and cons, and hardly exist an omnipotent sensor to handle the complex inspection task in an accurate and effective way. The prevailing solution is integrating multiple sensors and taking advantages of their strengths. For obtaining a holistic 3D profile, the data from different sensors should be registrated into a coherent coordinate system. However, some complex shape objects own thin wall feather such as blades, the ICP registration method would become unstable. Therefore, it is very important to calibrate the extrinsic parameters of each sensor in the integrated measurement system. This paper proposed an accurate and automatic extrinsic parameter calibration method for blade measurement system integrated by different optical sensors. In this system, fringe projection sensor (FPS) and conoscopic holography sensor (CHS) is integrated into a multi-axis motion platform, and the sensors can be optimally move to any desired position at the object's surface. In order to simple the calibration process, a special calibration artifact is designed according to the characteristics of the two sensors. An automatic registration procedure based on correlation and segmentation is used to realize the artifact datasets obtaining by FPS and CHS rough alignment without any manual operation and data pro-processing, and then the Generalized Gauss-Markoff model is used to estimate the optimization transformation parameters. The experiments show the measurement result of a blade, where several sampled patches are merged into one point cloud, and it verifies the performance of the proposed method.
NASA Astrophysics Data System (ADS)
Afanasyev, An. N.; Uralov, A. M.; Grechnev, V. V.
2011-12-01
Propagation of shock related Moreton and EUV waves in the solar atmosphere is simulated by the nonlinear geometrical acoustics method. This method is based on the ray approximation and takes account of nonlinear wave features: dependence of the wave velocity on its amplitude, nonlinear dissipation of wave energy in the shock front, and the increase in its duration with time. The paper describes ways of applying this method to solve the propagation problem of a blast magnetohydrodynamic shock wave. Results of analytical modeling of EUV and Moreton waves in the spherically symmetric and isothermal solar corona are also presented. The calculations demonstrate deceleration of these waves and an increase in their duration. The calculation results of the kinematics of the EUV wave observed on the Sun on January 17, 2010 are presented as an example.
Benazzi, S; Stansfield, E; Milani, C; Gruppioni, G
2009-07-01
The process of forensic identification of missing individuals is frequently reliant on the superimposition of cranial remains onto an individual's picture and/or facial reconstruction. In the latter, the integrity of the skull or a cranium is an important factor in successful identification. Here, we recommend the usage of computerized virtual reconstruction and geometric morphometrics for the purposes of individual reconstruction and identification in forensics. We apply these methods to reconstruct a complete cranium from facial remains that allegedly belong to the famous Italian humanist of the fifteenth century, Angelo Poliziano (1454-1494). Raw data was obtained by computed tomography scans of the Poliziano face and a complete reference skull of a 37-year-old Italian male. Given that the amount of distortion of the facial remains is unknown, two reconstructions are proposed: The first calculates the average shape between the original and its reflection, and the second discards the less preserved left side of the cranium under the assumption that there is no deformation on the right. Both reconstructions perform well in the superimposition with the original preserved facial surface in a virtual environment. The reconstruction by means of averaging between the original and reflection yielded better results during the superimposition with portraits of Poliziano. We argue that the combination of computerized virtual reconstruction and geometric morphometric methods offers a number of advantages over traditional plastic reconstruction, among which are speed, reproducibility, easiness of manipulation when superimposing with pictures in virtual environment, and assumptions control. PMID:19294402
NASA Astrophysics Data System (ADS)
Lan, Yihua; Li, Cunhua; Ren, Haozheng; Zhang, Yong; Min, Zhifang
2012-10-01
A new heuristic algorithm based on the so-called geometric distance sorting technique is proposed for solving the fluence map optimization with dose-volume constraints which is one of the most essential tasks for inverse planning in IMRT. The framework of the proposed method is basically an iterative process which begins with a simple linear constrained quadratic optimization model without considering any dose-volume constraints, and then the dose constraints for the voxels violating the dose-volume constraints are gradually added into the quadratic optimization model step by step until all the dose-volume constraints are satisfied. In each iteration step, an interior point method is adopted to solve each new linear constrained quadratic programming. For choosing the proper candidate voxels for the current dose constraint adding, a so-called geometric distance defined in the transformed standard quadratic form of the fluence map optimization model was used to guide the selection of the voxels. The new geometric distance sorting technique can mostly reduce the unexpected increase of the objective function value caused inevitably by the constraint adding. It can be regarded as an upgrading to the traditional dose sorting technique. The geometry explanation for the proposed method is also given and a proposition is proved to support our heuristic idea. In addition, a smart constraint adding/deleting strategy is designed to ensure a stable iteration convergence. The new algorithm is tested on four cases including head-neck, a prostate, a lung and an oropharyngeal, and compared with the algorithm based on the traditional dose sorting technique. Experimental results showed that the proposed method is more suitable for guiding the selection of new constraints than the traditional dose sorting method, especially for the cases whose target regions are in non-convex shapes. It is a more efficient optimization technique to some extent for choosing constraints than the dose
Semi-automated calibration method for modelling of mountain permafrost evolution in Switzerland
NASA Astrophysics Data System (ADS)
Marmy, A.; Rajczak, J.; Delaloye, R.; Hilbich, C.; Hoelzle, M.; Kotlarski, S.; Lambiel, C.; Noetzli, J.; Phillips, M.; Salzmann, N.; Staub, B.; Hauck, C.
2015-09-01
Permafrost is a widespread phenomenon in the European Alps. Many important topics such as the future evolution of permafrost related to climate change and the detection of permafrost related to potential natural hazards sites are of major concern to our society. Numerical permafrost models are the only tools which facilitate the projection of the future evolution of permafrost. Due to the complexity of the processes involved and the heterogeneity of Alpine terrain, models must be carefully calibrated and results should be compared with observations at the site (borehole) scale. However, a large number of local point data are necessary to obtain a broad overview of the thermal evolution of mountain permafrost over a larger area, such as the Swiss Alps, and the site-specific model calibration of each point would be time-consuming. To face this issue, this paper presents a semi-automated calibration method using the Generalized Likelihood Uncertainty Estimation (GLUE) as implemented in a 1-D soil model (CoupModel) and applies it to six permafrost sites in the Swiss Alps prior to long-term permafrost evolution simulations. We show that this automated calibration method is able to accurately reproduce the main thermal condition characteristics with some limitations at sites with unique conditions such as 3-D air or water circulation, which have to be calibrated manually. The calibration obtained was used for RCM-based long-term simulations under the A1B climate scenario specifically downscaled at each borehole site. The projection shows general permafrost degradation with thawing at 10 m, even partially reaching 20 m depths until the end of the century, but with different timing among the sites. The degradation is more rapid at bedrock sites whereas ice-rich sites with a blocky surface cover showed a reduced sensitivity to climate change. The snow cover duration is expected to be reduced drastically (between -20 to -37 %) impacting the ground thermal regime. However
Research on the method of establishing the total radiation meter calibration device
NASA Astrophysics Data System (ADS)
Gao, Jianqiang; Xia, Ming; Xia, Junwen; Zhang, Dong
2015-10-01
Pyranometer is an instrument used to measure the solar radiation, according to pyranometer differs as installation state, can be respectively measured total solar radiation, reflected radiation, or with the help of shading device for measuring scattering radiation. Pyranometer uses the principle of thermoelectric effect, inductive element adopts winding plating type multi junction thermopile, its surface is coated with black coating with high absorption rate. Hot junction in the induction surface, while the cold junction is located in the body, the cold and hot junction produce thermoelectric potential. In the linear range, the output signal is proportional to the solar irradiance. Traceability to national meteorological station, as the unit of the national legal metrology organizations, the responsibility is to transfer value of the sun and the earth radiation value about the national meteorological industry. Using the method of comparison, with indoor calibration of solar simulator, at the same location, standard pyranometer and measured pyranometer were alternately measured radiation irradiance, depending on the irradiation sensitivity standard pyranometer were calculated the radiation sensitivity of measured pyranometer. This paper is mainly about the design and calibration method of the pyranometer indoor device. The uncertainty of the calibration result is also evaluated.
NASA Astrophysics Data System (ADS)
Lee, S.; Lee, W.; Oh, S.
2008-12-01
It is difficult to produce and maintain the quality of calibration gas mixtures stable and reliable in gas cylinders for the identification and quantification of trace environmental contaminants. Dynamic method has attracted an attention because immediate and on-site generation of calibration gas mixture is achievable in the range of percent, sub-ppm, and micro-mole fraction. The dynamic method for the preparation of standard reference gas/vapour mixtures was carried out using polymeric permeation membrane. Permeation behaviour of various organic compounds including aliphatic and aromatic hydrocarbons and chlorohydrocarbons was tested through semi-permeable silicone polymer and fluoropolymers. Experimental results showed the constant permeation rate of target compounds under the constant temperature condition. The permeation rate, however, was largely influenced by chemical components, membrane materials, and temperature change. Mole fractions of generated vapour were calculated using the mass loss of permeation tubes and mass-flow rate of carrier gas. Dynamic volumetric techniques can be applicable for the generation of standard reference materials for the calibration of various types of organics (volatile organic compounds, polycyclic aromatic hydrocarbons, etc) in ambient air and water. This technology is also applicable to develop novel materials for passive samplers for long-term environmental monitoring.
A calibration method for lateral forces for use with colloidal probe force microscopy cantilevers
Quintanilla, M. A. S.; Goddard, D. T.
2008-02-15
A calibration method is described for colloidal probe cantilevers that enables friction force measurements obtained using lateral force microscopy (LFM) to be quantified. The method is an adaptation of the lever method of Feiler et al. [A. Feiler, P. Attard, and I. Larson, Rev. Sci. Instum. 71, 2746 (2000)] and uses the advantageous positioning of probe particles that are usually offset from the central axis of the cantilever. The main sources of error in the calibration method are assessed, in particular, the potential misalignment of the long axis of the cantilever that ideally should be perpendicular to the photodiode detector. When this is not taken into account, the misalignment is shown to have a significant effect on the cantilever torsional stiffness but not on the lateral photodiode sensitivity. Also, because the friction signal is affected by the topography of the substrate, the method presented is valid only against flat substrates. Two types of particles, 20 {mu}m glass beads and UO{sub 3} agglomerates attached to silicon tapping mode cantilevers were used to test the method against substrates including glass, cleaved mica, and UO{sub 2} single crystals. Comparisons with the lateral compliance method of Cain et al. [R. G. Cain, S. Biggs, and N. W. Page, J. Colloid Interface Sci. 227, 55 (2000)] are also made.
The development of in-situ calibration method for divertor IR thermography in ITER
Takeuchi, M.; Sugie, T.; Ogawa, H.; Takeyama, S.; Itami, K.
2014-08-21
For the development of the calibration method of the emissivity in IR light on the divertor plate in ITER divertor IR thermography system, the laboratory experiments have been performed by using IR instruments. The calibration of the IR camera was performed by the plane black body in the temperature of 100–600 degC. The radiances of the tungsten heated by 280 degC were measured by the IR camera without filter (2.5–5.1 μm) and with filter (2.95 μm, 4.67 μm). The preliminary data of the scattered light of the laser of 3.34 μm that injected into the tungsten were acquired.
Comparison of flume and towing methods for verifying the calibration of a suspended-sediment sampler
Beverage, J.P.; Futrell, J.C.
1986-01-01
Suspended-sediment samplers must sample isokinetically (at stream velocity) in order to collect representative water samples of rivers. Each sampler solo by the Federal Interagency Sedimentation Project or by the U.S. Geological Survey Hydrologic Instrumentation Facility has been adjusted to sample isokinetically and tested in a flume to verify the calibration. The test program for a modified U.S. P-61 sampler provided an opportunity to compare flume and towing tank tests. Although the two tests yielded statistically distinct results, the difference between them was quite small. The conclusion is that verifying the calibration of any suspended-sediment sampler by either the flume or towing method should give acceptable results.
Heterodyne interferometry method for calibration of a Soleil-Babinet compensator.
