A SVD-based method to assess the uniqueness and accuracy of SPECT geometrical calibration.
Ma, Tianyu; Yao, Rutao; Shao, Yiping; Zhou, Rong
2009-12-01
Geometrical calibration is critical to obtaining high resolution and artifact-free reconstructed image for SPECT and CT systems. Most published calibration methods use analytical approach to determine the uniqueness condition for a specific calibration problem, and the calibration accuracy is often evaluated through empirical studies. In this work, we present a general method to assess the characteristics of both the uniqueness and the quantitative accuracy of the calibration. The method uses a singular value decomposition (SVD) based approach to analyze the Jacobian matrix from a least-square cost function for the calibration. With this method, the uniqueness of the calibration can be identified by assessing the nonsingularity of the Jacobian matrix, and the estimation accuracy of the calibration parameters can be quantified by analyzing the SVD components. A direct application of this method is that the efficacy of a calibration configuration can be quantitatively evaluated by choosing a figure-of-merit, e.g., the minimum required number of projection samplings to achieve desired calibration accuracy. The proposed method was validated with a slit-slat SPECT system through numerical simulation studies and experimental measurements with point sources and an ultra-micro hot-rod phantom. The predicted calibration accuracy from the numerical studies was confirmed by the experimental point source calibrations at approximately 0.1 mm for both the center of rotation (COR) estimation of a rotation stage and the slit aperture position (SAP) estimation of a slit-slat collimator by an optimized system calibration protocol. The reconstructed images of a hot rod phantom showed satisfactory spatial resolution with a proper calibration and showed visible resolution degradation with artificially introduced 0.3 mm COR estimation error. The proposed method can be applied to other SPECT and CT imaging systems to analyze calibration method assessment and calibration protocol
NASA Astrophysics Data System (ADS)
Gonsalves, Michael Oliver
This dissertation describes an automated technique for ascertaining the values of the geometric calibration parameters of an airborne lidar. A least squares approach is employed that adjusts the point cloud to a single planar surface which could be either a narrow airport runway or a dynamic sea surface. Going beyond the customary three boresight angles, the proposed adjustment can determine up to eleven calibration parameters to a precision that renders a negligible contribution to the point cloud's positional uncertainty. Presently under development is the Coastal Zone Mapping and Imaging Lidar (CZMIL), which, unlike most contemporary systems that use oscillating mirrors to reflect the beam, will use a circular spinning prism to refract the laser in the desired direction. This departure from the traditional scanner presents the potential for internal geometric misalignments not previously experienced. Rather than relying on past calibration practices (like requiring data be acquired over a pitched-roof), a more robust method of calibration is established which does not depend on the presence of any cultural features. To develop this new method of calibration, the laser point positioning equation for this lidar was developed first. The system was then simulated in the MATLAB environment. Using these artificial datasets, the behavior of each geometric parameter iii was systematically manipulated, understood and calibrated, while an optimal flight strategy for the calibration acquisition was simultaneously developed. Finally, the total propagated uncertainty (TPU) of the point cloud was determined using a propagation of variances. Using this TPU module, the strength of the calibration solution was assessed. For example, four flight lines each of 20 seconds in duration contained sufficient information to determine the calibration parameters to such a degree of confidence that their contribution to the final point cloud uncertainty was only 0.012m in the horizontal
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.
A geometric calibration method for inverse geometry computed tomography using P-matrices.
Slagowski, Jordan M; Dunkerley, David A P; Hatt, Charles R; Speidel, Michael A
2016-02-27
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 root-mean-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.
NASA Astrophysics Data System (ADS)
Jacobson, M. W.; Ketcha, M. D.; Capostagno, S.; Martin, A.; Uneri, A.; Goerres, J.; De Silva, T.; Reaungamornrat, S.; Han, R.; Manbachi, A.; Stayman, J. W.; Vogt, S.; Kleinszig, G.; Siewerdsen, J. H.
2018-01-01
Modern cone-beam CT systems, especially C-arms, are capable of diverse source-detector orbits. However, geometric calibration of these systems using conventional configurations of spherical fiducials (BBs) may be challenged for novel source-detector orbits and system geometries. In part, this is because the BB configurations are designed with careful forethought regarding the intended orbit so that BB marker projections do not overlap in projection views. Examples include helical arrangements of BBs (Rougee et al 1993 Proc. SPIE 1897 161–9) such that markers do not overlap in projections acquired from a circular orbit and circular arrangements of BBs (Cho et al 2005 Med. Phys. 32 968–83). As a more general alternative, this work proposes a calibration method based on an array of line-shaped, radio-opaque wire segments. With this method, geometric parameter estimation is accomplished by relating the 3D line equations representing the wires to the 2D line equations of their projections. The use of line fiducials simplifies many challenges with fiducial recognition and extraction in an orbit-independent manner. For example, their projections can overlap only mildly, for any gantry pose, as long as the wires are mutually non-coplanar in 3D. The method was tested in application to circular and non-circular trajectories in simulation and in real orbits executed using a mobile C-arm prototype for cone-beam CT. Results indicated high calibration accuracy, as measured by forward and backprojection/triangulation error metrics. Triangulation errors on the order of microns and backprojected ray deviations uniformly less than 0.2 mm were observed in both real and simulated orbits. Mean forward projection errors less than 0.1 mm were observed in a comprehensive sweep of different C-arm gantry angulations. Finally, successful integration of the method into a CT imaging chain was demonstrated in head phantom scans.
Geometric calibration of rotational kaleidoscopic instrument
NASA Astrophysics Data System (ADS)
Havran, Vlastimil; Němcová, Šárka; Čáp, Jiří; Hošek, Jan; Bittner, Jiří; Macúchová, Karolina
2016-11-01
The measurement of spatially varying surface reflectance is required for faithful reproduction of real world to allow for predictive look of computer generated images. One such proposed method uses a rotational kaleidoscopic imaging, where illumination and imaging paths are realized by subimages on kaleidoscopic mirrors and illumination is carried out by a DLP projector. We describe a novel geometric calibration method for a rotational kaleidoscope that is necessary to get aligned and accurate data from measurement. The calibration has two stages. The first stage mechanically adjusts the camera, the projector, and the autocollimator against the kaleidoscope mirrors. The second stage is based on the software. By random perturbation of camera and projector in corresponding mathematical model of the kaleidoscope we estimate better real positions of camera and projector in a physical setup, comparing the computed images from the software simulator and the acquired images from the physical setup.
Uav Cameras: Overview and Geometric Calibration Benchmark
NASA Astrophysics Data System (ADS)
Cramer, M.; Przybilla, H.-J.; Zurhorst, A.
2017-08-01
Different UAV platforms and sensors are used in mapping already, many of them equipped with (sometimes) modified cameras as known from the consumer market. Even though these systems normally fulfil their requested mapping accuracy, the question arises, which system performs best? This asks for a benchmark, to check selected UAV based camera systems in well-defined, reproducible environments. Such benchmark is tried within this work here. Nine different cameras used on UAV platforms, representing typical camera classes, are considered. The focus is laid on the geometry here, which is tightly linked to the process of geometrical calibration of the system. In most applications the calibration is performed in-situ, i.e. calibration parameters are obtained as part of the project data itself. This is often motivated because consumer cameras do not keep constant geometry, thus, cannot be seen as metric cameras. Still, some of the commercial systems are quite stable over time, as it was proven from repeated (terrestrial) calibrations runs. Already (pre-)calibrated systems may offer advantages, especially when the block geometry of the project does not allow for a stable and sufficient in-situ calibration. Especially for such scenario close to metric UAV cameras may have advantages. Empirical airborne test flights in a calibration field have shown how block geometry influences the estimated calibration parameters and how consistent the parameters from lab calibration can be reproduced.
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
Sky camera geometric calibration using solar observations
Urquhart, Bryan; Kurtz, Ben; Kleissl, Jan
2016-09-05
A camera model and associated automated calibration procedure for stationary daytime sky imaging cameras is presented. The specific modeling and calibration needs are motivated by remotely deployed cameras used to forecast solar power production where cameras point skyward and use 180° fisheye lenses. Sun position in the sky and on the image plane provides a simple and automated approach to calibration; special equipment or calibration patterns are not required. Sun position in the sky is modeled using a solar position algorithm (requiring latitude, longitude, altitude and time as inputs). Sun position on the image plane is detected using a simple image processing algorithm. Themore » performance evaluation focuses on the calibration of a camera employing a fisheye lens with an equisolid angle projection, but the camera model is general enough to treat most fixed focal length, central, dioptric camera systems with a photo objective lens. Calibration errors scale with the noise level of the sun position measurement in the image plane, but the calibration is robust across a large range of noise in the sun position. In conclusion, calibration performance on clear days ranged from 0.94 to 1.24 pixels root mean square error.« less
Sky camera geometric calibration using solar observations
Urquhart, Bryan; Kurtz, Ben; Kleissl, Jan
2016-09-05
A camera model and associated automated calibration procedure for stationary daytime sky imaging cameras is presented. The specific modeling and calibration needs are motivated by remotely deployed cameras used to forecast solar power production where cameras point skyward and use 180° fisheye lenses. Sun position in the sky and on the image plane provides a simple and automated approach to calibration; special equipment or calibration patterns are not required. Sun position in the sky is modeled using a solar position algorithm (requiring latitude, longitude, altitude and time as inputs). Sun position on the image plane is detected using a simple image processing algorithm. The performance evaluation focuses on the calibration of a camera employing a fisheye lens with an equisolid angle projection, but the camera model is general enough to treat most fixed focal length, central, dioptric camera systems with a photo objective lens. Calibration errors scale with the noise level of the sun position measurement in the image plane, but the calibration is robust across a large range of noise in the sun position. In conclusion, calibration performance on clear days ranged from 0.94 to 1.24 pixels root mean square error.
SENTINEL-2: geometric calibration during commissioning phase
NASA Astrophysics Data System (ADS)
Dechoz, Cécile; Languille, Florie; Tremas, Thierry; Nosavan, Julien; Petrucci, Beatrice; Massera, Stephane; Gachet, Roland; Martimort, Philippe; Isola, Claudia
2014-10-01
Sentinel-2 is a multispectral, high-resolution, optical imaging mission, developed by the European Space Agency (ESA) in the frame of the Copernicus program of the European Commission. In cooperation with ESA, the Centre National d'Etudes Spatiales (CNES) is responsible for the image quality of the project, and will ensure the CAL/VAL commissioning phase. Sentinel-2 mission is devoted the operational monitoring of land and coastal areas, and will provide a continuity of SPOT- and Landsat-type data. Sentinel-2 will also deliver information for emergency services. Launched in 2015 and 2016, there will be a constellation of 2 satellites on a polar sun-synchronous orbit, imaging systematically terrestrial surfaces with a revisit time of 5 days, in 13 spectral bands in visible and shortwave infra-red. Therefore, multi-temporal series of images, taken under the same viewing conditions, will be available. This paper first briefly presents Sentinel-2 system, the design, the level-1 products, and the main geometric image quality requirements: geolocation with and without ground control points, multi-temporal and multi-spectral registration. Then, it presents the methods foreseen during commissioning: the viewing frames orientation, the focal plane mapping, the global reference image generation. Finally, it presents the Sentinel-2 image simulation tool, used to provide data for the validation of these developments.
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.
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.
Geometric Calibration and Accuracy Verification of the GF-3 Satellite
Deng, Mingjun; Xu, Kai; Guo, Fengcheng
2017-01-01
The GF-3 satellite is the first multi-polarization synthetic aperture radar (SAR) imaging satellite in China, which operates in the C band with a resolution of 1 m. Although the SAR satellite system was geometrically calibrated during the in-orbit commissioning phase, there are still some system errors that affect its geometric positioning accuracy. In this study, these errors are classified into three categories: fixed system error, time-varying system error, and random error. Using a multimode hybrid geometric calibration of spaceborne SAR, and considering the atmospheric propagation delay, all system errors can be effectively corrected through high-precision ground control points and global atmospheric reference data. The geometric calibration experiments and accuracy evaluation for the GF-3 satellite are performed using ground control data from several regions. The experimental results show that the residual system errors of the GF-3 SAR satellite have been effectively eliminated, and the geometric positioning accuracy can be better than 3 m. PMID:28850055
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.
Research on Geometric Calibration of Spaceborne Linear Array Whiskbroom Camera.
Sheng, Qinghong; Wang, Qi; Xiao, Hui; Wang, Qing
2018-01-16
The geometric calibration of a spaceborne thermal-infrared camera with a high spatial resolution and wide coverage can set benchmarks for providing an accurate geographical coordinate for the retrieval of land surface temperature. The practice of using linear array whiskbroom Charge-Coupled Device (CCD) arrays to image the Earth can help get thermal-infrared images of a large breadth with high spatial resolutions. Focusing on the whiskbroom characteristics of equal time intervals and unequal angles, the present study proposes a spaceborne linear-array-scanning imaging geometric model, whilst calibrating temporal system parameters and whiskbroom angle parameters. With the help of the YG-14-China's first satellite equipped with thermal-infrared cameras of high spatial resolution-China's Anyang Imaging and Taiyuan Imaging are used to conduct an experiment of geometric calibration and a verification test, respectively. Results have shown that the plane positioning accuracy without ground control points (GCPs) is better than 30 pixels and the plane positioning accuracy with GCPs is better than 1 pixel.
Research on Geometric Calibration of Spaceborne Linear Array Whiskbroom Camera
Sheng, Qinghong; Wang, Qi; Xiao, Hui; Wang, Qing
2018-01-01
The geometric calibration of a spaceborne thermal-infrared camera with a high spatial resolution and wide coverage can set benchmarks for providing an accurate geographical coordinate for the retrieval of land surface temperature. The practice of using linear array whiskbroom Charge-Coupled Device (CCD) arrays to image the Earth can help get thermal-infrared images of a large breadth with high spatial resolutions. Focusing on the whiskbroom characteristics of equal time intervals and unequal angles, the present study proposes a spaceborne linear-array-scanning imaging geometric model, whilst calibrating temporal system parameters and whiskbroom angle parameters. With the help of the YG-14—China’s first satellite equipped with thermal-infrared cameras of high spatial resolution—China’s Anyang Imaging and Taiyuan Imaging are used to conduct an experiment of geometric calibration and a verification test, respectively. Results have shown that the plane positioning accuracy without ground control points (GCPs) is better than 30 pixels and the plane positioning accuracy with GCPs is better than 1 pixel. PMID:29337885
Geometric calibration of Colour and Stereo Surface Imaging System of ESA's Trace Gas Orbiter
NASA Astrophysics Data System (ADS)
Tulyakov, Stepan; Ivanov, Anton; Thomas, Nicolas; Roloff, Victoria; Pommerol, Antoine; Cremonese, Gabriele; Weigel, Thomas; Fleuret, Francois
2018-01-01
There are many geometric calibration methods for "standard" cameras. These methods, however, cannot be used for the calibration of telescopes with large focal lengths and complex off-axis optics. Moreover, specialized calibration methods for the telescopes are scarce in literature. We describe the calibration method that we developed for the Colour and Stereo Surface Imaging System (CaSSIS) telescope, on board of the ExoMars Trace Gas Orbiter (TGO). Although our method is described in the context of CaSSIS, with camera-specific experiments, it is general and can be applied to other telescopes. We further encourage re-use of the proposed method by making our calibration code and data available on-line.
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.
Geometric Calibration and Radiometric Correction of the Maia Multispectral Camera
NASA Astrophysics Data System (ADS)
Nocerino, E.; Dubbini, M.; Menna, F.; Remondino, F.; Gattelli, M.; Covi, D.
2017-10-01
Multispectral imaging is a widely used remote sensing technique, whose applications range from agriculture to environmental monitoring, from food quality check to cultural heritage diagnostic. A variety of multispectral imaging sensors are available on the market, many of them designed to be mounted on different platform, especially small drones. This work focuses on the geometric and radiometric characterization of a brand-new, lightweight, low-cost multispectral camera, called MAIA. The MAIA camera is equipped with nine sensors, allowing for the acquisition of images in the visible and near infrared parts of the electromagnetic spectrum. Two versions are available, characterised by different set of band-pass filters, inspired by the sensors mounted on the WorlView-2 and Sentinel2 satellites, respectively. The camera details and the developed procedures for the geometric calibrations and radiometric correction are presented in the paper.
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.
Simulation on the Measurement Method of Geometric Distortion of Telescopes
NASA Astrophysics Data System (ADS)
Fan, Li; Shu-lin, Ren
2016-07-01
The accurate measurement on the effect of telescope geometric distortion is conducive to improving the astrometric positioning accuracy of telescopes, which is of significant importance for many disciplines of astronomy, such as stellar clusters, natural satellites, asteroids, comets, and other celestial bodies in the solar system. For this reason, the predecessors have developed an iterative self-calibration method to measure the telescope geometric distortion by dithering observations in a dense star field, and achieved fine results. However, the previous work did not make constraints on the density of star field, and the dithering mode, but chose empirically some good conditions (for example, a denser star field and a larger dithering number) to observe, which took up much observing time, and caused a rather low efficiency. In order to explore the validity of the self-calibration method, and optimize its observational conditions, it is necessary to carry out the corresponding simulations. In this paper, we introduce first the self-calibration method in detail, then by the simulation method, we verify the effectiveness of the self-calibration method, and make further optimizations on the observational conditions, such as the density of star field and the dithering number, to achieve a higher accuracy of geometric distortion measurement. Finally, taking consideration of the practical application for correcting the geometric distortion effect, we have analyzed the relationship between the number of reference stars in the field of view and the astrometric accuracy by virtue of the simulation method.
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.
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.
Jiang, Changhui; Zhang, Na; Gao, Juan; Hu, Zhanli
2017-01-01
Stationary digital breast tomosynthesis (sDBT) with distributed X-ray sources based on carbon nanotube (CNT) field emission cathodes has been recently proposed as an approach that can prevent motion blur produced by traditional DBT systems. In this paper, we simulate a geometric calibration method based on a proposed multi-source CNT X-ray sDBT system. This method is a projection matrix-based approach with seven geometric parameters, all of which can be obtained from only one projection datum of the phantom. To our knowledge, this study reports the first application of this approach in a CNT-based multi-beam X-ray sDBT system. The simulation results showed that the extracted geometric parameters from the calculated projection matrix are extremely close to the input values and that the proposed method is effective and reliable for a square sDBT system. In addition, a traditional cone-beam computed tomography (CT) system was also simulated, and the uncalibrated and calibrated geometric parameters were used in image reconstruction based on the filtered back-projection (FBP) method. The results indicated that the images reconstructed with calibrated geometric parameters have fewer artifacts and are closer to the reference image. All the simulation tests showed that this geometric calibration method is optimized for sDBT systems but can also be applied to other application-specific CT imaging systems.
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
Self-calibration of biplanar radiographic images through geometric spine shape descriptors.
Kadoury, Samuel; Cheriet, Farida; Labelle, Hubert
2010-07-01
This paper presents a novel self-calibration method of an X-ray scene applied for the 3-D reconstruction of the scoliotic spine. Current calibration techniques either use a cumbersome calibration apparatus or depend on manually identified landmarks to determine the geometric configuration, thus limiting routine clinical evaluation. The proposed approach uses high-level information automatically extracted from biplanar X-rays to solve the radiographic scene parameters. We first present a segmentation method that takes into account the variable appearance and geometry of a scoliotic spine in order to isolate and extract the silhouettes of the anterior vertebral body. By incorporating prior anatomical information through a Bayesian formulation of the morphological distribution, a multiscale spine segmentation framework is proposed for scoliotic patients. An iterative nonlinear optimization procedure, integrating a 3-D visual hull reconstruction and geometrical torsion properties of the spine, is then applied to globally refine the geometrical parameters of the 3-D viewing scene and obtain the optimal 3-D reconstruction. An experimental comparison with data provided from reference synthetic models yields similar accuracy on the retroprojection of low-level primitives such as anatomical landmarks identified on each vertebra (2.2 mm). Results obtained from a clinical validation on 60 pairs of uncalibrated digitized X-rays of adolescents with scoliosis show that the 3-D reconstructions from the new system offer geometrically accurate models with insignificant differences for 3-D clinical indexes commonly used in the evaluation of spinal deformities. The reported experiments demonstrate a viable and accurate alternative to previous reconstruction techniques, offering the first automatic approach for routine 3-D clinical assessment in radiographic suites.
Modern Geometric Methods of Distance Determination
NASA Astrophysics Data System (ADS)
Thévenin, Frédéric; Falanga, Maurizio; Kuo, Cheng Yu; Pietrzyński, Grzegorz; Yamaguchi, Masaki
2017-11-01
Building a 3D picture of the Universe at any distance is one of the major challenges in astronomy, from the nearby Solar System to distant Quasars and galaxies. This goal has forced astronomers to develop techniques to estimate or to measure the distance of point sources on the sky. While most distance estimates used since the beginning of the 20th century are based on our understanding of the physics of objects of the Universe: stars, galaxies, QSOs, the direct measures of distances are based on the geometric methods as developed in ancient Greece: the parallax, which has been applied to stars for the first time in the mid-19th century. In this review, different techniques of geometrical astrometry applied to various stellar and cosmological (Megamaser) objects are presented. They consist in parallax measurements from ground based equipment or from space missions, but also in the study of binary stars or, as we shall see, of binary systems in distant extragalactic sources using radio telescopes. The Gaia mission will be presented in the context of stellar physics and galactic structure, because this key space mission in astronomy will bring a breakthrough in our understanding of stars, galaxies and the Universe in their nature and evolution with time. Measuring the distance to a star is the starting point for an unbiased description of its physics and the estimate of its fundamental parameters like its age. Applying these studies to candles such as the Cepheids will impact our large distance studies and calibration of other candles. The text is constructed as follows: introducing the parallax concept and measurement, we shall present briefly the Gaia satellite which will be the future base catalogue of stellar astronomy in the near future. Cepheids will be discussed just after to demonstrate the state of the art in distance measurements in the Universe with these variable stars, with the objective of 1% of error in distances that could be applied to our closest
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.
NASA Astrophysics Data System (ADS)
Wang, Mi; Cheng, Yufeng; Chang, Xueli; Jin, Shuying; Zhu, Ying
2017-03-01
The Chinese GaoFen4 (GF4) remote sensing satellite, launched at the end of December 2015, is China's first civilian high-resolution geostationary optical satellite and has the world's highest resolution from geostationary orbit. High accuracy geometric calibration is the key factor in the geometrical quality of satellite imagery. This paper proposes an on-orbit geometric calibration approach for the high-resolution geostationary optical satellite GF4 in which a stepwise calibration is performed, external parameters are estimated, and internal parameters are then estimated in a generalized camera frame determined by external parameters. First, the correlation of the imaging error sources and the rigorous imaging model of GF4 are introduced. Second, the geometric calibration model based on the two-dimensional detector directional angle and the parameters estimation method for the planar array camera are presented. LandSat 8 digital orthophoto maps (DOM) and GDEM2 digital elevation models (DEM) are used to validate the efficiency of the proposed method and to make a geometric quality assessment of GF4. The results indicate that changing imaging time and imaging area will dramatically affect the absolute positioning accuracy because of the change of the camera's installation angles caused by thermal environment changes around the satellite in a high orbit. After calibration, the internal distortion is well-compensated, and the positioning accuracy with relatively few ground control points (GCPs) is demonstrated to be better than 1.0 pixels for both the panchromatic and near-infrared sensor and the intermediate infrared sensor.
Direct and fast measurement of CT beam filter profiles with simultaneous geometrical calibration
Yang, Kai; Li, Xinhua; Xu, X. George; Liu, Bob
2017-01-01
Purpose To accurately measure the beam filter profiles from a variety of CT scanner models and to provide reference data for Monte Carlo simulations of CT scanners. Methods This study proposed a new method to measure CT beam filter profiles using a linear-array x-ray detector (X-Scan 0.8f3–512, Detection Technology Inc, Finland) under gantry rotation mode. A robust geometrical calibration approach was developed to determine key geometrical parameters, by considering the x-ray focal spot location relative to the linear-array detector and the gantry’s angular increment at each acquisition point. CT beam intensity profiles were synthesized from continuously measured data during a 10° gantry rotation range, with calibrated detector response and system geometry information. Relative transmission profiles of nineteen sets of beam filters were then derived for nine different CT scanner models from three different manufacturers. Equivalent aluminum thickness profiles of these beam filters were determined by analytical calculation using the Spektr Matlab software package to match the measured transmission profiles. Three experiments were performed to validate the accuracy of the geometrical calibration, detector response modeling, and the derived equivalent aluminum thickness profiles. Results The beam intensity profiles measured from gantry rotational mode showed very good agreement with those measured with gantry stationary mode, with a maximal difference of 3%. The equivalent aluminum thickness determined by this proposed method agreed well with what was measured by an ion chamber, with a mean difference of 0.4%. The determined HVL profiles matched well with data from a previous study (max difference of 4.7%). Conclusions An accurate and robust method to directly measure profiles from a broad list of beam filters and CT scanner models was developed, implemented, and validated. Useful reference data was provided for future research on CT system modeling. PMID
Geometric calibration for a next-generation digital breast tomosynthesis system
NASA Astrophysics Data System (ADS)
Ferris, William S.; Vent, Trevor L.; Maidment, Tristan D.; Acciavatti, Raymond J.; Wurtele, David E.; Maidment, Andrew D. A.
2017-03-01
A method for geometric calibration of a next-generation tomosynthesis (NGT) system is proposed and tested. The NGT system incorporates additional geometric movements between projections over conventional DBT. These movements require precise geometric calibration to support magnification DBT and isotropic SR. A phantom was created to project small tungsten-carbide ball bearings (BB's) onto the detector at four different magnifications. Using a bandpass filter and template matching, a MATLAB program was written to identify the centroid locations of each BB projection on the images. An optimization algorithm calculated an effective location for the source and detector that mathematically projected the BB's onto the same locations on the detector as found on the projection images. The average distance between the BB projections on the image and the mathematically computed projections was 0.11 mm. The effective locations for the source and detector were encoded in the DICOM file for each projection; these were then used by the reconstruction algorithm. Tomographic image reconstructions were performed for three acquisition modes of the NGT system; these successfully demonstrated isotropic SR, magnified SR, and oblique reconstruction.
NASA Astrophysics Data System (ADS)
Jacobson, M. W.; Ketcha, M.; Uneri, A.; Goerres, J.; De Silva, T.; Reaungamornrat, S.; Vogt, S.; Kleinszig, G.; Siewerdsen, J. H.
2017-03-01
Purpose: Traditional BB-based geometric calibration methods for cone-beam CT (CBCT) rely strongly on foreknowledge of the scan trajectory shape. This is a hindrance to the implementation of variable trajectory CBCT systems, normally requiring a dedicated calibration phantom or software algorithm for every scan orbit of interest. A more flexible method of calibration is proposed here that accommodates multiple orbit types - including strongly noncircular trajectories - with a single phantom and software routine. Methods: The proposed method uses a calibration phantom consisting of multiple line-shaped wire segments. Geometric models relating the 3D line equations of the wires to the 2D line equations of their projections are used as the basis for system geometry estimation. This method was tested using a mobile C-arm CT system and comparisons were made to standard BB-based calibrations. Simulation studies were also conducted using a sinusoid-on-sphere orbit. Calibration performance was quantified in terms of Point Spread Function (PSF) width and back projection error. Visual image quality was assessed with respect to spatial resolution in trabecular bone in an anthropomorphic head phantom. Results: The wire-based calibration method performed equal to or better than BB-based calibrations in all evaluated metrics. For the sinusoidal scans, the method provided reliable calibration, validating its application to non-circular trajectories. Furthermore, the ability to improve image quality using non-circular orbits in conjunction with this calibration method was demonstrated. Conclusion: The proposed method has been shown feasible for conventional circular CBCT scans and offers a promising tool for non-circular scan orbits that can improve image quality, reduce dose, and extend field of view.
Jacobson, M W; Ketcha, M; Uneri, A; Goerres, J; De Silva, T; Reaungamornrat, S; Vogt, S; Kleinszig, G; Siewerdsen, J H
2017-03-01
Traditional BB-based geometric calibration methods for cone-beam CT (CBCT) rely strongly on foreknowledge of the scan trajectory shape. This is a hindrance to the implementation of variable trajectory CBCT systems, normally requiring a dedicated calibration phantom or software algorithm for every scan orbit of interest. A more flexible method of calibration is proposed here that accommodates multiple orbit types - including strongly noncircular trajectories - with a single phantom and software routine. The proposed method uses a calibration phantom consisting of multiple line-shaped wire segments. Geometric models relating the 3D line equations of the wires to the 2D line equations of their projections are used as the basis for system geometry estimation. This method was tested using a mobile C-arm CT system and comparisons were made to standard BB-based calibrations. Simulation studies were also conducted using a sinusoid-on-sphere orbit. Calibration performance was quantified in terms of Point Spread Function (PSF) width and back projection error. Visual image quality was assessed with respect to spatial resolution in trabecular bone in an anthropomorphic head phantom. The wire-based calibration method performed equal to or better than BB-based calibrations in all evaluated metrics. For the sinusoidal scans, the method provided reliable calibration, validating its application to non-circular trajectories. Furthermore, the ability to improve image quality using non-circular orbits in conjunction with this calibration method was demonstrated. The proposed method has been shown feasible for conventional circular CBCT scans and offers a promising tool for non-circular scan orbits that can improve image quality, reduce dose, and extend field of view.
Sentinel-2A image quality commissioning phase final results: geometric calibration and performances
NASA Astrophysics Data System (ADS)
Languille, F.; Gaudel, A.; Dechoz, C.; Greslou, D.; de Lussy, F.; Trémas, T.; Poulain, V.; Massera, S.
2016-10-01
In the frame of the Copernicus program of the European Commission, Sentinel-2 offers multispectral high-spatial-resolution optical images over global terrestrial surfaces. In cooperation with ESA, the Centre National d'Etudes Spatiales (CNES) is in charge of the image quality of the project, and so ensures the CAL/VAL commissioning phase during the months following the launch. Sentinel-2 is a constellation of 2 satellites on a polar sun-synchronous orbit with a revisit time of 5 days (with both satellites), a high field of view - 290km, 13 spectral bands in visible and shortwave infrared, and high spatial resolution - 10m, 20m and 60m. The Sentinel-2 mission offers a global coverage over terrestrial surfaces. The satellites acquire systematically terrestrial surfaces under the same viewing conditions in order to have temporal images stacks. The first satellite was launched in June 2015. Following the launch, the CAL/VAL commissioning phase is then lasting during 6 months for geometrical calibration. This paper will point on observations and results seen on Sentinel-2 images during commissioning phase. It will provide explanations about Sentinel-2 products delivered with geometric corrections. This paper will detail calibration sites, and the methods used for geometrical parameters calibration and will present linked results. The following topics will be presented: viewing frames orientation assessment, focal plane mapping for all spectral bands, results on geolocation assessment, and multispectral registration. There is a systematic images recalibration over a same reference which is a set of S2 images produced during the 6 months of CAL/VAL. This set of images will be presented as well as the geolocation performance and the multitemporal performance after refining over this ground reference.
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.
The Geometric Calibration and Validation for The ZY3-02 Satellite Optical Image
NASA Astrophysics Data System (ADS)
Tang, X.; Zhu, X.
2017-05-01
Chinese ZY3-02 satellite, which is the second of ZY3 series satellites, was launched in May 30th 2016 for complementing the mapping and earth observation. In order to eliminate various system errors of the platform and payload, the on-orbit geometric validation and calibration was carried out. Firstly, we introduced the parameters of the three-line stereo camera and multispectral camera bound on ZY3-02 in this paper. There are four optical cameras on ZY3-02: a 4-band nadir-looking multi-spectral camera with 5.8 m resolution, a 2.1m resolution nadir-looking panchromatic band camera, as well as 2.5m resolution forward- and backward-looking panchromatic band cameras. Compared with ZY3-01, the resolution of the forward- and backward-looking cameras on ZY3-02 were upgraded from 3.5 m to 2.5 m. Then we presented the methods and datasets used for calibration in details. After our calibration, the total positioning accuracy of the three-line camera images is better than 10m without ground control points (GCPs). The plane and height accuracy are improved to 3 and 2 m respectively, with few control points. The band-to-band registration accuracy of the multispectral camera is better than 0.15 pixels.
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.
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
Wang, Mi; Fan, Chengcheng; Yang, Bo; Jin, Shuying; Pan, Jun
2016-07-30
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%.
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
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.
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
Holographic stereograms using new geometrical sampling method
NASA Astrophysics Data System (ADS)
Kim, Eun-Seok; Choi, Yoon-Sun; Kim, Nam
1998-02-01
Sampling method for making 3D animation using computer animation data is presented. Computer animation data has 3D information and displayed with 2D images on the screen or CRT. We divide these 3D animation data into several aspect of views (2D images) and synthesize onto holographic film. After chemical processing we can see 3D images the same as what they have when they are made. Also, using the TFT LCD (liquid crystal device), holographic stereograms can be made easily. In this paper, geometrical method is used in order to easily calculate the sampling angles and TFT LCD to display the 2D images. Experimental results show that this method is very tolerable to be shown with 17 degree for several people. In addition, with these series of stereograms and holographic screen, the 3D movie will be possible.
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.
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%.