Zhang, Wenjing; Zhang, Zhiwei
2016-05-20
A method based on the common-path heterodyne interferometer system is proposed for the calibration of a Soleil-Babinet compensator. In this heterodyne interferometer system, which consists of two acousto-optic modulators, the compensator being calibrated is inserted into the signal path. By using the reference beam as the benchmark and a lock-in amplifier (SR844) as the phase retardation collector, retardations of 0 and λ (one wavelength) can be located accurately, and an arbitrary retardation between 0 and λ can also be measured accurately and continuously. By fitting a straight line to the experimental data, we obtained a linear correlation coefficient (R) of 0.995, which indicates that this system is capable of linear phase detection. The experimental results demonstrate determination accuracies of 0.212° and 0.26° and measurement precisions of 0.054° and 0.608° for retardations of 0 and λ, respectively. PMID:27411154
The development of in-situ calibration method for divertor IR thermography in ITER
NASA Astrophysics Data System (ADS)
Takeuchi, M.; Sugie, T.; Ogawa, H.; Takeyama, S.; Itami, K.
2014-08-01
For the development of the calibration method of the emissivity in IR light on the divertor plate in ITER divertor IR thermography system, the laboratory experiments have been performed by using IR instruments. The calibration of the IR camera was performed by the plane black body in the temperature of 100-600 degC. The radiances of the tungsten heated by 280 degC were measured by the IR camera without filter (2.5-5.1 μm) and with filter (2.95 μm, 4.67 μm). The preliminary data of the scattered light of the laser of 3.34 μm that injected into the tungsten were acquired.
Note: A calibration method to determine the lumped-circuit parameters of a magnetic probe
NASA Astrophysics Data System (ADS)
Li, Fuming; Chen, Zhipeng; Zhu, Lizhi; Liu, Hai; Wang, Zhijiang; Zhuang, Ge
2016-06-01
This paper describes a novel method to determine the lumped-circuit parameters of a magnetic inductive probe for calibration by using Helmholtz coils with high frequency power supply (frequency range: 10 kHz-400 kHz). The whole calibration circuit system can be separated into two parts: "generator" circuit and "receiver" circuit. By implementing the Fourier transform, two analytical lumped-circuit models, with respect to these separated circuits, are constructed to obtain the transfer function between each other. Herein, the precise lumped-circuit parameters (including the resistance, inductance, and capacitance) of the magnetic probe can be determined by fitting the experimental data to the transfer function. Regarding the fitting results, the finite impedance of magnetic probe can be used to analyze the transmission of a high-frequency signal between magnetic probes, cables, and acquisition system.
A method for automating calibration and records management for instrumentation and dosimetry
O`Brien, J.M. Jr.; Rushton, R.O.; Burns, R.E. Jr.
1993-12-31
Current industry requirements are becoming more stringent on quality assurance records and documentation for calibration of instruments and dosimetry. A novel method is presented here that will allow a progressive automation scheme to be used in pursuit of that goal. This concept is based on computer-controlled irradiators that can act as stand-alone devices or be interfaced to other components via a computer local area network. In this way, complete systems can be built with modules to create a records management system to meet the needs of small laboratories or large multi-building calibration groups. Different database engines or formats can be used simply by replacing a module. Modules for temperature and pressure monitoring or shipping and receiving can be added, as well as equipment modules for direct IEEE-488 interface to electrometers and other instrumentation.
On-orbit calibration approach for star cameras based on the iteration method with variable weights.
Wang, Mi; Cheng, Yufeng; Yang, Bo; Chen, Xiao
2015-07-20
To perform efficient on-orbit calibration for star cameras, we developed an attitude-independent calibration approach for global optimization and noise removal by least-square estimation using multiple star images, with which the optimal principal point, focal length, and the high-order focal plane distortion can be obtained in one step in full consideration of the interaction among star camera parameters. To avoid the problem when stars could be misidentified in star images, an iteration method with variable weights is introduced to eliminate the influence of misidentified star pairs. The approach can increase the precision of least-square estimation and use fewer star images. The proposed approach has been well verified to be precise and robust in three experiments. PMID:26367824
Absolute calibration method for fast-streaked, fiber optic light collection, spectroscopy systems.
Johnston, Mark D.; Frogget, Brent; Oliver, Bryan Velten; Maron, Yitzhak; Droemer, Darryl W.; Crain, Marlon D.
2010-04-01
This report outlines a convenient method to calibrate fast (<1ns resolution) streaked, fiber optic light collection, spectroscopy systems. Such a system is used to collect spectral data on plasmas generated in the A-K gap of electron beam diodes fielded on the RITS-6 accelerator (8-12MV, 140-200kA). On RITS, light is collected through a small diameter (200 micron) optical fiber and recorded on a fast streak camera at the output of 1 meter Czerny-Turner monochromator (F/7 optics). To calibrate such a system, it is necessary to efficiently couple light from a spectral lamp into a 200 micron diameter fiber, split it into its spectral components, with 10 Angstroms or less resolution, and record it on a streak camera with 1ns or less temporal resolution.
Moen, Stephan Craig; Meyers, Craig Glenn; Petzen, John Alexander; Foard, Adam Muhling
2012-08-07
A method of calibrating a nuclear instrument using a gamma thermometer may include: measuring, in the instrument, local neutron flux; generating, from the instrument, a first signal proportional to the neutron flux; measuring, in the gamma thermometer, local gamma flux; generating, from the gamma thermometer, a second signal proportional to the gamma flux; compensating the second signal; and calibrating a gain of the instrument based on the compensated second signal. Compensating the second signal may include: calculating selected yield fractions for specific groups of delayed gamma sources; calculating time constants for the specific groups; calculating a third signal that corresponds to delayed local gamma flux based on the selected yield fractions and time constants; and calculating the compensated second signal by subtracting the third signal from the second signal. The specific groups may have decay time constants greater than 5.times.10.sup.-1 seconds and less than 5.times.10.sup.5 seconds.
Easy and direct method for calibrating atomic force microscopy lateral force measurements
Liu, Wenhua; Bonin, Keith; Guthold, Martin
2010-01-01
We have designed and tested a new, inexpensive, easy-to-make and easy-to-use calibration standard for atomic force microscopy (AFM) lateral force measurements. This new standard simply consists of a small glass fiber of known dimensions and Young’s modulus, which is fixed at one end to a substrate and which can be bent laterally with the AFM tip at the other end. This standard has equal or less error than the commonly used method of using beam mechanics to determine a cantilever’s lateral force constant. It is transferable, thus providing a universal tool for comparing the calibrations of different instruments. It does not require knowledge of the cantilever dimensions and composition or its tip height. This standard also allows direct conversion of the photodiode signal to force and, thus, circumvents the requirement for a sensor response (sensitivity) measurement. PMID:17614616
NASA Astrophysics Data System (ADS)
Lee, Ming-Wei; Chen, Yi-Chun
2014-02-01
In pinhole SPECT applied to small-animal studies, it is essential to have an accurate imaging system matrix, called H matrix, for high-spatial-resolution image reconstructions. Generally, an H matrix can be obtained by various methods, such as measurements, simulations or some combinations of both methods. In this study, a distance-weighted Gaussian interpolation method combined with geometric parameter estimations (DW-GIMGPE) is proposed. It utilizes a simplified grid-scan experiment on selected voxels and parameterizes the measured point response functions (PRFs) into 2D Gaussians. The PRFs of missing voxels are interpolated by the relations between the Gaussian coefficients and the geometric parameters of the imaging system with distance-weighting factors. The weighting factors are related to the projected centroids of voxels on the detector plane. A full H matrix is constructed by combining the measured and interpolated PRFs of all voxels. The PRFs estimated by DW-GIMGPE showed similar profiles as the measured PRFs. OSEM reconstructed images of a hot-rod phantom and normal rat myocardium demonstrated the effectiveness of the proposed method. The detectability of a SKE/BKE task on a synthetic spherical test object verified that the constructed H matrix provided comparable detectability to that of the H matrix acquired by a full 3D grid-scan experiment. The reduction in the acquisition time of a full 1.0-mm grid H matrix was about 15.2 and 62.2 times with the simplified grid pattern on 2.0-mm and 4.0-mm grid, respectively. A finer-grid H matrix down to 0.5-mm spacing interpolated by the proposed method would shorten the acquisition time by 8 times, additionally.
Towards in-vivo K-edge imaging using a new semi-analytical calibration method
NASA Astrophysics Data System (ADS)
Schirra, Carsten; Thran, Axel; Daerr, Heiner; Roessl, Ewald; Proksa, Roland
2014-03-01
Flat field calibration methods are commonly used in computed tomography (CT) to correct for system imperfections. Unfortunately, they cannot be applied in energy-resolving CT when using bow-tie filters owing to spectral distortions imprinted by the filter. This work presents a novel semi-analytical calibration method for photon-counting spectral CT systems, which is applicable with a bow-tie filter in place and efficiently compensates pile-up effects at fourfold increased photon flux compared to a previously published method without degradation of image quality. The achieved reduction of the scan time enabled the first K-edge imaging in-vivo. The method employs a calibration measurement with a set of flat sheets of only a single absorber material and utilizes an analytical model to predict the expected photon counts, taking into account factors such as x-ray spectrum and detector response. From the ratios of the measured x-ray intensities and the corresponding simulated photon counts, a look-up table is generated. By use of this look-up table, measured photon-counts can be corrected yielding data in line with the analytical model. The corrected data show low pixel-to-pixel variations and pile-up effects are mitigated. Consequently, operations like material decomposition based on the same analytical model yield accurate results. The method was validated on a experimental spectral CT system equipped with a bow-tie filter in a phantom experiment and an in-vivo animal study. The level of artifacts in the resulting images is considerably lower than in images generated with a previously published method. First in-vivo K-edge images of a rabbit selectively depict vessel occlusion by an ytterbium-based thermoresponsive polymer.
A time-delay calibrated method for cornea hysteresis and intraocular pressure measurement
NASA Astrophysics Data System (ADS)
Wang, Kuo-Jen; Tsai, Che-Liang; Wang, Wai; Hsu, Long; Hsu, Ken-Yuh
2016-04-01
The presence of cornea hysteresis (CH) in characterizing the intraocular pressure (IOP) of a human eye deteriorates the accuracy of IOP. To suppress CH, the pressure gauge of a tonometer must be located as close as possible to the cornea. However, this arrangement is unpractical because appropriate working distance to the cornea is required. In this paper, a time-delay calibrated (TDC) method is proposed to counteract the undesired effect of CH in characterizing the IOP. Employing this TDC method, the CH approaches to zero for most eyes measured.
Wang, Yusu
2013-03-25
Shape analysis plays an important role in many applications. In particular, in molecular biology, analyzing molecular shapes is essential to the fundamental problem of understanding how molecules interact. This project aims at developing efficient and effective algorithms to characterize and analyze molecular structures using geometric and topological methods. Two main components of this project are (1) developing novel molecular shape descriptors; and (2) identifying and representing meaningful features based on those descriptors. The project also produces accompanying (visualization) software. Results from this project (09/2006-10/2009) include the following publications. We have also set up web-servers for the software developed in this period, so that our new methods are accessible to a broader scientific community. The web sites are given below as well. In this final technical report, we first list publications and software resulted from this project. We then briefly explain the research conducted and main accomplishments during the period of this project.
Zhang, Yong; Chen, Bin; Li, Dong
2016-04-01
To investigate the influence of polarization on the polarized light propagation in biological tissue, a polarized geometric Monte Carlo method is developed. The Stokes-Mueller formalism is expounded to describe the shifting of light polarization during propagation events, including scattering and interface interaction. The scattering amplitudes and optical parameters of different tissue structures are obtained using Mie theory. Through simulations of polarized light (pulsed dye laser at wavelength of 585 nm) propagation in an infinite slab tissue model and a discrete vessel tissue model, energy depositions in tissue structures are calculated and compared with those obtained through general geometric Monte Carlo simulation under the same parameters but without consideration of polarization effect. It is found that the absorption depth of the polarized light is about one half of that determined by conventional simulations. In the discrete vessel model, low penetrability manifests in three aspects: diffuse reflection became the main contributor to the energy escape, the proportion of epidermal energy deposition increased significantly, and energy deposition in the blood became weaker and more uneven. This may indicate that the actual thermal damage of epidermis during the real-world treatment is higher and the deep buried blood vessels are insufficiently damaged by consideration of polarization effect, compared with the conventional prediction. PMID:27139673
NASA Astrophysics Data System (ADS)
Iwema, J.; Rosolem, R.; Baatz, R.; Wagener, T.; Bogena, H. R.
2015-02-01
The Cosmic-Ray Neutron Sensor (CRNS) can provide soil moisture information at scales relevant to hydrometeorological modeling applications. Site-specific calibration is needed to translate CRNS neutron intensities into sensor footprint average soil moisture contents. We investigated temporal sampling strategies for calibration of three CRNS parameterisations (modified N0, HMF, and COSMIC) by assessing the effects of the number of sampling days and soil wetness conditions on the performance of the calibration results, for three sites with distinct climate and land use: a semi-arid site, a temperate grassland and a temperate forest. When calibrated with a year of data, COSMIC performed relatively good at all three sites, and the modified N0 method performed best at the two humid sites. It is advisable to collect soil moisture samples on more than a single day regardless of which parameterisation is used. In any case, sampling on more than ten days would, despite the strong increase in work effort, improve calibration results only little. COSMIC needed the least number of days at each site. At the semi-arid site, the N0mod method was calibrated better under average wetness conditions, whereas HMF and COSMIC were calibrated better under drier conditions. Average soil wetness condition gave better calibration results at the two humid sites. The calibration results for the HMF method were better when calibrated with combinations of days with similar soil wetness conditions, opposed to N0mod and COSMIC, which profited from using days with distinct wetness conditions. The outcomes of this study can be used by researchers as a CRNS calibration strategy guideline.
Tanaka, Masahito; Yagi-Watanabe, Kazutoshi; Kaneko, Fusae; Nakagawa, Kazumichi
2008-08-15
An accurate calibration method in which an ac-modulated polarizing undulator is used for polarization modulation spectroscopy such as circular dichroism (CD) and linear dichroism (LD) has been proposed and successfully applied to vacuum ultraviolet (vuv) CD and LD spectra measured at beamline BL-5B in the electron storage ring, TERAS, at AIST. This calibration method employs an undulator-modulation spectroscopic method with a multireflection polarimeter, and it uses electronic and optical elements identical to those used for the CD and LD measurements. This method regards the polarimeter as a standard sample for the CD and LD measurements in the vuv region in which a standard sample has not yet been established. The calibration factors for the CD and LD spectra are obtained over a wide range of wavelengths, from 120 to 230 nm, at TERAS BL-5B. The calibrated CD and LD spectra measured at TERAS exhibit good agreement with the standard spectra for wavelengths greater than 170 nm; the mean differences between the standard and calibrated CD and LD spectra are approximately 7% and 4%, respectively. This method enables a remarkable reduction in the experimental time, from approximately 1 h to less than 10 min that is sufficient to observe the storage-ring current dependence of the calibration factors. This method can be applied to the calibration of vuv-CD spectra measured using a conventional photoelastic modulator and for performing an accurate analysis of protein secondary structures.
NASA Technical Reports Server (NTRS)
Siu, Marie-Michele; Martos, Borja; Foster, John V.
2013-01-01
As part of a joint partnership between the NASA Aviation Safety Program (AvSP) and the University of Tennessee Space Institute (UTSI), research on advanced air data calibration methods has been in progress. This research was initiated to expand a novel pitot-static calibration method that was developed to allow rapid in-flight calibration for the NASA Airborne Subscale Transport Aircraft Research (AirSTAR) facility. This approach uses Global Positioning System (GPS) technology coupled with modern system identification methods that rapidly computes optimal pressure error models over a range of airspeed with defined confidence bounds. Subscale flight tests demonstrated small 2-s error bounds with significant reduction in test time compared to other methods. Recent UTSI full scale flight tests have shown airspeed calibrations with the same accuracy or better as the Federal Aviation Administration (FAA) accepted GPS 'four-leg' method in a smaller test area and in less time. The current research was motivated by the desire to extend this method for inflight calibration of angle of attack (AOA) and angle of sideslip (AOS) flow vanes. An instrumented Piper Saratoga research aircraft from the UTSI was used to collect the flight test data and evaluate flight test maneuvers. Results showed that the output-error approach produces good results for flow vane calibration. In addition, maneuvers for pitot-static and flow vane calibration can be integrated to enable simultaneous and efficient testing of each system.
Performance of three reflectance calibration methods for airborne hyperspectral spectrometer data.
Miura, Tomoaki; Huete, Alfredo R
2009-01-01
In this study, the performances and accuracies of three methods for converting airborne hyperspectral spectrometer data to reflectance factors were characterized and compared. The "reflectance mode (RM)" method, which calibrates a spectrometer against a white reference panel prior to mounting on an aircraft, resulted in spectral reflectance retrievals that were biased and distorted. The magnitudes of these bias errors and distortions varied significantly, depending on time of day and length of the flight campaign. The "linear-interpolation (LI)" method, which converts airborne spectrometer data by taking a ratio of linearly-interpolated reference values from the preflight and post-flight reference panel readings, resulted in precise, but inaccurate reflectance retrievals. These reflectance spectra were not distorted, but were subject to bias errors of varying magnitudes dependent on the flight duration length. The "continuous panel (CP)" method uses a multi-band radiometer to obtain continuous measurements over a reference panel throughout the flight campaign, in order to adjust the magnitudes of the linear-interpolated reference values from the preflight and post-flight reference panel readings. Airborne hyperspectral reflectance retrievals obtained using this method were found to be the most accurate and reliable reflectance calibration method. The performances of the CP method in retrieving accurate reflectance factors were consistent throughout time of day and for various flight durations. Based on the dataset analyzed in this study, the uncertainty of the CP method has been estimated to be 0.0025 ± 0.0005 reflectance units for the wavelength regions not affected by atmospheric absorptions. The RM method can produce reasonable results only for a very short-term flight (e.g., < 15 minutes) conducted around a local solar noon. The flight duration should be kept shorter than 30 minutes for the LI method to produce results with reasonable accuracies. An important
Performance of Three Reflectance Calibration Methods for Airborne Hyperspectral Spectrometer Data
Miura, Tomoaki; Huete, Alfredo R.
2009-01-01
In this study, the performances and accuracies of three methods for converting airborne hyperspectral spectrometer data to reflectance factors were characterized and compared. The “reflectance mode (RM)” method, which calibrates a spectrometer against a white reference panel prior to mounting on an aircraft, resulted in spectral reflectance retrievals that were biased and distorted. The magnitudes of these bias errors and distortions varied significantly, depending on time of day and length of the flight campaign. The “linear-interpolation (LI)” method, which converts airborne spectrometer data by taking a ratio of linearly-interpolated reference values from the preflight and post-flight reference panel readings, resulted in precise, but inaccurate reflectance retrievals. These reflectance spectra were not distorted, but were subject to bias errors of varying magnitudes dependent on the flight duration length. The “continuous panel (CP)” method uses a multi-band radiometer to obtain continuous measurements over a reference panel throughout the flight campaign, in order to adjust the magnitudes of the linear-interpolated reference values from the preflight and post-flight reference panel readings. Airborne hyperspectral reflectance retrievals obtained using this method were found to be the most accurate and reliable reflectance calibration method. The performances of the CP method in retrieving accurate reflectance factors were consistent throughout time of day and for various flight durations. Based on the dataset analyzed in this study, the uncertainty of the CP method has been estimated to be 0.0025 ± 0.0005 reflectance units for the wavelength regions not affected by atmospheric absorptions. The RM method can produce reasonable results only for a very short-term flight (e.g., < 15 minutes) conducted around a local solar noon. The flight duration should be kept shorter than 30 minutes for the LI method to produce results with reasonable accuracies
Byun, Jong-In; Yun, Ju-Yong
2015-08-01
It is shown that the gamma-ray linear attenuation coefficient of a sample with unknown chemical composition can be determined through a systematic calibration of the correlation between the linear attenuation coefficient, gamma-ray energy and the relative degree of attenuation. For calibration, H2O, MnO2, NaCl, Na2CO3 and (NH4)2SO4 were used as reference materials. Point-like gamma-ray sources with modest activity of approximately 37kBq, along with an HPGe detector, were used in the measurements. A semi-empirical formula was derived to calculate the linear attenuation coefficients as a function of the relative count rate and the gamma-ray energy. The method was applied to the determination of the linear attenuation coefficients for K2CrO4 and SiO2 test samples in the same setup used in calibration. The experimental result agreed well with the ones calculated by elementary data. PMID:25997111
Calibration method for division of focal plane polarimeters in the optical and near-infrared regime
NASA Astrophysics Data System (ADS)
York, Timothy; Gruev, Viktor
2011-06-01
Advances in nanofabrication allow for the creation of metallic nanowires acting as linear polarizers in the visible and near infrared regime. The monolithic integration of silicon detectors and pixelated nanowire metallic polarization filters allows for an efficient realization of high resolution polarization imaging sensors. These silicon sensors, known as division of focal plane polarimeters, capture polarization information of the imaged environment from ~400nm to 1050nm wavelength. The performance of the polarization sensor can be degraded by both irregularities in the fabrication of the nanowires and possible misalignment errors during the final deposition of the optical nanowire filters on the surface of the imaging sensor. In addition, electronic offsets due to the readout circuitry, electronic crosstalk, and optical crosstalk will also negatively affect the quality of the polarization information. Partial compensation for many of these post-fabrication errors can be accomplished through the use of a camera calibration routine. This paper will describe one such routine, and show how its application can increase the quality of measurements in both the degree of linear polarization and angle of polarization in the visible spectrum. The imaging array of the division of focal plane polarimeter is segmented into two by two blocks of superpixels. The calibration method chooses one of the four pixels as a reference, and then a gain and offset for each of the remaining three is computed based on this reference. The output is a calibration matrix for each pixel in the image array.
NASA Astrophysics Data System (ADS)
Dai, Xianglu; Xie, Huimin; Wang, Huaixi; Li, Chuanwei; Liu, Zhanwei; Wu, Lifu
2014-02-01
The geometric phase analysis (GPA) method based on the local high resolution discrete Fourier transform (LHR-DFT) for deformation measurement, defined as LHR-DFT GPA, is proposed to improve the measurement accuracy. In the general GPA method, the fundamental frequency of the image plays a crucial role. However, the fast Fourier transform, which is generally employed in the general GPA method, could make it difficult to locate the fundamental frequency accurately when the fundamental frequency is not located at an integer pixel position in the Fourier spectrum. This study focuses on this issue and presents a LHR-DFT algorithm that can locate the fundamental frequency with sub-pixel precision in a specific frequency region for the GPA method. An error analysis is offered and simulation is conducted to verify the effectiveness of the proposed method; both results show that the LHR-DFT algorithm can accurately locate the fundamental frequency and improve the measurement accuracy of the GPA method. Furthermore, typical tensile and bending tests are carried out and the experimental results verify the effectiveness of the proposed method.
A calibration method for patient specific IMRT QA using a single therapy verification film
Shukla, Arvind Kumar; Oinam, Arun S.; Kumar, Sanjeev; Sandhu, I.S.; Sharma, S.C.