Geometric calibration of multi-sensor image fusion system with thermal infrared and low-light camera
NASA Astrophysics Data System (ADS)
Peric, Dragana; Lukic, Vojislav; Spanovic, Milana; Sekulic, Radmila; Kocic, Jelena
2014-10-01
A calibration platform for geometric calibration of multi-sensor image fusion system is presented in this paper. The accurate geometric calibration of the extrinsic geometric parameters of cameras that uses planar calibration pattern is applied. For calibration procedure specific software is made. Patterns used in geometric calibration are prepared with aim to obtain maximum contrast in both visible and infrared spectral range - using chessboards which fields are made of different emissivity materials. Experiments were held in both indoor and outdoor scenarios. Important results of geometric calibration for multi-sensor image fusion system are extrinsic parameters in form of homography matrices used for homography transformation of the object plane to the image plane. For each camera a corresponding homography matrix is calculated. These matrices can be used for image registration of images from thermal and low light camera. We implemented such image registration algorithm to confirm accuracy of geometric calibration procedure in multi-sensor image fusion system. Results are given for selected patterns - chessboard with fields made of different emissivity materials. For the final image registration algorithm in surveillance system for object tracking we have chosen multi-resolution image registration algorithm which naturally combines with a pyramidal fusion scheme. The image pyramids which are generated at each time step of image registration algorithm may be reused at the fusion stage so that overall number of calculations that must be performed is greatly reduced.
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.
Geometric calibration of head-mounted displays and its effects on distance estimation.
Kellner, Falko; Bolte, Benjamin; Bruder, Gerd; Rautenberg, Ulrich; Steinicke, Frank; Lappe, Markus; Koch, Reinhard
2012-04-01
Head-mounted displays (HMDs) allow users to observe virtual environments (VEs) from an egocentric perspective. However, several experiments have provided evidence that egocentric distances are perceived as compressed in VEs relative to the real world. Recent experiments suggest that the virtual view frustum set for rendering the VE has an essential impact on the user's estimation of distances. In this article we analyze if distance estimation can be improved by calibrating the view frustum for a given HMD and user. Unfortunately, in an immersive virtual reality (VR) environment, a full per user calibration is not trivial and manual per user adjustment often leads to mini- or magnification of the scene. Therefore, we propose a novel per user calibration approach with optical see-through displays commonly used in augmented reality (AR). This calibration takes advantage of a geometric scheme based on 2D point - 3D line correspondences, which can be used intuitively by inexperienced users and requires less than a minute to complete. The required user interaction is based on taking aim at a distant target marker with a close marker, which ensures non-planar measurements covering a large area of the interaction space while also reducing the number of required measurements to five. We found the tendency that a calibrated view frustum reduced the average distance underestimation of users in an immersive VR environment, but even the correctly calibrated view frustum could not entirely compensate for the distance underestimation effects.
Mathematical methods in geometrization of coal field
NASA Astrophysics Data System (ADS)
Shurygin, D. N.; Kalinchenko, V. M.; Tkachev, V. A.; Tretyak, A. Ya
2017-10-01
In the work, the approach to increase overall performance of collieries on the basis of an increase in accuracy of geometrization of coal thicknesses is considered. The sequence of stages of mathematical modelling of spatial placing of indicators of a deposit taking into account allocation of homogeneous sites of thickness and an establishment of quantitative interrelations between mountain-geological indicators of coal layers is offered. As a uniform mathematical method for modelling of various interrelations, it is offered to use a method of the group accounting of arguments (MGUA), one of versions of the regressive analysis. This approach can find application during delimitation between geological homogeneous sites of coal thicknesses in the form of a linear discriminant function. By an example of division into districts of a mine field in the conditions of mine “Sadkinsky” (East Donbass), the use of the complex approach for forecasting of zones of the small amplitude of disturbance of a coal layer on the basis of the discriminant analysis and MGUA is shown.
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.
Langley method of calibrating UV filter radiometers
NASA Astrophysics Data System (ADS)
Slusser, James; Gibson, James; Bigelow, David; Kolinski, Donald; Disterhoft, Patrick; Lantz, Kathleen; Beaubien, Arthur
2000-02-01
The Langley method of calibrating UV multifilter shadow band radiometers (UV-MFRSR) is explored in this paper. This method has several advantages over the traditional standard lamp calibrations: the Sun is a free, universally available, and very constant source, and nearly continual automated field calibrations can be made. Although 20 or so Langley events are required for an accurate calibration, the radiometer remains in the field during calibration. Difficulties arise as a result of changing ozone optical depth during the Langley event and the breakdown of the Beer-Lambert law over the finite filter band pass since optical depth changes rapidly with wavelength. The Langley calibration of the radiometers depends critically upon the spectral characterization of each channel and on the wavelength and absolute calibration of the extraterrestrial spectrum used. Results of Langley calibrations for two UV-MFRSRs at Mauna Loa, Hawaii were compared to calibrations using two National Institute of Standards and Technology (NIST) traceable lamps. The objectives of this study were to compare Langley calibration factors with those from standard lamps and to compare field-of-view effects. The two radiometers were run simultaneously: one on a Sun tracker and the other in the conventional shadow-band configuration. Both radiometers were calibrated with two secondary 1000 W lamp, and later, the spectral response functions of the channels were measured. The ratio of Langley to lamp calibration factors for the seven channels from 300 nm to 368 nm using the shadow-band configuration ranged from 0.988 to 1.070. The estimated uncertainty in accuracy of the Langley calibrations ranged from ±3.8% at 300 nm to ±2.1% at 368 nm. For all channels calibrated with Central Ultraviolet Calibration Facility (CUCF) lamps the estimated uncertainty was ±2.5% for all channels.
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
Geometric calibration of lens and filter distortions for multispectral filter-wheel cameras.
Brauers, Johannes; Aach, Til
2011-02-01
High-fidelity color image acquisition with a multispectral camera utilizes optical filters to separate the visible electromagnetic spectrum into several passbands. This is often realized with a computer-controlled filter wheel, where each position is equipped with an optical bandpass filter. For each filter wheel position, a grayscale image is acquired and the passbands are finally combined to a multispectral image. However, the different optical properties and non-coplanar alignment of the filters cause image aberrations since the optical path is slightly different for each filter wheel position. As in a normal camera system, the lens causes additional wavelength-dependent image distortions called chromatic aberrations. When transforming the multispectral image with these aberrations into an RGB image, color fringes appear, and the image exhibits a pincushion or barrel distortion. In this paper, we address both the distortions caused by the lens and by the filters. Based on a physical model of the bandpass filters, we show that the aberrations caused by the filters can be modeled by displaced image planes. The lens distortions are modeled by an extended pinhole camera model, which results in a remaining mean calibration error of only 0.07 pixels. Using an absolute calibration target, we then geometrically calibrate each passband and compensate for both lens and filter distortions simultaneously. We show that both types of aberrations can be compensated and present detailed results on the remaining calibration errors.
Torralba, Marta; Díaz-Pérez, Lucía C.
2017-01-01
This article presents a self-calibration procedure and the experimental results for the geometrical characterisation of a 2D laser system operating along a large working range (50 mm × 50 mm) with submicrometre uncertainty. Its purpose is to correct the geometric errors of the 2D laser system setup generated when positioning the two laser heads and the plane mirrors used as reflectors. The non-calibrated artefact used in this procedure is a commercial grid encoder that is also a measuring instrument. Therefore, the self-calibration procedure also allows the determination of the geometrical errors of the grid encoder, including its squareness error. The precision of the proposed algorithm is tested using virtual data. Actual measurements are subsequently registered, and the algorithm is applied. Once the laser system is characterised, the error of the grid encoder is calculated along the working range, resulting in an expanded submicrometre calibration uncertainty (k = 2) for the X and Y axes. The results of the grid encoder calibration are comparable to the errors provided by the calibration certificate for its main central axes. It is, therefore, possible to confirm the suitability of the self-calibration methodology proposed in this article. PMID:28858239
Calibration methods for microwave free space measurements
NASA Astrophysics Data System (ADS)
Rolfes, I.; Schiek, B.
2004-05-01
In this article calibration methods for the precise, contact-less measurement of the permittivity, permeability or humidity of materials are presented. The free space measurement system principally consists of a pair of focusing horn-lens antennas connected to the ports of a vector network analyzer. Based on the measured scattering parameters, the dielectric material parameters are calculable. Due to systematic errors as e.g. transmission losses of the cables or mismatches of the antennas, a calibration of the measurement setup is necessary. For this purpose calibration methods with calibration standards of equal mechanical lengths are presented. They have the advantage, that the measurement setup can be kept in a fixed position, for example no displacement of the antennas is needed. The presented self-calibration methods have in common that the calibration structures consist of a so-called obstacle network which can be partly unknown. The obstacle can either be realized as a transmissive or a reflective network depending on the chosen method. An increase of the frequency bandwidth is achievable with the reflective realization. The theory of the calibration methods and some experimental results will be presented.
Single-view geometric calibration for C-arm inverse geometry CT.
Slagowski, Jordan M; Dunkerley, David A P; Hatt, Charles R; Speidel, Michael A
2017-01-01
Accurate and artifact-free reconstruction of tomographic images requires precise knowledge of the imaging system geometry. A projection matrix-based calibration method to enable C-arm inverse geometry CT (IGCT) is proposed. 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 three-dimensional-to-two-dimensional 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. The relative root-mean-square error in a reconstruction of a numerical thorax phantom was 0.4% using the calibration method versus 7.7% without calibration. In phantom studies, reconstruction of SBDX projections using the proposed method eliminated artifacts present in noncalibrated reconstructions. The proposed IGCT calibration method reduces image artifacts when uncertainties exist in system geometry.
A geometric Newton method for Oja's vector field.
Absil, P A; Ishteva, M; De Lathauwer, L; Van Huffel, S
2009-05-01
Newton's method for solving the matrix equation F(X) identical to AX-XX(T) AX = 0 runs up against the fact that its zeros are not isolated. This is due to a symmetry of F by the action of the orthogonal group. We show how differential-geometric techniques can be exploited to remove this symmetry and obtain a "geometric" Newton algorithm that finds the zeros of F. The geometric Newton method does not suffer from the degeneracy issue that stands in the way of the original Newton method.
Geometrical distortion calibration of the stereo camera for the BepiColombo mission to Mercury
NASA Astrophysics Data System (ADS)
Simioni, Emanuele; Da Deppo, Vania; Re, Cristina; Naletto, Giampiero; Martellato, Elena; Borrelli, Donato; Dami, Michele; Aroldi, Gianluca; Ficai Veltroni, Iacopo; Cremonese, Gabriele
2016-07-01
The ESA-JAXA mission BepiColombo that will be launched in 2018 is devoted to the observation of Mercury, the innermost planet of the Solar System. SIMBIOSYS is its remote sensing suite, which consists of three instruments: the High Resolution Imaging Channel (HRIC), the Visible and Infrared Hyperspectral Imager (VIHI), and the Stereo Imaging Channel (STC). The latter will provide the global three dimensional reconstruction of the Mercury surface, and it represents the first push-frame stereo camera on board of a space satellite. Based on a new telescope design, STC combines the advantages of a compact single detector camera to the convenience of a double direction acquisition system; this solution allows to minimize mass and volume performing a push-frame imaging acquisition. The shared camera sensor is divided in six portions: four are covered with suitable filters; the others, one looking forward and one backwards with respect to nadir direction, are covered with a panchromatic filter supplying stereo image pairs of the planet surface. The main STC scientific requirements are to reconstruct in 3D the Mercury surface with a vertical accuracy better than 80 m and performing a global imaging with a grid size of 65 m along-track at the periherm. Scope of this work is to present the on-ground geometric calibration pipeline for this original instrument. The selected STC off-axis configuration forced to develop a new distortion map model. Additional considerations are connected to the detector, a Si-Pin hybrid CMOS, which is characterized by a high fixed pattern noise. This had a great impact in pre-calibration phases compelling to use a not common approach to the definition of the spot centroids in the distortion calibration process. This work presents the results obtained during the calibration of STC concerning the distortion analysis for three different temperatures. These results are then used to define the corresponding distortion model of the camera.
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 measuring method of catenary geometric parameters based on laser scanning and imaging
NASA Astrophysics Data System (ADS)
Fu, Luhua; Chang, Songhong; Liu, Changjie
2018-01-01
The catenary geometric parameters are important factors that affect the safe operation of the railway. Among them, height of conductor and stagger value are two key parameters. At present, the two parameters are mainly measured by laser distance sensor and angle measuring device with manual aiming method, with low measuring speed and poor efficiency. In order to improve the speed and accuracy of catenary geometric parameters detection, a new automatic measuring method of contact wire's parameters based on laser scanning and imaging is proposed. The DLT method is used to calibrate the parameters of the linear array CCD camera. The direction of the scanning laser beam and the spatial coordinate of the starting point of the beam are calculated by geometric method. Finally, the equation is established using the calibrated parameters and the imaginary coordinates of the imaging point, to solve the spatial coordinate of the measured point on the contact wire, so as to calculate height of conductor and stagger value. Different from the traditional hand-held laser phase measuring method, the new method can achieve measurement of the catenary geometric parameters automatically without manual aiming. Through measurement results, accuracy can reach 2mm.
A Method to Test Model Calibration Techniques
Judkoff, Ron; Polly, Ben; Neymark, Joel
2016-08-26
This paper describes a method for testing model calibration techniques. Calibration is commonly used in conjunction with energy retrofit audit models. An audit is conducted to gather information about the building needed to assemble an input file for a building energy modeling tool. A calibration technique is used to reconcile model predictions with utility data, and then the 'calibrated model' is used to predict energy savings from a variety of retrofit measures and combinations thereof. Current standards and guidelines such as BPI-2400 and ASHRAE-14 set criteria for 'goodness of fit' and assume that if the criteria are met, then themore » calibration technique is acceptable. While it is logical to use the actual performance data of the building to tune the model, it is not certain that a good fit will result in a model that better predicts post-retrofit energy savings. Therefore, the basic idea here is that the simulation program (intended for use with the calibration technique) is used to generate surrogate utility bill data and retrofit energy savings data against which the calibration technique can be tested. This provides three figures of merit for testing a calibration technique, 1) accuracy of the post-retrofit energy savings prediction, 2) closure on the 'true' input parameter values, and 3) goodness of fit to the utility bill data. The paper will also discuss the pros and cons of using this synthetic surrogate data approach versus trying to use real data sets of actual buildings.« less
Calibration Methods of Acoustic Emission Sensors
Ono, Kanji
2016-01-01
This study examined outstanding issues of sensitivity calibration methods for ultrasonic and acoustic emission transducers and provides workable solutions based on physically measureable quantities, laser-based displacement measurement in particular. This leads to mutually consistent determination of transmitting and receiving sensitivities of sensors and transducers. Methods of circumventing problems of extraneous vibrations on free transmitters are used, giving the foundation for face-to-face calibration methods. Working on many ultrasonic and acoustic emission transducers, their receiving and transmitting sensitivities are found to be always different, while their ratios exhibit unexpected similarity. This behavior is attributed to monopolar pulse generation and bipolar received signals due to electrical charge transfer during elastic wave motion and reflection on the back face. This is verified through a quantitative piezoelectric sensing experiment. Displacement vs. velocity calibration terminology is clarified, redefining the “V/µbar” reference for contact sensor calibration. With demonstrated differences in the transmitting and receiving sensitivities of transducers, the requirement of the Hill-Adams equation invalidates the basic premise of the currently formulated reciprocity calibration methods for acoustic emission transducers. In addition, the measured reciprocity parameter for the case of through-transmission significantly deviates from the approximate theoretical prediction. It is demonstrated that three methods provide reliable sensor calibration results that are complimentary among them. PMID:28773632
Comparison of infusion pumps calibration methods
NASA Astrophysics Data System (ADS)
Batista, Elsa; Godinho, Isabel; do Céu Ferreira, Maria; Furtado, Andreia; Lucas, Peter; Silva, Claudia
2017-12-01
Nowadays, several types of infusion pump are commonly used for drug delivery, such as syringe pumps and peristaltic pumps. These instruments present different measuring features and capacities according to their use and therapeutic application. In order to ensure the metrological traceability of these flow and volume measuring equipment, it is necessary to use suitable calibration methods and standards. Two different calibration methods can be used to determine the flow error of infusion pumps. One is the gravimetric method, considered as a primary method, commonly used by National Metrology Institutes. The other calibration method, a secondary method, relies on an infusion device analyser (IDA) and is typically used by hospital maintenance offices. The suitability of the IDA calibration method was assessed by testing several infusion instruments at different flow rates using the gravimetric method. In addition, a measurement comparison between Portuguese Accredited Laboratories and hospital maintenance offices was performed under the coordination of the Portuguese Institute for Quality, the National Metrology Institute. The obtained results were directly related to the used calibration method and are presented in this paper. This work has been developed in the framework of the EURAMET projects EMRP MeDD and EMPIR 15SIP03.
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.
Geometrical Calibration of X-Ray Imaging With RGB Cameras for 3D Reconstruction.
Albiol, Francisco; Corbi, Alberto; Albiol, Alberto
2016-08-01
We present a methodology to recover the geometrical calibration of conventional X-ray settings with the help of an ordinary video camera and visible fiducials that are present in the scene. After calibration, equivalent points of interest can be easily identifiable with the help of the epipolar geometry. The same procedure also allows the measurement of real anatomic lengths and angles and obtains accurate 3D locations from image points. Our approach completely eliminates the need for X-ray-opaque reference marks (and necessary supporting frames) which can sometimes be invasive for the patient, occlude the radiographic picture, and end up projected outside the imaging sensor area in oblique protocols. Two possible frameworks are envisioned: a spatially shifting X-ray anode around the patient/object and a moving patient that moves/rotates while the imaging system remains fixed. As a proof of concept, experiences with a device under test (DUT), an anthropomorphic phantom and a real brachytherapy session have been carried out. The results show that it is possible to identify common points with a proper level of accuracy and retrieve three-dimensional locations, lengths and shapes with a millimetric level of precision. The presented approach is simple and compatible with both current and legacy widespread diagnostic X-ray imaging deployments and it can represent a good and inexpensive alternative to other radiological modalities like CT.
Geometric Calibration and Validation of Kompsat-3A AEISS-A Camera
Seo, Doocheon; Oh, Jaehong; Lee, Changno; Lee, Donghan; Choi, Haejin
2016-01-01
Kompsat-3A, which was launched on 25 March 2015, is a sister spacecraft of the Kompsat-3 developed by the Korea Aerospace Research Institute (KARI). Kompsat-3A’s AEISS-A (Advanced Electronic Image Scanning System-A) camera is similar to Kompsat-3’s AEISS but it was designed to provide PAN (Panchromatic) resolution of 0.55 m, MS (multispectral) resolution of 2.20 m, and TIR (thermal infrared) at 5.5 m resolution. In this paper we present the geometric calibration and validation work of Kompsat-3A that was completed last year. A set of images over the test sites was taken for two months and was utilized for the work. The workflow includes the boresight calibration, CCDs (charge-coupled devices) alignment and focal length determination, the merge of two CCD lines, and the band-to-band registration. Then, the positional accuracies without any GCPs (ground control points) were validated for hundreds of test sites across the world using various image acquisition modes. In addition, we checked the planimetric accuracy by bundle adjustments with GCPs. PMID:27783054
Method of calibrating clutches in transmissions
Bulgrien, G.H.
1991-02-05
This paper describes a microprocessor controlling a shuttle shift transmission programmed to effect a calibration of the final drive clutches in the transmission so that the microprocessor can efficiently effect engagement of each respective clutch by applying the proper hydraulic pressure to cause proper engagement thereof. This method of calibrating the final drive clutches in the transmission includes braking the output shaft of the transmission so that any engagement of the selected final drive clutch being calibrated will cause a load to be applied to the engine. The hydraulic pressure is then incrementally increased until the engine RPM's decrease because of the load being placed on the engine. The value of this engagement hydraulic pressure is stored in the microprocessor for use when effecting engagement of the selected clutch during operation of the transmission. Service indicators are programmed into the microprocessor should the selected clutch not be capable of being calibrated.
The variational method for density states a geometrical approach
NASA Astrophysics Data System (ADS)
Figueroa, Armando; Castaños, Octavio; López-Peña, Ramón; Marmo, Giuseppe
2017-09-01
The conventional variational method is reformulated within a geometrical approach to quantum mechanics, both for finite and infinite dimensional Hilbert spaces. This geometrical setting allows us to deal not only with approximated eigenvalues and eigenstates, but also with approximated Schrödinger equations by means of Hamiltonian evolution equations associated with expectation value functions. We shall consider some specific examples where we extend our approach also to density matrices.
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
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.
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
Geometric Variational Methods for Controlled Active Vision
2006-08-01
Shape analysis of structures using spherical wavelets ’’ (with S. Haker and D. Nain), Proceeedings of MICCAI, 2005. ``Affine surface evolution for 3D...spherical wavelets ’’ (with D. Nain, S. Haker), MICCAI, 2006. ``Comparative analysis of kernel methods for statistical shape learning’’ (with Y. Rathi...submitted to IEEE Trans. Image Processing. ’’Multiscale 3D shape representation and segmentation using spherical wavelets ’’ (with D. Nain and S. Haker
Mathematical limitations when choosing psychophysical methods: geometric versus linear grey scales
NASA Astrophysics Data System (ADS)
Dekker, Niels; Lucassen, Marcel; Kirchner, Eric; Urban, Philipp; Huertas, Rafael
2014-02-01
The grey scale method is commonly used for investigating differences in material appearance. Specifically, for testing color difference equations, perceived color differences between sample pairs are obtained by visually comparing to differences in a series of achromatic sample pairs. Two types of grey scales are known: linear and geometric. Their instrumental color differences vary linearly or geometrically (i.e., exponentially), respectively. Geometric grey scales are used in ISO standards and standard procedures of the textile industries. We compared both types of grey scale in a psychophysical study. Color patches were shown on a color-calibrated display. Ten observers assessed color differences in sample pairs, with color differences between ΔEab = 0.13 and 2.50. Assessments were scored by comparison to either a linear or a geometric grey scale, both consisting of six achromatic pairs. For the linear scale we used color differences ΔEab = 0.0, 0.6, 1.2,..., 3.0. For the geometric scale this was ΔEab=0.0, 0.4, 0.8, 1.6, 3.2, 6.4. Our results show that for the geometric scale, data from visual scores clutter at the low end of the scale and do not match the ΔEab range of the grey scale pairs. We explain why this happens, and why this is mathematically inevitable when studying small color differences with geometric grey scales. Our analysis explains why previous studies showed larger observer variability for geometric than for linear scales.
A geometric method for contour extraction of Drosophila embryos.
Li, Qi; Gong, Yongyi
2017-12-14
High resolution images of Drosophila embryos in their developmental stages contain rich spatial and temporal information of gene expression. Automatic extraction of the contour of an embryo of interest in an embryonic image is a critical step of a computational system used to discover gene-gene interaction on Drosophila. We propose a geometric method for contour extraction of Drosophila embryos. The key of the proposed geometric method is k-dominant point extraction that is a generalization of 3-dominant point extraction proposed in our previous work. Based on k-dominant point extraction, we can approximate a connected component of edge pixels by a polygon that can be either convex or concave. The test on BDGP data shows that the proposed method outputforms two existing methods designed for contour extraction of Drosophila embryos. The main advantage of the proposed geometric method in the context of contour extraction of Drosophila embryos is its ability of segmenting embryos touching each other. The proposed geometric method can also be applied to applications relevant to contour extraction.
Habte, Aron; Sengupta, Manajit; Andreas, Afshin
2016-10-07
Accurate solar radiation measured by radiometers depends on instrument performance specifications, installation method, calibration procedure, measurement conditions, maintenance practices, location, and environmental conditions. This study addresses the effect of different calibration methodologies and resulting differences provided by radiometric calibration service providers such as the National Renewable Energy Laboratory (NREL) and manufacturers of radiometers. Some of these methods calibrate radiometers indoors and some outdoors. To establish or understand the differences in calibration methodologies, we processed and analyzed field-measured data from radiometers deployed for 10 months at NREL's Solar Radiation Research Laboratory. These different methods of calibration resulted in a difference ofmore » +/-1% to +/-2% in solar irradiance measurements. Analyzing these differences will ultimately assist in determining the uncertainties of the field radiometer data and will help develop a consensus on a standard for calibration. Further advancing procedures for precisely calibrating radiometers to world reference standards that reduce measurement uncertainties will help the accurate prediction of the output of planned solar conversion projects and improve the bankability of financing solar projects.« less
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.
System calibration method for Fourier ptychographic microscopy
NASA Astrophysics Data System (ADS)
Pan, An; Zhang, Yan; Zhao, Tianyu; Wang, Zhaojun; Dan, Dan; Lei, Ming; Yao, Baoli
2017-09-01
Fourier ptychographic microscopy (FPM) is a recently proposed computational imaging technique with both high-resolution and wide field of view. In current FPM imaging platforms, systematic error sources come from aberrations, light-emitting diode (LED) intensity fluctuation, parameter imperfections, and noise, all of which may severely corrupt the reconstruction results with similar artifacts. Therefore, it would be unlikely to distinguish the dominating error from these degraded reconstructions without any preknowledge. In addition, systematic error is generally a mixture of various error sources in the real situation, and it cannot be separated due to their mutual restriction and conversion. To this end, we report a system calibration procedure, termed SC-FPM, to calibrate the mixed systematic errors simultaneously from an overall perspective, based on the simulated annealing algorithm, the LED intensity correction method, the nonlinear regression process, and the adaptive step-size strategy, which involves the evaluation of an error metric at each iteration step, followed by the re-estimation of accurate parameters. The performance achieved both in simulations and experiments demonstrates that the proposed method outperforms other state-of-the-art algorithms. The reported system calibration scheme improves the robustness of FPM, relaxes the experiment conditions, and does not require any preknowledge, which makes the FPM more pragmatic.
Development of a Geoid Model by Geometric Method
NASA Astrophysics Data System (ADS)
Mishra, Upendra Nath; Ghosh, Jayanta Kumar
2017-12-01
Engineering projects require orthometric heights of points where as Global Navigation Satellite System (GNSS) provide height above ellipsoid. Thus, to make use of GNSS in engineering surveying, the relationship between ellipsoidal height and orthometric height as a function of position needs to be established through geoid modeling. In this study, an attempt has been made to develop a geoid model using the geometric method. Observations were taken in a network of sixteen stations spread over 600 km2 around Dehra Dun, India. GPS observations were taken using dual frequency geodetic GPS receivers and leveling done using digital levels with 0.1 mm accuracy. Orthometric height of stations from developed model have been found to be near to those from field levelling which is considered most accurate. Further, the values have been compared with those obtained from the recent GOCE-GRACE-LAGEOS geoid model EIGEN6C3stat. It has been found that the geometric model provides far better accuracy than that obtained from the global geoid model. Therefore, it can be concluded that the geometric method of geoid modeling can better be used for reduction of GPS observed ellipsoidal height to orthometric height in a local area. This model may gainfully be employed in a project area as a substitute for densification of leveling lines, thereby reducing the project cost substantially.
A novel calibration method of focused light field camera for 3-D reconstruction of flame temperature
NASA Astrophysics Data System (ADS)
Sun, Jun; Hossain, Md. Moinul; Xu, Chuan-Long; Zhang, Biao; Wang, Shi-Min
2017-05-01
This paper presents a novel geometric calibration method for focused light field camera to trace the rays of flame radiance and to reconstruct the three-dimensional (3-D) temperature distribution of a flame. A calibration model is developed to calculate the corner points and their projections of the focused light field camera. The characteristics of matching main lens and microlens f-numbers are used as an additional constrains for the calibration. Geometric parameters of the focused light field camera are then achieved using Levenberg-Marquardt algorithm. Total focused images in which all the points are in focus, are utilized to validate the proposed calibration method. Calibration results are presented and discussed in details. The maximum mean relative error of the calibration is found less than 0.13%, indicating that the proposed method is capable of calibrating the focused light field camera successfully. The parameters obtained by the calibration are then utilized to trace the rays of flame radiance. A least square QR-factorization algorithm with Plank's radiation law is used to reconstruct the 3-D temperature distribution of a flame. Experiments were carried out on an ethylene air fired combustion test rig to reconstruct the temperature distribution of flames. The flame temperature obtained by the proposed method is then compared with that obtained by using high-precision thermocouple. The difference between the two measurements was found no greater than 6.7%. Experimental results demonstrated that the proposed calibration method and the applied measurement technique perform well in the reconstruction of the flame temperature.
Polarimetric and Interferometric SAR Calibration Verification Methods
NASA Technical Reports Server (NTRS)
Kim, Y.; Zyl, J van
2001-01-01
It is necessary to calibrate SAR data in order to use the data for science applications. When both polarimetric and interferometric data are collected simultaneously, these SAR data can be used for cross-calibration and verification.
A Novel Camera Calibration Method Based on Polar Coordinate
Gai, Shaoyan; Da, Feipeng; Fang, Xu
2016-01-01
A novel calibration method based on polar coordinate is proposed. The world coordinates are expressed in the form of polar coordinates, which are converted to world coordinates in the calibration process. In the beginning, the calibration points are obtained in polar coordinates. By transformation between polar coordinates and rectangular coordinates, the points turn into form of rectangular coordinates. Then, the points are matched with the corresponding image coordinates. At last, the parameters are obtained by objective function optimization. By the proposed method, the relationships between objects and cameras are expressed in polar coordinates easily. It is suitable for multi-camera calibration. Cameras can be calibrated with fewer points. The calibration images can be positioned according to the location of cameras. The experiment results demonstrate that the proposed method is an efficient calibration method. By the method, cameras are calibrated conveniently with high accuracy. PMID:27798651
Iterative-decreasing calibration method based on regional circle
NASA Astrophysics Data System (ADS)
Zhao, Hongyang
2017-07-01
In the field of computer vision, camera calibration is a hot issue. For the existing coupled problem of calculating distortion center and the distortion factor in the process of camera calibration, this paper presents an iterative-decreasing calibration method based on regional circle, uses the local area of the circle plate to calculate the distortion center coordinates by iterative declining, and then uses the distortion center to calculate the local area calibration factors. Finally, makes distortion center and the distortion factor for the global optimization. The calibration results show that the proposed method has high calibration accuracy.
NASA Astrophysics Data System (ADS)
Huber, Martin C. E.; Pauluhn, Anuschka; Timothy, J. Gethyn; Zehnder, Alex
Calibrating instruments for photon observations in space involves a number of parameters, most basic among them the pointing accuracy and stability. Wavelength accuracy is important as well. A particularly demanding and complex set of parameters to be determined concerns the responsivity (sometimes also referred to as effective area or detection efficiency) of the telescope-spectrometer combination. The responsivity is a function of wavelength, and for its determination the full set of geometric and spectro-optical properties of the system needs to be quantified. High photon arrival rates may also lead to nonlinearities that have to be assessed. A realistic physical and chemical description of an astronomical object, i.e., the goal of astrophysics, can only be reached with spectroradiometrically calibrated telescopes and spectrometers. We stress that there is no a priori celestial standard. A radiometric calibration must thus assure that observed spectral irradiances (or radiances) are measured in the units of the systeme International, which in turn are defined by radiometric standards realised on Earth.
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.
Model Calibration in the Continual Reassessment Method
Lee, Shing M.; Cheung, Ying Kuen
2010-01-01
Background The continual reassessment method (CRM) is an adaptive model-based design used to estimate the maximum tolerated dose in dose finding clinical trials. A way to evaluate the sensitivity of a given CRM model including the functional form of the dose-toxicity curve, the prior distribution on the model parameter, and the initial guesses of toxicity probability at each dose is using indifference intervals. While the indifference interval technique provides a succinct summary of model sensitivity, there are infinitely many possible ways to specify the initial guesses of toxicity probability. In practice, these are generally specified by trial and error through extensive simulations. Methods By using indifference intervals, the initial guesses used in the CRM can be selected by specifying a range of acceptable toxicity probabilities in addition to the target probability of toxicity. An algorithm is proposed for obtaining the indifference interval that maximizes the average percentage of correct selection across a set of scenarios of true probabilities of toxicity and providing a systematic approach for selecting initial guesses in a much less time consuming manner than the trial and error method. The methods are compared in the context of two real CRM trials. Results For both trials, the initial guesses selected by the proposed algorithm had similar operating characteristics as measured by percentage of correct selection, average absolute difference between the true probability of the dose selected and the target probability of toxicity, percentage treated at each dose and overall percentage of toxicity compared to the initial guesses used during the conduct of the trials which were obtained by trial and error through a time consuming calibration process. The average percentage of correct selection for the scenarios considered were 61.5% and 62.0% in the lymphoma trial, and 62.9% and 64.0% in the stroke trial for the trial and error method versus the proposed
A digital calibration method for synthetic aperture radar systems
NASA Technical Reports Server (NTRS)
Larson, Richard W.; Jackson, P. L.; Kasischke, Eric S.
1988-01-01
A basic method to calibrate imagery from synthetic aperture radar (SAR) systems is presented. SAR images are calibrated by monitoring all the terms of the radar equation. This procedure includes the use of both external (calibrated reference reflectors) and internal (system-generated calibration signals) sources to monitor the total SAR system transfer function. To illustrate the implementation of the procedure, two calibrated SAR images (X-band, 3.2-cm wavelength) are presented, along with the radar cross-section measurements of specific scenes within each image. The sources of error within the SAR image calibration procedure are identified.
Geometric correction methods for Timepix based large area detectors
NASA Astrophysics Data System (ADS)
Zemlicka, J.; Dudak, J.; Karch, J.; Krejci, F.
2017-01-01
X-ray micro radiography with the hybrid pixel detectors provides versatile tool for the object inspection in various fields of science. It has proven itself especially suitable for the samples with low intrinsic attenuation contrast (e.g. soft tissue in biology, plastics in material sciences, thin paint layers in cultural heritage, etc.). The limited size of single Medipix type detector (1.96 cm2) was recently overcome by the construction of large area detectors WidePIX assembled of Timepix chips equipped with edgeless silicon sensors. The largest already built device consists of 100 chips and provides fully sensitive area of 14.3 × 14.3 cm2 without any physical gaps between sensors. The pixel resolution of this device is 2560 × 2560 pixels (6.5 Mpix). The unique modular detector layout requires special processing of acquired data to avoid occurring image distortions. It is necessary to use several geometric compensations after standard corrections methods typical for this type of pixel detectors (i.e. flat-field, beam hardening correction). The proposed geometric compensations cover both concept features and particular detector assembly misalignment of individual chip rows of large area detectors based on Timepix assemblies. The former deals with larger border pixels in individual edgeless sensors and their behaviour while the latter grapple with shifts, tilts and steps between detector rows. The real position of all pixels is defined in Cartesian coordinate system and together with non-binary reliability mask it is used for the final image interpolation. The results of geometric corrections for test wire phantoms and paleo botanic material are presented in this article.
Autonomous Landmark Calibration Method for Indoor Localization
Kim, Jae-Hoon; Kim, Byoung-Seop
2017-01-01
Machine-generated data expansion is a global phenomenon in recent Internet services. The proliferation of mobile communication and smart devices has increased the utilization of machine-generated data significantly. One of the most promising applications of machine-generated data is the estimation of the location of smart devices. The motion sensors integrated into smart devices generate continuous data that can be used to estimate the location of pedestrians in an indoor environment. We focus on the estimation of the accurate location of smart devices by determining the landmarks appropriately for location error calibration. In the motion sensor-based location estimation, the proposed threshold control method determines valid landmarks in real time to avoid the accumulation of errors. A statistical method analyzes the acquired motion sensor data and proposes a valid landmark for every movement of the smart devices. Motion sensor data used in the testbed are collected from the actual measurements taken throughout a commercial building to demonstrate the practical usefulness of the proposed method. PMID:28837071
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
An improved solution to geometric distortion using an orthogonal method
NASA Astrophysics Data System (ADS)
Peng, Huan-Wen; Peng, Qing-Yu; Wang, Na
2017-02-01
The geometric distortion of a CCD field of view has a direct influence on the positional measurements of CCD observations. In order to obtain high precision astrometric results, the geometric distortion should be derived and corrected precisely. As presented in our previous work, a convenient solution has been carried out and has also been applied to observations of Phoebe. In order to further improve the solution, an orthogonal method based on Zernike polynomials is used in this work. Four nights of CCD observations including Himalia, the sixth satellite of Jupiter, and open clusters (NGC 1664 or NGC 2324) on each night have been processed as an application. The observations were obtained from the 2.4 m telescope administered by Yunnan Observatories. The catalog UCAC4 was used to match reference stars in all of the CCD frames. The ephemeris of Himalia is retrieved from the Institut de Mécanique Céleste et de Calcul des Éphémérides (IMCCE). Our results show that the means of observed minus calculated (O-C) positional residuals are -0.034 and -0.026 arcsec in right ascension and declination, respectively. The corresponding standard deviations are {0.031}^{\\prime\\prime } and {0.028}^{\\prime\\prime }. The measurement dispersion is significantly improved compared to that by using our previous solution.
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.
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.
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.
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 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
Li, Zhengqiang; Li, Kaitao; Li, Donghui; Yang, Jiuchun; Xu, Hua; Goloub, Philippe; Victori, Stephane
2016-09-20
The Cimel new technologies allow both daytime and nighttime aerosol optical depth (AOD) measurements. Although the daytime AOD calibration protocols are well established, accurate and simple nighttime calibration is still a challenging task. Standard lunar-Langley and intercomparison calibration methods both require specific conditions in terms of atmospheric stability and site condition. Additionally, the lunar irradiance model also has some known limits on its uncertainty. This paper presents a simple calibration method that transfers the direct-Sun calibration constant, V_{0,Sun}, to the lunar irradiance calibration coefficient, C_{Moon}. Our approach is a pure calculation method, independent of site limits, e.g., Moon phase. The method is also not affected by the lunar irradiance model limitations, which is the largest error source of traditional calibration methods. Besides, this new transfer calibration approach is easy to use in the field since C_{Moon} can be obtained directly once V_{0,Sun} is known. Error analysis suggests that the average uncertainty of C_{Moon} over the 440-1640 nm bands obtained with the transfer method is 2.4%-2.8%, depending on the V_{0,Sun} approach (Langley or intercomparison), which is comparable with that of lunar-Langley approach, theoretically. In this paper, the Sun-Moon transfer and the Langley methods are compared based on site measurements in Beijing, and the day-night measurement continuity and performance are analyzed.
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.
Analysis and optimization of calibration method of digital energy meter
NASA Astrophysics Data System (ADS)
Hou, Songxue; Liu, Yuyou; Xu, Yunying; Wang, Shunchao; Xu, Dan
2017-08-01
At present, the short of calibration of digital energy meter include deficiency of standard, inefficiency, and the lack of proper methods. In this paper, based on four commonly used methods(Watt-second method, standard digital meter method, standard digital power source method, standard analog meter method), the factors that cause the error of these calibration methods are introduced, and relevant measures of improvement and optimization are put forward.
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.
Method for lateral force calibration in atomic force microscope using MEMS microforce sensor.
Dziekoński, Cezary; Dera, Wojciech; Jarząbek, Dariusz M
2017-11-01
In this paper we present a simple and direct method for the lateral force calibration constant determination. Our procedure does not require any knowledge about material or geometrical parameters of an investigated cantilever. We apply a commercially available microforce sensor with advanced electronics for direct measurement of the friction force applied by the cantilever's tip to a flat surface of the microforce sensor measuring beam. Due to the third law of dynamics, the friction force of the equal value tilts the AFM cantilever. Therefore, torsional (lateral force) signal is compared with the signal from the microforce sensor and the lateral force calibration constant is determined. The method is easy to perform and could be widely used for the lateral force calibration constant determination in many types of atomic force microscopes. Copyright © 2017 Elsevier B.V. All rights reserved.
Simultaneous multi-headed imager geometry calibration method
Tran, Vi-Hoa [Newport News, VA; Meikle, Steven Richard [Penshurst, AU; Smith, Mark Frederick [Yorktown, VA
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.
A visualization method for teaching the geometric design of highways
DOT National Transportation Integrated Search
2000-04-11
In this project the authors employed state-of-the-art technology for developing visualization tools for teaching highway design. Specifically, the authors used photolog images as the basis for developing dynamic 3-D models of selected geometric eleme...
Progress Report of CNES Activities Regarding the Absolute Calibration Method
2010-11-01
several receivers (Ashtech Z12-T, Septentrio PolaRx2, and Dicom GTR50) and a GNSS signal simulator (Spirent 4760) according to the temperature and...laboratories, Ashtech Z12- T, Septentrio PolaRx2, and Dicom GTR50, can be calibrated with the absolute method [6,8]. The last works concerned the...Ashtech, Septentrio, and Dicom receiver calibrations. Table 2. Uncertainty of the different receiver calibrations. Uncertainty Source
NASA Astrophysics Data System (ADS)
Hung, Yi-Ping
1989-03-01
For a vision system to infer 3D object features (e.g., point features or line features) from 2D image features and to predict 2D image features from 3D object features, the transformation between the 2D image coordinate system and the 3D object coordinate system must be known. Determining this transformation is called (geometric) camera calibration. This 2D-3D transformation varies when the camera is moved by a robot. This paper presents a simple two-stage (off-line stage and on-line stage) method for calibrating a camera mounted on a robot. The off-line stage includes off-line calibration of the camera, the robot, and the robot-camera (or hand-eye) relation. The on-line stage can be divided into an initial calculation step and a re-calibration step. The initial step is computationally simple since it only involves one or two matrix multiplications of dimension less than four. The derived calibration accuracy from this initial step depends on the accuracy of the off-line camera/robot calibration. Experimental results show that the calibration accuracy is better than "1 part in 1000" without special robot calibration. Higher accuracy can be obtained with more sophisticated robot calibration, or with the re-calibration step using the extended Kalman filtering techniques. Some new insights to the conventional camera calibration methods are also given.
Landmark-free geometric methods in biological shape analysis
Koehl, Patrice; Hass, Joel
2015-01-01
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
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 [Oak Ridge, TN; Fabris, Lorenzo [Knoxville, TN; Gee, Timothy F [Oak Ridge, TN; Goddard, Jr., James S.; Karnowski, Thomas P [Knoxville, TN; Ziock, Klaus-peter [Clinton, TN
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.
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 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 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.
Separate versus Concurrent Calibration Methods in Vertical Scaling.
ERIC Educational Resources Information Center
Karkee, Thakur; Lewis, Daniel M.; Hoskens, Machteld; Yao, Lihua; Haug, Carolyn
Two methods to establish a common scale across grades within a content area using a common item design (separate and concurrent) have previously been studied under simulated conditions. Separate estimation is accomplished through separate calibration and grade-by-grade chained linking. Concurrent calibration established the vertical scale in a…
NASA Astrophysics Data System (ADS)
Zechner, A.; Stock, M.; Kellner, D.; Ziegler, I.; Keuschnigg, P.; Huber, P.; Mayer, U.; Sedlmayer, F.; Deutschmann, H.; Steininger, P.
2016-11-01
Image guidance during highly conformal radiotherapy requires accurate geometric calibration of the moving components of the imager. Due to limited manufacturing accuracy and gravity-induced flex, an x-ray imager’s deviation from the nominal geometrical definition has to be corrected for. For this purpose a ball bearing phantom applicable for nine degrees of freedom (9-DOF) calibration of a novel cone-beam computed tomography (CBCT) scanner was designed and validated. In order to ensure accurate automated marker detection, as many uniformly distributed markers as possible should be used with a minimum projected inter-marker distance of 10 mm. Three different marker distributions on the phantom cylinder surface were simulated. First, a fixed number of markers are selected and their coordinates are randomly generated. Second, the quasi-random method is represented by setting a constraint on the marker distances in the projections. The third approach generates the ball coordinates helically based on the Golden ratio, ϕ. Projection images of the phantom incorporating the CBCT scanner’s geometry were simulated and analysed with respect to uniform distribution and intra-marker distance. Based on the evaluations a phantom prototype was manufactured and validated by a series of flexmap calibration measurements and analyses. The simulation with randomly distributed markers as well as the quasi-random approach showed an insufficient uniformity of the distribution over the detector area. The best compromise between uniform distribution and a high packing fraction of balls is provided by the Golden section approach. A prototype was manufactured accordingly. The phantom was validated for 9-DOF geometric calibrations of the CBCT scanner with independently moveable source and detector arms. A novel flexmap calibration phantom intended for 9-DOF was developed. The ball bearing distribution based on the Golden section was found to be highly advantageous. The phantom showed
Zechner, A; Stock, M; Kellner, D; Ziegler, I; Keuschnigg, P; Huber, P; Mayer, U; Sedlmayer, F; Deutschmann, H; Steininger, P
2016-11-21
Image guidance during highly conformal radiotherapy requires accurate geometric calibration of the moving components of the imager. Due to limited manufacturing accuracy and gravity-induced flex, an x-ray imager's deviation from the nominal geometrical definition has to be corrected for. For this purpose a ball bearing phantom applicable for nine degrees of freedom (9-DOF) calibration of a novel cone-beam computed tomography (CBCT) scanner was designed and validated. In order to ensure accurate automated marker detection, as many uniformly distributed markers as possible should be used with a minimum projected inter-marker distance of 10 mm. Three different marker distributions on the phantom cylinder surface were simulated. First, a fixed number of markers are selected and their coordinates are randomly generated. Second, the quasi-random method is represented by setting a constraint on the marker distances in the projections. The third approach generates the ball coordinates helically based on the Golden ratio, ϕ. Projection images of the phantom incorporating the CBCT scanner's geometry were simulated and analysed with respect to uniform distribution and intra-marker distance. Based on the evaluations a phantom prototype was manufactured and validated by a series of flexmap calibration measurements and analyses. The simulation with randomly distributed markers as well as the quasi-random approach showed an insufficient uniformity of the distribution over the detector area. The best compromise between uniform distribution and a high packing fraction of balls is provided by the Golden section approach. A prototype was manufactured accordingly. The phantom was validated for 9-DOF geometric calibrations of the CBCT scanner with independently moveable source and detector arms. A novel flexmap calibration phantom intended for 9-DOF was developed. The ball bearing distribution based on the Golden section was found to be highly advantageous. The phantom showed
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.
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
Bayesian Methods for Calibrating Health Policy Models: A Tutorial.
Menzies, Nicolas A; Soeteman, Djøra I; Pandya, Ankur; Kim, Jane J
2017-06-01
Mathematical simulation models are commonly used to inform health policy decisions. These health policy models represent the social and biological mechanisms that determine health and economic outcomes, combine multiple sources of evidence about how policy alternatives will impact those outcomes, and synthesize outcomes into summary measures salient for the policy decision. Calibrating these health policy models to fit empirical data can provide face validity and improve the quality of model predictions. Bayesian methods provide powerful tools for model calibration. These methods summarize information relevant to a particular policy decision into (1) prior distributions for model parameters, (2) structural assumptions of the model, and (3) a likelihood function created from the calibration data, combining these different sources of evidence via Bayes' theorem. This article provides a tutorial on Bayesian approaches for model calibration, describing the theoretical basis for Bayesian calibration approaches as well as pragmatic considerations that arise in the tasks of creating calibration targets, estimating the posterior distribution, and obtaining results to inform the policy decision. These considerations, as well as the specific steps for implementing the calibration, are described in the context of an extended worked example about the policy choice to provide (or not provide) treatment for a hypothetical infectious disease. Given the many simplifications and subjective decisions required to create prior distributions, model structure, and likelihood, calibration should be considered an exercise in creating a reasonable model that produces valid evidence for policy, rather than as a technique for identifying a unique theoretically optimal summary of the evidence.
Developing new online calibration methods for multidimensional computerized adaptive testing.
Chen, Ping; Wang, Chun; Xin, Tao; Chang, Hua-Hua
2017-02-01
Multidimensional computerized adaptive testing (MCAT) has received increasing attention over the past few years in educational measurement. Like all other formats of CAT, item replenishment is an essential part of MCAT for its item bank maintenance and management, which governs retiring overexposed or obsolete items over time and replacing them with new ones. Moreover, calibration precision of the new items will directly affect the estimation accuracy of examinees' ability vectors. In unidimensional CAT (UCAT) and cognitive diagnostic CAT, online calibration techniques have been developed to effectively calibrate new items. However, there has been very little discussion of online calibration in MCAT in the literature. Thus, this paper proposes new online calibration methods for MCAT based upon some popular methods used in UCAT. Three representative methods, Method A, the 'one EM cycle' method and the 'multiple EM cycles' method, are generalized to MCAT. Three simulation studies were conducted to compare the three new methods by manipulating three factors (test length, item bank design, and level of correlation between coordinate dimensions). The results showed that all the new methods were able to recover the item parameters accurately, and the adaptive online calibration designs showed some improvements compared to the random design under most conditions. © 2017 The British Psychological Society.
Automated discrete element method calibration using genetic and optimization algorithms
NASA Astrophysics Data System (ADS)
Do, Huy Q.; Aragón, Alejandro M.; Schott, Dingena L.
2017-06-01
This research aims at developing a universal methodology for automated calibration of microscopic properties of modelled granular materials. The proposed calibrator can be applied for different experimental set-ups. Two optimization approaches: (1) a genetic algorithm and (2) DIRECT optimization, are used to identify discrete element method input model parameters, e.g., coefficients of sliding and rolling friction. The algorithms are used to minimize the objective function characterized by the discrepancy between the experimental macroscopic properties and the associated numerical results. Two test cases highlight the robustness, stability, and reliability of the two algorithms used for automated discrete element method calibration with different set-ups.
Adaptive Prior Variance Calibration in the Bayesian Continual Reassessment Method
Zhang, Jin; Braun, Thomas M.; Taylor, Jeremy M.G.
2012-01-01
Use of the Continual Reassessment Method (CRM) and other model-based approaches to design in Phase I clinical trials has increased due to the ability of the CRM to identify the maximum tolerated dose (MTD) better than the 3+3 method. However, the CRM can be sensitive to the variance selected for the prior distribution of the model parameter, especially when a small number of patients are enrolled. While methods have emerged to adaptively select skeletons and to calibrate the prior variance only at the beginning of a trial, there has not been any approach developed to adaptively calibrate the prior variance throughout a trial. We propose three systematic approaches to adaptively calibrate the prior variance during a trial and compare them via simulation to methods proposed to calibrate the variance at the beginning of a trial. PMID:22987660
Calibration method for an ultrasonic gray-scale recorder
NASA Technical Reports Server (NTRS)
Moorhead, P. E.
1978-01-01
Calibrated method for ultrasonic C-scanning is based on direct correlation of gray-scale response to electronic signal used. In procedure, optical density of reference recording is measured to generate curve of reflective intensity versus transmission.
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.
A Method to Test Model Calibration Techniques: Preprint
Judkoff, Ron; Polly, Ben; Neymark, Joel
2016-09-01
This paper describes a method for testing model calibration techniques. Calibration is commonly used in conjunction with energy retrofit audit models. An audit is conducted to gather information about the building needed to assemble an input file for a building energy modeling tool. A calibration technique is used to reconcile model predictions with utility data, and then the 'calibrated model' is used to predict energy savings from a variety of retrofit measures and combinations thereof. Current standards and guidelines such as BPI-2400 and ASHRAE-14 set criteria for 'goodness of fit' and assume that if the criteria are met, then the calibration technique is acceptable. While it is logical to use the actual performance data of the building to tune the model, it is not certain that a good fit will result in a model that better predicts post-retrofit energy savings. Therefore, the basic idea here is that the simulation program (intended for use with the calibration technique) is used to generate surrogate utility bill data and retrofit energy savings data against which the calibration technique can be tested. This provides three figures of merit for testing a calibration technique, 1) accuracy of the post-retrofit energy savings prediction, 2) closure on the 'true' input parameter values, and 3) goodness of fit to the utility bill data. The paper will also discuss the pros and cons of using this synthetic surrogate data approach versus trying to use real data sets of actual buildings.
A Method to Test Model Calibration Techniques: Preprint
Judkoff, Ron; Polly, Ben; Neymark, Joel
2016-09-01
This paper describes a method for testing model calibration techniques. Calibration is commonly used in conjunction with energy retrofit audit models. An audit is conducted to gather information about the building needed to assemble an input file for a building energy modeling tool. A calibration technique is used to reconcile model predictions with utility data, and then the 'calibrated model' is used to predict energy savings from a variety of retrofit measures and combinations thereof. Current standards and guidelines such as BPI-2400 and ASHRAE-14 set criteria for 'goodness of fit' and assume that if the criteria are met, then themore » calibration technique is acceptable. While it is logical to use the actual performance data of the building to tune the model, it is not certain that a good fit will result in a model that better predicts post-retrofit energy savings. Therefore, the basic idea here is that the simulation program (intended for use with the calibration technique) is used to generate surrogate utility bill data and retrofit energy savings data against which the calibration technique can be tested. This provides three figures of merit for testing a calibration technique, 1) accuracy of the post-retrofit energy savings prediction, 2) closure on the 'true' input parameter values, and 3) goodness of fit to the utility bill data. The paper will also discuss the pros and cons of using this synthetic surrogate data approach versus trying to use real data sets of actual buildings.« less
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.
NASA Astrophysics Data System (ADS)
Lin, Gwo-Fong; Wang, Chun-Ming
2007-08-01
SummaryThe purpose of this paper is to develop an automated calibration method for the nonlinear computational units cascaded (NCUC) model. The simple genetic algorithm (SGA), a popular and robust optimization technique, is introduced in this paper as the basis of the automated calibration method. Therefore, the way to transform the model calibration problem into the optimization problem is first proposed. The general scheme to appropriately arrange the parameters of the NCUC model is then developed, so that the chromosomes of the SGA can be properly constructed. Two performance criterion functions, which are frequently used to evaluate the performance of the rainfall-runoff modeling, are adopted in this paper as the objective function to calibrate the NCUC model. Since the SGA imposes two restrictions on the fitness values, the key of the proposed automated calibration method is the evaluation of the fitness values. The methods to evaluate the fitness values according to the two objective functions are both given in this paper. With the proposed automated calibration method, high-quality parameters of the NCUC model can be obtained without modelers' subjective interventions.
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.
A new camera calibration method for phase measuring profilometry
NASA Astrophysics Data System (ADS)
Wu, Di; Lu, Naiguang
2008-03-01
In structured light vision measurement, it is vital to keep the measurement system stable because the system organization determines some important parameters used in 3D reconstruction. Aimed at this feature, a new camera calibration method is presented in the paper. This method utilizes a digital guide and a planar pattern to construct a visual 3D target. Through linear transformation and nonlinear optimization, the extrinsic and intrinsic camera parameters can be obtained iteratively. This method combines the merits of 3D pattern with planar pattern. The procedure of calibration is simple and convenient. The result is accurate by this method and meets the need of structured light vision measurement.
BESSELING, TH; JOSE, J; BLAADEREN, A VAN
2015-01-01
Accurate distance measurement in 3D confocal microscopy is important for quantitative analysis, volume visualization and image restoration. However, axial distances can be distorted by both the point spread function (PSF) and by a refractive-index mismatch between the sample and immersion liquid, which are difficult to separate. Additionally, accurate calibration of the axial distances in confocal microscopy remains cumbersome, although several high-end methods exist. In this paper we present two methods to calibrate axial distances in 3D confocal microscopy that are both accurate and easily implemented. With these methods, we measured axial scaling factors as a function of refractive-index mismatch for high-aperture confocal microscopy imaging. We found that our scaling factors are almost completely linearly dependent on refractive index and that they were in good agreement with theoretical predictions that take the full vectorial properties of light into account. There was however a strong deviation with the theoretical predictions using (high-angle) geometrical optics, which predict much lower scaling factors. As an illustration, we measured the PSF of a correctly calibrated point-scanning confocal microscope and showed that a nearly index-matched, micron-sized spherical object is still significantly elongated due to this PSF, which signifies that care has to be taken when determining axial calibration or axial scaling using such particles. PMID:25444358
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
Optimization of porthole die geometrical variables by Taguchi method
NASA Astrophysics Data System (ADS)
Gagliardi, F.; Ciancio, C.; Ambrogio, G.; Filice, L.
2017-10-01
Porthole die extrusion is commonly used to manufacture hollow profiles made of lightweight alloys for numerous industrial applications. The reliability of extruded parts is affected strongly by the quality of the longitudinal and transversal seam welds. According to that, the die geometry must be designed correctly and the process parameters must be selected properly to achieve the desired product quality. In this study, numerical 3D simulations have been created and run to investigate the role of various geometrical variables on punch load and maximum pressure inside the welding chamber. These are important outputs to take into account affecting, respectively, the necessary capacity of the extrusion press and the quality of the welding lines. The Taguchi technique has been used to reduce the number of the required numerical simulations necessary for considering the influence of twelve different geometric variables. Moreover, the Analysis of variance (ANOVA) has been implemented to individually analyze the effect of each input parameter on the two responses. Then, the methodology has been utilized to determine the optimal process configuration individually optimizing the two investigated process outputs. Finally, the responses of the optimized parameters have been verified through finite element simulations approximating the predicted value closely. This study shows the feasibility of the Taguchi technique for predicting performance, optimization and therefore for improving the design of a porthole extrusion process.
Method and apparatus for calibrating a linear variable differential transformer
Pokrywka, Robert J [North Huntingdon, PA
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.
Stage Cartesian self-calibration: a second method
NASA Astrophysics Data System (ADS)
Takac, Michael T.; Whittey, John M.
1998-12-01
A physical two-dimensional Cartesian reference has been demonstrated using group theory principles pioneered by Michael Raugh. The first stage Cartesian self-calibration introduction to the microlithographic industry was developed by Stanford University, Hewlett Packard, and IBM San Jose using Leica's LMS-2000 and LMS-2020 platforms. Recently Leica developed a different method based on a similar theory to achieve a Cartesian calibration for their LMS-IPRO x-y metrology system. A review of these methods and a comparison of the results obtained between the methods are presented.
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.
Reliably detectable flaw size for NDE methods that use calibration
NASA Astrophysics Data System (ADS)
Koshti, Ajay M.
2017-04-01
Probability of detection (POD) analysis is used in assessing reliably detectable flaw size in nondestructive evaluation (NDE). MIL-HDBK-1823 and associated mh18232 POD software gives most common methods of POD analysis. In this paper, POD analysis is applied to an NDE method, such as eddy current testing, where calibration is used. NDE calibration standards have known size artificial flaws such as electro-discharge machined (EDM) notches and flat bottom hole (FBH) reflectors which are used to set instrument sensitivity for detection of real flaws. Real flaws such as cracks and crack-like flaws are desired to be detected using these NDE methods. A reliably detectable crack size is required for safe life analysis of fracture critical parts. Therefore, it is important to correlate signal responses from real flaws with signal responses form artificial flaws used in calibration process to determine reliably detectable flaw size.
Projector calibration method based on stereo vision system
NASA Astrophysics Data System (ADS)
Yang, Shourui; Liu, Miao; Song, Jiahui; Yin, Shibin; Guo, Yin; Ren, Yongjie; Zhu, Jigui
2017-12-01
Digital projectors have been widely used in many accuracy-sensitive fields and the projector should be calibrated precisely. Different from the existing methods using a single camera and a high-accuracy diffuse planar target, the projector calibration method is proposed based on a stereo vision system and a white board. A calibration pattern with several virtual mark points is projected onto the white board at different poses and captured by the stereo vision system. A two-step optimization algorithm is proposed to calculate the intrinsic parameters with roughly coplanar points. The white board has no mark points on it and there is no need to guarantee its flatness, so it avoids using the expensive and fragile diffuse target. Finally, the experimental results have demonstrated the improvement in accuracy of the proposed method.
Watts, Seth; Tortorelli, Daniel A.
2017-07-27
Topology optimization is a methodology for assigning material or void to each point in a design domain in a way that extremizes some objective function, such as the compliance of a structure under given loads, subject to various imposed constraints, such as an upper bound on the mass of the structure. Geometry projection is a means to parameterize the topology optimization problem, by describing the design in a way that is independent of the mesh used for analysis of the design's performance; it results in many fewer design parameters, necessarily resolves the ill-posed nature of the topology optimization problem, andmore » provides sharp descriptions of the material interfaces. We extend previous geometric projection work to 3 dimensions and design unit cells for lattice materials using inverse homogenization. We perform a sensitivity analysis of the geometric projection and show it has smooth derivatives, making it suitable for use with gradient-based optimization algorithms. The technique is demonstrated by designing unit cells comprised of a single constituent material plus void space to obtain light, stiff materials with cubic and isotropic material symmetry. We also design a single-constituent isotropic material with negative Poisson's ratio and a light, stiff material comprised of 2 constituent solids plus void space.« less
Watts, Seth; Tortorelli, Daniel A.
2017-07-27
Topology optimization is a methodology for assigning material or void to each point in a design domain in a way that extremizes some objective function, such as the compliance of a structure under given loads, subject to various imposed constraints, such as an upper bound on the mass of the structure. Geometry projection is a means to parameterize the topology optimization problem, by describing the design in a way that is independent of the mesh used for analysis of the design's performance; it results in many fewer design parameters, necessarily resolves the ill-posed nature of the topology optimization problem, and provides sharp descriptions of the material interfaces. We extend previous geometric projection work to 3 dimensions and design unit cells for lattice materials using inverse homogenization. We perform a sensitivity analysis of the geometric projection and show it has smooth derivatives, making it suitable for use with gradient-based optimization algorithms. The technique is demonstrated by designing unit cells comprised of a single constituent material plus void space to obtain light, stiff materials with cubic and isotropic material symmetry. We also design a single-constituent isotropic material with negative Poisson's ratio and a light, stiff material comprised of 2 constituent solids plus void space.
A comparison of calibration methods for stereo fluoroscopic imaging systems.
Kaptein, Bart L; Shelburne, Kevin B; Torry, Michael R; Giphart, J Erik
2011-09-02
Stereo (biplane) fluoroscopic imaging systems are considered the most accurate and precise systems to study joint kinematics in vivo. Calibration of a biplane fluoroscopy system consists of three steps: (1) correction for spatial image distortion; (2) calculation of the focus position; and (3) calculation of the relative position and orientation of the two fluoroscopy systems with respect to each other. In this study we compared 6 methods for calibrating a biplane fluoroscopy system including a new method using a novel nested-optimization technique. To quantify bias and precision, an electronic digital caliper instrumented with two tantalum markers on radiolucent posts was imaged in three configurations, and for each configuration placed in ten static poses distributed throughout the viewing volume. Bias and precision were calculated as the mean and standard deviation of the displacement of the markers measured between the three caliper configurations. The data demonstrated that it is essential to correct for image distortion when sub-millimeter accuracy is required. We recommend calibrating a stereo fluoroscopic imaging system using an accurately machined plate and a calibration cube, which improved accuracy 2-3 times compared to the other calibration methods. Once image distortion is properly corrected, the focus position should be determined using the Direct Linear Transformation (DLT) method for its increased speed and equivalent accuracy compared to the novel nested-optimization method. The DLT method also automatically provides the 3D fluoroscopy configuration. Using the recommended calibration methodology, bias and precision of 0.09 and 0.05 mm or better can be expected for measuring inter-marker distances. Copyright © 2011 Elsevier Ltd. All rights reserved.
A Consistency Evaluation and Calibration Method for Piezoelectric Transmitters
Zhang, Kai; Tan, Baohai; Liu, Xianping
2017-01-01
Array transducer and transducer combination technologies are evolving rapidly. While adapting transmitter combination technologies, the parameter consistencies between each transmitter are extremely important because they can determine a combined effort directly. This study presents a consistency evaluation and calibration method for piezoelectric transmitters by using impedance analyzers. Firstly, electronic parameters of transmitters that can be measured by impedance analyzers are introduced. A variety of transmitter acoustic energies that are caused by these parameter differences are then analyzed and certified and, thereafter, transmitter consistency is evaluated. Lastly, based on the evaluations, consistency can be calibrated by changing the corresponding excitation voltage. Acoustic experiments show that this method accurately evaluates and calibrates transducer consistencies, and is easy to realize. PMID:28452947
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
An Improved Calibration Method for a Rotating 2D LIDAR System.
Zeng, Yadan; Yu, Heng; Dai, Houde; Song, Shuang; Lin, Mingqiang; Sun, Bo; Jiang, Wei; Meng, Max Q-H
2018-02-07
This paper presents an improved calibration method of a rotating two-dimensional light detection and ranging (R2D-LIDAR) system, which can obtain the 3D scanning map of the surroundings. The proposed R2D-LIDAR system, composed of a 2D LIDAR and a rotating unit, is pervasively used in the field of robotics owing to its low cost and dense scanning data. Nevertheless, the R2D-LIDAR system must be calibrated before building the geometric model because there are assembled deviation and abrasion between the 2D LIDAR and the rotating unit. Hence, the calibration procedures should contain both the adjustment between the two devices and the bias of 2D LIDAR itself. The main purpose of this work is to resolve the 2D LIDAR bias issue with a flat plane based on the Levenberg-Marquardt (LM) algorithm. Experimental results for the calibration of the R2D-LIDAR system prove the reliability of this strategy to accurately estimate sensor offsets with the error range from -15 mm to 15 mm for the performance of capturing scans.
NASA Astrophysics Data System (ADS)
Carlberg, Joleen K.; Monroe, TalaWanda R.; Sohn, Sangmo Tony; Branton, Doug; Debes, John; Lockwood, Sean; Proffitt, Charles R.; Riley, Allyssa; Sonnentrucker, Paule G.; Welty, Daniel; Walborn, Nolan R.; Jedrzejewski, Robert I.
2018-01-01
We present updates to two sets of reference files used by the STIS calibration pipeline: the time-dependent sensitivity (TDS) and the geometric distortion reference files. The sensitivity of STIS is known to degrade with time across all spectral elements, at a rate that varies with wavelength. The TDS is routinely monitored by observing standard stars, and the reference files are periodically updated when the TDS begins to diverge from previously determined relationships. Here, we describe the analysis that led to the March 2017 update. Most observing modes saw 2-3% improvements in the flux calibration. Some modes, generally the bluest wavelength settings at far- and near-ultraviolet wavelengths, saw flux calibration improvements of ~8%.Additionally, we have derived a new geometric distortion solution for the STIS FUV-MAMA. To do this, positions of stars in 89 FUV-MAMA observations of NGC 6681 were compared to the astrometric standard catalog created using WFC3/UVIS imaging data to derive a fourth-order polynomial solution that transforms raw (x, y) positions to geometrically- corrected (x, y) positions. When compared to astrometric catalog positions, the FUV- MAMA position measurements based on the old geometric distortion reference file (IDCTAB) showed residuals with an RMS of ∼ 30 mas in each coordinate. Using the new IDCTAB, the RMS is reduced to ∼ 4 mas, or 0.16 FUV-MAMA pixels, in each coordinate. The updated IDCTAB is applied automatically to all new FUV-MAMA imaging data starting in Sept 2017, and all existing FUV-MAMA imaging data taken since SM4 (2009) have been recalibrated with the new IDCTAB as well.
In-Flight Methods for Satellite Sensor Absolute Radiometric Calibration.