2013-01-01
Aim The aim of the present study is to develop and verify the single film calibration procedure used in intensity-modulated radiation therapy (IMRT) quality assurance. Background Radiographic films have been regularly used in routine commissioning of treatment modalities and verification of treatment planning system (TPS). The radiation dosimetery based on radiographic films has ability to give absolute two-dimension dose distribution and prefer for the IMRT quality assurance. However, the single therapy verification film gives a quick and significant reliable method for IMRT verification. Materials and methods A single extended dose rate (EDR 2) film was used to generate the sensitometric curve of film optical density and radiation dose. EDR 2 film was exposed with nine 6 cm × 6 cm fields of 6 MV photon beam obtained from a medical linear accelerator at 5-cm depth in solid water phantom. The nine regions of single film were exposed with radiation doses raging from 10 to 362 cGy. The actual dose measurements inside the field regions were performed using 0.6 cm3 ionization chamber. The exposed film was processed after irradiation using a VIDAR film scanner and the value of optical density was noted for each region. Ten IMRT plans of head and neck carcinoma were used for verification using a dynamic IMRT technique, and evaluated using the gamma index method with TPS calculated dose distribution. Results Sensitometric curve has been generated using a single film exposed at nine field region to check quantitative dose verifications of IMRT treatments. The radiation scattered factor was observed to decrease exponentially with the increase in the distance from the centre of each field region. The IMRT plans based on calibration curve were verified using the gamma index method and found to be within acceptable criteria. Conclusion The single film method proved to be superior to the traditional calibration method and produce fast daily film calibration for highly
A Method to Solve Interior and Exterior Camera Calibration Parameters for Image Resection
NASA Technical Reports Server (NTRS)
Samtaney, Ravi
1999-01-01
An iterative method is presented to solve the internal and external camera calibration parameters, given model target points and their images from one or more camera locations. The direct linear transform formulation was used to obtain a guess for the iterative method, and herein lies one of the strengths of the present method. In all test cases, the method converged to the correct solution. In general, an overdetermined system of nonlinear equations is solved in the least-squares sense. The iterative method presented is based on Newton-Raphson for solving systems of nonlinear algebraic equations. The Jacobian is analytically derived and the pseudo-inverse of the Jacobian is obtained by singular value decomposition.
Symmetrizable connection and combined calibration method for accuracy measurement of CMM
NASA Astrophysics Data System (ADS)
Fei, Yetai; Xie, Shao-Feng; Chen, Xia-Huai
1993-09-01
In this paper, a new method of syrmetrizab1e connection and ciribined calibration is presented based on an analysis of accuracy of the 1Mt The novel measuring principle and succinct mathematical model are described. By experimental ctparison, the correctness and practicability of the method are proved. In order to assess the M,i accuracy and conpensate for errors, all errors should be measured with high accuracy and efficiency. At the same time, a succinct mathematical model should be developed. For this reason seeking an efficient measuring method for the IM1 has all along been an important subject in this field. All currently used measuring methods for the lMv! have their limitations. To remedy such a situation, the synmetrizable connection method is presented. It solves current problems of the M1 accuracy verification.
An improved method for calibrating time-of-flight Laue single-crystal neutron diffractometers
Bull, Craig L.; Johnson, Michael W.; Hamidov, Hayrullo; Komatsu, Kazuki; Guthrie, Malcolm; Gutmann, Matthias J.; Loveday, John S.; Nelmes, Richard J.
2014-01-01
A robust and comprehensive method for determining the orientation matrix of a single-crystal sample using the neutron Laue time-of-flight (TOF) technique is described. The new method enables the measurement of the unit-cell parameters with an uncertainty in the range 0.015–0.06%, depending upon the crystal symmetry and the number of reflections measured. The improved technique also facilitates the location and integration of weak reflections, which are often more difficult to discern amongst the increased background at higher energies. The technique uses a mathematical model of the relative positions of all the detector pixels of the instrument, together with a methodology that establishes a reproducible reference frame and a method for determining the parameters of the instrument detector model. Since all neutron TOF instruments require precise detector calibration for their effective use, it is possible that the method described here may be of use on other instruments where the detector calibration cannot be determined by other means. PMID:24904244
NASA Astrophysics Data System (ADS)
Jha, Abhishek Kumar; Azizurrahaman; Akhtar, Mohammad Jaleel
2015-06-01
A generalized cavity method relaxing the major assumptions of conventional cavity perturbation technique is presented for characterization of the powdered sample in the microwave frequency range. The unified method, which is based on the inverse optimization technique, eliminates the complexity of measurement caused due to the existence of sample holder and produces an accurate result. In this paper, an attractive numerical calibration approach is proposed in lieu of the practical calibration technique which usually requires either a set of standards or a number of reference samples. The sample holder especially made of borosilicate glass is designed to contain the powdered samples, and the X-band rectangular cavity is fabricated. For verification of the proposed technique, the pulverized alumina and polyethylene oxide with various packing fractions are measured using the fabricated cavity and the vector network analyzer. The dielectric constant of these samples is extracted using the proposed unified approach which is found to be in good agreement with the theoretical data obtained by Landau-Lifshitz and Looyenga model. The accuracy of the proposed generalized cavity method for powdered samples is found to be better than the conventional resonator methods available in the literature.
Jha, Abhishek Kumar; Azizurrahaman; Akhtar, Mohammad Jaleel
2015-06-01
A generalized cavity method relaxing the major assumptions of conventional cavity perturbation technique is presented for characterization of the powdered sample in the microwave frequency range. The unified method, which is based on the inverse optimization technique, eliminates the complexity of measurement caused due to the existence of sample holder and produces an accurate result. In this paper, an attractive numerical calibration approach is proposed in lieu of the practical calibration technique which usually requires either a set of standards or a number of reference samples. The sample holder especially made of borosilicate glass is designed to contain the powdered samples, and the X-band rectangular cavity is fabricated. For verification of the proposed technique, the pulverized alumina and polyethylene oxide with various packing fractions are measured using the fabricated cavity and the vector network analyzer. The dielectric constant of these samples is extracted using the proposed unified approach which is found to be in good agreement with the theoretical data obtained by Landau-Lifshitz and Looyenga model. The accuracy of the proposed generalized cavity method for powdered samples is found to be better than the conventional resonator methods available in the literature. PMID:26144529
The three-measurement two-calibration method for measuring the transfer matrix.
Rodriguez, S; Gibiat, V; Lefebvre, A; Guilain, Stephane
2011-05-01
Extensive use of transfer matrices (TMs) is made in determining the acoustic properties of a duct and in in-duct acoustic propagation models in the automotive industry and for musical acoustics purposes. The experimental apparatuses of classical TM measurement methods feature two measurement heads. Two microphones are flush with the walls of each head. The pressure signals are processed following the transfer function method constructed on an analytical model of acoustic propagation in measurement heads. The present paper aims at presenting a measurement method based on a three-microphone experimental apparatus and on its acoustic calibration through two reference measurements: the three-measurement two-calibration method for measuring the TM (3M2C-TM). Two microphones are flush with the measurement head walls and one is in the cap closing one side of the measured duct. 3M2C-TM proved essential for an accurate measurement of the four TM elements of two different ducts: a cylindrical duct and an expansion chamber. PMID:21568409
A calibration method of self-referencing interferometry based on maximum likelihood estimation
NASA Astrophysics Data System (ADS)
Zhang, Chen; Li, Dahai; Li, Mengyang; E, Kewei; Guo, Guangrao
2015-05-01
Self-referencing interferometry has been widely used in wavefront sensing. However, currently the results of wavefront measurement include two parts, one is the real phase information of wavefront under test and the other is the system error in self-referencing interferometer. In this paper, a method based on maximum likelihood estimation is presented to calibrate the system error in self-referencing interferometer. Firstly, at least three phase difference distributions are obtained by three position measurements of the tested component: one basic position, one rotation and one lateral translation. Then, combining the three phase difference data and using the maximum likelihood method to create a maximum likelihood function, reconstructing the wavefront under test and the system errors by least square estimation and Zernike polynomials. The simulation results show that the proposed method can deal with the issue of calibration of a self-referencing interferometer. The method can be used to reduce the effect of system errors on extracting and reconstructing the wavefront under test, and improve the measurement accuracy of the self-referencing interferometer.
Taverniers, Isabel; Van Bockstaele, Erik; De Loose, Marc
2004-03-01
Analytical real-time PCR technology is a powerful tool for implementation of the GMO labeling regulations enforced in the EU. The quality of analytical measurement data obtained by quantitative real-time PCR depends on the correct use of calibrator and reference materials (RMs). For GMO methods of analysis, the choice of appropriate RMs is currently under debate. So far, genomic DNA solutions from certified reference materials (CRMs) are most often used as calibrators for GMO quantification by means of real-time PCR. However, due to some intrinsic features of these CRMs, errors may be expected in the estimations of DNA sequence quantities. In this paper, two new real-time PCR methods are presented for Roundup Ready soybean, in which two types of plasmid DNA fragments are used as calibrators. Single-target plasmids (STPs) diluted in a background of genomic DNA were used in the first method. Multiple-target plasmids (MTPs) containing both sequences in one molecule were used as calibrators for the second method. Both methods simultaneously detect a promoter 35S sequence as GMO-specific target and a lectin gene sequence as endogenous reference target in a duplex PCR. For the estimation of relative GMO percentages both "delta C(T)" and "standard curve" approaches are tested. Delta C(T) methods are based on direct comparison of measured C(T) values of both the GMO-specific target and the endogenous target. Standard curve methods measure absolute amounts of target copies or haploid genome equivalents. A duplex delta C(T) method with STP calibrators performed at least as well as a similar method with genomic DNA calibrators from commercial CRMs. Besides this, high quality results were obtained with a standard curve method using MTP calibrators. This paper demonstrates that plasmid DNA molecules containing either one or multiple target sequences form perfect alternative calibrators for GMO quantification and are especially suitable for duplex PCR reactions. PMID:14689155
NMR Stark Spectroscopy: New Methods to Calibrate NMR Sensitivity to Electric Fields
NASA Astrophysics Data System (ADS)
Tarasek, Matthew R.
The influence of electrostatics on NMR parameters is well accepted. Thus, NMR is a promising route to probe electrical features within molecules and materials. However, applications of NMR Stark effects (E-field induced changes in spin energy levels) have been elusive. I have developed new approaches to resolve NMR Stark effects from an applied E field. This calibrates nuclear probes whose spectral response might later be used to evaluate internal E fields that are critical to function, such as those due to local charge distributions or sample structure. I will present two novel experimental approaches for direct calibration of NMR quadrupolar Stark effects (QSEs). In the first, steady-state (few-second) excitation by an E field at twice the NMR frequency (2ω 0) is used to saturate spin magnetization. The extent of saturation vs. E-field amplitude calibrates the QSE response rate, while measurements vs sample orientation determine tensorial character. The second method instead synchronizes short (few µs) pulses of the 2ω0 E field with a multiple-pulse NMR sequence. This, “POWER” (Perturbations Observed With Enhanced Resolution) approach enables more accurate measure of small QSEs (i.e. few Hz spectral changes). A 2nd key advantage is the ability to define tensorial response without reorienting the sample, but instead varying the phase of the 2ω0 field. I will describe these experiments and my home-built NMR “Stark probe”, employed on a conventional wide-bore solid-state NMR system. Results with GaAs demonstrate each method, while extensions to a wider array of molecular and material systems may now be possible using these methods.
Liu, Song; Su, Bo-min; Li, Qing-hui; Gan, Fu-xi
2015-01-01
The authors tried to find a method for quantitative analysis using pXRF without solid bulk stone/jade reference samples. 24 nephrite samples were selected, 17 samples were calibration samples and the other 7 are test samples. All the nephrite samples were analyzed by Proton induced X-ray emission spectroscopy (PIXE) quantitatively. Based on the PIXE results of calibration samples, calibration curves were created for the interested components/elements and used to analyze the test samples quantitatively; then, the qualitative spectrum of all nephrite samples were obtained by pXRF. According to the PIXE results and qualitative spectrum of calibration samples, partial least square method (PLS) was used for quantitative analysis of test samples. Finally, the results of test samples obtained by calibration method, PLS method and PIXE were compared to each other. The accuracy of calibration curve method and PLS method was estimated. The result indicates that the PLS method is the alternate method for quantitative analysis of stone/jade samples. PMID:25993858
NASA Astrophysics Data System (ADS)
Cornic, Philippe; Illoul, Cédric; Cheminet, Adam; Le Besnerais, Guy; Champagnat, Frédéric; Le Sant, Yves; Leclaire, Benjamin
2016-09-01
We address calibration and self-calibration of tomographic PIV experiments within a pinhole model of cameras. A complete and explicit pinhole model of a camera equipped with a 2-tilt angles Scheimpflug adapter is presented. It is then used in a calibration procedure based on a freely moving calibration plate. While the resulting calibrations are accurate enough for Tomo-PIV, we confirm, through a simple experiment, that they are not stable in time, and illustrate how the pinhole framework can be used to provide a quantitative evaluation of geometrical drifts in the setup. We propose an original self-calibration method based on global optimization of the extrinsic parameters of the pinhole model. These methods are successfully applied to the tomographic PIV of an air jet experiment. An unexpected by-product of our work is to show that volume self-calibration induces a change in the world frame coordinates. Provided the calibration drift is small, as generally observed in PIV, the bias on the estimated velocity field is negligible but the absolute location cannot be accurately recovered using standard calibration data.