NASA Astrophysics Data System (ADS)
Biggar, Stuart Frick
1990-01-01
Three methods for the in-flight absolute radiometric calibration of satellite sensors are presented. The Thematic Mapper (TM) on the Landsat satellites and the HRV on the SPOT satellite have been calibrated using the three methods at the White Sands Missile Range in New Mexico. Ground and airborne measurements of ground reflectance, radiance, atmospheric, and weather parameters are made coincident with satellite image acquisition. The data are analyzed to determine inputs to radiative transfer codes. The codes compute the radiance at the sensor entrance pupil which is compared to the average digital count from the measured ground area. The three methods are the reflectance-based, radiance-based and irradiance-based methods. The relevant theory of radiative transfer through an atmosphere is reviewed. The partition of extinction optical depth into Rayleigh, aerosol and absorption optical depths is discussed. The reflectance-based method is described along with the assumptions made. The reflectance-based method accuracy is no better than the measurement of the ground reflectance which is made in reference to a standard of spectral reflectance. The radiance-based method is described. The standard for the radiance method is a standard of spectral irradiance used to calibrate a radiometer. The calibration of a radiometer is discussed along with the use of radiative transfer computations to correct for the residual atmosphere above the radiometer. The irradiance-based method is described. It uses the measurement of the downward direct and total irradiance at ground level to determine the apparent reflectance seen by a sensor. This method uses an analytic approximation to compute the reflectance without the use of an "exact" radiative transfer code. The direct-to-total irradiance ratio implicitly gives the description of the scattering normally calculated from the size distribution and assumption of Mie scattering by the aerosols. The three methods give independent results
Chen, Chenglong; Ni, Jiangqun; Shen, Zhaoyi; Shi, Yun Qing
2017-06-01
Geometric transformations, such as resizing and rotation, are almost always needed when two or more images are spliced together to create convincing image forgeries. In recent years, researchers have developed many digital forensic techniques to identify these operations. Most previous works in this area focus on the analysis of images that have undergone single geometric transformations, e.g., resizing or rotation. In several recent works, researchers have addressed yet another practical and realistic situation: successive geometric transformations, e.g., repeated resizing, resizing-rotation, rotation-resizing, and repeated rotation. We will also concentrate on this topic in this paper. Specifically, we present an in-depth analysis in the frequency domain of the second-order statistics of the geometrically transformed images. We give an exact formulation of how the parameters of the first and second geometric transformations influence the appearance of periodic artifacts. The expected positions of characteristic resampling peaks are analytically derived. The theory developed here helps to address the gap left by previous works on this topic and is useful for image security and authentication, in particular, the forensics of geometric transformations in digital images. As an application of the developed theory, we present an effective method that allows one to distinguish between the aforementioned four different processing chains. The proposed method can further estimate all the geometric transformation parameters. This may provide useful clues for image forgery detection.
A point cloud modeling method based on geometric constraints mixing the robust least squares method
NASA Astrophysics Data System (ADS)
Yue, JIanping; Pan, Yi; Yue, Shun; Liu, Dapeng; Liu, Bin; Huang, Nan
2016-10-01
The appearance of 3D laser scanning technology has provided a new method for the acquisition of spatial 3D information. It has been widely used in the field of Surveying and Mapping Engineering with the characteristics of automatic and high precision. 3D laser scanning data processing process mainly includes the external laser data acquisition, the internal industry laser data splicing, the late 3D modeling and data integration system. For the point cloud modeling, domestic and foreign researchers have done a lot of research. Surface reconstruction technology mainly include the point shape, the triangle model, the triangle Bezier surface model, the rectangular surface model and so on, and the neural network and the Alfa shape are also used in the curved surface reconstruction. But in these methods, it is often focused on single surface fitting, automatic or manual block fitting, which ignores the model's integrity. It leads to a serious problems in the model after stitching, that is, the surfaces fitting separately is often not satisfied with the well-known geometric constraints, such as parallel, vertical, a fixed angle, or a fixed distance. However, the research on the special modeling theory such as the dimension constraint and the position constraint is not used widely. One of the traditional modeling methods adding geometric constraints is a method combing the penalty function method and the Levenberg-Marquardt algorithm (L-M algorithm), whose stability is pretty good. But in the research process, it is found that the method is greatly influenced by the initial value. In this paper, we propose an improved method of point cloud model taking into account the geometric constraint. We first apply robust least-squares to enhance the initial value's accuracy, and then use penalty function method to transform constrained optimization problems into unconstrained optimization problems, and finally solve the problems using the L-M algorithm. The experimental results
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
Calibration of weather radar using region probability matching method (RPMM)
NASA Astrophysics Data System (ADS)
Ayat, Hooman; Reza Kavianpour, M.; Moazami, Saber; Hong, Yang; Ghaemi, Esmail
2017-09-01
This research aims to develop a novel method named region probability matching method (RPMM) for calibrating the Amir-Abad weather radar located in the north of Iran. This approach also can overcome the limitations of probability matching method (PMM), window probability matching method (WPMM), and window correlation matching method (WCMM). The employing of these methods for calibrating the radars in light precipitation is associated with many errors. Additionally, in developing countries like Iran where ground stations have low temporal resolution, these methods cannot be benefited from. In these circumstances, RPMM by utilizing 18 synoptic stations with a temporal resolution of 6 h and radar data with a temporal resolution of 15 min has indicated an accurate estimation of cumulative precipitation over the entire study area in a specific period. Through a comparison of the two methods (RPMM and traditional matching method (TMM)) on March 22, 2014, the obtained correlation coefficients for TMM and RPMM were 0.13 and 0.95, respectively. It is noted that the cumulative precipitation of the whole rain gauges and the calibrated radar precipitation at the same pixels were 38.5 and 36.9 mm, respectively. Therefore, the obtained results prove the inefficiency of TMM and the capability of RPMM in the calibration process of the Amir-Abad weather radar. Besides, in determining the uncertainty associated with the calculated values of A and B in the Z e -R relation, a sensitivity analysis method was employed during the estimation of cumulative light precipitation for the period from 2014 to 2015. The results expressed that in the worst conditions, 69% of radar data are converted to R values by a maximum error less than 30%.
Calibration of prior variance in the Bayesian Continual Reassessment Method
Lee, Shing M.; Cheung, Ying Kuen
2010-01-01
SUMMARY The continual reassessment method (CRM) is an adaptive model-based design used to estimate the maximum tolerated dose in phase I clinical trials. Asymptotically, the method has been shown to select the correct dose given that certain conditions are satisfied. When sample size is small, specifying a reasonable model is important. While an algorithm has been proposed for the calibration of the initial guesses of the probabilities of toxicity, the calibration of the prior distribution of the parameter for the Bayesian CRM has not been addressed. In this paper, we introduce the concept of least informative prior variance for a normal prior distribution. We also propose two systematic approaches to jointly calibrate the prior variance and the initial guesses of the probability of toxicity at each dose. The proposed calibration approaches are compared with existing approaches in the context of two examples via simulations. The new approaches and the previously proposed methods yield very similar results since the latter used appropriate vague priors. However, the new approaches yield a smaller interval of toxicity probabilities in which a neighboring dose may be selected. PMID:21413054
In-flight methods for satellite sensor absolute radiometric calibration
NASA Astrophysics Data System (ADS)
Biggar, Stuart Frick
Three methods for the in-flight absolute radiometric calibration of satellite sensors are presented. The thematic mapper (TM) on the LANDSAT satellites and the high resolution visibility (HRV) on the SPOT satellite were calibrated using the three methods. Ground and airborne measurements of ground reflectance, radiance, atmospheric, and weather parameters are made coincident with satellite image acquisition. The data are analyzed to determine inputs to radiative transfer codes. The codes compute the radiance at the sensor entrance pupil which is compared to the average digital count from the measured ground area. The three methods are the reflectance-based, radiance-based, and irradiance-based methods. Radiative transfer through an atmosphere is reviewed. The partition of extinction optical depth into Rayleigh, aerosol, and absorption optical depths is discussed. The reflectance-based method is described along with the assumptions made. The radiance-based method is described. The standard for the radiance method is a standard of spectral irradiance used to calibrate a radiometer. The calibration of a radiometer is discussed along with the use of radiative transfer computations to correct for the residual atmosphere above the radiometer. The irradiance-based method is described. It uses the measurement of the downward direct and total irradiance at ground level to determine the apparent reflectance seen by a sensor. This method uses an analytic approximation to compute the reflectance without the use of an exact radiative transfer code. The direct-to-total irradiance ratio implicitly gives the description of the scattering normally calculated from the size distribution and assumption of Mie scattering by the aerosols.
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.
Azizian, Saeid; Haerifar, Monireh; Basiri-Parsa, Jalal
2007-08-01
A new and simple equation has been presented here for calculation of adsorption and desorption rate constants of Langmuir-Freundlich kinetic equation. The derivation of new equation is on the basis of extension and correction to the geometric method which has been presented by Kuan et al. [Kuan, W.-H., Lo, S.-L., Chang, C.M., Wang, M.K., 2000. A geometric approach to determine adsorption and desorption kinetic constants. Chemosphere 41, 1741-1747] for the kinetics of adsorption/desorption in aqueous solutions. The correction is to consider that the concentration of solute is not constant and changes as adsorption proceeds. The extension is that we applied Langmuir-Freundlich kinetic model instead of Langmuir kinetic model to consider the heterogeneity and therefore it is more applicable to the real systems. For solving Langmuir-Freundlich kinetic model, some geometric methods and also Taylor expansion were used and finally a simple and novel equation was derived (Eq. (20)) for calculation of adsorption rate constant. This new method was named "extended geometric method". The input data of the obtained equation can be simply derived from initial data of adsorption kinetics. Finally the adsorption of methyl orange onto granular activated carbon was carried out at dynamic and equilibrium conditions and the capabilities of extended geometric method were examined by the experimental data.
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.
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.
GEMPIC: geometric electromagnetic particle-in-cell methods
NASA Astrophysics Data System (ADS)
Kraus, Michael; Kormann, Katharina; Morrison, Philip J.; Sonnendrücker, Eric
2017-08-01
We present a novel framework for finite element particle-in-cell methods based on the discretization of the underlying Hamiltonian structure of the Vlasov-Maxwell system. We derive a semi-discrete Poisson bracket, which retains the defining properties of a bracket, anti-symmetry and the Jacobi identity, as well as conservation of its Casimir invariants, implying that the semi-discrete system is still a Hamiltonian system. In order to obtain a fully discrete Poisson integrator, the semi-discrete bracket is used in conjunction with Hamiltonian splitting methods for integration in time. Techniques from finite element exterior calculus ensure conservation of the divergence of the magnetic field and Gauss' law as well as stability of the field solver. The resulting methods are gauge invariant, feature exact charge conservation and show excellent long-time energy and momentum behaviour. Due to the generality of our framework, these conservation properties are guaranteed independently of a particular choice of the finite element basis, as long as the corresponding finite element spaces satisfy certain compatibility conditions.
Calibration method of microgrid polarimeters with image interpolation.
Chen, Zhenyue; Wang, Xia; Liang, Rongguang
2015-02-10
Microgrid polarimeters have large advantages over conventional polarimeters because of the snapshot nature and because they have no moving parts. However, they also suffer from several error sources, such as fixed pattern noise (FPN), photon response nonuniformity (PRNU), pixel cross talk, and instantaneous field-of-view (IFOV) error. A characterization method is proposed to improve the measurement accuracy in visible waveband. We first calibrate the camera with uniform illumination so that the response of the sensor is uniform over the entire field of view without IFOV error. Then a spline interpolation method is implemented to minimize IFOV error. Experimental results show the proposed method can effectively minimize the FPN and PRNU.
Research on calibrating rock mechanical parameters with a statistical method
Guo, Ye; Du, Shuheng; Wu, Gengyu; Pan, Mao
2017-01-01
Research on the modeling of rock mechanics parameters is of great significance to the exploration of oil and gas. The use of logging data with the Kriging interpolation to study rock mechanics parameters has been proven to be effective in reservoir prediction and other oilfield applications and can provide additional data. However, there will sometimes be a great deviation due to the limited samples and the strong heterogeneity of a layer. To solve this problem, a new approach was proposed to calibrate rock mechanical models through the statistical analysis of logging data. A module was developed to calibrate rock mechanics parameters automatically, which was then applied to the Wangyao area of the Ansai oilfield. This method significantly improved the accuracy of rock mechanics modeling. PMID:28545105
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
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.
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.
Yu, Lei; Lin, Guan-Yu; Chen, Bin
2013-01-01
The present paper studied spectral irradiation responsivities calibration method which can be applied to the far ultraviolet spectrometer for upper atmosphere remote sensing. It is difficult to realize the calibration for far ultraviolet spectrometer for many reasons. Standard instruments for far ultraviolet waveband calibration are few, the degree of the vacuum experiment system is required to be high, the stabilities of the experiment are hardly maintained, and the limitation of the far ultraviolet waveband makes traditional diffuser and the integrating sphere radiance calibration method difficult to be used. To solve these problems, a new absolute spectral irradiance calibration method was studied, which can be applied to the far ultraviolet calibration. We build a corresponding special vacuum experiment system to verify the calibration method. The light source system consists of a calibrated deuterium lamp, a vacuum ultraviolet monochromater and a collimating system. We used the calibrated detector to obtain the irradiance responsivities of it. The three instruments compose the calibration irradiance source. We used the "calibration irradiance source" to illuminate the spectrometer prototype and obtained the spectral irradiance responsivities. It realized the absolute spectral irradiance calibration for the far ultraviolet spectrometer utilizing the calibrated detector. The absolute uncertainty of the calibration is 7.7%. The method is significant for the ground irradiation calibration of the far ultraviolet spectrometer in upper atmosphere remote sensing.
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.
Simplified methods for coincidence summing corrections in HPGe efficiency calibration.
Mauring, Alexander; Drefvelin, Jon
2012-09-01
Simple and practical coincidence summing corrections for n-type HPGe detectors are presented for the common calibration nuclides (57)Co and (60)Co using a defined "virtual peak" and accounting for the summing of gamma photons with x-rays having energies up to 40 keV ((88)Y and (139)Ce). These corrections make it possible to easily and effectively establish peak and total efficiency curves suitable for subsequent summing corrections in routine gamma spectrometry analyses. Experimental verification of the methods shows excellent agreement for measurements of different reference solutions. Copyright © 2012 Elsevier Ltd. All rights reserved.
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.
Method for radiometric calibration of an endoscope's camera and light source
NASA Astrophysics Data System (ADS)
Rai, Lav; Higgins, William E.
2008-03-01
An endoscope is a commonly used instrument for performing minimally invasive visual examination of the tissues inside the body. A physician uses the endoscopic video images to identify tissue abnormalities. The images, however, are highly dependent on the optical properties of the endoscope and its orientation and location with respect to the tissue structure. The analysis of endoscopic video images is, therefore, purely subjective. Studies suggest that the fusion of endoscopic video images (providing color and texture information) with virtual endoscopic views (providing structural information) can be useful for assessing various pathologies for several applications: (1) surgical simulation, training, and pedagogy; (2) the creation of a database for pathologies; and (3) the building of patient-specific models. Such fusion requires both geometric and radiometric alignment of endoscopic video images in the texture space. Inconsistent estimates of texture/color of the tissue surface result in seams when multiple endoscopic video images are combined together. This paper (1) identifies the endoscope-dependent variables to be calibrated for objective and consistent estimation of surface texture/color and (2) presents an integrated set of methods to measure them. Results show that the calibration method can be successfully used to estimate objective color/texture values for simple planar scenes, whereas uncalibrated endoscopes performed very poorly for the same tests.
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.
NASA Astrophysics Data System (ADS)
Chang, Yau-Zen; Wang, Huai-Ming; Lee, Shih-Tseng; Wu, Chieh-Tsai; Hsu, Ming-Hsi
2014-02-01
This work investigates the calibration of a stereo vision system based on two PTZ (Pan-Tilt-Zoom) cameras. As the accuracy of the system depends not only on intrinsic parameters, but also on the geometric relationships between rotation axes of the cameras, the major concern is the development of an effective and systematic way to obtain these relationships. We derived a complete geometric model of the dual-PTZ-camera system and proposed a calibration procedure for the intrinsic and external parameters of the model. The calibration method is based on Zhang's approach using an augmented checkerboard composed of eight small checkerboards, and is formulated as an optimization problem to be solved by an improved particle swarm optimization (PSO) method. Two Sony EVI-D70 PTZ cameras were used for the experiments. The root-mean-square errors (RMSE) of corner distances in the horizontal and vertical direction are 0.192 mm and 0.115 mm, respectively. The RMSE of overlapped points between the small checkerboards is 1.3958 mm.
Method for calibration accuracy improvement of projector-camera-based structured light system
NASA Astrophysics Data System (ADS)
Nie, Lei; Ye, Yuping; Song, Zhan
2017-07-01
Calibration is a critical step for the projector-camera-based structured light system (SLS). Conventional SLS calibration means usually use the calibrated camera to calibrate the projector device, and the optimization of calibration parameters is applied to minimize the two-dimensional (2-D) reprojection errors. A three-dimensional (3-D)-based method is proposed for the optimization of SLS calibration parameters. The system is first calibrated with traditional calibration methods to obtain the primary calibration parameters. Then, a reference plane with some precisely printed markers is used for the optimization of primary calibration results. Three metric error criteria are introduced to evaluate the 3-D reconstruction accuracy of the reference plane. By treating all the system parameters as a global optimization problem and using the primary calibration parameters as initial values, a nonlinear multiobjective optimization problem can be established and solved. Compared with conventional calibration methods that adopt the 2-D reprojection errors for the camera and projector separately, a global optimal calibration result can be obtained by the proposed calibration procedure. Experimental results showed that, with the optimized calibration parameters, measurement accuracy and 3-D reconstruction quality of the system can be greatly improved.
First in-flight results of Pleiades 1A innovative methods for optical calibration
NASA Astrophysics Data System (ADS)
Kubik, Philippe; Lebègue, Laurent; Fourest, Sébastien; Delvit, Jean-Marc; de Lussy, Françoise; Greslou, Daniel; Blanchet, Gwendoline
2017-11-01
The PLEIADES program is a space Earth Observation system led by France, under the leadership of the French Space Agency (CNES). Since it was successfully launched on December 17th, 2011, Pleiades 1A high resolution optical satellite has been thoroughly tested and validated during the commissioning phase led by CNES. The whole system has been designed to deliver submetric optical images to users whose needs were taken into account very early in the design process. This satellite opens a new era in Europe since its off-nadir viewing capability delivers a worldwide 2- days access, and its great agility will make possible to image numerous targets, strips and stereo coverage from the same orbit. Its imaging capability of more than 450 images of 20 km x 20 km per day can fulfill a broad spectrum of applications for both civilian and defence users. For an earth observing satellite with no on-board calibration source, the commissioning phase is a critical quest of wellcharacterized earth landscapes and ground patterns that have to be imaged by the camera in order to compute or fit the parameters of the viewing models. It may take a long time to get the required scenes with no cloud, whilst atmosphere corrections need simultaneous measurements that are not always possible. The paper focuses on new in-flight calibration methods that were prepared before the launch in the framework of the PLEIADES program : they take advantage of the satellite agility that can deeply relax the operational constraints and may improve calibration accuracy. Many performances of the camera were assessed thanks to a dedicated innovative method that was successfully validated during the commissioning period : Modulation Transfer Function (MTF), refocusing, absolute calibration, line of sight stability were estimated on stars and on the Moon. Detectors normalization and radiometric noise were computed on specific pictures on Earth with a dedicated guidance profile. Geometric viewing frame was
Methods for Calibration of Prout-Tompkins Kinetics Parameters Using EZM Iteration and GLO
Wemhoff, A P; Burnham, A K; de Supinski, B; Sexton, J; Gunnels, J
2006-11-07
This document contains information regarding the standard procedures used to calibrate chemical kinetics parameters for the extended Prout-Tompkins model to match experimental data. Two methods for calibration are mentioned: EZM calibration and GLO calibration. EZM calibration matches kinetics parameters to three data points, while GLO calibration slightly adjusts kinetic parameters to match multiple points. Information is provided regarding the theoretical approach and application procedure for both of these calibration algorithms. It is recommended that for the calibration process, the user begin with EZM calibration to provide a good estimate, and then fine-tune the parameters using GLO. Two examples have been provided to guide the reader through a general calibrating process.
A new camera calibration method for robotic vision
NASA Astrophysics Data System (ADS)
Paquette, Louis; Stampfler, Robert; Davis, Wayne A.; Caelli, Terry M.
1990-08-01
The interior/exterior orientation problem or hand-eye calibration problem is formulated as the problem of finding the best parameters that fit the observations of known test points. A novel numerical procedure for obtaining the best parameters in the least square sense is then described. The main result is that the errors corresponding to each test point can be approximated by two linear equations in terms of the independent camera parameters (ICPs). These linear equations are then combined to produce a least square matrix equation in terms of the ICPs. This numerical method employs only several systems of small-size linear equations. The proposed method was tested with data obtained from a CCD camera.
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.
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.
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.
Assessment of three methods of geometric image reconstruction for digital subtraction radiography.
Queiroz, Polyane M; Oliveira, Matheus L; Tanaka, Jefferson L O; Soares, Milton G; Haiter-Neto, Francisco; Ono, Evelise
To evaluate three methods of geometric image reconstruction for digital subtraction radiography (DSR). Digital periapical radiographs were acquired of 24 teeth with the X-ray tube at 6 different geometric configurations of vertical (V) and horizontal (H) angles: V0°H0°, V0°H10°, V10°H0°, V10°H10°, V20°H0° and V20°H10°. All 144 images were registered in pairs (Group V0°H0° + 1 of the 6 groups) 3 times by using the Emago(®) (Oral Diagnostic Systems, Amsterdam, Netherlands) with manual selection and Regeemy with manual and automatic selections. After geometric reconstruction on the two software applications under different modes of selection, all images were subtracted and the standard deviation of grey values was obtained as a measure of image noise. All measurements were repeated after 15 days to evaluate the method error. Values of image noise were statistically analyzed by one-way ANOVA for differences between methods and between projection angles, followed by Tukey's test at a level of significance of 5%. Significant differences were found between most of the projection angles for the three reconstruction methods. Image subtraction after manual selection-based reconstruction on Regeemy presented the lowest values of image noise, except on group V0°H0°. The groups V10°H0° and V20°H0° were not significantly different between the manual selection-based reconstruction in Regeemy and automatic selection-based reconstruction in Regeemy methods. The Regeemy software on manual mode revealed better quality of geometric image reconstruction for DSR than the Regeemy on automatic mode and the Emago on manual mode, when the radiographic images were obtained at V and H angles used in the present investigation.
On-site calibration method for outdoor binocular stereo vision sensors
NASA Astrophysics Data System (ADS)
Liu, Zhen; Yin, Yang; Wu, Qun; Li, Xiaojing; Zhang, Guangjun
2016-11-01
Using existing calibration methods for binocular stereo vision sensors (BSVS), it is very difficult to extract target characteristic points in outdoor environments under complex light conditions. To solve the problem, an online calibration method for BSVS based a double parallel cylindrical target and a line laser projector is proposed in this paper. The intrinsic parameters of two cameras are calibrated offline. Laser strips on the double parallel cylindrical target are mediated to calibrate the configuration parameters of BSVS. The proposed method only requires images of laser strips on the target and is suitable for the calibration of BSVS in outdoor environments. The effectiveness of the proposed method is validated through physical experiments.
Geometric correction method for 3d in-line X-ray phase contrast image reconstruction
2014-01-01
Background Mechanical system with imperfect or misalignment of X-ray phase contrast imaging (XPCI) components causes projection data misplaced, and thus result in the reconstructed slice images of computed tomography (CT) blurred or with edge artifacts. So the features of biological microstructures to be investigated are destroyed unexpectedly, and the spatial resolution of XPCI image is decreased. It makes data correction an essential pre-processing step for CT reconstruction of XPCI. Methods To remove unexpected blurs and edge artifacts, a mathematics model for in-line XPCI is built by considering primary geometric parameters which include a rotation angle and a shift variant in this paper. Optimal geometric parameters are achieved by finding the solution of a maximization problem. And an iterative approach is employed to solve the maximization problem by using a two-step scheme which includes performing a composite geometric transformation and then following a linear regression process. After applying the geometric transformation with optimal parameters to projection data, standard filtered back-projection algorithm is used to reconstruct CT slice images. Results Numerical experiments were carried out on both synthetic and real in-line XPCI datasets. Experimental results demonstrate that the proposed method improves CT image quality by removing both blurring and edge artifacts at the same time compared to existing correction methods. Conclusions The method proposed in this paper provides an effective projection data correction scheme and significantly improves the image quality by removing both blurring and edge artifacts at the same time for in-line XPCI. It is easy to implement and can also be extended to other XPCI techniques. PMID:25069768
NASA Astrophysics Data System (ADS)
Cui, Enkun; Wang, YanJie; Zhang, Tao; Di, Nan; Yin, YanHe; Wu, Pei; Sun, HongHai
2017-10-01
This paper presents an effective technique to calibrate the binocular system. A collinear geometry transformation is derived and introduced into the calibration process. First, we construct a virtual binocular system with every two point pair in the same image, and then an analytic method based on the virtual binocular system is proposed to calculate the internal and external parameters of left and right cameras. The structure parameters are solved from the calibrated extrinsic parameters of each camera. All the parameters of the binocular system are calculated with only one image pair. Furthermore, an iterative refinement by minimizing the metric distance error between the reconstructed point and the real point in a three-dimensional measurement coordinate system is applied to enhance the calibration accuracy. Simulations and real experiments have been carried out. The calibration accuracy is compared with the traditional calibration method. The results show that the proposed calibration methods are efficient in improving the calibration accuracy and simply equipped.
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.
Hellier, Pierre; Coupé, Pierrick; Morandi, Xavier; Collins, D Louis
2010-04-01
In ultrasound images, acoustic shadows appear as regions of low signal intensity linked to boundaries with very high acoustic impedance differences. Acoustic shadows can be viewed either as informative features to detect lesions or calcifications, or as damageable artifacts for image processing tasks such as segmentation, registration or 3D reconstruction. In both cases, the detection of these acoustic shadows is useful. This paper proposes a new method to detect these shadows that combines a geometrical approach to estimate the B-scans shape, followed by a statistical test based on a dedicated modeling of ultrasound image statistics. Results demonstrate that the combined geometrical-statistical technique is more robust and yields better results than the previous statistical technique. Integration of regularization over time further improves robustness. Application of the procedure results in (1) improved 3D reconstructions with fewer artifacts, and (2) reduced mean registration error of tracked intraoperative brain ultrasound images. Copyright 2009 Elsevier B.V. All rights reserved.
Geometric and material modeling environment for the finite-difference time-domain method
NASA Astrophysics Data System (ADS)
Lee, Yong-Gu; Muhammad, Waleed
2012-02-01
The simulation of electromagnetic problems using the Finite-Difference Time-Domain method starts with the geometric design of the devices and their surroundings with appropriate materials and boundary conditions. This design stage is one of the most time consuming part in the Finite-Difference Time-Domain (FDTD) simulation of photonics devices. Many FDTD solvers have their own way of providing the design environment which can be burdensome for a new user to learn. In this work, geometric and material modeling features are developed on the freely available Google SketchUp, allowing users who are fond of its environment to easily model photonics simulations. The design and implementation of the modeling environment are discussed.
Geometric correction method for linear array pushbroom infrared imagery using compressive sampling
NASA Astrophysics Data System (ADS)
Chen, Jun; An, Wei; Yang, Jungang; Wang, Pu
2016-10-01
The imagery vendors of the most advanced remote sensing satellites usually only provide the coefficients of rational function model (RFM) to replace the sensor model and the precise imaging parameters (orbit parameter, attitude parameter, and so on). So, the rigorous imaging model was limited to use in the geometric correction of remote sensing image. The RFM method could obtain a better correction performance in most cases. However, when the image contains few numbers or uneven distribution of ground control points (GCPs), such as infrared image, the RFM method could not obtain the expected performance. Therefore, a geometric correction method for linear pushbroom infrared imagery using compressive sampling (CS) is proposed. The core idea of the proposed method is to use the equivalent bias angles to approximate the influence of the errors (thermal distortion, optical distortion, assembly error, satellite orbit errors, attitude errors, and so on) in the imaging process and adopt the CS method to recover the equivalent bias angle signals. Most of the data are processed scene by scene with enough GCPs for each scene in conventional methods. This restriction is broken by using the sparsity of equivalent bias angle signals in the proposed method. The infrared images from the Hyperion of EO-1 are used as experiment data, and the results of experiments demonstrate the feasibility and superior performance of proposed method.
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
Transmission electron microscope calibration methods for critical dimension standards
NASA Astrophysics Data System (ADS)
Orji, Ndubuisi G.; Dixson, Ronald G.; Garcia-Gutierrez, Domingo I.; Bunday, Benjamin D.; Bishop, Michael; Cresswell, Michael W.; Allen, Richard A.; Allgair, John A.
2016-10-01
One of the key challenges in critical dimension (CD) metrology is finding suitable dimensional calibration standards. The transmission electron microscope (TEM), which produces lattice-resolved images having scale traceability to the SI (International System of Units) definition of length through an atomic lattice constant, has gained wide usage in different areas of CD calibration. One such area is critical dimension atomic force microscope (CD-AFM) tip width calibration. To properly calibrate CD-AFM tip widths, errors in the calibration process must be quantified. Although the use of TEM for CD-AFM tip width calibration has been around for about a decade, there is still confusion on what should be considered in the uncertainty analysis. We characterized CD-AFM tip-width samples using high-resolution TEM and high angle annular dark field scanning TEM and two CD-AFMs that are implemented as reference measurement systems. The results are used to outline how to develop a rigorous uncertainty estimate for TEM/CD-AFM calibration, and to compare how information from the two electron microscopy modes are applied to practical CD-AFM measurements. The results also represent a separate validation of previous TEM/CD-AFM calibration. Excellent agreement was observed.
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
Zhang, Mingjun; Mao, Kaixuan; Tao, Weimin; Tarn, Tzyh-Jong
2006-04-01
Geometric measures (volume, area and length) of biological particles are of fundamental interest for biological studies. Many times, the measures are at micro-/nano-scale, and based on images of the biological particles. This paper proposes a computational method to geometric measure of biological particles. The method has been applied to DNA microarray spot size estimation. Compared with existing algorithms for microarray spot size estimation, the proposed method is computational efficient and also provides confidence probability on the measure. The contributions of this paper include a generic computational method to geometric measure of biological particles and application to DNA microarray spot size estimation.
A new systematic calibration method of ring laser gyroscope inertial navigation system
NASA Astrophysics Data System (ADS)
Wei, Guo; Gao, Chunfeng; Wang, Qi; Wang, Qun; Xiong, Zhenyu; Long, Xingwu
2016-10-01
Inertial navigation system has been the core component of both military and civil navigation systems. Before the INS is put into application, it is supposed to be calibrated in the laboratory in order to compensate repeatability error caused by manufacturing. Discrete calibration method cannot fulfill requirements of high-accurate calibration of the mechanically dithered ring laser gyroscope navigation system with shock absorbers. This paper has analyzed theories of error inspiration and separation in detail and presented a new systematic calibration method for ring laser gyroscope inertial navigation system. Error models and equations of calibrated Inertial Measurement Unit are given. Then proper rotation arrangement orders are depicted in order to establish the linear relationships between the change of velocity errors and calibrated parameter errors. Experiments have been set up to compare the systematic errors calculated by filtering calibration result with those obtained by discrete calibration result. The largest position error and velocity error of filtering calibration result are only 0.18 miles and 0.26m/s compared with 2 miles and 1.46m/s of discrete calibration result. These results have validated the new systematic calibration method and proved its importance for optimal design and accuracy improvement of calibration of mechanically dithered ring laser gyroscope inertial navigation system.
NASA Astrophysics Data System (ADS)
Zhang, Yang; Yang, Fan; Liu, Wei; Zhang, Zhiyuan; Zhao, Haiyang; Lan, Zhiguang; Gao, Peng; Jia, Zhenyuan
2017-07-01
An accurate measurement of large aviation part plays a key role in the assembly of aircraft. However, due to the limitation of spatial size, a calibration with large field of view and an accurate surface measurement of large part is hard to achieve. In this paper, an improved measurement method with spatial constraint calibration method and feature compression extraction method is proposed. Firstly, based on the proposed spatial constraint calibration method, the vision system is conveniently and precisely calibrated by using the designed SBA and SLT. Images of scanning laser stripes are captured by the calibrated cameras, simultaneously. Then the proposed feature compression extraction method is adopted to accurately extract centers of laser stripes. Finally, based on the binocular vision principle, the surface of part is reconstructed. The accuracy of proposed calibration method is verified in the lab. The results of the measurement of a standard part show the validity and precision of the proposed method.
NASA Astrophysics Data System (ADS)
Hepson, Ozlem Ersoy; Daǧ, Idris
2018-01-01
In this paper, a subdomain Galerkin method is set up to find solutions of singularly perturbed boundary value problems which are used widely in many areas such as chemical reactor theory, aerodynamics, quantum mechanics, reaction-diffusion process, optimal control, etc. A combination of the cubic B-spline base functions as an approximation function is used to build up the presented method over the geometrically graded mesh. Thus finer mesh can be established through the end parts of the problem domain where steep solutions exist.
Method of calibration of a fluorescence microscope for quantitative studies.
Kedziora, Katarzyna M; Prehn, Johen H M; Dobrucki, Jurek; Bernas, Tytus
2011-10-01
Confocal microscopy is based on measurement of intensity of fluorescence originating from a limited volume in the imaged specimen. The intensity is quantized in absolute (albeit arbitrary) units, producing a digital 3D micrograph. Thus, one may obtain quantitative information on local concentration of biomolecules in cells and tissues. This approach requires estimation of precision of light measurement (limited by noise) and conversion of the digital intensity units to absolute values of concentration (or number) of molecules of interest. To meet the first prerequisite we propose a technique for measurement of signal and noise. This method involves registration of a time series of images of any stationary microscope specimen. The analysis is a multistep process, which separates monotonic, periodic and random components of pixel intensity change. This approach permits simultaneous determination of dark and photonic components of noise. Consequently, confidence interval (total noise estimation) is obtained for every level of signal. The algorithm can also be applied to detect mechanical instability of a microscope and instability of illumination source. The presented technique is combined with a simple intensity standard to provide conversion of relative intensity units into their absolute counterparts (the second prerequisite of quantitative imaging). Moreover, photobleaching kinetics of the standard is used to estimate the power of light delivered to a microscope specimen. Thus, the proposed method provides in one step an absolute intensity calibration, estimate of precision and sensitivity of a microscope system. © 2011 The Authors Journal of Microscopy © 2011 Royal Microscopical Society.
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%.
Improvement of Gaofen-3 Absolute Positioning Accuracy Based on Cross-Calibration
Deng, Mingjun; Li, Jiansong
2017-01-01
The Chinese Gaofen-3 (GF-3) mission was launched in August 2016, equipped with a full polarimetric synthetic aperture radar (SAR) sensor in the C-band, with a resolution of up to 1 m. The absolute positioning accuracy of GF-3 is of great importance, and in-orbit geometric calibration is a key technology for improving absolute positioning accuracy. Conventional geometric calibration is used to accurately calibrate the geometric calibration parameters of the image (internal delay and azimuth shifts) using high-precision ground control data, which are highly dependent on the control data of the calibration field, but it remains costly and labor-intensive to monitor changes in GF-3’s geometric calibration parameters. Based on the positioning consistency constraint of the conjugate points, this study presents a geometric cross-calibration method for the rapid and accurate calibration of GF-3. The proposed method can accurately calibrate geometric calibration parameters without using corner reflectors and high-precision digital elevation models, thus improving absolute positioning accuracy of the GF-3 image. GF-3 images from multiple regions were collected to verify the absolute positioning accuracy after cross-calibration. The results show that this method can achieve a calibration accuracy as high as that achieved by the conventional field calibration method. PMID:29240675
Liver vessels segmentation using a hybrid geometrical moments/graph cuts method
Esneault, Simon; Lafon, Cyril; Dillenseger, Jean-Louis
2010-01-01
This paper describes a fast and fully-automatic method for liver vessel segmentation on CT scan pre-operative images. The basis of this method is the introduction of a 3-D geometrical moment-based detector of cylindrical shapes within the min-cut/max-flow energy minimization framework. This method represents an original way to introduce a data term as a constraint into the widely used Boykov’s graph cuts algorithm and hence, to automate the segmentation. The method is evaluated and compared with others on a synthetic dataset. Finally, the relevancy of our method regarding the planning of a -necessarily accurate- percutaneous high intensity focused ultrasound surgical operation is demonstrated with some examples. PMID:19783500
Antenna Calibration Using the 3-Antenna Method with the In-Phase Synthetic Method
NASA Astrophysics Data System (ADS)
Fujii, Katsumi; Yamanaka, Yukio; Koike, Kunimasa; Sugiura, Akira
The use of the in-phase synthetic method is proposed for antenna calibration using the three-antenna method (TAM) in order to make the TAM applicable even in a semi-anechoic chamber (SAC) or on an open-area test site. Suitable antenna arrangements are theoretically investigated for this improved calibration method. Experimental analyses demonstrate that the in-phase synthetic method can remarkably reduce unwanted effects of the ground-reflected wave. Therefore, even on a metal ground plane, the proposed TAM with the in-phase synthetic method can yield an accurate actual gain of a double ridged guide antenna at frequencies from 4GHz to 14GHz with differences of +0.16/-0.37dB from the results of the conventional TAM performed in an fully anechoic room (FAR).
The JCMT Transient Survey: Data Reduction and Calibration Methods
NASA Astrophysics Data System (ADS)
Mairs, Steve; Lane, James; Johnstone, Doug; Kirk, Helen; Lacaille, Kevin; Bower, Geoffrey C.; Bell, Graham S.; Graves, Sarah; Chapman, Scott; The JCMT Transient Team
2017-07-01
Though there has been a significant amount of work investigating the early stages of low-mass star formation in recent years, the evolution of the mass assembly rate onto the central protostar remains largely unconstrained. Examining in depth the variation in this rate is critical to understanding the physics of star formation. Instabilities in the outer and inner circumstellar disk can lead to episodic outbursts. Observing these brightness variations at infrared or submillimeter wavelengths constrains the current accretion models. The JCMT Transient Survey is a three-year project dedicated to studying the continuum variability of deeply embedded protostars in eight nearby star-forming regions at a one-month cadence. We use the SCUBA-2 instrument to simultaneously observe these regions at wavelengths of 450 and 850 μm. In this paper, we present the data reduction techniques, image alignment procedures, and relative flux calibration methods for 850 μm data. We compare the properties and locations of bright, compact emission sources fitted with Gaussians over time. Doing so, we achieve a spatial alignment of better than 1″ between the repeated observations and an uncertainty of 2%-3% in the relative peak brightness of significant, localized emission. This combination of imaging performance is unprecedented in ground-based, single-dish submillimeter observations. Finally, we identify a few sources that show possible and confirmed brightness variations. These sources will be closely monitored and presented in further detail in additional studies throughout the duration of the survey.
Calibration of CNC milling machine by direct method
NASA Astrophysics Data System (ADS)
Khan, Abdul Wahid; Chen, Wuyi
2008-12-01
Calibration refers to the system of quantity value determination of instruments, equipments and test devices according to industrial requirement, based on metrological characteristics. In present research critical parameter which affects the accuracy and product quality of a CNC milling machine, was investigated and quantified by using direct method. These parameters consist of position dependent or position independent parameters, like linear displacement errors, angular errors of linear axes, straightness error of linear axes and squareness error between the axes. Repeatability, lead screw and resolution error of the CNC milling machine were also quantified to provide additional information to the user, because in absence of this additional information a misconception persists causing a major contributor to the inaccuracy and quality of the product. Parameters were measured and quantified by using a laser interferometer and artifacts as working standards under controlled environmental conditions on a manufacturing CNC milling machine. Polynomial regression analyses were carried out for finding the coefficients to predict the errors at each and every desired position which is quite useful for compensation and enhancing the accuracy of a machine system. Machine accuracy detailed chart was also made to assess and assure the accuracy, capability or for accuracy monitoring of the CNC milling machine
A New Wavelength Calibration Method for LAMOST Based on Piecewise Fitting
NASA Astrophysics Data System (ADS)
Ye, Gen-hong; Ye, Zhong-fu; Zhu, Jia
2014-04-01
The traditional methods of wavelength calibration for the LAM-OST (Large Area Multi-Object Fiber Spectroscopic Telescope) usually use a fifth-order polynomial to perform fitting and calibration in a broad wavelength range. Obviously, it is unable to reflect very well the local dispersion relations by using only one polynomial to fit the whole waveband. In order to reflect accurately the dispersion characteristics of local wavebands, a new wavelength calibration method based on piecewise fitting is proposed. In this method, the entire wavelength range is divided into several sub-bands according to certain principles, and a proper polynomial is used to perform fitting and calibration for each sub-band separately. Compared with the traditional methods of wave-length calibration, the experimental results show that this new method can get a more precise description of the dispersion characteristics of local wavebands. Therefore, the accuracy of wavelength calibration in the whole waveband will be further improved.
Analysis on the geometrical shape of T-honeycomb structure by finite element method (FEM)
NASA Astrophysics Data System (ADS)
Zain, Fitri; Rosli, Muhamad Farizuan; Effendi, M. S. M.; Abdullah, Mohamad Hariri
2017-09-01
Geometric in design is much related with our life. Each of the geometrical structure interacts with each other. The overall shape of an object contains other shape inside, and there shapes create a relationship between each other in space. Besides that, how geometry relates to the function of the object have to be considerate. In this project, the main purpose was to design the geometrical shape of modular furniture with the shrinking of Polyethylene Terephthalate (PET) jointing system that has good strength when applied load on it. But, the goal of this paper is focusing on the analysis of Static Cases by FEM of the hexagonal structure to obtain the strength when load apply on it. The review from the existing product has many information and very helpful to finish this paper. This project focuses on hexagonal shape that distributed to become a shelf inspired by honeycomb structure. It is very natural look and simple in shape and its modular structure more easily to separate and combine. The method discusses on chapter methodology are the method used to analysis the strength when the load applied to the structure. The software used to analysis the structure is Finite Element Method from CATIA V5R21 software. Bending test is done on the jointing part between the edges of the hexagonal shape by using Universal Tensile Machine (UTM). The data obtained have been calculate by bending test formulae and sketch the graph between flexural strains versus flexural stress. The material selection of the furniture is focused on wood. There are three different types of wood such as balsa, pine and oak, while the properties of jointing also be mentioned in this thesis. Hence, the design structural for honeycomb shape already have in the market but this design has main objective which has a good strength that can withstand maximum load and offers more potentials in the form of furniture.
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
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.
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
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.
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.
2017-11-01
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 20° separation of each channel with respect to nadir
The JCMT Transient Survey: Data Reduction and Calibration Methods
Mairs, Steve; Lane, James; Johnstone, Doug
2017-07-01
Though there has been a significant amount of work investigating the early stages of low-mass star formation in recent years, the evolution of the mass assembly rate onto the central protostar remains largely unconstrained. Examining in depth the variation in this rate is critical to understanding the physics of star formation. Instabilities in the outer and inner circumstellar disk can lead to episodic outbursts. Observing these brightness variations at infrared or submillimeter wavelengths constrains the current accretion models. The JCMT Transient Survey is a three-year project dedicated to studying the continuum variability of deeply embedded protostars in eight nearby star-formingmore » regions at a one-month cadence. We use the SCUBA-2 instrument to simultaneously observe these regions at wavelengths of 450 and 850 μ m. In this paper, we present the data reduction techniques, image alignment procedures, and relative flux calibration methods for 850 μ m data. We compare the properties and locations of bright, compact emission sources fitted with Gaussians over time. Doing so, we achieve a spatial alignment of better than 1″ between the repeated observations and an uncertainty of 2%–3% in the relative peak brightness of significant, localized emission. This combination of imaging performance is unprecedented in ground-based, single-dish submillimeter observations. Finally, we identify a few sources that show possible and confirmed brightness variations. These sources will be closely monitored and presented in further detail in additional studies throughout the duration of the survey.« less
Liu, Shoubin; Zhou, Yanming
2015-01-01
Because protons in fat do not exhibit a temperature-dependent frequency shift, proton resonance frequency shift (PRFS)-based MR thermometry always suffers from disturbances due to the presence of fats or lipids. A new fat suppression method for PRFS-based MR thermometry is proposed to obtain accurate variation of phase angle. Similar to the approach of separating fat and water with the two-point Dixon technique, we first scan a complex MR image for reference and then scan another complex image varying with temperature at the same TE point. Based on the conventional PRFS method, we use geometric relationships to remove the effect of fat on the variation of the phase angle. Two phantoms with different water-to-fat ratios are involved in the temperature mapping test. Experimental results show that the temperature images of two phantoms are approximated under the same conditions. The proposed fat suppression method is simple and effective for PRFS-based MR thermometry.
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
A Comparison Study of IRT Calibration Methods for Mixed-Format Tests in Vertical Scaling
ERIC Educational Resources Information Center
Meng, Huijuan
2007-01-01
The purpose of this dissertation was to investigate how different Item Response Theory (IRT)-based calibration methods affect student achievement growth pattern recovery. Ninety-six vertical scales (4 x 2 x 2 x 2 x 3) were constructed using different combinations of IRT calibration methods (separate, pair-wise concurrent, semi-concurrent, and…
Calibration methods of force sensors in the micro-Newton range
NASA Astrophysics Data System (ADS)
Nafari, Alexandra; Alavian Ghavanini, Farzan; Bring, Martin; Svensson, Krister; Enoksson, Peter
2007-10-01
A micromachined capacitive force sensor operating in the micro-Newton range has been calibrated using both dynamic and static methods. Both calibrations are non-destructive, accurate and traceable to Système International (SI) fundamental units. The dynamic calibration is a differential mass loading resonant method where the resonance frequency with and without an added mass is measured. This gives enough information to compute the spring constant. In this paper, we evaluate the resonant mass loading method for more complex MEMS devices. Analytical calculations and finite element analysis have been performed to investigate the dynamic properties of the sensor, e.g. modal interference. The frequency response was measured with the third harmonic method where the third harmonic of the current through the sensor was measured. To detect and analyse the resonance mode of the structure during excitation, a scanning laser Doppler vibrometer was used. Two designs of a capacitive nanoindenter force sensor with flexure-type springs have been evaluated using these methods. The quality of the resonant calibration method has been tested using static mass loading in combination with transmission electron microscopy imaging of the sensor displacement. This shows that the resonant method can be extended to calibrate more complex structures than plain cantilevers. Both calibration methods used are traceable to SI fundamental units as they are based on masses weighed on a calibrated scale. The masses used do not need to be fixed or glued in any way, making the calibration non-destructive.
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
Geometric shapes inversion method of space targets by ISAR image segmentation
NASA Astrophysics Data System (ADS)
Huo, Chao-ying; Xing, Xiao-yu; Yin, Hong-cheng; Li, Chen-guang; Zeng, Xiang-yun; Xu, Gao-gui
2017-11-01
The geometric shape of target is an effective characteristic in the process of space targets recognition. This paper proposed a method of shape inversion of space target based on components segmentation from ISAR image. The Radon transformation, Hough transformation, K-means clustering, triangulation will be introduced into ISAR image processing. Firstly, we use Radon transformation and edge detection to extract space target's main body spindle and solar panel spindle from ISAR image. Then the targets' main body, solar panel, rectangular and circular antenna are segmented from ISAR image based on image detection theory. Finally, the sizes of every structural component are computed. The effectiveness of this method is verified using typical targets' simulation data.
Digital calibration method for defects evaluation of large fine optical surfaces
NASA Astrophysics Data System (ADS)
Chen, Xiaoyu; Liu, Dong; Yang, Yongying; Yan, Lu; Li, Lu; Cao, Pin; Wang, Shitong; Shen, Yibing
2014-08-01
The digital calibration method, which is employed in the Surface Defects Evaluation System (SDES) for the defects evaluation of large fine optical surfaces, is presented in this paper. A criterion board, which comes from special design and careful fabrication, is employed to relate the dimensions of the defects and those of their images. The calibration procedure, including collecting of calibration images, digital image processing and calibration function fitting, is described in detail in this paper. Calibration experiments on scratch width and dig diameter were carried out at three different microscope magnification conditions. Experiment results show that following the proposed digital calibration method, micron-sized defects distributed sparsely on a large-aperture fine optical surface can be evaluated with micron accuracy and high efficiency.
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.
NASA Astrophysics Data System (ADS)
Kuznetsova, Y. S.; Vorobyev, N. A.; Trufanov, N. A.
2017-02-01
The fundamentals of the geometric immersion stress method for axisymmetric problems of elasticity theory have been stated. The geometric immersion method involves reduction of the initial problem for Clapeyron’s free form elastic body to an iteration sequence of elasticity theory problems on some canonical domain. The iteration procedure for the variational equation of the geometric immersion method has been stated, as well as its discrete analog construction technique suggested with the finite-element stress method for the axisymmetric problem of the elasticity theory in the cylindrical coordinates. A practical application of the method has been demonstrated by a test problem. A reasonably good fit between the stress fields definition and the numerical solution by the traditional finite-element displacement method has been obtained.
Calibration method for geometry relationships of nonoverlapping cameras using light planes
NASA Astrophysics Data System (ADS)
Liu, Qianzhe; Sun, Junhua; Zhao, Yuntao; Liu, Zhen
2013-07-01
In some computer vision applications, it is necessary to calibrate the geometry relationships of nonoverlapping cameras. However, due to lacking a common field of view, the calibration of this camera topology is quite difficult. A calibration method for nonoverlapping cameras is proposed and investigated. The proposed method utilizes several light planes, which can be generated by a line laser projector or a rotary laser level, as the calibration objects. The fact that local light planes available in different cameras are identical in global coordinates is used to recover the geometries. Results on both synthetic and real data show the validity and performance of the proposed method. The given method is simple and flexible, which can be used to calibrate geometry relationships of cameras located in large-scale space without expensive equipment such as theodolites and laser trackers.
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.
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.
Calibration of resistance factors for drilled shafts for the new FHWA design method.
DOT National Transportation Integrated Search
2013-01-01
The Load and Resistance Factor Design (LRFD) calibration of deep foundation in Louisiana was first completed for driven piles (LTRC Final Report 449) in May 2009 and then for drilled shafts using 1999 FHWA design method (ONeill and Reese method) (...
NASA Astrophysics Data System (ADS)
Talman, Richard
1999-10-01
Mechanics for the nonmathematician-a modern approach For physicists, mechanics is quite obviously geometric, yet the classical approach typically emphasizes abstract, mathematical formalism. Setting out to make mechanics both accessible and interesting for nonmathematicians, Richard Talman uses geometric methods to reveal qualitative aspects of the theory. He introduces concepts from differential geometry, differential forms, and tensor analysis, then applies them to areas of classical mechanics as well as other areas of physics, including optics, crystal diffraction, electromagnetism, relativity, and quantum mechanics. For easy reference, Dr. Talman treats separately Lagrangian, Hamiltonian, and Newtonian mechanics-exploring their geometric structure through vector fields, symplectic geometry, and gauge invariance respectively. Practical perturbative methods of approximation are also developed. Geometric Mechanics features illustrative examples and assumes only basic knowledge of Lagrangian mechanics. Of related interest . . . APPLIED DYNAMICS With Applications to Multibody and Mechatronic Systems Francis C. Moon A contemporary look at dynamics at an intermediate level, including nonlinear and chaotic dynamics. 1998 (0-471-13828-2) 504 pp. MATHEMATICAL PHYSICS Applied Mathematics for Scientists and Engineers Bruce Kusse and Erik Westwig A comprehensive treatment of the mathematical methods used to solve practical problems in physics and engineering. 1998 (0-471-15431-8) 680 pp.
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.
Habte, Aron; Sengupta, Manajit; Andreas, Afshin
2016-11-21
Banks financing solar energy projects require assurance that these systems will produce the energy predicted. Furthermore, utility planners and grid system operators need to understand the impact of the variable solar resource on solar energy conversion system performance. Accurate solar radiation data sets reduce the expense associated with mitigating performance risk and assist in understanding the impacts of solar resource variability. The accuracy of solar radiation measured by radiometers depends on the instrument performance specification, installation method, calibration procedure, measurement conditions, maintenance practices, location, and environmental conditions. This study addresses the effect of different calibration methods provided by radiometric calibrationmore » service providers, such as NREL and manufacturers of radiometers, on the resulting calibration responsivity. Some of these radiometers are calibrated indoors and some outdoors. To establish or understand the differences in calibration methodology, we processed and analyzed field-measured data from these radiometers. This study investigates calibration responsivities provided by NREL's broadband outdoor radiometer calibration (BORCAL) and a few prominent manufacturers. The BORCAL method provides the outdoor calibration responsivity of pyranometers and pyrheliometers at 45 degree solar zenith angle, and as a function of solar zenith angle determined by clear-sky comparisons with reference irradiance. The BORCAL method also employs a thermal offset correction to the calibration responsivity of single-black thermopile detectors used in pyranometers. Indoor calibrations of radiometers by their manufacturers are performed using a stable artificial light source in a side-by-side comparison between the test radiometer under calibration and a reference radiometer of the same type. In both methods, the reference radiometer calibrations are traceable to the World Radiometric Reference (WRR). These
An automated calibration method for non-see-through head mounted displays
Gilson, Stuart J.; Fitzgibbon, Andrew W.; Glennerster, Andrew
2011-01-01
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
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. Copyright © 2011 Elsevier B.V. All rights reserved.
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…
NASA Astrophysics Data System (ADS)
Brezina, Tadej; Graser, Anita; Leth, Ulrich
2017-04-01
Space, and in particular public space for movement and leisure, is a valuable and scarce resource, especially in today's growing urban centres. The distribution and absolute amount of urban space—especially the provision of sufficient pedestrian areas, such as sidewalks—is considered crucial for shaping living and mobility options as well as transport choices. Ubiquitous urban data collection and today's IT capabilities offer new possibilities for providing a relation-preserving overview and for keeping track of infrastructure changes. This paper presents three novel methods for estimating representative sidewalk widths and applies them to the official Viennese streetscape surface database. The first two methods use individual pedestrian area polygons and their geometrical representations of minimum circumscribing and maximum inscribing circles to derive a representative width of these individual surfaces. The third method utilizes aggregated pedestrian areas within the buffered street axis and results in a representative width for the corresponding road axis segment. Results are displayed as city-wide means in a 500 by 500 m grid and spatial autocorrelation based on Moran's I is studied. We also compare the results between methods as well as to previous research, existing databases and guideline requirements on sidewalk widths. Finally, we discuss possible applications of these methods for monitoring and regression analysis and suggest future methodological improvements for increased accuracy.
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.
A calibration method based on virtual large planar target for cameras with large FOV
NASA Astrophysics Data System (ADS)
Yu, Lei; Han, Yangyang; Nie, Hong; Ou, Qiaofeng; Xiong, Bangshu
2018-02-01
In order to obtain high precision in camera calibration, a target should be large enough to cover the whole field of view (FOV). For cameras with large FOV, using a small target will seriously reduce the precision of calibration. However, using a large target causes many difficulties in making, carrying and employing the large target. In order to solve this problem, a calibration method based on the virtual large planar target (VLPT), which is virtually constructed with multiple small targets (STs), is proposed for cameras with large FOV. In the VLPT-based calibration method, first, the positions and directions of STs are changed several times to obtain a number of calibration images. Secondly, the VLPT of each calibration image is created by finding the virtual point corresponding to the feature points of the STs. Finally, intrinsic and extrinsic parameters of the camera are calculated by using the VLPTs. Experiment results show that the proposed method can not only achieve the similar calibration precision as those employing a large target, but also have good stability in the whole measurement area. Thus, the difficulties to accurately calibrate cameras with large FOV can be perfectly tackled by the proposed method with good operability.
An Effective Optimization Method for Initial Wavelength Calibration of LAMOST Based on PSO
NASA Astrophysics Data System (ADS)
Wang, S.; Zhu, Z. Q.; Zhu, J.; Ye, G. H.; Ye, Z. F.
2011-09-01
The initial wavelength calibration procedure of Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) consists of three steps. Firstly, for each certain point in the search space near the prior calibration coefficients, its corresponding simulation arc spectrum could be obtained with the interpolation method. Then, the cross correlation between the simulation arc spectrum and the observed one will be calculated. Finally, the result of initial wavelength calibration is the calibration coefficient corresponding to the maximum correlation coefficient. Thus, multi-parameter optimization problem is essential in the calibration procedure. Particle swarm optimization (PSO) is a stochastic global optimization algorithm that is based on swarm intelligence. It has the advantages of easy to implement, high accuracy and fast convergence. Considering the excellent performance of PSO, we propose an optimization method for initial wavelength calibration of LAMOST based on PSO, and design the corresponding algorithm and the initial wavelength calibration test experiments. The experimental results show that the proposed PSO-based algorithm outperforms the improved genetic algorithm in terms of convergence speed, solution quality and CPU time. Therefore, the proposed method is a more effective method for initial wavelength calibration.
ERIC Educational Resources Information Center
Chen, Ping
2017-01-01
Calibration of new items online has been an important topic in item replenishment for multidimensional computerized adaptive testing (MCAT). Several online calibration methods have been proposed for MCAT, such as multidimensional "one expectation-maximization (EM) cycle" (M-OEM) and multidimensional "multiple EM cycles"…
Two-step camera calibration method based on the SPGD algorithm.
Qi, Zhaohui; Xiao, Longxu; Fu, Sihua; Li, Tan; Jiang, Guangwen; Long, Xuejun
2012-09-10
Given the rapid convergence characteristic of the stochastic parallel gradient descent (SPGD) algorithm, this study proposes a method that applies the algorithm to a two-step camera calibration method to resolve the frequent iteration and long calibration time deficiencies that exist under the traditional two-step camera calibration method, thereby achieving rapid calibration. The method first uses image coordinates obtained with subpixel positioning technology as initial values of control variables, in addition to positive disturbances produced on a two-dimensional plane, then uses two-step theory to calculate the average value of aberrations. Based on the same rationale, negative disturbances are then produced and the average value of the aberrations is calculated. Finally if, after assessing whether to continue with further iterations based on the difference in these values, continued iterations confirm new control variables based on the SPGD algorithm iteration formula, a new cycle is started until the results satisfy requirements. Theoretical analysis and experimental results show that the proposed rapid calibration method using the SPGD algorithm in the two-step camera calibration method is 3-4 times faster than the traditional two-step calibration method, and that it has significant potential value for use in certain time-constrained projects.
Scalable smoothing strategies for a geometric multigrid method for the immersed boundary equations
Bhalla, Amneet Pal Singh; Knepley, Matthew G.; Adams, Mark F.; Guy, Robert D.; Griffith, Boyce E.
2016-12-20
The immersed boundary (IB) method is a widely used approach to simulating fluid-structure interaction (FSI). Although explicit versions of the IB method can suffer from severe time step size restrictions, these methods remain popular because of their simplicity and generality. In prior work (Guy et al., Adv Comput Math, 2015), some of us developed a geometric multigrid preconditioner for a stable semi-implicit IB method under Stokes flow conditions; however, this solver methodology used a Vanka-type smoother that presented limited opportunities for parallelization. This work extends this Stokes-IB solver methodology by developing smoothing techniques that are suitable for parallel implementation. Specifically, we demonstrate that an additive version of the Vanka smoother can yield an effective multigrid preconditioner for the Stokes-IB equations, and we introduce an efficient Schur complement-based smoother that is also shown to be effective for the Stokes-IB equations. We investigate the performance of these solvers for a broad range of material stiffnesses, both for Stokes flows and flows at nonzero Reynolds numbers, and for thick and thin structural models. We show here that linear solver performance degrades with increasing Reynolds number and material stiffness, especially for thin interface cases. Nonetheless, the proposed approaches promise to yield effective solution algorithms, especially at lower Reynolds numbers and at modest-to-high elastic stiffnesses.
Scalable smoothing strategies for a geometric multigrid method for the immersed boundary equations
Bhalla, Amneet Pal Singh; Knepley, Matthew G.; Adams, Mark F.
2016-12-20
The immersed boundary (IB) method is a widely used approach to simulating fluid-structure interaction (FSI). Although explicit versions of the IB method can suffer from severe time step size restrictions, these methods remain popular because of their simplicity and generality. In prior work (Guy et al., Adv Comput Math, 2015), some of us developed a geometric multigrid preconditioner for a stable semi-implicit IB method under Stokes flow conditions; however, this solver methodology used a Vanka-type smoother that presented limited opportunities for parallelization. This work extends this Stokes-IB solver methodology by developing smoothing techniques that are suitable for parallel implementation. Specifically,more » we demonstrate that an additive version of the Vanka smoother can yield an effective multigrid preconditioner for the Stokes-IB equations, and we introduce an efficient Schur complement-based smoother that is also shown to be effective for the Stokes-IB equations. We investigate the performance of these solvers for a broad range of material stiffnesses, both for Stokes flows and flows at nonzero Reynolds numbers, and for thick and thin structural models. We show here that linear solver performance degrades with increasing Reynolds number and material stiffness, especially for thin interface cases. Nonetheless, the proposed approaches promise to yield effective solution algorithms, especially at lower Reynolds numbers and at modest-to-high elastic stiffnesses.« less
ISS Payload Racks Automated Flow Control Calibration Method
NASA Technical Reports Server (NTRS)
Simmonds, Boris G.
2003-01-01
Payload Racks utilize MTL and/or LTL station water for cooling of payloads and avionics. Flow control range from valves of fully closed, to up to 300 Ibmhr. Instrument accuracies are as high as f 7.5 Ibm/hr for flow sensors and f 3 Ibm/hr for valve controller, for a total system accuracy of f 10.5 Ibm/hr. Improved methodology was developed, tested and proven that reduces accuracy of the commanded flows to less than f 1 Ibmhr. Uethodology could be packed in a "calibration kit" for on- orbit flow sensor checkout and recalibration, extending the rack operations before return to earth. -
A method for soil moisture probes calibration and validation of satellite estimates.
Holzman, Mauro; Rivas, Raúl; Carmona, Facundo; Niclòs, Raquel
2017-01-01
Optimization of field techniques is crucial to ensure high quality soil moisture data. The aim of the work is to present a sampling method for undisturbed soil and soil water content to calibrated soil moisture probes, in a context of the SMOS (Soil Moisture and Ocean Salinity) mission MIRAS Level 2 soil moisture product validation in Pampean Region of Argentina. The method avoids soil alteration and is recommended to calibrated probes based on soil type under a freely drying process at ambient temperature. A detailed explanation of field and laboratory procedures to obtain reference soil moisture is shown. The calibration results reflected accurate operation for the Delta-T thetaProbe ML2x probes in most of analyzed cases (RMSE and bias ≤ 0.05 m3/m3). Post-calibration results indicated that the accuracy improves significantly applying the adjustments of the calibration based on soil types (RMSE ≤ 0.022 m3/m3, bias ≤ -0.010 m3/m3). •A sampling method that provides high quality data of soil water content for calibration of probes is described.•Importance of calibration based on soil types.•A calibration process for similar soil types could be suitable in practical terms, depending on the required accuracy level.
Reciprocity Calibration of an Underwater Transducer by the Delta-Z Method.
1987-12-01
GtASILECTE FEB2 THESIS RECIPROCITY CALIBRATION OF AN UNDERWATER TRANSDUCER BY THE DELTA-Z METHOD by Raynald Bedard December 1987 Thesis advisor: S.R. Baker...ACCESSION NO. RECIPROCITY CALIBRATION OF AN UNDERWATER TRANSDUCER USING THE DELTA-Z METHOD 12. PERSONAL AUTHOR(S) 16 SUPPLEMENTARY NOTATION thor tak s itoD...Calibration of an Underwater Transducer by the Delta-Z Method by Raynald Bdard Major, Canadian Forces B.Eng., Royal Military College, 1980 Submitted in
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.
Simulation of Ultrasound in Tomographic Imaging: Theory and Methods Based on Geometrical Acoustics.
NASA Astrophysics Data System (ADS)
Brandenburger, Gary H.
Imaging based upon ultrasound has found extensive application both in medicine for non-invasive diagnosis and in industry for the nondestructive testing of materials. Present commercially available devices are capable of producing images primarily of the geometry of objects (internal shapes and boundaries). A goal for the next generation of ultrasonic imaging devices is the additional capability of depicting, quantitatively, mechanical properties of the tissue or materials under investigation. To achieve this goal, researchers must: (i) identify measurable acoustic parameters capable of characterizing meaningful mechanical properties; and (ii) develop methods for producing quantitative images based upon these parameters. A major stumbling block in quantitative imaging is incomplete understanding of the interaction between imaging methods and the physics of acoustic propagation and measurement. The goal of this thesis is the development of theory and methods for studying this interaction. To study this interaction, methods are developed for simulating the measurements associated with computed ultrasonic transmission tomography based on ultrasonic attenuation. Modern geometrical acoustics theory is applied and novel simulation methods are developed. In conjunction with this, a general theory of discontinuities in partial differential equations is developed. The result is a novel set of rules for transforming first-order linear partial differential equations into corresponding sets of constraints on the surface of the discontinuity. Both the accuracy and the limitations of the method for simulation of measurements of ultrasonic attenuation are demonstrated by comparison with experiment. The simulation is then used to investigate the effects of inhomogeneities on ultrasound measurements. Such results would be difficult to achieve experimentally. Various sources of error in ultrasonic imaging are assessed, and are rank ordered according to their severity. These methods
Honda, Michitaka
2014-04-01
Several improvements were implemented in the edge method of presampled modulation transfer function measurements (MTFs). The estimation technique for edge angle was newly developed by applying an algorithm for principal components analysis. The error in the estimation was statistically confirmed to be less than 0.01 even in the presence of quantum noise. Secondly, the geometrical edge slope was approximated using a rationalized number, making it possible to obtain an oversampled edge response function (ESF) with equal intervals. Thirdly, the final MTFs were estimated using the average of multiple MTFs calculated for local areas. This averaging operation eliminates the errors caused by the rationalized approximation. Computer-simulated images were used to evaluate the accuracy of our method. The relative error between the estimated MTF and the theoretical MTF at the Nyquist frequency was less than 0.5% when the MTF was expressed as a sinc function. For MTFs representing an indirect detector and phase-contrast detector, good agreement was also observed for the estimated MTFs for each. The high accuracy of the MTF estimation was also confirmed, even for edge angles of around 10 degrees, which suggests the potential for simplification of the measurement conditions. The proposed method could be incorporated into an automated measurement technique using a software application.
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.