A calibration method for optical trap force by use of electrokinetic phenomena
NASA Astrophysics Data System (ADS)
Yu, Youli; Zhang, Zhenxi; Zhang, Xiaolin
2006-09-01
An experimental method for calibration of optical trap force upon cells by use of electrokinetic phenomena is demonstrated. An electronkinetic sample chamber system (ESCS) is designed instead of a common sample chamber and a costly automatism stage, thus the experimental setup is simpler and cheaper. Experiments indicate that the range of the trap force measured by this method is piconewton and sub-piconewton, which makes it fit for study on non-damage interaction between light and biological particles with optical tweezers especially. Since this method is relevant to particle electric charge, by applying an alternating electric field, the new method may overcome the problem of correcting drag force and allow us to measure simultaneously optical trap stiffness and particle electric charge.
NASA Astrophysics Data System (ADS)
Shoemaker, C. A.; Singh, A.
2008-12-01
This paper will describe some new optimization algorithms and their application to hydrologic models. The approaches include a parallel version of a new heuristic algorithm combined with tabu search and a mathematically derived global optimization method that is based on trust region methods. The goals of these methods are to find optimal solutions to calibration problems and to design problems with relatively few simulations or (in a parallel environment) relatively little wallclock time. This is important because currently it is not possible to apply global optimization methods like genetic algorithms to computationally expensive simulation models like partial differential equations (with many nodes in groundwater) because it is not feasible to do thousands of simulations to evaluate the objective/fitness function. Results of the application of the algorithms to some complex models of groundwater contamination and phosphorous transport in watersheds will be presented.
A New Method to Calibrate Attachment Angles of Data Loggers in Swimming Sharks
NASA Astrophysics Data System (ADS)
Kawatsu, Shizuka; Sato, Katsufumi; Watanabe, Yuuki; Hyodo, Susumu; Breves, Jason P.; Fox, Bradley K.; Grau, E. Gordon; Miyazaki, Nobuyuki
2009-12-01
Recently, animal-borne accelerometers have been used to record the pitch angle of aquatic animals during swimming. When evaluating pitch angle, it is necessary to consider a discrepancy between the angle of an accelerometer and the long axis of an animal. In this study, we attached accelerometers to 17 free-ranging scalloped hammerhead shark ( Sphyrna lewini) pups from Kaneohe Bay, Hawaii. Although there are methods to calibrate attachment angles of accelerometers, we confirmed that previous methods were not applicable for hammerhead pups. According to raw data, some sharks ascended with a negative angle, which differs from tank observations of captive sharks. In turn, we developed a new method to account for this discrepancy in swimming sharks by estimating the attachment angle from the relationship between vertical speed (m/s) and pitch angle obtained by each accelerometer. The new method can be utilized for field observation of a wide range of species.
Verification of Geometric Model-Based Plant Phenotyping Methods for Studies of Xerophytic Plants
Drapikowski, Paweł; Kazimierczak-Grygiel, Ewa; Korecki, Dominik; Wiland-Szymańska, Justyna
2016-01-01
This paper presents the results of verification of certain non-contact measurement methods of plant scanning to estimate morphological parameters such as length, width, area, volume of leaves and/or stems on the basis of computer models. The best results in reproducing the shape of scanned objects up to 50 cm in height were obtained with the structured-light DAVID Laserscanner. The optimal triangle mesh resolution for scanned surfaces was determined with the measurement error taken into account. The research suggests that measuring morphological parameters from computer models can supplement or even replace phenotyping with classic methods. Calculating precise values of area and volume makes determination of the S/V (surface/volume) ratio for cacti and other succulents possible, whereas for classic methods the result is an approximation only. In addition, the possibility of scanning and measuring plant species which differ in morphology was investigated. PMID:27355949
Verification of Geometric Model-Based Plant Phenotyping Methods for Studies of Xerophytic Plants.
Drapikowski, Paweł; Kazimierczak-Grygiel, Ewa; Korecki, Dominik; Wiland-Szymańska, Justyna
2016-01-01
This paper presents the results of verification of certain non-contact measurement methods of plant scanning to estimate morphological parameters such as length, width, area, volume of leaves and/or stems on the basis of computer models. The best results in reproducing the shape of scanned objects up to 50 cm in height were obtained with the structured-light DAVID Laserscanner. The optimal triangle mesh resolution for scanned surfaces was determined with the measurement error taken into account. The research suggests that measuring morphological parameters from computer models can supplement or even replace phenotyping with classic methods. Calculating precise values of area and volume makes determination of the S/V (surface/volume) ratio for cacti and other succulents possible, whereas for classic methods the result is an approximation only. In addition, the possibility of scanning and measuring plant species which differ in morphology was investigated. PMID:27355949
Towards a shock tube method for the dynamic calibration of pressure sensors
Downes, Stephen; Knott, Andy; Robinson, Ian
2014-01-01
In theory, shock tubes provide a pressure change with a very fast rise time and calculable amplitude. This pressure step could provide the basis for the calibration of pressure transducers used in highly dynamic applications. However, conventional metal shock tubes can be expensive, unwieldy and difficult to modify. We describe the development of a 1.4 MPa (maximum pressure) shock tube made from unplasticized polyvinyl chloride pressure tubing which provides a low-cost, light and easily modifiable basis for establishing a method for determining the dynamic characteristics of pressure sensors. PMID:25071242
NASA Technical Reports Server (NTRS)
Mumma, M. J.
1972-01-01
A state-of-the-art review is given of the molecular branching ratio method for intensity calibration in the vacuum ultraviolet. Ways are described for determining both relative and quantitative responses in the wavelength range 1000 A to 3000 A. The molecular band systems which are discussed are the following: H2(B 1 Sigma u +)-(X 1 Sigma g +), H2(C 1 Pi u)-(X 1 Sigma g +), N2(A 1 Pi g)-(X 1 Sigma g +), CO(A 1 Pi)-(X 1 Sigma +), NO(A 2 Sigma +)-(X 2 Pi r), and NO(+) (A 1 Pi)-(X 1 Sigma +).
Linear Calibration of Radiographic Mineral Density Using Video-Digitizing Methods
NASA Technical Reports Server (NTRS)
Martin, R. Bruce; Papamichos, Thomas; Dannucci, Greg A.
1990-01-01
Radiographic images can provide quantitative as well as qualitative information if they are subjected to densitometric analysis. Using modem video-digitizing techniques, such densitometry can be readily accomplished using relatively inexpensive computer systems. However, such analyses are made more difficult by the fact that the density values read from the radiograph have a complex, nonlinear relationship to bone mineral content. This article derives the relationship between these variables from the nature of the intermediate physical processes, and presents a simple mathematical method for obtaining a linear calibration function using a step wedge or other standard.
Linear Calibration of Radiographic Mineral Density Using Video-Digitizing Methods
NASA Technical Reports Server (NTRS)
Martin, R. Bruce; Papamichos, Thomas; Dannucci, Greg A.
1990-01-01
Radiographic images can provide quantitative as well as qualitative information if they are subjected to densitometric analysis. Using modern video-digitizing techniques, such densitometry can be readily accomplished using relatively inexpensive computer systems. However, such analyses are made more difficult by the fact that the density values read from the radiograph have a complex, nonlinear relationship to bone mineral content. This article derives the relationship between these variables from the nature of the intermediate physical processes, and presents a simple mathematical method for obtaining a linear calibration function using a step wedge or other standard.
NASA Astrophysics Data System (ADS)
Nitta, Naotaka; Hyodo, Koji; Misawa, Masaki; Hayashi, Kazuhiko; Shirasaki, Yoshio; Homma, Kazuhiro; Shiina, Tsuyoshi
2013-07-01
It is important in regenerative medicine to evaluate the maturity of regenerating tissue. In the maturity evaluation of regenerating cartilage, it is useful to measure the temporal change in elasticity because the maturity of regenerating tissue is closely related to its elasticity. In this study, a quantitative elasticity evaluation of extracted regenerating cartilage samples, which is based on the laser Doppler measurement of ultrasonic particle velocity and calibration, was experimentally investigated using agar-based phantoms with different Young's moduli and regenerating cartilage samples extracted from beagles in animal experiments. The experimental results verified the feasibility of the proposed method for the elasticity evaluation of regenerating cartilage samples.
Optimization of method a load cell calibration for the measurement of coefficient of friction
NASA Astrophysics Data System (ADS)
Castro, R. M.; Pereira, M.; Sousa, A. R.; Curi, E. I. M.; Izidoro, C. L.; Correa, L. C.
2016-07-01
The instrumentation of equipment for mechanical testing is used to optimize the time to deliver a result, besides minimizing errors associated with manual measurements. Given this context, this work aims to present a calibration method for a load cell to determine the measurement results of force and friction coefficient, developed from on rotary pin-on-disk tribometer. The results indicate that the procedure provides measurements reliable for the tribological phenomena, resulting in with proximity the values provided by the ASTM G99-04.
NASA Astrophysics Data System (ADS)
Brigode, P.; Bernardara, P.; Paquet, E.; Gailhard, J.; Garavaglia, F.; Ribstein, P.; Micovic, Z.
2013-12-01
Extreme floods estimation methods are developed since many years within the hydrological and statistical communities. More recently, approaches based on the statistical analysis of flood streamflow samples simulated by rainfall-runoff models which are forced by simulated rainfall spread in the scientific literature. These approaches, called stochastic simulation methods, are typically composed by a probabilistic rainfall model and a rainfall-runoff model. Each of these two models are calibrated over observed hydrometeorological series such as daily precipitation series for the probabilistic rainfall models or such as daily streamflow, precipitation and temperature series for the rainfall-runoff models. Since extreme flood observations are by definition particularly rare, the validation of the proposed extreme flood estimations is one of the main critical issues, whatever the method - statistical or physically-based - used. Moreover, the observed hydrometeorological series used for the calibration of the stochastic simulation methods may be subject to significant variability over time, due to global climate oscillations such as El Niño Southern Oscillations for example. If the estimation of total involved uncertainty is a difficult task, investigating to what extent the proposed extreme flood values are dependent on the calibration period is an interesting first step. The general aim of this study is to propose a methodology for performing a sensitivity analysis of extreme flood estimations to the variability of observed series used for the model calibrations in a stochastic simulation framework. The methodology proposed is based on the nonparametric bootstrap concept and consists to perform a set of block-bootstrap experiments, thus generating different sets of observed series sub-samples. The generated observed series sub-samples are then used for the calibration of the different models considered within the stochastic simulation method. The main originality of
NASA Astrophysics Data System (ADS)
Wang, Huaguo; Chen, Xiaosong; Jawitz, James W.
2008-11-01
Five locally-calibrated light transmission visualization (LTV) methods were tested to quantify nonaqueous phase liquid (NAPL) mass and mass reduction in porous media. Tetrachloroethylene (PCE) was released into a two-dimensional laboratory flow chamber packed with water-saturated sand which was then flushed with a surfactant solution (2% Tween 80) until all of the PCE had been dissolved. In all the LTV methods employed here, the water phase was dyed, rather than the more common approach of dyeing the NAPL phase, such that the light adsorption characteristics of NAPL did not change as dissolution progressed. Also, none of the methods used here required the use of external calibration chambers. The five visualization approaches evaluated included three methods developed from previously published models, a binary method, and a novel multiple wavelength method that has the advantage of not requiring any assumptions about the intra-pore interface structure between the various phases (sand/water/NAPL). The new multiple wavelength method is also expected to be applicable to any translucent porous media containing two immiscible fluids (e.g., water-air, water-NAPL). Results from the sand-water-PCE system evaluated here showed that the model that assumes wetting media of uniform pore size (Model C of Niemet and Selker, 2001) and the multiple wavelength model with no interface structure assumptions were able to accurately quantify PCE mass reduction during surfactant flushing. The average mass recoveries from these two imaging methods were greater than 95% for domain-average NAPL saturations of approximately 2.6 × 10 - 2 , and were approximately 90% during seven cycles of surfactant flushing that sequentially reduced the average NAPL saturation to 7.5 × 10 - 4 .