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
In-flight absolute radiometric calibration of MODIS using the irradiance-based method
NASA Astrophysics Data System (ADS)
Wei, Wei; Li, Xin; Zhao, Chun-yan; Qiu, Gang-gang; Zheng, Xiao-bing
2016-10-01
In order to reduce the calibration uncertainty of the reflectance-based method brought by the assumption of the aerosol model, the irradiance-based method, known as improved reflectance-based method, was proposed. The irradiance-based method is described in this paper. The radiometric calibration field campaign was performed at Dunhuang test site on 27 August, 2014. A hyperspectral irradiance meter (HSIM) developed by Anhui Institute of Optics and Fine Mechanics (AIOFM) was used to measure the diffuse-to-global spectral irradiance ratio. The irradiance-based method and the reflectance-based method were performed to calibrate the first four bands of Moderate Resolution Imaging Spectroradiometer (MODIS). The results of two methods were compared with result of MODIS on-board calibrator. The comparison shows that the result of irradiance-based method has a good consistency with on-board calibration and reflectance-based method results. The difference of calibration coefficients between irradiance-based and on-board method was less than 1.4%. Due to the limitations of the irradiance-based method, a clear sky and stable atmospheric condition is required for the entire half of the calibration day to provide the data necessary for the extrapolation of diffuse-to-global ratio in viewing direction. A study on the effects of aerosol mode assumption on the final apparent reflectance was performed on both the irradiance-based method and the reflectance-based method by selecting different aerosol modes to predict the apparent reflectance. The results show that aerosol mode assumption has a great effect on the reflectance-based method, however slight effect on the irradiance-based method.
Burke, Sienna R; Rogers, Abigail R; Neely, Stephen T; Kopun, Judy G; Tan, Hongyang; Gorga, Michael P
2010-08-01
Calibration errors in distortion-product otoacoustic emission (DPOAE) measurements because of standing waves cause unpredictable changes in stimulus and DPOAE response level. The purpose of this study was to assess the extent to which these errors affect DPOAE test performance. Standard calibration procedures use sound pressure level (SPL) to determine specified levels. Forward pressure level (FPL) is an alternate calibration method that is less susceptible to standing waves. However, FPL derivation requires prior cavity measurements, which have associated variability. In an attempt to address this variability, four FPL methods were compared with SPL: a reference calibration derived from 25 measurements before all data collection and a daily calibration measurement, both of which were made at body and room temperature. Data were collected from 52 normal-hearing and 103 hearing-impaired subjects. DPOAEs were measured for f2 frequencies ranging from 2 to 8 kHz in half-octave steps, with L2 ranging from -20 to 70 dB SPL (5-dB steps). At each f2, DPOAEs were measured in five calibration conditions: SPL, daily FPL at body temperature (daily body), daily FPL at room temperature (daily room), reference FPL at body temperature (ref body), and reference FPL at room temperature (ref room). Data were used to construct receiver operating characteristic (ROC) curves for each f2, calibration method, and L2. From these curves, areas under the ROC curve (AROC) were estimated. The results of this study are summarized by the following observations: (1) DPOAE test performance was sensitive to stimulus level, regardless of calibration method, with the best test performance observed for moderate stimulus level conditions. (2) An effect of frequency was observed for all calibration methods, with the best test performance at 6 kHz and the worst performance at 8 kHz. (3) At clinically applicable stimulus levels, little difference in test performance among calibration methods was noted
New methods to calibrate simulation parameters for chemically amplified resists
NASA Astrophysics Data System (ADS)
Tollkuehn, Bernd; Erdmann, Andreas; Kivel, Niko; Robertson, Stewart A.; Kang, Doris; Hansen, Steven G.; Fumar-Pici, Anita; Chiou, Tsann-Bim; Hoppe, Wolfgang
2002-07-01
In this paper we examine new models and the indispensability of model parameters of chemically amplified resists (CAR) for their usage in predictive process simulation. Based on a careful exploration of different modeling options we calibrate the model parameters with different experimental data. Furthermore, we investigate different modeling approaches: (1) Mode of coupling between diffusion and kinetic reactions, sequence of quencher base events (Hinsberg model); (2) Mode of diffusion: Fickian and linear diffusion model; (3) Development rate model: Performance of the Enhanced Notch model. The resulting models are evaluated with respect to their performance by comparing with experimental line-width for semidense (1-2, 1-1.6, 1-1.4, 1-1.2) and dense features, the bias between different features and full resist profiles. The investigations are applied to the Shipley resist UVTM 113. Finally, a parameter extraction procedure for chemically amplified resists is proposed.
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.
Zhang, Zhi-Feng; Gao, Zhan; Liu, Yuan-Yuan; Jiang, Feng-Chun; Yang, Yan-Li; Ren, Yu-Fen; Yang, Hong-Jun; Yang, Kun; Zhang, Xiao-Dong
2012-01-01
Train wheel sets must be periodically inspected for possible or actual premature failures and it is very significant to record the wear history for the full life of utilization of wheel sets. This means that an online measuring system could be of great benefit to overall process control. An online non-contact method for measuring a wheel set's geometric parameters based on the opto-electronic measuring technique is presented in this paper. A charge coupled device (CCD) camera with a selected optical lens and a frame grabber was used to capture the image of the light profile of the wheel set illuminated by a linear laser. The analogue signals of the image were transformed into corresponding digital grey level values. The 'mapping function method' is used to transform an image pixel coordinate to a space coordinate. The images of wheel sets were captured when the train passed through the measuring system. The rim inside thickness and flange thickness were measured and analyzed. The spatial resolution of the whole image capturing system is about 0.33 mm. Theoretic and experimental results show that the online measurement system based on computer vision can meet wheel set measurement requirements.
Emery, K.A.; Waddington, D.; Rummel, S.
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 amore » +-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.« less
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. © The Author(s) 2016.
[Study of preparation of the calibration standard for the crustacean protein detection method].
Seiki, Kosuke; Oda, Hiroshi; Shibahara, Yuusuke; Gamo, Reiko; Arima, Masami; Sakai, Shinobu; Nakamura, Atsushi; Adachi, Reiko; Shiomi, Kazuo; Akiyama, Hiroshi; Teshima, Reiko
2010-01-01
We examined the preparation method of the calibration standard for an ELISA kit for measuring crustacean protein in food products. The initial extract of the calibration standard was stabilized by addition of protease inhibitor to the extracting solution and heating at 100 degrees C for 10 min. In accordance with the preparation procedure for calibrators, we prepared 3 lots of initial extract of calibration standard and analyzed the protein concentration and SDS-electrophoretic pattern. Single bands at 160, 41, 37 kDa and 4 bands in the range of 16-20 kDa were observed on SDS-PAGE. The range of protein concentration of the initial extract of the calibration standard was 2.74-4.10 mg/mL.
Novel Method for Processing the Dynamic Calibration Signal of Pressure Sensor.
Wang, Zhongyu; Li, Qiang; Wang, Zhuoran; Yan, Hu
2015-07-21
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.
Holland, Rebecca; Underwood, Sarah; Fairlie, Jennifer; Psifidi, Androniki; Ilska, Joanna J.; Bagnall, Ainsley; Whitelaw, Bruce; Coffey, Mike; Banos, Georgios; Nussey, Daniel H.
2016-01-01
Telomere length (TL) is increasingly being used as a biomarker in epidemiological, biomedical and ecological studies. A wide range of DNA extraction techniques have been used in telomere experiments and recent quantitative PCR (qPCR) based studies suggest that the choice of DNA extraction method may influence average relative TL (RTL) measurements. Such extraction method effects may limit the use of historically collected DNA samples extracted with different methods. However, if extraction method effects are systematic an extraction method specific (MS) calibrator might be able to correct for them, because systematic effects would influence the calibrator sample in the same way as all other samples. In the present study we tested whether leukocyte RTL in blood samples from Holstein Friesian cattle and Soay sheep measured by qPCR was influenced by DNA extraction method and whether MS calibration could account for any observed differences. We compared two silica membrane-based DNA extraction kits and a salting out method. All extraction methods were optimized to yield enough high quality DNA for TL measurement. In both species we found that silica membrane-based DNA extraction methods produced shorter RTL measurements than the non-membrane-based method when calibrated against an identical calibrator. However, these differences were not statistically detectable when a MS calibrator was used to calculate RTL. This approach produced RTL measurements that were highly correlated across extraction methods (r > 0.76) and had coefficients of variation lower than 10% across plates of identical samples extracted by different methods. Our results are consistent with previous findings that popular membrane-based DNA extraction methods may lead to shorter RTL measurements than non-membrane-based methods. However, we also demonstrate that these differences can be accounted for by using an extraction method-specific calibrator, offering researchers a simple means of accounting for
Seeker, Luise A; Holland, Rebecca; Underwood, Sarah; Fairlie, Jennifer; Psifidi, Androniki; Ilska, Joanna J; Bagnall, Ainsley; Whitelaw, Bruce; Coffey, Mike; Banos, Georgios; Nussey, Daniel H
2016-01-01
Telomere length (TL) is increasingly being used as a biomarker in epidemiological, biomedical and ecological studies. A wide range of DNA extraction techniques have been used in telomere experiments and recent quantitative PCR (qPCR) based studies suggest that the choice of DNA extraction method may influence average relative TL (RTL) measurements. Such extraction method effects may limit the use of historically collected DNA samples extracted with different methods. However, if extraction method effects are systematic an extraction method specific (MS) calibrator might be able to correct for them, because systematic effects would influence the calibrator sample in the same way as all other samples. In the present study we tested whether leukocyte RTL in blood samples from Holstein Friesian cattle and Soay sheep measured by qPCR was influenced by DNA extraction method and whether MS calibration could account for any observed differences. We compared two silica membrane-based DNA extraction kits and a salting out method. All extraction methods were optimized to yield enough high quality DNA for TL measurement. In both species we found that silica membrane-based DNA extraction methods produced shorter RTL measurements than the non-membrane-based method when calibrated against an identical calibrator. However, these differences were not statistically detectable when a MS calibrator was used to calculate RTL. This approach produced RTL measurements that were highly correlated across extraction methods (r > 0.76) and had coefficients of variation lower than 10% across plates of identical samples extracted by different methods. Our results are consistent with previous findings that popular membrane-based DNA extraction methods may lead to shorter RTL measurements than non-membrane-based methods. However, we also demonstrate that these differences can be accounted for by using an extraction method-specific calibrator, offering researchers a simple means of accounting for
Quantitative calibration of sound pressure in ultrasonic standing waves using the Schlieren method.
Xu, Zheng; Chen, Hao; Yan, Xu; Qian, Menglu; Cheng, Qian
2017-08-21
We investigated the use of the Schlieren method to calibrate the sound pressure in an ultrasonic standing-wave field. Specifically, we derived an equation to calculate the light intensity of the diffraction fringe induced by the standing-wave field. The results indicated that the sound pressure in the standing-wave field relates to the light intensity of the diffraction fringe. Simulations and experiments were conducted to verify the theoretical calculation. We demonstrated that the ratio of the light intensity of different diffraction orders relates to the sound pressure amplitude, allowing the pressure amplitude to be calibrated with the Schlieren method. Therefore, this work presents a non-intrusive calibration method that is particularly suitable for calibrating high-frequency ultrasonic standing-wave fields.
Shen, Jesse; Kadoury, Samuel; Labelle, Hubert; Roy-Beaudry, Marjolaine; Aubin, Carl-Éric; Parent, Stefan
2017-05-01
Consecutive case series. To study geometric torsion in thoracic adolescent idiopathic scoliosis (AIS) to propose it as a numerical three-dimensional (3D) parameter that quantifies the scoliosis deformity. AIS is a 3D deformity of the spine. The most widely accepted and used classification systems, however, still rely on two-dimensional aspects of x-rays. Yet, a 3D classification of AIS remains elusive because there is no widely accepted 3D parameter in the clinical practice. Analysis of 141 patients with Lenke type-1 deformity recruited in our institution. The Lenke classification was identified by two observers and 3D reconstructions were obtained using biplanar radiographs. Geometric torsion measuring the twisting effect of the spine was computed using a novel technique by approximating local arc lengths at the neutral vertebra in the thoracolumbar segment. An inter- and intragroup statistical analysis was performed to evaluate the torsion index, and how it relates to other 3D indices. A statistically significant increase in torsion was observed between Lenke 1A (1.15 mm) and Lenke 1C (2.10 mm) subgroups. No differences were found between the Lenke 1B (1.75 mm) subgroup with either of the other two subgroups. An automatic classification based on torsion indices identified two groups: one with high torsion values (3.02 mm) and one with low torsion values (0.82 mm). Statistically significant differences were found between the main thoracic planes of maximum curvature (PMC) orientation of the high-torsion group (73.72°) and the low-torsion group (79.85°). Statistically significant differences were also found for the thoracolumbar/lumbar PMC orientation between the high-torsion group (56.41°) and the low-torsion group (49.25°). These results suggest that a numerical method of describing scoliosis in 3D is within reach. They also suggest the existence of two subgroups of 3D deformations based on torsion values (high and low) with links to PMC orientation
Zhang, Zhi-Feng; Gao, Zhan; Liu, Yuan-Yuan; Jiang, Feng-Chun; Yang, Yan-Li; Ren, Yu-Fen; Yang, Hong-Jun; Yang, Kun; Zhang, Xiao-Dong
2012-01-01
Train wheel sets must be periodically inspected for possible or actual premature failures and it is very significant to record the wear history for the full life of utilization of wheel sets. This means that an online measuring system could be of great benefit to overall process control. An online non-contact method for measuring a wheel set’s geometric parameters based on the opto-electronic measuring technique is presented in this paper. A charge coupled device (CCD) camera with a selected optical lens and a frame grabber was used to capture the image of the light profile of the wheel set illuminated by a linear laser. The analogue signals of the image were transformed into corresponding digital grey level values. The ‘mapping function method’ is used to transform an image pixel coordinate to a space coordinate. The images of wheel sets were captured when the train passed through the measuring system. The rim inside thickness and flange thickness were measured and analyzed. The spatial resolution of the whole image capturing system is about 0.33 mm. Theoretic and experimental results show that the online measurement system based on computer vision can meet wheel set measurement requirements. PMID:22368472
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.
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.
Calibration with confidence: a principled method for panel assessment
MacKay, R. S.; Low, R. J.; Parker, S.
2017-01-01
Frequently, a set of objects has to be evaluated by a panel of assessors, but not every object is assessed by every assessor. A problem facing such panels is how to take into account different standards among panel members and varying levels of confidence in their scores. Here, a mathematically based algorithm is developed to calibrate the scores of such assessors, addressing both of these issues. The algorithm is based on the connectivity of the graph of assessors and objects evaluated, incorporating declared confidences as weights on its edges. If the graph is sufficiently well connected, relative standards can be inferred by comparing how assessors rate objects they assess in common, weighted by the levels of confidence of each assessment. By removing these biases, ‘true’ values are inferred for all the objects. Reliability estimates for the resulting values are obtained. The algorithm is tested in two case studies: one by computer simulation and another based on realistic evaluation data. The process is compared to the simple averaging procedure in widespread use, and to Fisher's additive incomplete block analysis. It is anticipated that the algorithm will prove useful in a wide variety of situations such as evaluation of the quality of research submitted to national assessment exercises; appraisal of grant proposals submitted to funding panels; ranking of job applicants; and judgement of performances on degree courses wherein candidates can choose from lists of options. PMID:28386432
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.
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)
Burk, D. R.; Mackey, K. G.; Hartse, H. E.
2016-12-01
We have developed a simplified field calibration method for use in seismic networks that still employ the classical electro-mechanical seismometer. Smaller networks may not always have the financial capability to purchase and operate modern, state of the art equipment. Therefore these networks generally operate a modern, low-cost digitizer that is paired to an existing electro-mechanical seismometer. These systems are typically poorly calibrated. Calibration of the station is difficult to estimate because coil loading, digitizer input impedance, and amplifier gain differences vary by station and digitizer model. Therefore, it is necessary to calibrate the station channel as a complete system to take into account all components from instrument, to amplifier, to even the digitizer. Routine calibrations at the smaller networks are not always consistent, because existing calibration techniques require either specialized equipment or significant technical expertise. To improve station data quality at the small network, we developed a calibration method that utilizes open source software and a commonly available laser position sensor. Using a signal generator and a small excitation coil, we force the mass of the instrument to oscillate at various frequencies across its operating range. We then compare the channel voltage output to the laser-measured mass displacement to determine the instrument voltage sensitivity at each frequency point. Using the standard equations of forced motion, a representation of the calibration curve as a function of voltage per unit of ground velocity is calculated. A computer algorithm optimizes the curve and then translates the instrument response into a Seismic Analysis Code (SAC) poles & zeros format. Results have been demonstrated to fall within a few percent of a standard laboratory calibration. This method is an effective and affordable option for networks that employ electro-mechanical seismometers, and it is currently being deployed in
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.
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 themore » 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
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. Copyright © 2015 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
NASA Astrophysics Data System (ADS)
Pang, Hongfeng; Zhu, XueJun; Pan, Mengchun; Zhang, Qi; Wan, Chengbiao; Luo, Shitu; Chen, Dixiang; Chen, Jinfei; Li, Ji; Lv, Yunxiao
2016-12-01
Misalignment error is one key factor influencing the measurement accuracy of geomagnetic vector measurement system, which should be calibrated with the difficulties that sensors measure different physical information and coordinates are invisible. A new misalignment calibration method by rotating a parallelepiped frame is proposed. Simulation and experiment result show the effectiveness of calibration method. The experimental system mainly contains DM-050 three-axis fluxgate magnetometer, INS (inertia navigation system), aluminium parallelepiped frame, aluminium plane base. Misalignment angles are calculated by measured data of magnetometer and INS after rotating the aluminium parallelepiped frame on aluminium plane base. After calibration, RMS error of geomagnetic north, vertical and east are reduced from 349.441 nT, 392.530 nT and 562.316 nT to 40.130 nT, 91.586 nT and 141.989 nT respectively.
Novel Local Calibration Method for Chemical Oxygen Demand Measurements by Using UV-Vis Spectrometry
NASA Astrophysics Data System (ADS)
Yingtian, Hu; Chao, Liu; Xiaoping, Wang
2017-05-01
In recent years, ultraviolet-visible spectroscopy has been widely used for chemical oxygen demand (COD) measurements of water. However, chemical compositions of substance in different water samples can cause measurement deviations, so a local calibration is needed. In this study, a novel local calibration method is proposed. The absorption spectra of COD standard solutions and wastewater samples taken from four factories were collected. We analyzed the impact of chemical compositions of substance in different water samples and extracted the morphology features of their absorptive spectra for recognition models. Furthermore, we calculated the local calibration parameters of the four categories of real water samples by specific modification based on the ability of light absorption in various water environments. After the process of local calibration, the root mean square errors (RMSEs) of the predictions were very small, which highlights the potential of this method for improving the accuracy and adaptability of COD measurements based on ultraviolet-visible spectrum.
Comparison of calibration methods for accelerometers used in human motion analysis.
Nez, Alexis; Fradet, Laetitia; Laguillaumie, Pierre; Monnet, Tony; Lacouture, Patrick
2016-11-01
In the fields of medicine and biomechanics, MEMS accelerometers are increasingly used to perform activity recognition by directly measuring acceleration; to calculate speed and position by numerical integration of the signal; or to estimate the orientation of body parts in combination with gyroscopes. For some of these applications, a highly accurate estimation of the acceleration is required. Many authors suggest improving result accuracy by updating sensor calibration parameters. Yet navigating the vast array of published calibration methods can be confusing. In this context, this paper reviews and evaluates the main measurement models and calibration methods. It also gives useful recommendations for better selection of a calibration process with regard to a specific application, which boils down to a compromise between accuracy, required installation, algorithm complexity, and time. Copyright © 2016 IPEM. Published by Elsevier Ltd. All rights reserved.
Lotfy, Hayam M; Saleh, Sarah S; Hassan, Nagiba Y; Salem, Hesham
2015-01-01
Novel spectrophotometric methods were applied for the determination of the minor component tetryzoline HCl (TZH) in its ternary mixture with ofloxacin (OFX) and prednisolone acetate (PA) in the ratio of (1:5:7.5), and in its binary mixture with sodium cromoglicate (SCG) in the ratio of (1:80). The novel spectrophotometric methods determined the minor component (TZH) successfully in the two selected mixtures by computing the geometrical relationship of either standard addition or subtraction. The novel spectrophotometric methods are: geometrical amplitude modulation (GAM), geometrical induced amplitude modulation (GIAM), ratio H-point standard addition method (RHPSAM) and compensated area under the curve (CAUC). The proposed methods were successfully applied for the determination of the minor component TZH below its concentration range. The methods were validated as per ICH guidelines where accuracy, repeatability, inter-day precision and robustness were found to be within the acceptable limits. The results obtained from the proposed methods were statistically compared with official ones where no significant difference was observed. No difference was observed between the obtained results when compared to the reported HPLC method, which proved that the developed methods could be alternative to HPLC techniques in quality control laboratories. Copyright © 2015 Elsevier B.V. All rights reserved.
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.
A new method to calibrate the absolute sensitivity of a soft X-ray streak camera
NASA Astrophysics Data System (ADS)
Yu, Jian; Liu, Shenye; Li, Jin; Yang, Zhiwen; Chen, Ming; Guo, Luting; Yao, Li; Xiao, Shali
2016-12-01
In this paper, we introduce a new method to calibrate the absolute sensitivity of a soft X-ray streak camera (SXRSC). The calibrations are done in the static mode by using a small laser-produced X-ray source. A calibrated X-ray CCD is used as a secondary standard detector to monitor the X-ray source intensity. In addition, two sets of holographic flat-field grating spectrometers are chosen as the spectral discrimination systems of the SXRSC and the X-ray CCD. The absolute sensitivity of the SXRSC is obtained by comparing the signal counts of the SXRSC to the output counts of the X-ray CCD. Results show that the calibrated spectrum covers the range from 200 eV to 1040 eV. The change of the absolute sensitivity in the vicinity of the K-edge of the carbon can also be clearly seen. The experimental values agree with the calculated values to within 29% error. Compared with previous calibration methods, the proposed method has several advantages: a wide spectral range, high accuracy, and simple data processing. Our calibration results can be used to make quantitative X-ray flux measurements in laser fusion research.
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
Gafchromic EBT2 film dosimetry in reflection mode with a novel plan-based calibration method
Mendez, I.; Hartman, V.; Hudej, R.
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 significantmore » 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
Variational, geometric, and statistical methods for modeling brain anatomy and function.
Faugeras, Olivier; Adde, Geoffray; Charpiat, Guillaume; Chefd'hotel, Christophe; Clerc, Maureen; Deneux, Thomas; Deriche, Rachid; Hermosillo, Gerardo; Keriven, Renaud; Kornprobst, Pierre; Kybic, Jan; Lenglet, Christophe; Lopez-Perez, Lucero; Papadopoulo, Théo; Pons, Jean-Philippe; Segonne, Florent; Thirion, Bertrand; Tschumperlé, David; Viéville, Thierry; Wotawa, Nicolas
2004-01-01
We survey the recent activities of the Odyssée Laboratory in the area of the application of mathematics to the design of models for studying brain anatomy and function. We start with the problem of reconstructing sources in MEG and EEG, and discuss the variational approach we have developed for solving these inverse problems. This motivates the need for geometric models of the head. We present a method for automatically and accurately extracting surface meshes of several tissues of the head from anatomical magnetic resonance (MR) images. Anatomical connectivity can be extracted from diffusion tensor magnetic resonance images but, in the current state of the technology, it must be preceded by a robust estimation and regularization stage. We discuss our work based on variational principles and show how the results can be used to track fibers in the white matter (WM) as geodesics in some Riemannian space. We then go to the statistical modeling of functional magnetic resonance imaging (fMRI) signals from the viewpoint of their decomposition in a pseudo-deterministic and stochastic part that we then use to perform clustering of voxels in a way that is inspired by the theory of support vector machines and in a way that is grounded in information theory. Multimodal image matching is discussed next in the framework of image statistics and partial differential equations (PDEs) with an eye on registering fMRI to the anatomy. The paper ends with a discussion of a new theory of random shapes that may prove useful in building anatomical and functional atlases.
Photometric calibration of the COMBO-17 survey with the Softassign Procrustes Matching method
NASA Astrophysics Data System (ADS)
Sheikhbahaee, Z.; Nakajima, R.; Erben, T.; Schneider, P.; Hildebrandt, H.; Becker, A. C.
2017-11-01
Accurate photometric calibration of optical data is crucial for photometric redshift estimation. We present the Softassign Procrustes Matching (SPM) method to improve the colour calibration upon the commonly used Stellar Locus Regression (SLR) method for the COMBO-17 survey. Our colour calibration approach can be categorised as a point-set matching method, which is frequently used in medical imaging and pattern recognition. We attain a photometric redshift precision Δz/(1 + zs) of better than 2 per cent. Our method is based on aligning the stellar locus of the uncalibrated stars to that of a spectroscopic sample of the Sloan Digital Sky Survey standard stars. We achieve our goal by finding a correspondence matrix between the two point-sets and applying the matrix to estimate the appropriate translations in multidimensional colour space. The SPM method is able to find the translation between two point-sets, despite the existence of noise and incompleteness of the common structures in the sets, as long as there is a distinct structure in at least one of the colour-colour pairs. We demonstrate the precision of our colour calibration method with a mock catalogue. The SPM colour calibration code is publicly available at https://neuronphysics@bitbucket.org/neuronphysics/spm.git.
A new calibration method for tri-axial field sensors in strap-down navigation systems
NASA Astrophysics Data System (ADS)
Li, Xiang; Li, Zhi
2012-10-01
This paper presents a novel calibration method for tri-axial field sensors, such as magnetometers and accelerometers, in strap-down navigation systems. Strap-down tri-axial sensors have been widely used as they have the advantages of small size and low cost, but they need to be calibrated in order to ensure their accuracy. The most commonly used calibration method for a tri-axial field sensor is based on ellipsoid fitting, which has no requirement for external references. However, the self-calibration based on ellipsoid fitting is unable to determine and compensate the mutual misalignment between different sensors in a multi-sensor system. Therefore, a novel calibration method that employs the invariance of the dot product of two constant vectors is introduced in this paper. The proposed method, which is named dot product invariance method, brings a complete solution for the error model of tri-axial field sensors, and can solve the problem of alignment in a multi-sensor system. Its effectiveness and superiority over the ellipsoid fitting method are illustrated by numerical simulations, and its application on a digital magnetic compass shows significant enhancement of the heading accuracy.
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)
2017-01-01
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, over the Raleigh fading channel. 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.
Dynamic method of calibration and examination piezoresistive cantilevers
NASA Astrophysics Data System (ADS)
Sierakowski, Andrzej; Kopiec, Daniel; Ekwińska, Magdalena; Piasecki, Tomasz; Dobrowolski, Rafał; Płuska, Mariusz; Domański, Krzysztof; Grabiec, Piotr; Gotszalk, Teodor P.
2013-07-01
In this paper authors present two methods of determining the cantilever displacement sensitivity. In both cases the cantilevers are examined in dynamic condition for cantilever vibrating with frequency range close to resonance frequency. One of the method uses as measurement tool a white light interferometer, the another one uses the laser interferometric vibrometer. For adequate comparing methods, obtained results refer to the same cantilever with piezoresistive Wheatstone bridge. In this paper authors also present the fabrication process of piezoresistive cantilevers with planar tip adapted for working in a shear force [1]. Additionally the piezoresistive circuit characterization by impedance spectroscopy is presented. Finally the spring constant is determined basing on frequency response of the cantilever measured from thermal noise density [2]. Basing on obtained results authors made a conclusion that both methods can be successfully used for accurate characterization piazoresistive cantilevers work in a non-contact resonance mode.
Method for calibrating olfactometer output. Part 2. Amyl acetate.
Maiolo, K C; Walker, J C; Ogden, M W
2000-07-01
A method for measuring amyl acetate in air was developed and validated. Known volumes of air samples from the output of an olfactometer, a device used to generate odor stimuli, were passed through charcoal sorbent tubes. Following extraction of the sorbent with carbon disulfide, the amount of amyl acetate collected on each tube was determined by gas chromatography with flame ionization detection. The method was used to determine the actual concentrations of amyl acetate presented to experimental participants in odor sensitivity testing.
Flexible calibration method for line-structured light based on binocular vision
NASA Astrophysics Data System (ADS)
Zhu, Ye; Wang, Lianpo; Gu, Yonggang; Zhai, Chao; Jin, Yi
2017-10-01
A new calibration technique for line-structured light scanning systems is proposed in this study. Compared with existing methods, this technique is more flexible and practical. Complicated operations, precision calibration target and positioning devices are all unnecessary. Only a blank planar board, which is placed at several(at least two) arbitrary orientations, and an additional camera that is calibrated under the global coordinate system are required. Control points are obtained through improved binocular intersection algorithm that avoids corresponding points matching and then used to calculate the light stripe plane through least square fitting. Experiment results indicate that the system calibrated by this technique is able to conduct surface measurement, offering an accuracy superior to 32μm(RMS).
Development of dynamic calibration methods for POGO pressure transducers. [for space shuttle
NASA Technical Reports Server (NTRS)
Hilten, J. S.; Lederer, P. S.; Vezzetti, C. F.; Mayo-Wells, J. F.
1976-01-01
Two dynamic pressure sources are described for the calibration of pogo pressure transducers used to measure oscillatory pressures generated in the propulsion system of the space shuttle. Rotation of a mercury-filled tube in a vertical plane at frequencies below 5 Hz generates sinusoidal pressures up to 48 kPa, peak-to-peak; vibrating the same mercury-filled tube sinusoidally in the vertical plane extends the frequency response from 5 Hz to 100 Hz at pressures up to 140 kPa, peak-to-peak. The sinusoidal pressure fluctuations can be generated by both methods in the presence of high pressures (bias) up to 55 MPa. Calibration procedures are given in detail for the use of both sources. The dynamic performance of selected transducers was evaluated using these procedures; the results of these calibrations are presented. Calibrations made with the two sources near 5 Hz agree to within 3% of each other.
Calibration of Pyrometers by Using Extrapolation and Interpolation Methods at NIM
NASA Astrophysics Data System (ADS)
Lu, X.; Yuan, Z.; Wang, J.; Bai, C.; Wang, T.; Dong, W.
2018-01-01
High-temperature fixed points (HTFPs) have been thoroughly investigated, and the performance of variable temperature blackbodies (VTBB) has also improved rapidly. These two are beginning to be used in the calibration of pyrometers; however, tungsten strip lamps (STSL) still play a role in the dissemination of the high-temperature scale in China. International Temperature Scale of 1990 values of HTFPs and the lamps were assigned on a primary standard pyrometer (PSP) and were traced to the primary standard of the high-temperature scale at the National Institute of Metrology. In this paper, two pyrometers calibrated by using extrapolation and interpolation methods are reported. The values of the calibration were compared against the STSL values and the PSP values on HTBB, and their uncertainties are calculated as well. Because the stability of the HTFPs was better than that of the lamps, the calibration chains based on the lamps are starting to be replaced by HTFPs and VTBBs in China.
A calibration method for photon counters using a customized standard light source
NASA Astrophysics Data System (ADS)
Lin, Shulang; Gu, Huarong; Tan, Qiaofeng
2016-10-01
Photomultiplier tubes (PMTs) are the most common photoelectric conversion apparatus used as photon counters. Because of the sensitivity of the PMTs to the interference, calibration is necessary during the application of the PMTs. Traditional solutions for calibration are either based on the inverse square law of illumination, or using light-emitting diodes (LEDs) as standard light sources. However, rigid experimental techniques are required for these solutions. And the emission spectrum of LEDs does not cover the entire spectrum of detection. In this paper, a calibration method is presented by using a customized standard light source which can provide full spectrum of weak light from the dark count level to the saturation level of the PMTs. The photon counter in a light-shielding cavity is connected, via an optical fiber, to the customized standard light source attached with an intensity detector. The calibration process is discussed and experimental results with chemical reference substance are also presented for comparison.
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.
Liu, Fang; Wang, Wei; Wang, Lei; Feng, Peide
2013-11-10
By rotating a strapdown inertial navigation system (INS) over one or more axes, a number of error sources originating from the employed sensors cancel out during the integration process. Rotary angle accuracy has an effect on the performance of rotational INS (RINS). The application of existing calibration methods based on gyroscope measurements is restricted by the structure of the inertial measurement unit (IMU) and scale factor stability of the gyroscope. The multireadhead method has problems in miniaturization and cost. Hence, optical angle encoder calibration methods using accelerometers are proposed, on the basis of navigation error and accuracy requirement analyses for a single-axis RINS. The test results show that the accuracy of calibration methods proposed is higher than 4 arcsec (1σ).
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
SU-F-E-19: A Novel Method for TrueBeam Jaw Calibration
Corns, R; Zhao, Y; Huang, V
2016-06-15
Purpose: A simple jaw calibration method is proposed for Varian TrueBeam using an EPID-Encoder combination that gives accurate fields sizes and a homogeneous junction dose. This benefits clinical applications such as mono-isocentric half-beam block breast cancer or head and neck cancer treatment with junction/field matching. Methods: We use EPID imager with pixel size 0.392 mm × 0.392 mm to determine the radiation jaw position as measured from radio-opaque markers aligned with the crosshair. We acquire two images with different symmetric field sizes and record each individual jaw encoder values. A linear relationship between each jaw’s position and its encoder valuemore » is established, from which we predict the encoder values that produce the jaw positions required by TrueBeam’s calibration procedure. During TrueBeam’s jaw calibration procedure, we move the jaw with the pendant to set the jaw into position using the predicted encoder value. The overall accuracy is under 0.1 mm. Results: Our in-house software analyses images and provides sub-pixel accuracy to determine field centre and radiation edges (50% dose of the profile). We verified the TrueBeam encoder provides a reliable linear relationship for each individual jaw position (R{sup 2}>0.9999) from which the encoder values necessary to set jaw calibration points (1 cm and 19 cm) are predicted. Junction matching dose inhomogeneities were improved from >±20% to <±6% using this new calibration protocol. However, one technical challenge exists for junction matching, if the collimator walkout is large. Conclusion: Our new TrueBeam jaw calibration method can systematically calibrate the jaws to crosshair within sub-pixel accuracy and provides both good junction doses and field sizes. This method does not compensate for a larger collimator walkout, but can be used as the underlying foundation for addressing the walkout issue.« less
In-flight absolute calibration of radiometric sensors over dark targets using vicarious methods
NASA Astrophysics Data System (ADS)
Parada, Robert John, Jr.