A novel method for studying the buckling of nanotubes considering geometrical imperfections
NASA Astrophysics Data System (ADS)
Anoop Krishnan, N. M.; Ghosh, Debraj
2014-05-01
Buckling of nanotubes has been studied using many methods such as molecular dynamics (MD), molecular mechanics, and continuum-based shell theories. In MD, motion of the individual atoms is tracked under applied temperature and pressure, ensuring a reliable estimate of the material response. The response thus simulated varies for individual nanotubes and is only as accurate as the force field used to model the atomic interactions. On the other hand, there exists a rich literature on the understanding of continuum mechanics-based shell theories. Based on the observations on the behavior of nanotubes, there have been a number of shell theory-based approaches to study the buckling of nanotubes. Although some of these methods yield a reasonable estimate of the buckling stress, investigation and comparison of buckled mode shapes obtained from continuum analysis and MD are sparse. Previous studies show that the direct application of shell theories to study nanotube buckling often leads to erroneous results. The present study reveals that a major source of this error can be attributed to the departure of the shape of the nanotube from a perfect cylindrical shell. Analogous to the shell buckling in the macro-scale, in this work, the nanotube is modeled as a thin-shell with initial imperfection. Then, a nonlinear buckling analysis is carried out using the Riks method. It is observed that this proposed approach yields significantly improved estimate of the buckling stress and mode shapes. It is also shown that the present method can account for the variation of buckling stress as a function of the temperature considered. Hence, this can prove to be a robust method for a continuum analysis of nanosystems taking in the effect of variation of temperature as well.
Field, Christopher R; Lubrano, Adam L; Rogers, Duane A; Giordano, Braden C; Collins, Greg E
2013-03-22
A simple method for establishing calibration curves with sorbent-filled thermal desorption tubes has been demonstrated for nitroaromatic and nitramine vapor samples using a thermal desorption system with a cooled inlet system (TDS-CIS), which was coupled to a gas chromatograph (GC) with an electron capture detector (ECD). The method relies upon the direct liquid deposition of standard solutions onto the glass frit at the head of sorbent-filled thermal desorption tubes. Linear calibration results and ideal system conditions for the TDS-CIS-GC-ECD were established for mixtures containing both cyclotrimethylenetrinitramine, a.k.a. RDX, and 2,4,6-trinitrotoluene (TNT). Because of the chemical characteristics of RDX, a higher TDS-CIS flow rate relative to the optimized approach for TNT was required for efficient RDX desorption. Simultaneous quantitation of TNT and RDX using the direct liquid deposition method with optimized instrumentation parameters for RDX were compared to results from a standard split/splitless GC inlet and a CIS. PMID:23415141
Method to calibrate the absolute energy scale of air showers with ultrahigh energy photons.
Homola, Piotr; Risse, Markus
2014-04-18
Calibrating the absolute energy scale of air showers initiated by ultrahigh energy (UHE) cosmic rays is an important experimental issue. Currently, the corresponding systematic uncertainty amounts to 14%-21% using the fluorescence technique. Here, we describe a new, independent method which can be applied if ultrahigh energy photons are observed. While such photon-initiated showers have not yet been identified, the capabilities of present and future cosmic-ray detectors may allow their discovery. The method makes use of the geomagnetic conversion of UHE photons (preshower effect), which significantly affects the subsequent longitudinal shower development. The conversion probability depends on photon energy and can be calculated accurately by QED. The comparison of the observed fraction of converted photon events to the expected one allows the determination of the absolute energy scale of the observed photon air showers and, thus, an energy calibration of the air shower experiment. We provide details of the method and estimate the accuracy that can be reached as a function of the number of observed photon showers. Already a very small number of UHE photons may help to test and fix the absolute energy scale. PMID:24785024
NASA Astrophysics Data System (ADS)
Horňáčková, Michaela; Plavčan, Jozef; Rakovský, Jozef; Porubčan, Vladimír; Ozdín, Daniel; Veis, Pavel
2014-04-01
Calibration-free laser induced breakdown spectroscopy (CF-LIBS) was used for the determination of elemental composition and quantitative analysis of the Košice meteorite by means of time resolved and broadband emission spectroscopy (200-1000 nm). The electron temperature was determined using the Saha-Boltzmann plot method and the electron density from Stark broadening of the hydrogen Hα line (656 nm). Apart from magnesium, silicon and iron, which are the main elemental constituents of examined meteorite fragments, elements such as aluminum, nickel, potassium, sodium, chromium, calcium and manganese were also identified in the obtained LIBS spectra. Concentrations of Al, Ca, Cr, Fe, Mg, Mn, Na, Ni and Si were calculated using the calibration free approach and results were compared with ones obtained from the ICP-MS analyses. For the increase of the CF-LIBS accuracy, a selection of spectral lines was performed. Considering the transition probability, the population of absorbing level, the degree of ionization and predicted elemental concentration we calculated the probability of self-absorption and, consequently, spectral lines with highest self-absorption probability were rejected. CF-LIBS can be used as an alternative method for the meteorite fragments analysis (including the inner part and crust), because this method is quasi non-destructive and therefore analysis of all found fragments with minimal destruction is possible.
An Improvement of Pose Measurement Method Using Global Control Points Calibration
Sun, Changku; Sun, Pengfei; Wang, Peng
2015-01-01
During the last decade pose measurement technologies have gained an increasing interest in the computer vision. The vision-based pose measurement method has been widely applied in complex environments. However, the pose measurement error is a problem in the measurement applications. It grows rapidly with increasing measurement range. In order to meet the demand of high accuracy in large measurement range, a measurement error reduction solution to the vision-based pose measurement method, called Global Control Point Calibration (GCPC), is proposed. GCPC is an optimized process of existing visual pose measurement methods. The core of GCPC is to divide the measurement error into two types: the control point error and the control space error. Then by creating the global control points as well as performing error calibration of object pose, the two errors are processed. The control point error can be eliminated and the control space error is minimized. GCPC is experimented on the moving target in the camera’s field of view. The results show that the RMS error is 0.175° in yaw angle, 0.189° in pitch angle, and 0.159° in roll angle, which demonstrate that GCPC works effectively and stably. PMID:26207825
NASA Astrophysics Data System (ADS)
Bodammer, N. C.; Kaufmann, J.; Kanowski, M.; Tempelmann, C.
2009-02-01
Diffusion tensor tractography (DTT) allows one to explore axonal connectivity patterns in neuronal tissue by linking local predominant diffusion directions determined by diffusion tensor imaging (DTI). The majority of existing tractography approaches use continuous coordinates for calculating single trajectories through the diffusion tensor field. The tractography algorithm we propose is characterized by (1) a trajectory propagation rule that uses voxel centres as vertices and (2) orientation probabilities for the calculated steps in a trajectory that are obtained from the diffusion tensors of either two or three voxels. These voxels include the last voxel of each previous step and one or two candidate successor voxels. The precision and the accuracy of the suggested method are explored with synthetic data. Results clearly favour probabilities based on two consecutive successor voxels. Evidence is also provided that in any voxel-centre-based tractography approach, there is a need for a probability correction that takes into account the geometry of the acquisition grid. Finally, we provide examples in which the proposed fibre-tracking method is applied to the human optical radiation, the cortico-spinal tracts and to connections between Broca's and Wernicke's area to demonstrate the performance of the proposed method on measured data.
Cohen, A A; Shatzmiller, S E
1993-09-01
This study presents an algorithm that implements artificial-intelligence techniques for automated, and site-directed drug design. The aim of the method is to link two or more predetermined functional groups into a sensible molecular structure. The proposed designing process mimics the classical manual design method, in which the drug designer sits in front of the computer screen and with the aid of computer graphics attempts to design the new drug. Therefore, the key principle of the algorithm is the parameterization of some criteria that affect the decision-making process carried out by the drug designer. This parameterization is based on the generation of weighting factors that reflect the knowledge and knowledge-based intuition of the drug designer, and thus add further rationalization to the drug design process. The proposed algorithm has been shown to yield a large variety of different structures, of which the drug designer may choose the most sensible. Performance tests indicate that with the proper set of parameters, the method generates a new structure within a short time. PMID:8110662
Echocardiographic measurements of left ventricular mass by a non-geometric method
NASA Technical Reports Server (NTRS)
Parra, Beatriz; Buckey, Jay; Degraff, David; Gaffney, F. Andrew; Blomqvist, C. Gunnar
1987-01-01
The accuracy of a new nongeometric method for calculating left ventricular myocardial volumes from two-dimensional echocardiographic images was assessed in vitro using 20 formalin-fixed normal human hearts. Serial oblique short-axis images were acquired from one point at 5-deg intervals, for a total of 10-12 cross sections. Echocardiographic myocardial volumes were calculated as the difference between the volumes defined by the epi- and endocardial surfaces. Actual myocardial volumes were determined by water displacement. Volumes ranged from 80 to 174 ml (mean 130.8 ml). Linear regression analysis demonstrated excellent agreement between the echocardiographic and direct measurements.
NASA Astrophysics Data System (ADS)
Huang, Meng; Zhou, Yuanxiang; Chen, Weijiang; Lu, Licheng; Jin, Fubao; Huang, Jianwen
2014-10-01
Pulsed electroacoustic (PEA) method is widely used, but measurement conditions not always agree with the underlying PEA assumptions. This necessitates space charge recovery; however, existing research only addresses the attenuation and dispersion in lossy media. The effects of electrode-dielectric interface contact status and porosity on the accuracy of space charge distribution are discussed in the present article. It is shown that the presence of nonlinear interface and porosity can introduce severe error. However, because the properties of acoustic propagation of waves (which are generated from charge on the electrode and in the bulk) are different, the conventional recovery algorithm is no longer suitable for calibrating the charge density. To obtain accurate space charge profiles, it is necessary to eliminate these effects. A method has been proposed which is based on the original measurement process. The validity of the proposed method was tested by reasonable post-recovery electric field distributions.
NASA Astrophysics Data System (ADS)
Lu, Zenghai; Kasaragod, Deepa K.; Matcher, Stephen J.
2011-07-01
We present a phase fluctuation calibration method for polarization-sensitive swept-source optical coherence tomography (PS-SS-OCT) using continuous polarization modulation. The method uses a low-voltage broadband polarization modulator driven by a synchronized sinusoidal burst waveform rather than an asynchronous waveform, together with the removal of the global phases of the measured Jones matrices by the use of matrix normalization. This makes it possible to average the measured Jones matrices to remove the artifact due to the speckle noise of the signal in the sample without introducing auxiliary optical components into the sample arm. This method was validated on measurements of an equine tendon sample by the PS-SS-OCT system.
NASA Astrophysics Data System (ADS)
Chang, Liyun; Ho, Sheng-Yow; Du, Yi-Chun; Lin, Chih-Ming; Chen, Tainsong
2007-06-01
The calibration of the gantry angle indicator is an important and basic quality assurance (QA) item for the radiotherapy linear accelerator. In this study, we propose a new and practical method, which uses only the digital level, V-film, and general solid phantoms. By taking the star shot only, we can accurately calculate the true gantry angle according to the geometry of the film setup. The results on our machine showed that the gantry angle was shifted by -0.11° compared with the digital indicator, and the standard deviation was within 0.05°. This method can also be used for the simulator. In conclusion, this proposed method could be adopted as an annual QA item for mechanical QA of the accelerator.
RAPID COMMUNICATION: Traceability of acoustic emission measurements using energy calibration methods
NASA Astrophysics Data System (ADS)
Yan, T.; Jones, B. E.