1997-10-01
The ability to conduct in-flight, absolute radiometric calibrations of ocean color sensors will determine their usefulness in the decade to come. On-board calibration systems are often integrated into the overall design of such sensors and have claimed uncertainty levels below 5%. Independent means of system calibration are needed to confirm that the sensor is accurately calibrated. Vicarious (i.e. ground-referencing) methods are an attractive way to conduct this verification. This research describes the development of in-flight, absolute radiometric calibration methods which reference dark (i.e. low-reflectance) sites. The high sensitivity of ocean color sensors results in saturation over bright surfaces. Low-reflectance targets, such as water bodies, are therefore required for their vicarious calibration. Sensitivity analyses of the reflectance-based and radiance-based techniques, when applied to a water target, are performed. Uncertainties in atmospheric parameters, surface reflectance measurements, and instrument characterization are evaluated for calibrations of a representative ocean color sensor. For a viewing geometry near the sun glint region, reflectance-based uncertainties range between 1.6% and 2.3% for visible and near-IR wavelengths; radiance-based uncertainties range between 6.8% and 20.5%. These studies indicate that better characterization of aerosol parameters is desired and that radiometer pointing accuracy must be improved to make the radiance-based method useful. The uncertainty estimates are evaluated using data from a field campaign at Lake Tahoe in June, 1995. This lake is located on the California-Nevada border and has optical characteristics similar to oceanic waters. Aircraft-based radiance data and surface measurements of water reflectance are used to calibrate visible and near infrared bands of the Airborne Visible/InfraRed Imaging Spectrometer (AVIRIS). The vicariously-derived calibration coefficients are compared to those obtained
Solvers and Calibration Methods for Ground and Surface Water Models
2010-07-18
East Asia SIAM Conference, Kuala Lumpur, Malaysia , June 2010 * Workshop for the 60th birthday of Prof. E. W. Sachs, Trier, Germany, June 2010 * IFIP...and with PEST [3] when the iteration is near convergence. While genetic algorithms are based on heuristics, there are methods to couple reduced order...2002), pp. 182–197. [3] J. Doherty, PEST : Model-Independent Parameter Estimation User Manual, Water- mark Numerical Computing, 5 ed., 2004. [4] K. R
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.
A novel calibration method for non-orthogonal shaft laser theodolite measurement system
NASA Astrophysics Data System (ADS)
Wu, Bin; Yang, Fengting; Ding, Wen; Xue, Ting
2016-03-01
Non-orthogonal shaft laser theodolite (N-theodolite) is a new kind of large-scale metrological instrument made up by two rotary tables and one collimated laser. There are three axes for an N-theodolite. According to naming conventions in traditional theodolite, rotary axes of two rotary tables are called as horizontal axis and vertical axis, respectively, and the collimated laser beam is named as sight axis. And the difference between N-theodolite and traditional theodolite is obvious, since the former one with no orthogonal and intersecting accuracy requirements. So the calibration method for traditional theodolite is no longer suitable for N-theodolite, while the calibration method applied currently is really complicated. Thus this paper introduces a novel calibration method for non-orthogonal shaft laser theodolite measurement system to simplify the procedure and to improve the calibration accuracy. A simple two-step process, calibration for intrinsic parameters and for extrinsic parameters, is proposed by the novel method. And experiments have shown its efficiency and accuracy.
Brightness checkerboard lattice method for the calibration of the coaxial reverse Hartmann test
NASA Astrophysics Data System (ADS)
Li, Xinji; Hui, Mei; Li, Ning; Hu, Shinan; Liu, Ming; Kong, Lingqin; Dong, Liquan; Zhao, Yuejin
2018-01-01
The coaxial reverse Hartmann test (RHT) is widely used in the measurement of large aspheric surfaces as an auxiliary method for interference measurement, because of its large dynamic range, highly flexible test with low frequency of surface errors, and low cost. And the accuracy of the coaxial RHT depends on the calibration. However, the calibration process remains inefficient, and the signal-to-noise ratio limits the accuracy of the calibration. In this paper, brightness checkerboard lattices were used to replace the traditional dot matrix. The brightness checkerboard method can reduce the number of dot matrix projections in the calibration process, thus improving efficiency. An LCD screen displayed a brightness checkerboard lattice, in which the brighter checkerboard and the darker checkerboard alternately arranged. Based on the image on the detector, the relationship between the rays at certain angles and the photosensitive positions of the detector coordinates can be obtained. And a differential de-noising method can effectively reduce the impact of noise on the measurement results. Simulation and experimentation proved the feasibility of the method. Theoretical analysis and experimental results show that the efficiency of the brightness checkerboard lattices is about four times that of the traditional dot matrix, and the signal-to-noise ratio of the calibration is significantly improved.
A novel calibration method for non-orthogonal shaft laser theodolite measurement system
Wu, Bin E-mail: xueting@tju.edu.cn; Yang, Fengting; Ding, Wen; Xue, Ting E-mail: xueting@tju.edu.cn
2016-03-15
Non-orthogonal shaft laser theodolite (N-theodolite) is a new kind of large-scale metrological instrument made up by two rotary tables and one collimated laser. There are three axes for an N-theodolite. According to naming conventions in traditional theodolite, rotary axes of two rotary tables are called as horizontal axis and vertical axis, respectively, and the collimated laser beam is named as sight axis. And the difference between N-theodolite and traditional theodolite is obvious, since the former one with no orthogonal and intersecting accuracy requirements. So the calibration method for traditional theodolite is no longer suitable for N-theodolite, while the calibration method applied currently is really complicated. Thus this paper introduces a novel calibration method for non-orthogonal shaft laser theodolite measurement system to simplify the procedure and to improve the calibration accuracy. A simple two-step process, calibration for intrinsic parameters and for extrinsic parameters, is proposed by the novel method. And experiments have shown its efficiency and accuracy.
A novel calibration method for non-orthogonal shaft laser theodolite measurement system.
Wu, Bin; Yang, Fengting; Ding, Wen; Xue, Ting
2016-03-01
Non-orthogonal shaft laser theodolite (N-theodolite) is a new kind of large-scale metrological instrument made up by two rotary tables and one collimated laser. There are three axes for an N-theodolite. According to naming conventions in traditional theodolite, rotary axes of two rotary tables are called as horizontal axis and vertical axis, respectively, and the collimated laser beam is named as sight axis. And the difference between N-theodolite and traditional theodolite is obvious, since the former one with no orthogonal and intersecting accuracy requirements. So the calibration method for traditional theodolite is no longer suitable for N-theodolite, while the calibration method applied currently is really complicated. Thus this paper introduces a novel calibration method for non-orthogonal shaft laser theodolite measurement system to simplify the procedure and to improve the calibration accuracy. A simple two-step process, calibration for intrinsic parameters and for extrinsic parameters, is proposed by the novel method. And experiments have shown its efficiency and accuracy.
Alam, Md Anik; Drennen, James; Anderson, Carl
2017-10-25
Designing a calibration set is the first step in developing a multivariate spectroscopic calibration method for quantitative analysis of pharmaceutical tablets. This step is critical because successful model development depends on the suitability of the calibration data. For spectroscopic-based methods, traditional concentration based techniques for designing calibration sets are prone to have redundant information while simultaneously lacking necessary information for a successful calibration model. A method for designing a calibration set in spectral space was developed. The pure component spectra of a tablet formulation were used to define the spectral space of that formulation. This method maximizes the information content of measurements and minimizes sample requirements to provide an efficient means for developing multivariate spectroscopic calibration. A comparative study was conducted between a commonly employed full factorial approach to calibration development and the newly developed technique. The comparison was based on a system to quantify a model drug, acetaminophen, in pharmaceutical compacts using near infrared spectroscopy. A 2-factor full factorial design (acetaminophen with 5 levels and MCC:Lactose with 3 levels) was used for calibration development. Three replicates at each design point resulted in a total of 45 tablets for the calibration set. Using the newly developed spectral based method, 11 tablets were prepared for the calibration set. Partial least square (PLS) models were developed from respective calibration sets. Model performance was comprehensively assessed based on the ability to predict acetaminophen concentrations in multiple prediction sets. One prediction set contained similar information to calibration set while the other prediction sets contained different information from calibration set in order to assess the model accuracy and robustness. Similar prediction performance was achieved using the 11-tablet design (spectral space
Research on direct calibration method of eye-to-hand system of robot
NASA Astrophysics Data System (ADS)
Hu, Xiaoping; Xie, Ke; Peng, Tao
2013-10-01
In the position-based visual servoing control for robot, the hand-eye calibration is very important because it can affect the control precision of the system. According to the robot with eye-to-hand stereovision system, this paper proposes a direct method of hand-eye calibration. The method utilizes the triangle measuring principle to solve the coordinates in the camera coordinate system of scene point. It calculates the estimated coordinates by the hand-eye calibration equation set which indicates the transformational relation from the robot to the camera coordinate system, and then uses the error of actual and estimated coordinates to establish the objective function. Finally the method substitutes the parameters into the function repeatedly until it converged to optimize the result. The related experiment compared the measured coordinates with the actual coordinates, shows the efficiency and the precision of it.
Pressure balance cross-calibration method using a pressure transducer as transfer standard.
Scherschligt, J; Olson, D; Driver, R G; Yang, Y
2016-01-01
Piston gauges or pressure balances are widely used to realize the SI unit of pressure, the pascal, and to calibrate pressure sensing devices. However, their calibration is time consuming and requires a lot of technical expertise. In this paper, we propose an alternate method of performing a piston gauge cross calibration that incorporates a pressure transducer as an immediate in-situ transfer standard. For a sufficiently linear transducer, the requirement to exactly balance the weights on the two pressure gauges under consideration is greatly relaxed. Our results indicate that this method can be employed without a significant increase in measurement uncertainty. Indeed, in the test case explored here, our results agreed with the traditional method within standard uncertainty, which was less than 6 parts per million.
Pressure balance cross-calibration method using a pressure transducer as transfer standard
Olson, D; Driver, R. G.; Yang, Y
2016-01-01
Piston gauges or pressure balances are widely used to realize the SI unit of pressure, the pascal, and to calibrate pressure sensing devices. However, their calibration is time consuming and requires a lot of technical expertise. In this paper, we propose an alternate method of performing a piston gauge cross calibration that incorporates a pressure transducer as an immediate in-situ transfer standard. For a sufficiently linear transducer, the requirement to exactly balance the weights on the two pressure gauges under consideration is greatly relaxed. Our results indicate that this method can be employed without a significant increase in measurement uncertainty. Indeed, in the test case explored here, our results agreed with the traditional method within standard uncertainty, which was less than 6 parts per million. PMID:28303167
Calibration Method and Uncertainty Assessment of a High-Temperature GHP Apparatus
NASA Astrophysics Data System (ADS)
Yao, Kai; Zheng, Huibao; Liu, Yunchuan; Meng, Xiangyan; Zhou, Yanping; Wang, Xuerong; Wang, Kang; Wang, Qianqian
2018-02-01
In this research, a calibration method of a high-temperature guarded hot plate (GHP) apparatus was proposed in order to improve the measurement accuracy of thermal conductivity. The measurement uncertainties of this GHP apparatus were assessed to validate the reliability of this calibration method. The temperature difference across the guarded gap was set as the bias value to eliminate the heat exchange over the guarded gap. The effects of the thermal expansion and pressure of the apparatus on thickness were investigated to revise the measurement results of in- situ thickness and meter area, respectively. The assessed uncertainty indicated that the related expanded uncertainty approximately increased with the increase in testing temperature and the calibration method should be valid in the temperature range. The contribution of each factor on the combined uncertainty showed that the temperature distribution in plane direction was the main factor in influencing the measurement of thermal conductivity.
Broadband PVDF membrane hydrophone for comparisons of hydrophone calibration methods up to 140 MHz.
Wilkens, Volker; Molkenstruck, Walter
2007-09-01
A PVDF membrane hydrophone has been constructed in particular for comparisons of broadband ultrasound hydrophone calibration methods and of the results obtained by different laboratories. Intercomparisons have to accompany the efforts currently undertaken to enhance the calibration frequency ranges and to implement the extension from the determination of amplitude-only to complex-valued calibration data. It can be expected that such hydrophone data will be used much more frequently in the future for exposure measurements on medical ultrasound equipment, in particular for the detection of nonlinearly distorted waveforms. The hydrophone design chosen has a foil thickness of 9 microm and an electrode diameter of 210 microm. A broadband differential preamplifier (-3 dB roll-off frequency: 95 MHz) is integrated to achieve a high signal-to-noise ratio over a broad frequency range (e.g., 26 dB-30 dB in the range 50 MHz to 140 MHz for measurements of nonlinearly distorted pulses). The hydrophone response was characterized by means of a primary interferometric calibration technique, by substitution calibration using time-delay spectrometry, and by complex broadband pulse calibration using nonlinear sound propagation. The results show a flat frequency response up to 40 MHz (maximum variations below +/-0.6 dB) and a thickness mode resonance at about 105 MHz. They indicate a useable bandwidth up to 140 MHz. The effective diameter as derived from directional response measurements is 240 microm at frequencies beyond 15 MHz.
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
Calibration of groundwater vulnerability mapping using the generalized reduced gradient method
NASA Astrophysics Data System (ADS)
Elçi, Alper
2017-12-01
Groundwater vulnerability assessment studies are essential in water resources management. Overlay-and-index methods such as DRASTIC are widely used for mapping of groundwater vulnerability, however, these methods mainly suffer from a subjective selection of model parameters. The objective of this study is to introduce a calibration procedure that results in a more accurate assessment of groundwater vulnerability. The improvement of the assessment is formulated as a parameter optimization problem using an objective function that is based on the correlation between actual groundwater contamination and vulnerability index values. The non-linear optimization problem is solved with the generalized-reduced-gradient (GRG) method, which is numerical algorithm based optimization method. To demonstrate the applicability of the procedure, a vulnerability map for the Tahtali stream basin is calibrated using nitrate concentration data. The calibration procedure is easy to implement and aims the maximization of correlation between observed pollutant concentrations and groundwater vulnerability index values. The influence of each vulnerability parameter in the calculation of the vulnerability index is assessed by performing a single-parameter sensitivity analysis. Results of the sensitivity analysis show that all factors are effective on the final vulnerability index. Calibration of the vulnerability map improves the correlation between index values and measured nitrate concentrations by 19%. The regression coefficient increases from 0.280 to 0.485. It is evident that the spatial distribution and the proportions of vulnerability class areas are significantly altered with the calibration process. Although the applicability of the calibration method is demonstrated on the DRASTIC model, the applicability of the approach is not specific to a certain model and can also be easily applied to other overlay-and-index methods.
Calibration of groundwater vulnerability mapping using the generalized reduced gradient method.
Elçi, Alper
2017-12-01
Groundwater vulnerability assessment studies are essential in water resources management. Overlay-and-index methods such as DRASTIC are widely used for mapping of groundwater vulnerability, however, these methods mainly suffer from a subjective selection of model parameters. The objective of this study is to introduce a calibration procedure that results in a more accurate assessment of groundwater vulnerability. The improvement of the assessment is formulated as a parameter optimization problem using an objective function that is based on the correlation between actual groundwater contamination and vulnerability index values. The non-linear optimization problem is solved with the generalized-reduced-gradient (GRG) method, which is numerical algorithm based optimization method. To demonstrate the applicability of the procedure, a vulnerability map for the Tahtali stream basin is calibrated using nitrate concentration data. The calibration procedure is easy to implement and aims the maximization of correlation between observed pollutant concentrations and groundwater vulnerability index values. The influence of each vulnerability parameter in the calculation of the vulnerability index is assessed by performing a single-parameter sensitivity analysis. Results of the sensitivity analysis show that all factors are effective on the final vulnerability index. Calibration of the vulnerability map improves the correlation between index values and measured nitrate concentrations by 19%. The regression coefficient increases from 0.280 to 0.485. It is evident that the spatial distribution and the proportions of vulnerability class areas are significantly altered with the calibration process. Although the applicability of the calibration method is demonstrated on the DRASTIC model, the applicability of the approach is not specific to a certain model and can also be easily applied to other overlay-and-index methods. Copyright © 2017 Elsevier B.V. All rights reserved.
K-edge energy-based calibration method for photon counting detectors
NASA Astrophysics Data System (ADS)
Ge, Yongshuai; Ji, Xu; Zhang, Ran; Li, Ke; Chen, Guang-Hong
2018-01-01
In recent years, potential applications of energy-resolved photon counting detectors (PCDs) in the x-ray medical imaging field have been actively investigated. Unlike conventional x-ray energy integration detectors, PCDs count the number of incident x-ray photons within certain energy windows. For PCDs, the interactions between x-ray photons and photoconductor generate electronic voltage pulse signals. The pulse height of each signal is proportional to the energy of the incident photons. By comparing the pulse height with the preset energy threshold values, x-ray photons with specific energies are recorded and sorted into different energy bins. To quantitatively understand the meaning of the energy threshold values, and thus to assign an absolute energy value to each energy bin, energy calibration is needed to establish the quantitative relationship between the threshold values and the corresponding effective photon energies. In practice, the energy calibration is not always easy, due to the lack of well-calibrated energy references for the working energy range of the PCDs. In this paper, a new method was developed to use the precise knowledge of the characteristic K-edge energy of materials to perform energy calibration. The proposed method was demonstrated using experimental data acquired from three K-edge materials (viz., iodine, gadolinium, and gold) on two different PCDs (Hydra and Flite, XCounter, Sweden). Finally, the proposed energy calibration method was further validated using a radioactive isotope (Am-241) with a known decay energy spectrum.
A novel calibration method for non-orthogonal shaft laser theodolite measurement system
Wu, Bin, E-mail: wubin@tju.edu.cn, E-mail: xueting@tju.edu.cn; Yang, Fengting; Ding, Wen
2016-03-15
Non-orthogonal shaft laser theodolite (N-theodolite) is a new kind of large-scale metrological instrument made up by two rotary tables and one collimated laser. There are three axes for an N-theodolite. According to naming conventions in traditional theodolite, rotary axes of two rotary tables are called as horizontal axis and vertical axis, respectively, and the collimated laser beam is named as sight axis. And the difference between N-theodolite and traditional theodolite is obvious, since the former one with no orthogonal and intersecting accuracy requirements. So the calibration method for traditional theodolite is no longer suitable for N-theodolite, while the calibration methodmore » applied currently is really complicated. Thus this paper introduces a novel calibration method for non-orthogonal shaft laser theodolite measurement system to simplify the procedure and to improve the calibration accuracy. A simple two-step process, calibration for intrinsic parameters and for extrinsic parameters, is proposed by the novel method. And experiments have shown its efficiency and accuracy.« less
Standardization of Laser Methods and Techniques for Vibration Measurements and Calibrations
NASA Astrophysics Data System (ADS)
von Martens, Hans-Jürgen
2010-05-01
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/s2). 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.
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.
Absolute x-ray energy calibration and monitoring using a diffraction-based method
Hong, Xinguo, E-mail: xhong@bnl.gov; Weidner, Donald J.; Duffy, Thomas S.
2016-07-27
In this paper, we report some recent developments of the diffraction-based absolute X-ray energy calibration method. In this calibration method, high spatial resolution of the measured detector offset is essential. To this end, a remotely controlled long-translation motorized stage was employed instead of the less convenient gauge blocks. It is found that the precision of absolute X-ray energy calibration (ΔE/E) is readily achieved down to the level of 10{sup −4} for high-energy monochromatic X-rays (e.g. 80 keV). Examples of applications to pair distribution function (PDF) measurements and energy monitoring for high-energy X-rays are presented.
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
Song, William; Battista, Jerry; Van Dyk, Jake
2004-11-01
The convolution method can be used to model the effect of random geometric uncertainties into planned dose distributions used in radiation treatment planning. This is effectively done by linearly adding infinitesimally small doses, each with a particular geometric offset, over an assumed infinite number of fractions. However, this process inherently ignores the radiobiological dose-per-fraction effect since only the summed physical dose distribution is generated. The resultant potential error on predicted radiobiological outcome [quantified in this work with tumor control probability (TCP), equivalent uniform dose (EUD), normal tissue complication probability (NTCP), and generalized equivalent uniform dose (gEUD)] has yet to bemore » thoroughly quantified. In this work, the results of a Monte Carlo simulation of geometric displacements are compared to those of the convolution method for random geometric uncertainties of 0, 1, 2, 3, 4, and 5 mm (standard deviation). The {alpha}/{beta}{sub CTV} ratios of 0.8, 1.5, 3, 5, and 10 Gy are used to represent the range of radiation responses for different tumors, whereas a single {alpha}/{beta}{sub OAR} ratio of 3 Gy is used to represent all the organs at risk (OAR). The analysis is performed on a four-field prostate treatment plan of 18 MV x rays. The fraction numbers are varied from 1-50, with isoeffective adjustments of the corresponding dose-per-fractions to maintain a constant tumor control, using the linear-quadratic cell survival model. The average differences in TCP and EUD of the target, and in NTCP and gEUD of the OAR calculated from the convolution and Monte Carlo methods reduced asymptotically as the total fraction number increased, with the differences reaching negligible levels beyond the treatment fraction number of {>=}20. The convolution method generally overestimates the radiobiological indices, as compared to the Monte Carlo method, for the target volume, and underestimates those for the OAR. These
NASA Astrophysics Data System (ADS)
Yang, Jinghao; Jia, Zhenyuan; Liu, Wei; Fan, Chaonan; Xu, Pengtao; Wang, Fuji; Liu, Yang
2016-10-01
Binocular vision systems play an important role in computer vision, and high-precision system calibration is a necessary and indispensable process. In this paper, an improved calibration method for binocular stereo vision measurement systems based on arbitrary translations and 3D-connection information is proposed. First, a new method for calibrating the intrinsic parameters of binocular vision system based on two translations with an arbitrary angle difference is presented, which reduces the effect of the deviation of the motion actuator on calibration accuracy. This method is simpler and more accurate than existing active-vision calibration methods and can provide a better initial value for the determination of extrinsic parameters. Second, a 3D-connection calibration and optimization method is developed that links the information of the calibration target in different positions, further improving the accuracy of the system calibration. Calibration experiments show that the calibration error can be reduced to 0.09%, outperforming traditional methods for the experiments of this study.
Farrell, Daniel W; Lei, Ming; Thorpe, M F
2011-04-01
Geometric targeting (GT) is a recently introduced method for rapidly generating all-atom pathways from one protein state to another, based on geometric rather than energetic considerations. To generate pathways, a bias is applied that gradually moves atoms toward a target structure, while a set of geometric constraints between atoms is enforced to keep the structure stereochemically acceptable. In this work, we compare conformational pathways generated from GT to pathways from the much more computationally intensive and commonly used targeted molecular dynamics (TMD) technique, for a complicated conformational change in the signaling protein nitrogen regulatory protein C. We show that the all-atom pathways from GT are similar to previously reported TMD pathways for this protein, by comparing motion along six progress variables that describe the various structural changes. The results suggest that for nitrogen regulatory protein C, finding an all-atom pathway is primarily a problem of geometry, and that a detailed force field in this case constitutes an unnecessary extra layer of detail. We also show that the pathway snapshots from GT have good structure quality, by measuring various structure quality metrics. Transient hydrogen bonds detected by the two methods show some similarities but also some differences. The results justify the usage of GT as a rapid, approximate alternative to TMD for generating stereochemically acceptable all-atom pathways in highly constrained protein systems.
SU-F-T-274: Modified Dose Calibration Methods for IMRT QA
Luo, W; Westlund, S
2016-06-15
Purpose: To investigate IMRT QA uncertainties caused by dose calibration and modify widely used dose calibration procedures to improve IMRT QA accuracy and passing rate. Methods: IMRT QA dose measurement is calibrated using a calibration factor (CF) that is the ratio between measured value and expected value corresponding to the reference fields delivered on a phantom. Two IMRT QA phantoms were used for this study: a 30×30×30 cm3 solid water cube phantom (Cube), and the PTW Octavius phantom. CF was obtained by delivering 100 MUs to the phantoms with different reference fields ranging from 3×3 cm2 to 20×20 cm{sup 2}.more » For Cube, CFs were obtained using the following beam arrangements: 2-AP Field - chamber at dmax, 2-AP Field - chamber at isocenter, 4-beam box - chamber at isocenter, and 8 equally spaced fields and chamber at isocenter. The same plans were delivered on Octavius and CFs were derived for the dose at the isocenter using the above beam arrangements. The Octavius plans were evaluated with PTW-VeriSoft (Gamma criteria of 3%/3mm). Results: Four head and neck IMRT plans were included in this study. For point dose measurement with Cube, the CFs with 4-Field gave the best agreement between measurement and calculation within 4% for large field plans. All the measurement results agreed within 2% for a small field plan. Compared with calibration field sizes, 5×5 to 15×15 were more accurate than other field sizes. For Octavius, 4-Field calibration increased passing rate by up to 10% compared to AP calibration. Passing rate also increased by up to 4% with the increase of field size from 3×3 to 20×20. Conclusion: IMRT QA results are correlated with calibration methods used. The dose calibration using 4-beam box with field sizes from 5×5 to 20×20 can improve IMRT QA accuracy and passing rate.« less
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.; ...
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
Pyrgeometer Calibration for DOE-Atmospheric System Research Program Using NREL Method (Presentation)
Reda, I.; Stoffel, T.
2010-03-15
Presented at the DOE-Atmospheric System Research Program, Science Team Meeting, 15-19 March 2010, Bethesda, Maryland. The presentation: Pyrgeometer Calibration for DOE-Atmospheric System Research program using NREL Method - was presented by Ibrahim Reda and Tom Stoffel on March 15, 2010 at the 2010 ASR Science Team Meeting. March 15-19, 2010, Bethesda, Maryland.
Calibration Method for IATS and Application in Multi-Target Monitoring Using Coded Targets
NASA Astrophysics Data System (ADS)
Zhou, Yueyin; Wagner, Andreas; Wunderlich, Thomas; Wasmeier, Peter
2017-06-01
The technique of Image Assisted Total Stations (IATS) has been studied for over ten years and is composed of two major parts: one is the calibration procedure which combines the relationship between the camera system and the theodolite system; the other is the automatic target detection on the image by various methods of photogrammetry or computer vision. Several calibration methods have been developed, mostly using prototypes with an add-on camera rigidly mounted on the total station. However, these prototypes are not commercially available. This paper proposes a calibration method based on Leica MS50 which has two built-in cameras each with a resolution of 2560 × 1920 px: an overview camera and a telescope (on-axis) camera. Our work in this paper is based on the on-axis camera which uses the 30-times magnification of the telescope. The calibration consists of 7 parameters to estimate. We use coded targets, which are common tools in photogrammetry for orientation, to detect different targets in IATS images instead of prisms and traditional ATR functions. We test and verify the efficiency and stability of this monitoring method with multi-target.
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 currentmore » 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.« less
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.
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.
NASA Astrophysics Data System (ADS)
Liu, Bai-Ling; Qu, Xing-Hua
2013-10-01
In view of present problem of low accuracy, limited range and low automaticity existing in the large-scale diameter inspection instrument, a precise measuring system (robot) was designed based on laser displacement sensor for large-scale inner diameter in this paper. Since the traditional measuring tool of the robot is expensive and hard to manufacture, an indirect calibration method is proposed. In this study, the system eccentric error is calibrated by ring gauge of laboratory. An experiment, which changes the installed order of located rods to introduce located rods' eccentric error, is designed to test whether the spindle eccentric error remains unchanged. The experiment result shows the variation of spindle's eccentricity after changing rods is within 0.02mm. Due to the spindle is an unchanged part of robot, based on Φ584 series robot calibrated by ring gauge, other series robot can be deduced combining with the length of extended arm.
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.
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.
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/cm(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.
Semi-automated calibration method for modelling of mountain permafrost evolution in Switzerland
NASA Astrophysics Data System (ADS)
Marmy, Antoine; Rajczak, Jan; Delaloye, Reynald; Hilbich, Christin; Hoelzle, Martin; Kotlarski, Sven; Lambiel, Christophe; Noetzli, Jeannette; Phillips, Marcia; Salzmann, Nadine; Staub, Benno; Hauck, Christian
2016-11-01
Permafrost is a widespread phenomenon in mountainous regions of the world such as 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 allow for 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, for large-scale applications, a site-specific model calibration for a multitude of grid points would be very time-consuming. To tackle this issue, this study 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. We show that this semi-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 global and regional climate model (GCM/RCM)-based long-term climate projections under the A1B climate scenario (EU-ENSEMBLES project) specifically downscaled at each borehole site. The projection shows general permafrost degradation with thawing at 10 m, even partially reaching 20 m depth by the end of the century, but with different timing among the sites and with partly considerable uncertainties due to the spread of the applied climatic forcing.
A star tracker on-orbit calibration method based on vector pattern match.
Li, Jian; Xiong, Kun; Wei, Xinguo; Zhang, Guangjun
2017-04-01
On-orbit calibration is aimed at revising the star trackers' measurement model parameters and maintaining its attitude accuracy. The performance of existing calibration methods is quite poor. Among all the model parameters, the estimation of the principal point location is very challenging due to its vulnerability against measurement errors, yet, that it is the only parameter depicting the optical axis' projecting position on the image plane makes it of great significance. Its estimation error adds fixed bias to the output attitudes. Based on the criterion of vector pattern match, an on-orbit calibration method is proposed. The principal point location is estimated according to the criterion first. The other model parameters are updated by maximum likelihood method, and measures of multiple succeeding frames optimization and star density weight are adopted in the method to guarantee the estimation of robustness. Simulation and night sky observation results proved the validity of the proposed method. In the simulation with a poor initial guess of the principal point location, novel method's result is better than the least square method and Samaan's method.
Watts, Seth; Tortorelli, Daniel A.
2017-04-13
Topology optimization is a methodology for assigning material or void to each point in a design domain in a way that extremizes some objective function, such as the compliance of a structure under given loads, subject to various imposed constraints, such as an upper bound on the mass of the structure. Geometry projection is a means to parameterize the topology optimization problem, by describing the design in a way that is independent of the mesh used for analysis of the design's performance; it results in many fewer design parameters, necessarily resolves the ill-posed nature of the topology optimization problem, andmore » provides sharp descriptions of the material interfaces. We extend previous geometric projection work to 3 dimensions and design unit cells for lattice materials using inverse homogenization. We perform a sensitivity analysis of the geometric projection and show it has smooth derivatives, making it suitable for use with gradient-based optimization algorithms. The technique is demonstrated by designing unit cells comprised of a single constituent material plus void space to obtain light, stiff materials with cubic and isotropic material symmetry. Here, we also design a single-constituent isotropic material with negative Poisson's ratio and a light, stiff material comprised of 2 constituent solids plus void space.« less
Research on a high-precision calibration method for tunable lasers
NASA Astrophysics Data System (ADS)
Xiang, Na; Li, Zhengying; Gui, Xin; Wang, Fan; Hou, Yarong; Wang, Honghai
2018-03-01
Tunable lasers are widely used in the field of optical fiber sensing, but nonlinear tuning exists even for zero external disturbance and limits the accuracy of the demodulation. In this paper, a high-precision calibration method for tunable lasers is proposed. A comb filter is introduced and the real-time output wavelength and scanning rate of the laser are calibrated by linear fitting several time-frequency reference points obtained from it, while the beat signal generated by the auxiliary interferometer is interpolated and frequency multiplied to find more accurate zero crossing points, with these points being used as wavelength counters to resample the comb signal to correct the nonlinear effect, which ensures that the time-frequency reference points of the comb filter are linear. A stability experiment and a strain sensing experiment verify the calibration precision of this method. The experimental result shows that the stability and wavelength resolution of the FBG demodulation can reach 0.088 pm and 0.030 pm, respectively, using a tunable laser calibrated by the proposed method. We have also compared the demodulation accuracy in the presence or absence of the comb filter, with the result showing that the introduction of the comb filter results to a 15-fold wavelength resolution enhancement.
NASA Astrophysics Data System (ADS)
Yao, Zhenjian; Wang, Zhongyu; Yi-Lin Forrest, Jeffrey; Wang, Qiyue; Lv, Jing
2017-04-01
In this paper, an approach combining empirical mode decomposition (EMD) with adaptive least squares (ALS) is proposed to improve the dynamic calibration accuracy of pressure sensors. With EMD, the original output of the sensor can be represented as sums of zero-mean amplitude modulation frequency modulation components. By identifying and excluding those components involved in noises, the noise-free output could be reconstructed with the useful frequency modulation ones. Then the least squares method is iteratively performed to estimate the optimal order and parameters of the mathematical model. The dynamic characteristic parameters of the sensor can be derived from the model in both time and frequency domains. A series of shock tube calibration tests are carried out to validate the performance of this method. Experimental results show that the proposed method works well in reducing the influence of noise and yields an appropriate mathematical model. Furthermore, comparative experiments also demonstrate the superiority of the proposed method over the existing ones.
Development and evaluation of a method of calibrating medical displays based on fixed adaptation
Sund, Patrik, E-mail: patrik.sund@vgregion.se; 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 contrastmore » 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
New structured light measurement and calibration method for 3D documenting of engineering structures
NASA Astrophysics Data System (ADS)
Sitnik, Robert; Kujawińska, Małgorzata; Błaszczyk, Paweł M.