2000-11-01
Passive acoustic emission (AE) methods are becoming useful tools for integrity assessment of structures, monitoring of industrial processes and machines, and materials characterization. Unfortunately, there are no measurement standards for estimating the absolute strength of the AE sources. The lack of standardization makes it very difficult to compare the results obtained in different laboratories or on different structures, and to obtain meaningful repeatability of measurements. Therefore, current methods only give a qualitative rather than quantitative indication of the change of state of structure or process. This communication outlines a way of calibrating AE transducer systems in situ using a pulsed-laser-generated thermoelastic AE energy source or a bouncing-ball-generated elastic impact AE energy source. The methods presented here should enable traceable measurement standards to be established for AE.
NASA Astrophysics Data System (ADS)
Shen, C. D.; Zhu, S.; Li, C.; Liang, Y. Y.
2009-07-01
In robotic remanufacturing measurement system, the 3D laser scanner is arranged by the robot and the object scanned is mounted on a turntable. This paper deals with the method of calibrating the relationship between the scanner coordinate and the robot Tool0 and furthermore locating the center axis of the turntable. The data of Tool0 can be directly obtained denoting its relationship with the robot base coordinate. So, the new methods of coordinate's transformation are effectively developed. Moreover some motivated experiments and optimized programs are designed for realizing process stabilization and reliability. This paper detailed explains the basic algorithm theory, practical operation instructions, the experiment data analysis, and etc. Theory deduction and experiments show the new methods are reasonable and efficient.
McGinitie, Teague M; Ebrahimi-Najafabadi, Heshmatollah; Harynuk, James J
2014-02-21
A new method for calibrating thermodynamic data to be used in the prediction of analyte retention times is presented. The method allows thermodynamic data collected on one column to be used in making predictions across columns of the same stationary phase but with varying geometries. This calibration is essential as slight variances in the column inner diameter and stationary phase film thickness between columns or as a column ages will adversely affect the accuracy of predictions. The calibration technique uses a Grob standard mixture along with a Nelder-Mead simplex algorithm and a previously developed model of GC retention times based on a three-parameter thermodynamic model to estimate both inner diameter and stationary phase film thickness. The calibration method is highly successful with the predicted retention times for a set of alkanes, ketones and alcohols having an average error of 1.6s across three columns. PMID:24484693
Liu, Miao; Yang, Shourui; Wang, Zhangying; Huang, Shujun; Liu, Yue; Niu, Zhenqi; Zhang, Xiaoxuan; Zhu, Jigui; Zhang, Zonghua
2016-05-30
Augmented reality system can be applied to provide precise guidance for various kinds of manual works. The adaptability and guiding accuracy of such systems are decided by the computational model and the corresponding calibration method. In this paper, a novel type of augmented reality guiding system and the corresponding designing scheme are proposed. Guided by external positioning equipment, the proposed system can achieve high relative indication accuracy in a large working space. Meanwhile, the proposed system is realized with a digital projector and the general back projection model is derived with geometry relationship between digitized 3D model and the projector in free space. The corresponding calibration method is also designed for the proposed system to obtain the parameters of projector. To validate the proposed back projection model, the coordinate data collected by a 3D positioning equipment is used to calculate and optimize the extrinsic parameters. The final projecting indication accuracy of the system is verified with subpixel pattern projecting technique. PMID:27410124
NASA Astrophysics Data System (ADS)
Štěpánková, K.; Novotný, K.; Vašinová Galiová, M.; Kanický, V.; Kaiser, J.; Hahn, D. W.
2013-03-01
Methods based on laser ablation, such as Laser-Induced Breakdown Spectroscopy (LIBS) and Laser-Ablation Inductively Coupled Plasma Mass/Optical Emission Spectrometry (LA-ICP-MS/OES) are particularly suitable for urinary calculi bulk and micro analysis. Investigation of spatial distribution of matrix and trace elements can help to explain their emergence and growth. However, quantification is still very problematic and these methods are often used only for qualitative elemental mapping. There are no commercially available standards, which would correspond to the urinary calculi matrix. Internal standardization is also difficult, mainly due to different crystalline phases in one kidney stone. The aim of this study is to demonstrate the calibration capabilities and examine the limitations of laser ablation based techniques. Calibration pellets were prepared from powdered human urinary calculi with phosphate, oxalate and urate matrix. For this comparative study, the most frequently used laser-ablation based analytical techniques were chosen, such as LIBS and LA-ICP-MS. Moreover, some alternative techniques such as simultaneous LIBS-LA-ICP-OES and laser ablation LA-LIBS were also utilized.
An Accurate Calibration Method Based on Velocity in a Rotational Inertial Navigation System
Zhang, Qian; Wang, Lei; Liu, Zengjun; Feng, Peide
2015-01-01
Rotation modulation is an effective method to enhance the accuracy of an inertial navigation system (INS) by modulating the gyroscope drifts and accelerometer bias errors into periodically varying components. The typical RINS drives the inertial measurement unit (IMU) rotation along the vertical axis and the horizontal sensors’ errors are modulated, however, the azimuth angle error is closely related to vertical gyro drift, and the vertical gyro drift also should be modulated effectively. In this paper, a new rotation strategy in a dual-axis rotational INS (RINS) is proposed and the drifts of three gyros could be modulated, respectively. Experimental results from a real dual-axis RINS demonstrate that the maximum azimuth angle error is decreased from 0.04° to less than 0.01° during 1 h. Most importantly, the changing of rotation strategy leads to some additional errors in the velocity which is unacceptable in a high-precision INS. Then the paper studies the basic reason underlying horizontal velocity errors in detail and a relevant new calibration method is designed. Experimental results show that after calibration and compensation, the fluctuation and stages in the velocity curve disappear and velocity precision is improved. PMID:26225983
An Accurate Calibration Method Based on Velocity in a Rotational Inertial Navigation System.
Zhang, Qian; Wang, Lei; Liu, Zengjun; Feng, Peide
2015-01-01
Rotation modulation is an effective method to enhance the accuracy of an inertial navigation system (INS) by modulating the gyroscope drifts and accelerometer bias errors into periodically varying components. The typical RINS drives the inertial measurement unit (IMU) rotation along the vertical axis and the horizontal sensors' errors are modulated, however, the azimuth angle error is closely related to vertical gyro drift, and the vertical gyro drift also should be modulated effectively. In this paper, a new rotation strategy in a dual-axis rotational INS (RINS) is proposed and the drifts of three gyros could be modulated, respectively. Experimental results from a real dual-axis RINS demonstrate that the maximum azimuth angle error is decreased from 0.04° to less than 0.01° during 1 h. Most importantly, the changing of rotation strategy leads to some additional errors in the velocity which is unacceptable in a high-precision INS. Then the paper studies the basic reason underlying horizontal velocity errors in detail and a relevant new calibration method is designed. Experimental results show that after calibration and compensation, the fluctuation and stages in the velocity curve disappear and velocity precision is improved. PMID:26225983
Methods for Calibrating Basin-Wide Hydroacoustic Propagation in the Indian Ocean
Blackman, D; de Groot-Hedlin, C; Orcutt, J A; Harben, P H; Clarke, D B; Ramirez, A L
2004-10-11
This collaborative project was designed to test and compare methods for achieving full ocean basin propagation of hydroacoustic signals in the 5-100 Hz frequency band. Plans for a systematic calibration of the International Monitoring System (IMS) for nuclear testing were under consideration in 2000/2001. The results from this project provide information to guide such planning for future ocean basin calibration work. Several acoustic source types were tested during two sea-going experiments and most were successful at generating signals that propagated hundreds to thousands of km to be recorded at the Indian Ocean IMS hydrophone stations. Development and numerical modeling of imploding glass sphere sources was one component of this testing. The intent was to design a relatively simple-to-use source that is not subject to restrictions that can limit use of explosive charges, but whose signal is large enough to propagate 100-1000's km range. Analysis of IMS hydrophone data recording during the experiments was used to illustrate the extent of energy loss during signal propagation and to assess the accuracy with which the small acoustic sources could be located using methods typically employed for nuclear monitoring.
NASA Astrophysics Data System (ADS)
Zhang, Yue; Sun, Xian; Thiele, Antje; Hinz, Stefan
2015-10-01
Synthetic aperture radar (SAR) systems, such as TanDEM-X, TerraSAR-X and Cosmo-SkyMed, acquire imagery with high spatial resolution (HR), making it possible to observe objects in urban areas with high detail. In this paper, we propose a new top-down framework for three-dimensional (3D) building reconstruction from HR interferometric SAR (InSAR) data. Unlike most methods proposed before, we adopt a generative model and utilize the reconstruction process by maximizing a posteriori estimation (MAP) through Monte Carlo methods. The reason for this strategy refers to the fact that the noisiness of SAR images calls for a thorough prior model to better cope with the inherent amplitude and phase fluctuations. In the reconstruction process, according to the radar configuration and the building geometry, a 3D building hypothesis is mapped to the SAR image plane and decomposed to feature regions such as layover, corner line, and shadow. Then, the statistical properties of intensity, interferometric phase and coherence of each region are explored respectively, and are included as region terms. Roofs are not directly considered as they are mixed with wall into layover area in most cases. When estimating the similarity between the building hypothesis and the real data, the prior, the region term, together with the edge term related to the contours of layover and corner line, are taken into consideration. In the optimization step, in order to achieve convergent reconstruction outputs and get rid of local extrema, special transition kernels are designed. The proposed framework is evaluated on the TanDEM-X dataset and performs well for buildings reconstruction.
Sheets, H David; Covino, Kristen M; Panasiewicz, Joanna M; Morris, Sara R
2006-01-01
Background Geometric morphometric methods of capturing information about curves or outlines of organismal structures may be used in conjunction with canonical variates analysis (CVA) to assign specimens to groups or populations based on their shapes. This methodological paper examines approaches to optimizing the classification of specimens based on their outlines. This study examines the performance of four approaches to the mathematical representation of outlines and two different approaches to curve measurement as applied to a collection of feather outlines. A new approach to the dimension reduction necessary to carry out a CVA on this type of outline data with modest sample sizes is also presented, and its performance is compared to two other approaches to dimension reduction. Results Two semi-landmark-based methods, bending energy alignment and perpendicular projection, are shown to produce roughly equal rates of classification, as do elliptical Fourier methods and the extended eigenshape method of outline measurement. Rates of classification were not highly dependent on the number of points used to represent a curve or the manner in which those points were acquired. The new approach to dimensionality reduction, which utilizes a variable number of principal component (PC) axes, produced higher cross-validation assignment rates than either the standard approach of using a fixed number of PC axes or a partial least squares method. Conclusion Classification of specimens based on feather shape was not highly dependent of the details of the method used to capture shape information. The choice of dimensionality reduction approach was more of a factor, and the cross validation rate of assignment may be optimized using the variable number of PC axes method presented herein. PMID:16978414
A 'Geometric' Downscaling Method for Coupling Dynamical Ice Sheet Models to GEOS-5
NASA Astrophysics Data System (ADS)
Zhao, B.; Cullather, R. I.; Nowicki, S.; Suarez, M.
2014-12-01
Plausible projection of future sea level rises requires coupled AOCGMs to include a dynamic ice sheet model (ISM) component. Getting the right forcing on the ice sheet models plays a critical role in the coupling process. The issue is further complicated by the mismatch between the grids used by atmosphere and ice sheet. Typically surface mass balance (SMB) and temperature fields are downscaled from the coarse atmospheric grid to the fine ice grid. We present one technique employed to couple NASA Goddard GEOS5 AGCM to JPL Ice Sheet System Model (ISSM). The Greenland ice surface from ISSM is explicitly embedded in the GEOS5 AGCM grid with a 'tile' representation. Atmospheric forcing fields are interpolated and further adjusted to account for elevation differences and fed into a SMB model operating on ice surface tiles. The coupling is done in such a way that mass and energy are conserved. The proposed method is independent of the underlying ice grid and can be used to couple any ISM. Comparison of resultant downscaled SMB fields from a suite of AGCM resolutions will be discussed.
NASA Astrophysics Data System (ADS)
Weres, Jerzy; Kujawa, Sebastian; Olek, Wiesław; Czajkowski, Łukasz
2016-04-01
Knowledge of physical properties of biomaterials is important in understanding and designing agri-food and wood processing industries. In the study presented in this paper computational methods were developed and combined with experiments to enhance identification of agri-food and forest product properties, and to predict heat and water transport in such products. They were based on the finite element model of heat and water transport and supplemented with experimental data. Algorithms were proposed for image processing, geometry meshing, and inverse/direct finite element modelling. The resulting software system was composed of integrated subsystems for 3D geometry data acquisition and mesh generation, for 3D geometry modelling and visualization, and for inverse/direct problem computations for the heat and water transport processes. Auxiliary packages were developed to assess performance, accuracy and unification of data access. The software was validated by identifying selected properties and using the estimated values to predict the examined processes, and then comparing predictions to experimental data. The geometry, thermal conductivity, specific heat, coefficient of water diffusion, equilibrium water content and convective heat and water transfer coefficients in the boundary layer were analysed. The estimated values, used as an input for simulation of the examined processes, enabled reduction in the uncertainty associated with predictions.
Online Calibration Methods for the DINA Model with Independent Attributes in CD-CAT
ERIC Educational Resources Information Center
Chen, Ping; Xin, Tao; Wang, Chun; Chang, Hua-Hua
2012-01-01
Item replenishing is essential for item bank maintenance in cognitive diagnostic computerized adaptive testing (CD-CAT). In regular CAT, online calibration is commonly used to calibrate the new items continuously. However, until now no reference has publicly become available about online calibration for CD-CAT. Thus, this study investigates the…
Ability of geometric morphometric methods to estimate a known covariance matrix.
Walker, J A
2000-12-01
Landmark-based morphometric methods must estimate the amounts of translation, rotation, and scaling (or, nuisance) parameters to remove nonshape variation from a set of digitized figures. Errors in estimates of these nuisance variables will be reflected in the covariance structure of the coordinates, such as the residuals from a superimposition, or any linear combination of the coordinates, such as the partial warp and standard uniform scores. A simulation experiment was used to compare the ability of the generalized resistant fit (GRF) and a relative warp analysis (RWA) to estimate known covariance matrices with various correlations and variance structures. Random covariance matrices were perturbed so as to vary the magnitude of the average correlation among coordinates, the number of landmarks with excessive variance, and the magnitude of the excessive variance. The covariance structure was applied to random figures with between 6 and 20 landmarks. The results show the expected performance of GRF and RWA across a broad spectrum of conditions. The performance of both GRF and RWA depended most strongly on the number of landmarks. RWA performance decreased slightly when one or a few landmarks had excessive variance. GRF performance peaked when approximately 25% of the landmarks had excessive variance. In general, both RWA and GRF performed better at estimating the direction of the first principal axis of the covariance matrix than the structure of the entire covariance matrix. RWA tended to outperform GRF when > approximately 75% of the coordinates had excessive variance. When < 75% of the coordinates had excessive variance, the relative performance of RWA and GRF depended on the magnitude of the excessive variance; when the landmarks with excessive variance had standard deviations (sigma) > or = 4 sigma minimum, GRF regularly outperformed RWA. PMID:12116434
NASA Astrophysics Data System (ADS)
Verreycken, T.; van der Horst, R. M.; Sadeghi, N.; Bruggeman, P. J.
2013-11-01
The absolute density of OH radicals generated in a nanosecond pulsed filamentary discharge in atmospheric pressure He +0.84% H2O is measured independently by UV absorption and laser induced fluorescence (LIF) calibrated with Rayleigh scattering. For the calibration of LIF with Rayleigh scattering, two LIF models, with six levels and four levels, are studied to investigate the influence of the rotational and vibrational energy transfers. In addition, a chemical model is used to deduce the OH density in the afterglow from the relative LIF intensity as function of time. The different models show good correspondence and by comparing these different methods, the accuracy and the effect of assumptions on the obtained OH density are discussed in detail. This analysis includes an analysis of the sensitivity to parameters used in the LIF models.
Nebulizer calibration using lithium chloride: an accurate, reproducible and user-friendly method.
Ward, R J; Reid, D W; Leonard, R F; Johns, D P; Walters, E H
1998-04-01
Conventional gravimetric (weight loss) calibration of jet nebulizers overestimates their aerosol output by up to 80% due to unaccounted evaporative loss. We examined two methods of measuring true aerosol output from jet nebulizers. A new adaptation of a widely available clinical assay for lithium (determined by flame photometry, LiCl method) was compared to an existing electrochemical method based on fluoride detection (NaF method). The agreement between the two methods and the repeatability of each method were examined. Ten Mefar jet nebulizers were studied using a Mefar MK3 inhalation dosimeter. There was no significant difference between the two methods (p=0.76) with mean aerosol output of the 10 nebulizers being 7.40 mg x s(-1) (SD 1.06; range 5.86-9.36 mg x s(-1)) for the NaF method and 7.27 mg x s(-1) (SD 0.82; range 5.52-8.26 mg x s(-1)) for the LiCl method. The LiCl method had a coefficient of repeatability of 13 mg x s(-1) compared with 3.7 mg x s(-1) for the NaF method. The LiCl method accurately measured true aerosol output and was considerably easier to use. It was also more repeatable, and hence more precise, than the NaF method. Because the LiCl method uses an assay that is routinely available from hospital biochemistry laboratories, it is easy to use and, thus, can readily be adopted by busy respiratory function departments. PMID:9623700
Avella, Joseph; Lehrer, Michael; Zito, S William
2008-10-01
1,1-Difluoroethane (DFE), also known as Freon 152A, is a member of a class of compounds known as halogenated hydrocarbons. A number of these compounds have gained notoriety because of their ability to induce rapid onset of intoxication after inhalation exposure. Abuse of DFE has necessitated development of methods for its detection and quantitation in postmortem and human performance specimens. Furthermore, methodologies applicable to research studies are required as there have been limited toxicokinetic and toxicodynamic reports published on DFE. This paper describes a method for the quantitation of DFE using a gas chromatography-flame-ionization headspace technique that employs solventless standards for calibration. Two calibration curves using 0.5 mL whole blood calibrators which ranged from A: 0.225-1.350 to B: 9.0-180.0 mg/L were developed. These were evaluated for linearity (0.9992 and 0.9995), limit of detection of 0.018 mg/L, limit of quantitation of 0.099 mg/L (recovery 111.9%, CV 9.92%), and upper limit of linearity of 27,000.0 mg/L. Combined curve recovery results of a 98.0 mg/L DFE control that was prepared using an alternate technique was 102.2% with CV of 3.09%. No matrix interference was observed in DFE enriched blood, urine or brain specimens nor did analysis of variance detect any significant differences (alpha = 0.01) in the area under the curve of blood, urine or brain specimens at three identical DFE concentrations. The method is suitable for use in forensic laboratories because validation was performed on instrumentation routinely used in forensic labs and due to the ease with which the calibration range can be adjusted. Perhaps more importantly it is also useful for research oriented studies because the removal of solvent from standard preparation eliminates the possibility for solvent induced changes to the gas/liquid partitioning of DFE or chromatographic interference due to the presence of solvent in specimens. PMID:19007521
Method for in-situ restoration of plantinum resistance thermometer calibration
Carroll, Radford M.
1989-01-01
A method is provided for in-situ restoration of platinum resistance thermometers (PRT's) that have undergone surface oxide contamination and/or strain-related damage causing decalibration. The method, which may be automated using a programmed computer control arrangement, consists of applying a dc heating current to the resistive sensing element of the PRT of sufficient magnitude to heat the element to an annealing temperature and maintaining the temperature for a specified period to restore the element to a stress-free calibration condition. The process anneals the sensing element of the PRT without subjecting the entire PRT assembly to the annealing temperature and may be used in the periodic maintenance of installed PRT's.
Method for in-situ restoration of platinum resistance thermometer calibration
Carroll, R.M.
1987-10-23
A method is provided for in-situ restoration of platinum resistance thermometers (PRT's) that have undergone surface oxide contamination and/or stain-related damage causing decalibration. The method, which may be automated using a programmed computer control arrangement, consists of applying a dc heating current to the resistive sensing element of the PRT of sufficient magnitude to heat the element to an annealing temperature and maintaining the temperature for a specified period to restore the element to a stress-free calibration condition. The process anneals the sensing element of the PRT without subjecting the entire PRT assembly to the annealing temperature and may be used in the periodic maintenance of installed PRT's. 1 fig.
A Novel Error Model of Optical Systems and an On-Orbit Calibration Method for Star Sensors
Wang, Shuang; Geng, Yunhai; Jin, Rongyu
2015-01-01
In order to improve the on-orbit measurement accuracy of star sensors, the effects of image-plane rotary error, image-plane tilt error and distortions of optical systems resulting from the on-orbit thermal environment were studied in this paper. Since these issues will affect the precision of star image point positions, in this paper, a novel measurement error model based on the traditional error model is explored. Due to the orthonormal characteristics of image-plane rotary-tilt errors and the strong nonlinearity among these error parameters, it is difficult to calibrate all the parameters simultaneously. To solve this difficulty, for the new error model, a modified two-step calibration method based on the Extended Kalman Filter (EKF) and Least Square Methods (LSM) is presented. The former one is used to calibrate the main point drift, focal length error and distortions of optical systems while the latter estimates the image-plane rotary-tilt errors. With this calibration method, the precision of star image point position influenced by the above errors is greatly improved from 15.42% to 1.389%. Finally, the simulation results demonstrate that the presented measurement error model for star sensors has higher precision. Moreover, the proposed two-step method can effectively calibrate model error parameters, and the calibration precision of on-orbit star sensors is also improved obviously. PMID:26703599
A Novel Error Model of Optical Systems and an On-Orbit Calibration Method for Star Sensors.
Wang, Shuang; Geng, Yunhai; Jin, Rongyu
2015-01-01
In order to improve the on-orbit measurement accuracy of star sensors, the effects of image-plane rotary error, image-plane tilt error and distortions of optical systems resulting from the on-orbit thermal environment were studied in this paper. Since these issues will affect the precision of star image point positions, in this paper, a novel measurement error model based on the traditional error model is explored. Due to the orthonormal characteristics of image-plane rotary-tilt errors and the strong nonlinearity among these error parameters, it is difficult to calibrate all the parameters simultaneously. To solve this difficulty, for the new error model, a modified two-step calibration method based on the Extended Kalman Filter (EKF) and Least Square Methods (LSM) is presented. The former one is used to calibrate the main point drift, focal length error and distortions of optical systems while the latter estimates the image-plane rotary-tilt errors. With this calibration method, the precision of star image point position influenced by the above errors is greatly improved from 15.42% to 1.389%. Finally, the simulation results demonstrate that the presented measurement error model for star sensors has higher precision. Moreover, the proposed two-step method can effectively calibrate model error parameters, and the calibration precision of on-orbit star sensors is also improved obviously. PMID:26703599
A new method for the absolute radiance calibration for UV/vis measurements of scattered sun light
NASA Astrophysics Data System (ADS)
Wagner, T.; Beirle, S.; Dörner, S.; Penning de Vries, M.; Remmers, J.; Rozanov, A.; Shaiganfar, R.
2015-05-01
Absolute radiometric calibrations are important for measurements of the atmospheric spectral radiance. Such measurements can be used to determine actinic fluxes, the properties of aerosols and clouds and the short wave energy budget. Conventional calibration methods in the laboratory are based on calibrated light sources and reflectors and are expensive, time consuming and subject to relatively large uncertainties. Also, the calibrated instruments might change during transport from the laboratory to the measurement sites. Here we present a new calibration method for UV/vis instruments that measure the spectrally resolved sky radiance, like for example zenith sky Differential Optical Absorption Spectroscopy (DOAS-) instruments or Multi-AXis (MAX-) DOAS instruments. Our method is based on the comparison of the solar zenith angle dependence of the measured zenith sky ra