2011-05-01
In the paper a new approach for two step calibration process allowing 3D measurement in large volumes is presented. The maximum assumed volume is equal to 20m x 15m x 6m and the developed system is portable and easy to operate by one person. To set-up a traditional 3D structured light system a long enough base distance between projector and detector is required to ensure sufficient measurement sensitivity. In this setup to achieve measurement uncertainty in the range of 20mm the minimum 10m base distance is required. For this base distance it is nearly impossible to set-up a rigid frame for fixing projector-detector configuration and allow to anyone for easy manipulation of such system. Taking into consideration the above mentioned requirements a new calibration method has been proposed. Its main assumption is that there is no requirement for fixing projector and detector during a calibration phase. The relation between projector and detector is established just before measurement where they are finally positioned to capture 3D shape of investigated surface. It works in two steps: the first one is based on independent calibration of projector and detector devices to establish relation between their the pixel (i, j) co-ordinates and lines in free space; the second one is based on a set of measurements of a known calibration model and their analysis allowing calculation of a relative transformation between detector and projector co-ordinate spaces. The first step is always done in laboratory and the second one is performed just after any change in a relative position between projector and detector. In the paper the initial assessment of measurement uncertainty is discussed in relation to the calibration model versus a measurement volume size. Also some exemplary measurements of real engineering structures will be presented and functionality of the system are discussed.
Reyes, Alessandra; Ferreira, Gisele E; Santos, Joyce; Mendes, Fausto M; Imparato, Jose C P; Braga, Mariana M
2013-03-01
Individual calibration (IC) for caries detection methods based on fluorescence is time-consuming, especially for paediatric dentists, if the calibration has to be performed tooth-by-tooth. However, it is not clear how this calibration actually interfere in laser fluorescence (LF) readings. This in vivo study was to verify the influence of different modes of IC on laser fluorescence (LF) readings. Ninety six occlusal and 95 buccal surfaces of 1st permanent molars were examined using LF device after IC performed on control (no IC), the examined teeth, a permanent incisor, a 1st primary molar or a 2nd primary molar. All modes of IC were performed in the same child. Wilcoxon test and Bland-Altman analysis were used to compare the readings. Intraclass correlation coefficients (ICC) were calculated. Laser fluorescence readings without prior calibration were higher than readings performed after any mode of IC and resulted in different values of ICC. After other IC modes, the LF readings were statistically similar. The absence of IC influences LF readings and LF reproducibility, but different IC methods can be considered in clinical practice. © 2012 The Authors. International Journal of Paediatric Dentistry © 2012 BSPD, IAPD and Blackwell Publishing Ltd.
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.
Hybrid PSO-ASVR-based method for data fitting in the calibration of infrared radiometer
Yang, Sen; Li, Chengwei
2016-06-15
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.
A simple and reliable method to calibrate respiratory magnetometers and Respitrace.
Banzett, R B; Mahan, S T; Garner, D M; Brughera, A; Loring, S H
1995-12-01
We present a simple and reliable method to calibrate respiratory magnetometers and Respitrace to infer respiratory volume changes. As in earlier methods, we assume two degrees of freedom in the chest wall and that volume displacement depends linearly on surface motion at the rib cage and abdomen. Because the area of the rib cage is larger, a given motion of its surface produces a greater lung volume change; therefore, the rib cage motion signal is given a larger gain before the two signals are added to estimate volume. In contrast to earlier methods, we use a "standard ratio" to weight relative gains of the rib cage and abdominal signals for all subjects rather than determining a gain ratio for each individual subject. Our procedure does not require subjects to perform the sometimes difficult isovolume maneuvers used in the calibration method of Konno and Mead (J. Appl. Physiol. 22: 407-422, 1967), does not require statistical computation used in the multiple-breath linear regression method, and does not produce the occasional substantial errors in gain ratio that may occur with the other methods. When magnetometers are used, the standard ratio is 4:1 (rib cage-to-abdomen); when Respitrace is used, the standard ratio is 2:1. In 11 subjects, calibration with standard ratios was as accurate as the isovolume and linear regression techniques. Accuracy during normal breathing was nearly always within 10% (median 2%), but occasional large errors occurred with both instruments.
Hybrid PSO-ASVR-based method for data fitting in the calibration of infrared radiometer
Yang, Sen; Li, Chengwei, E-mail: heikuanghit@163.com
2016-06-15
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 radiationmore » 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.« less
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.
Coifman, R. R.; Lafon, S.; Lee, A. B.; Maggioni, M.; Nadler, B.; Warner, F.; Zucker, S. W.
2005-01-01
In the companion article, a framework for structural multiscale geometric organization of subsets of \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\setlength{\\oddsidemargin}{-69pt} \\begin{document} \\begin{equation*}{\\mathbb{R}}^{n}\\end{equation*}\\end{document} and of graphs was introduced. Here, diffusion semigroups are used to generate multiscale analyses in order to organize and represent complex structures. We emphasize the multiscale nature of these problems and build scaling functions of Markov matrices (describing local transitions) that lead to macroscopic descriptions at different scales. The process of iterating or diffusing the Markov matrix is seen as a generalization of some aspects of the Newtonian paradigm, in which local infinitesimal transitions of a system lead to global macroscopic descriptions by integration. This article deals with the construction of fast-order N algorithms for data representation and for homogenization of heterogeneous structures. PMID:15899969
Isarangkool Na Ayutthaya, S; Do, F C; Pannengpetch, K; Junjittakarn, J; Maeght, J-L; Rocheteau, A; Cochard, H
2010-01-01
The transient thermal dissipation (TTD) method developed by Do and Rocheteau (2002b) is a close evolution of the original constant thermal dissipation (CTD) method of Granier (1985). The TTD method has the advantage of limiting the influence of passive natural temperature gradients and of yielding more stable zero-flux references at night. By analogy with the CTD method, the transient method was first calibrated on synthetic porous material (sawdust) on the assumption that the relationship was independent of the woody species. Here, our concern was to test the latter hypothesis with a 10-min heating time in three tropical species: Hevea brasiliensis Müll. Arg., Mangifera indica L. and Citrus maxima Merr. A complementary objective was to compare the field estimates of daily transpiration for mature rubber trees with estimates based on a simplified soil water balance in the dry season. The calibration experiments were carried out in the laboratory on cut stems using an HPFM device and gravimetric control of water flow up to 5 L dm(-2) h(-1). Nineteen response curves were assessed on fully conductive xylem, combining 11 cut stems and two probes. The field evaluation comprised five periods from November 2007 to February 2008. Estimates of daily transpiration from the measurement of sap flow were based on the 41 sensors set up on 11 trees. Soil water depletion was monitored by neutron probe and 12 access tubes to a depth of 1.8 m. The calibrations confirmed that the response of the transient thermal index to flow density was independent of the woody species that were tested. The best fit was a simple linear response (R(2) = 0.88, n = 276 and P < 0.0001). The previous calibration performed by Do and Rocheteau (2002b) on sawdust fell within the variability of the multi-species calibration; however, there were substantial differences with the average curve at extreme flow rates. Field comparison with soil water depletion in the dry season validated to a reasonable extent
NASA Astrophysics Data System (ADS)
Ogohara, Kazunori; Takagi, Masahiro; Murakami, Shin-ya; Horinouchi, Takeshi; Yamada, Manabu; Kouyama, Toru; Hashimoto, George L.; Imamura, Takeshi; Yamamoto, Yukio; Kashimura, Hiroki; Hirata, Naru; Sato, Naoki; Yamazaki, Atsushi; Satoh, Takehiko; Iwagami, Naomoto; Taguchi, Makoto; Watanabe, Shigeto; Sato, Takao M.; Ohtsuki, Shoko; Fukuhara, Tetsuya; Futaguchi, Masahiko; Sakanoi, Takeshi; Kameda, Shingo; Sugiyama, Ko-ichiro; Ando, Hiroki; Lee, Yeon Joo; Nakamura, Masato; Suzuki, Makoto; Hirose, Chikako; Ishii, Nobuaki; Abe, Takumi
2017-12-01
We provide an overview of data products from observations by the Japanese Venus Climate Orbiter, Akatsuki, and describe the definition and content of each data-processing level. Levels 1 and 2 consist of non-calibrated and calibrated radiance (or brightness temperature), respectively, as well as geometry information (e.g., illumination angles). Level 3 data are global-grid data in the regular longitude-latitude coordinate system, produced from the contents of Level 2. Non-negligible errors in navigational data and instrumental alignment can result in serious errors in the geometry calculations. Such errors cause mismapping of the data and lead to inconsistencies between radiances and illumination angles, along with errors in cloud-motion vectors. Thus, we carefully correct the boresight pointing of each camera by fitting an ellipse to the observed Venusian limb to provide improved longitude-latitude maps for Level 3 products, if possible. The accuracy of the pointing correction is also estimated statistically by simulating observed limb distributions. The results show that our algorithm successfully corrects instrumental pointing and will enable a variety of studies on the Venusian atmosphere using Akatsuki data.[Figure not available: see fulltext.
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.
Comparing Single-Point and Multi-point Calibration Methods in Modulated DSC
Van Buskirk, Caleb Griffith
2017-06-14
Heat capacity measurements for High Density Polyethylene (HDPE) and Ultra-high Molecular Weight Polyethylene (UHMWPE) were performed using Modulated Differential Scanning Calorimetry (mDSC) over a wide temperature range, -70 to 115 °C, with a TA Instruments Q2000 mDSC. The default calibration method for this instrument involves measuring the heat capacity of a sapphire standard at a single temperature near the middle of the temperature range of interest. However, this method often fails for temperature ranges that exceed a 50 °C interval, likely because of drift or non-linearity in the instrument's heat capacity readings over time or over the temperature range. Therefore, in this study a method was developed to calibrate the instrument using multiple temperatures and the same sapphire standard.
A focusing method in the calibration process of image sensors based on IOFBs.
Fernández, Pedro R; Lázaro, José L; Gardel, Alfredo; Cano, Angel 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.
Comparing Single-Point and Multi-point Calibration Methods in Modulated DSC
Van Buskirk, Caleb Griffith
2017-06-14
Heat capacity measurements for High Density Polyethylene (HDPE) and Ultra-high Molecular Weight Polyethylene (UHMWPE) were performed using Modulated Differential Scanning Calorimetry (mDSC) over a wide temperature range, -70 to 115 °C, with a TA Instruments Q2000 mDSC. The default calibration method for this instrument involves measuring the heat capacity of a sapphire standard at a single temperature near the middle of the temperature range of interest. However, this method often fails for temperature ranges that exceed a 50 °C interval, likely because of drift or non-linearity in the instrument's heat capacity readings over time or over the temperature range. Therefore,more » in this study a method was developed to calibrate the instrument using multiple temperatures and the same sapphire standard.« less
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
Zhang, Qian; Wang, Lei; Liu, Zengjun; Zhang, Yiming
2016-09-19
The calibration of an inertial measurement unit (IMU) is a key technique to improve the preciseness of the inertial navigation system (INS) for missile, especially for the calibration of accelerometer scale factor. Traditional calibration method is generally based on the high accuracy turntable, however, it leads to expensive costs and the calibration results are not suitable to the actual operating environment. In the wake of developments in multi-axis rotational INS (RINS) with optical inertial sensors, self-calibration is utilized as an effective way to calibrate IMU on missile and the calibration results are more accurate in practical application. However, the introduction of multi-axis RINS causes additional calibration errors, including non-orthogonality errors of mechanical processing and non-horizontal errors of operating environment, it means that the multi-axis gimbals could not be regarded as a high accuracy turntable. As for its application on missiles, in this paper, after analyzing the relationship between the calibration error of accelerometer scale factor and non-orthogonality and non-horizontal angles, an innovative calibration procedure using the signals of fiber optic gyro and photoelectric encoder is proposed. The laboratory and vehicle experiment results validate the theory and prove that the proposed method relaxes the orthogonality requirement of rotation axes and eliminates the strict application condition of the system.
Lu, Dan; Ricciuto, Daniel M.; Walker, Anthony P.; Safta, Cosmin; Munger, William
2017-09-27
Calibration of terrestrial ecosystem models is important but challenging. Bayesian inference implemented by Markov chain Monte Carlo (MCMC) sampling provides a comprehensive framework to estimate model parameters and associated uncertainties using their posterior distributions. The effectiveness and efficiency of the method strongly depend on the MCMC algorithm used. In this work, a differential evolution adaptive Metropolis (DREAM) algorithm is used to estimate posterior distributions of 21 parameters for the data assimilation linked ecosystem carbon (DALEC) model using 14 years of daily net ecosystem exchange data collected at the Harvard Forest Environmental Measurement Site eddy-flux tower. The calibration of DREAM results in a better model fit and predictive performance compared to the popular adaptive Metropolis (AM) scheme. Moreover, DREAM indicates that two parameters controlling autumn phenology have multiple modes in their posterior distributions while AM only identifies one mode. The application suggests that DREAM is very suitable to calibrate complex terrestrial ecosystem models, where the uncertain parameter size is usually large and existence of local optima is always a concern. In addition, this effort justifies the assumptions of the error model used in Bayesian calibration according to the residual analysis. Here, the result indicates that a heteroscedastic, correlated, Gaussian error model is appropriate for the problem, and the consequent constructed likelihood function can alleviate the underestimation of parameter uncertainty that is usually caused by using uncorrelated error models.
NASA Astrophysics Data System (ADS)
Lu, Dan; Ricciuto, Daniel; Walker, Anthony; Safta, Cosmin; Munger, William
2017-09-01
Calibration of terrestrial ecosystem models is important but challenging. Bayesian inference implemented by Markov chain Monte Carlo (MCMC) sampling provides a comprehensive framework to estimate model parameters and associated uncertainties using their posterior distributions. The effectiveness and efficiency of the method strongly depend on the MCMC algorithm used. In this work, a differential evolution adaptive Metropolis (DREAM) algorithm is used to estimate posterior distributions of 21 parameters for the data assimilation linked ecosystem carbon (DALEC) model using 14 years of daily net ecosystem exchange data collected at the Harvard Forest Environmental Measurement Site eddy-flux tower. The calibration of DREAM results in a better model fit and predictive performance compared to the popular adaptive Metropolis (AM) scheme. Moreover, DREAM indicates that two parameters controlling autumn phenology have multiple modes in their posterior distributions while AM only identifies one mode. The application suggests that DREAM is very suitable to calibrate complex terrestrial ecosystem models, where the uncertain parameter size is usually large and existence of local optima is always a concern. In addition, this effort justifies the assumptions of the error model used in Bayesian calibration according to the residual analysis. The result indicates that a heteroscedastic, correlated, Gaussian error model is appropriate for the problem, and the consequent constructed likelihood function can alleviate the underestimation of parameter uncertainty that is usually caused by using uncorrelated error models.
Lu, Dan; Ricciuto, Daniel M.; Walker, Anthony P.; ...
2017-09-27
Calibration of terrestrial ecosystem models is important but challenging. Bayesian inference implemented by Markov chain Monte Carlo (MCMC) sampling provides a comprehensive framework to estimate model parameters and associated uncertainties using their posterior distributions. The effectiveness and efficiency of the method strongly depend on the MCMC algorithm used. In this work, a differential evolution adaptive Metropolis (DREAM) algorithm is used to estimate posterior distributions of 21 parameters for the data assimilation linked ecosystem carbon (DALEC) model using 14 years of daily net ecosystem exchange data collected at the Harvard Forest Environmental Measurement Site eddy-flux tower. The calibration of DREAM results inmore » a better model fit and predictive performance compared to the popular adaptive Metropolis (AM) scheme. Moreover, DREAM indicates that two parameters controlling autumn phenology have multiple modes in their posterior distributions while AM only identifies one mode. The application suggests that DREAM is very suitable to calibrate complex terrestrial ecosystem models, where the uncertain parameter size is usually large and existence of local optima is always a concern. In addition, this effort justifies the assumptions of the error model used in Bayesian calibration according to the residual analysis. Here, the result indicates that a heteroscedastic, correlated, Gaussian error model is appropriate for the problem, and the consequent constructed likelihood function can alleviate the underestimation of parameter uncertainty that is usually caused by using uncorrelated error models.« less
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
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
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. 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. 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 cm(3) 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. 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. The single film method proved to be superior to the traditional calibration method and produce fast daily film calibration for highly accurate IMRT verification.
Huang, Bin
2015-07-01
A number of common issues related to the process of flexible tactile sensor calibration are discussed in this paper, and an estimate of the accuracy of classical calibration methods, as represented by a weight-pulley device, is presented. A flexible tactile sensor calibration method that is based on a six-dimensional force measurement is proposed on the basis of a theoretical analysis. A high-accuracy flexible tactile sensor calibration bench based on the air-bearing six-dimensional force measurement principle was developed to achieve a technically challenging measurement accuracy of 2% full scale (FS) for three-dimensional (3D) flexible tactile sensor calibration. The experimental results demonstrate that the accuracy of the air-bearing six-dimensional force measurement platform can reach 0.2% FS. Thus, the system satisfies the 3D flexible tactile sensor calibration requirement of 2% FS.
NASA Astrophysics Data System (ADS)
Huang, Bin
2015-07-01
A number of common issues related to the process of flexible tactile sensor calibration are discussed in this paper, and an estimate of the accuracy of classical calibration methods, as represented by a weight-pulley device, is presented. A flexible tactile sensor calibration method that is based on a six-dimensional force measurement is proposed on the basis of a theoretical analysis. A high-accuracy flexible tactile sensor calibration bench based on the air-bearing six-dimensional force measurement principle was developed to achieve a technically challenging measurement accuracy of 2% full scale (FS) for three-dimensional (3D) flexible tactile sensor calibration. The experimental results demonstrate that the accuracy of the air-bearing six-dimensional force measurement platform can reach 0.2% FS. Thus, the system satisfies the 3D flexible tactile sensor calibration requirement of 2% FS.
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%.
NASA Astrophysics Data System (ADS)
Dilecce, G.; Vigliotti, M.; DeBenedictis, S.
2000-03-01
In this communication we propose a calibration method for two-photon absorption laser induced fluorescence (TALIF). It can be carried out without any addition or modification to the O atom TALIF set-up. It is based on the measurement of the collision quenching of the laser-excited state (3p3 P2 ) in a pure O2 system in which a high dissociation degree can be achieved. Since the collision rate constant by O is largely lower than that by O2 , the quenching rate can be correlated to the O density. The incertitude in this procedure is comparable to other calibration techniques. We have applied this method to the spatially resolved measurement of O atom density in an O2 rf plasma jet.
Calibration method of focal plane for static multi-star simulator
NASA Astrophysics Data System (ADS)
Li, Zhaohui; Zhao, Jianke; Xu, Liang
2015-11-01
The calibration work was important to the development of star sensor, improving the accuracy of star simulator was very important for the calibration of star sensor. In reality, being limited in manufacturing technology, assembling and testing facility and so on, it was very difficult to achieve the precision of design theory, especially the star angular distance. In this paper, from the accuracy of angular distance of star simulator, combined with the installation practice, through real-time monitoring of theodolite, and put forward a quantitative method of focusing. Experimentation have shown that the method can realize the accurately focusing of star simulator, all the angle distance error finally were less than 7.72″, and can improve the installation efficiency.
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.
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.
NASA Astrophysics Data System (ADS)
Leman, Samuel; Hoeppe, Frederic
2016-05-01
This paper is about the first results of a new generation of ElectroMagnetic (EM) methodology applied to spacecraft systems modelling in the low frequency range (system's dimensions are of the same order of magnitude as the wavelength).This innovative approach aims at implementing appropriate simplifications of the real system based on the identification of the dominant electrical and geometrical parameters driving the global EM behaviour. One rigorous but expensive simulation is performed to quantify the error generated by the use of simpler multi-models. If both the speed up of the simulation time and the quality of the EM response are satisfied, uncertainty simulation could be performed based on the simple models library implementing in a flexible and robust Kron's network formalism.This methodology is expected to open up new perspectives concerning fast parametric analysis, and deep understanding of systems behaviour. It will ensure the identification of main radiated and conducted coupling paths and the sensitive EM parameters in order to optimize the protections and to control the disturbance sources in spacecraft design phases.
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.
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.
High-accuracy self-calibration method for dual-axis rotation-modulating RLG-INS
NASA Astrophysics Data System (ADS)
Wei, Guo; Gao, Chunfeng; Wang, Qi; Wang, Qun; Long, Xingwu
2017-05-01
Inertial navigation system has been the core component of both military and civil navigation systems. Dual-axis rotation modulation can completely eliminate the inertial elements constant errors of the three axes to improve the system accuracy. But the error caused by the misalignment angles and the scale factor error cannot be eliminated through dual-axis rotation modulation. And discrete calibration method cannot fulfill requirements of high-accurate calibration of the mechanically dithered ring laser gyroscope navigation system with shock absorbers. This paper has analyzed the effect of calibration error during one modulated period and presented a new systematic self-calibration method for dual-axis rotation-modulating RLG-INS. Procedure for self-calibration of dual-axis rotation-modulating RLG-INS has been designed. The results of self-calibration simulation experiment proved that: this scheme can estimate all the errors in the calibration error model, the calibration precision of the inertial sensors scale factor error is less than 1ppm and the misalignment is less than 5″. These results have validated the systematic self-calibration method and proved its importance for accuracy improvement of dual -axis rotation inertial navigation system with mechanically dithered ring laser gyroscope.
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. © The Author 2016. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
Gates, Richard S.; Reitsma, Mark G.; Kramar, John A.; Pratt, Jon R.
2011-01-01
The evolution of the atomic force microscope into a useful tool for measuring mechanical properties of surfaces at the nanoscale has spurred the need for more precise and accurate methods for calibrating the spring constants of test cantilevers. Groups within international standards organizations such as the International Organization for Standardization and the Versailles Project on Advanced Materials and Standards (VAMAS) are conducting studies to determine which methods are best suited for these calibrations and to try to improve the reproducibility and accuracy of these measurements among different laboratories. This paper expands on a recent mini round robin within VAMAS Technical Working Area 29 to measure the spring constant of a single batch of triangular silicon nitride cantilevers sent to three international collaborators. Calibration techniques included reference cantilever, added mass, and two forms of thermal methods. Results are compared to measurements traceable to the International System of Units provided by an electrostatic force balance. A series of guidelines are also discussed for procedures that can improve the running of round robins in atomic force microscopy. PMID:26989594
A novel method of strain - bending moment calibration for blade testing
NASA Astrophysics Data System (ADS)
Greaves, P.; Prieto, R.; Gaffing, J.; van Beveren, C.; Dominy, R.; Ingram, G.
2016-09-01
A new method of interpreting strain data in full scale static and fatigue tests has been implemented as part of the Offshore Renewable Energy Catapult's ongoing development of biaxial fatigue testing of wind turbine blades. During bi-axial fatigue tests, it is necessary to be able to distinguish strains arising from the flapwise motion of the blade from strains arising from the edgewise motion. The method exploits the beam-like structure of blades and is derived using the equations of beam theory. It offers several advantages over the current state of the art method of calibrating strain gauges.
NASA Astrophysics Data System (ADS)
Kraus, Michael; Kormann, Katharina; Sonnendrücker, Eric; Morrison, Philip
2016-10-01
In this talk we will describe recent work on the development of geometric particle-in-cell methods for the Vlasov-Maxwell system and gyrokinetics. We present a novel framework for particle-in-cell methods based on the discretization of the underlying Hamiltonian structure of the Vlasov-Maxwell system. We derive semi-discrete Poisson brackets which satisfy the Jacobi identity and apply Hamiltonian splitting schemes for time integration. Techniques from Finite Element Exterior Calculus and spline differential forms ensure conservation of the divergence of the magnetic field and Gauss' law as well as stability of the field solver. The resulting methods are gauge-invariant, feature exact charge conservation show excellent long-time energy behaviour. The talk will be concluded with an outline of how to extend these techniques towards gyrokinetics.
Comparison of Various Optimization Methods for Calibration of Conceptual Rainfall-Runoff Models
NASA Astrophysics Data System (ADS)
Bhatt, Divya; Jain, Ashu
2010-05-01
Runoff forecasts are needed in many water resources activities such as flood and drought management, irrigation practices, and water distribution systems, etc. Runoff is generally forecasted using rainfall-runoff models by using hydrologic data in the catchment. Computer based hydrologic models have become popular with practicing hydrologists and water resources engineers for performing hydrologic forecasts and for managing water systems. Rainfall-runoff library (RRL) is computer software developed by Cooperative Research Centre for Catchment Hydrology (CRCCH), Australia. The RRL consists of five different conceptual rainfall-runoff models and has been in operation in many water resources applications in Australia. RRL is designed to simulate catchment runoff by using daily rainfall and evapotranspiration data. In this paper, the results from an investigation on the use of different optimization methods for the calibration of various conceptual rainfall-runoff models available in RRL toolkit are presented. Out of the five conceptual models in the RRL toolkit, AWBM (The Australian Water Balance Model) has been employed. Seven different optimization methods are investigated for the calibration of the AWBM model. The optimization methods investigated include uniform random sampling, pattern search, multi start pattern search, Rosenbrock search, Rosenbrock multi-start search, Shuffled Complex Evolution (SCE-UA) and Genetic Algorithm (GA). Trial and error procedures were employed to arrive at the best values of various parameters involved in the optimizers for all to develop the AWBM. The results obtained from the best configuration of the AWBM are presented here for all optimization methods. The daily rainfall and runoff data derived from Bird Creek Basin, Oklahoma, USA have been employed to develop all the models included here. A wide range of error statistics have been used to evaluate the performance of all the models developed in this study. It has been found that
New Calibration Method of Accelerometers in GRACE Satellites Based on Precise Solar Radiation Model
NASA Astrophysics Data System (ADS)
Wang, Hong-bo; Xiong, Yong-qing; Zhao, Chang-yin
2017-10-01
Adopting the precise radiation pressure model, we compute the real perturbation force caused by the solar radiation on the GRACE satellites and estimate the scale factors of accelerometer's y axis and z axis. Setting these scale factors constant and using the dynamical orbit determination (OD), we estimate the rest four calibration parameters, i.e. the scale factor of the x axis and the biases of three axes. On this basis, we obtain the daily calibration parameters from 2002 to 2014. The average values and standard deviations of scale factors of the x, y and z axes are 0.9435 ± 0.0187, 0.9393 ± 0.0444, 1.0371 ± 0.0391 for GRACE-A, and 0.9313 ± 0.0170, 0.9488 ± 0.0452, 1.0274 ± 0.0446 for GRACE-B, respectively. Compared with our previous work, this new method constrains the scale factors of the y and z axes with the precise radiation pressure model, which can reduce the influence of data errors on the weak-signal axes (y, z), as well as reduce the correlation between scale factors and biases, and eventually improve the stability of calibration parameters. Taking the y and z axes of GRACE-A as an example, the standard deviations of scale factors with this new method are about 0.0391-0.0444, while the previous results obtained by the unconstrained dynamical orbit determination were about 0.21-0.31. It is shown that the standard deviations of scale factors in this paper have been reduced by more than 78%, and those of biases have been reduced by more than 85%. Therefore, the calibration parameters estimated with the new method are more stable and will be of particular interest for the study on the rotation speed and wind field of the Earth's thermosphere.
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)
Close, D. A.; Atwater, H. F.
1990-09-01
The two-geometry method is an approved technique to verify the uranium enrichment of UF 6 in centrifuge cascade header pipes. Two analytical calculations, Monte Carlo and numerical integration of expressions derived from geometrical arguments, have been applied to determine the detector geometry constants to simplify optimizing the pair of detector collimator geometries. Comparisons are presented for two pairs of collimators: an uncollimated and a collimated geometry; and a parallel collimated and a perpendicular collimated geometry. Both Monte Carlo and numerical integration techniques qualitatively predict the characteristics of this enrichment measurement.
NASA Astrophysics Data System (ADS)
Chatzistergos, Theodosios; Usoskin, Ilya G.; Kovaltsov, Gennady A.; Krivova, Natalie A.; Solanki, Sami K.
2017-06-01
Context. The group sunspot number (GSN) series constitute the longest instrumental astronomical database providing information on solar activity. This database is a compilation of observations by many individual observers, and their inter-calibration has usually been performed using linear rescaling. There are multiple published series that show different long-term trends for solar activity. Aims: We aim at producing a GSN series, with a non-linear non-parametric calibration. The only underlying assumptions are that the differences between the various series are due to different acuity thresholds of the observers, and that the threshold of each observer remains constant throughout the observing period. Methods: We used a daisy chain process with backbone (BB) observers and calibrated all overlapping observers to them. We performed the calibration of each individual observer with a probability distribution function (PDF) matrix constructed considering all daily values for the overlapping period with the BB. The calibration of the BBs was carried out in a similar manner. The final series was constructed by merging different BB series. We modelled the propagation of errors straightforwardly with Monte Carlo simulations. A potential bias due to the selection of BBs was investigated and the effect was shown to lie within the 1σ interval of the produced series. The exact selection of the reference period was shown to have a rather small effect on our calibration as well. Results: The final series extends back to 1739 and includes data from 314 observers. This series suggests moderate activity during the 18th and 19th century, which is significantly lower than the high level of solar activity predicted by other recent reconstructions applying linear regressions. Conclusions: The new series provides a robust reconstruction, based on modern and non-parametric methods, of sunspot group numbers since 1739, and it confirms the existence of the modern grand maximum of solar
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
Line-feature-based calibration method of structured light plane parameters for robot hand-eye system
NASA Astrophysics Data System (ADS)
Qi, Yuhan; Jing, Fengshui; Tan, Min
2013-03-01
For monocular-structured light vision measurement, it is essential to calibrate the structured light plane parameters in addition to the camera intrinsic parameters. A line-feature-based calibration method of structured light plane parameters for a robot hand-eye system is proposed. Structured light stripes are selected as calibrating primitive elements, and the robot moves from one calibrating position to another with constraint in order that two misaligned stripe lines are generated. The images of stripe lines could then be captured by the camera fixed at the robot's end link. During calibration, the equations of two stripe lines in the camera coordinate system are calculated, and then the structured light plane could be determined. As the robot's motion may affect the effectiveness of calibration, so the robot's motion constraints are analyzed. A calibration experiment and two vision measurement experiments are implemented, and the results reveal that the calibration accuracy can meet the precision requirement of robot thick plate welding. Finally, analysis and discussion are provided to illustrate that the method has a high efficiency fit for industrial in-situ calibration.
A Quantitative Comparison of Calibration Methods for RGB-D Sensors Using Different Technologies.
Villena-Martínez, Víctor; Fuster-Guilló, Andrés; Azorín-López, Jorge; Saval-Calvo, Marcelo; Mora-Pascual, Jeronimo; Garcia-Rodriguez, Jose; Garcia-Garcia, Alberto
2017-01-27
RGB-D (Red Green Blue and Depth) sensors are devices that can provide color and depth information from a scene at the same time. Recently, they have been widely used in many solutions due to their commercial growth from the entertainment market to many diverse areas (e.g., robotics, CAD, etc.). In the research community, these devices have had good uptake due to their acceptable levelofaccuracyformanyapplicationsandtheirlowcost,butinsomecases,theyworkatthelimitof their sensitivity, near to the minimum feature size that can be perceived. For this reason, calibration processes are critical in order to increase their accuracy and enable them to meet the requirements of such kinds of applications. To the best of our knowledge, there is not a comparative study of calibration algorithms evaluating its results in multiple RGB-D sensors. Speciﬁcally, in this paper, a comparison of the three most used calibration methods have been applied to three different RGB-D sensors based on structured light and time-of-ﬂight. The comparison of methods has been carried out by a set of experiments to evaluate the accuracy of depth measurements. Additionally, an object reconstruction application has been used as example of an application for which the sensor works at the limit of its sensitivity. The obtained results of reconstruction have been evaluated through visual inspection and quantitative measurements.
Lu, Dan; Ricciuto, Daniel; Walker, Anthony; Safta, Cosmin; Munger, William
2017-02-22
Calibration of terrestrial ecosystem models is important but challenging. Bayesian inference implemented by Markov chain Monte Carlo (MCMC) sampling provides a comprehensive framework to estimate model parameters and associated uncertainties using their posterior distributions. The effectiveness and efficiency of the method strongly depend on the MCMC algorithm used. In this study, a Differential Evolution Adaptive Metropolis (DREAM) algorithm was used to estimate posterior distributions of 21 parameters for the data assimilation linked ecosystem carbon (DALEC) model using 14 years of daily net ecosystem exchange data collected at the Harvard Forest Environmental Measurement Site eddy-flux tower. The DREAM is a multi-chain method and uses differential evolution technique for chain movement, allowing it to be efficiently applied to high-dimensional problems, and can reliably estimate heavy-tailed and multimodal distributions that are difficult for single-chain schemes using a Gaussian proposal distribution. The results were evaluated against the popular Adaptive Metropolis (AM) scheme. DREAM indicated that two parameters controlling autumn phenology have multiple modes in their posterior distributions while AM only identified one mode. The calibration of DREAM resulted in a better model fit and predictive performance compared to the AM. DREAM provides means for a good exploration of the posterior distributions of model parameters. Lastly, it reduces the risk of false convergence to a local optimum and potentially improves the predictive performance of the calibrated model.
In-Flight Calibration Methods for Temperature-Dependent Offsets in the MMS Fluxgate Magnetometers
NASA Technical Reports Server (NTRS)
Bromund, K. R.; Plaschke, F.; Strangeway, R. J.; Anderson, B. J.; Huang, B. G.; Magnes, W.; Fischer, D.; Nakamura, R.; Leinweber, H. K.; Russell, C. T.;
2016-01-01
During the first dayside season of the Magnetospheric Multiscale (MMS) mission, the in-flight calibration process for the Fluxgate magnetometers (FGM) implemented an algorithm that selected a constant offset (zero-level) for each sensor on each orbit. This method was generally able to reduce the amplitude of residual spin tone to less than 0.2 nT within the region of interest. However, there are times when the offsets do show significant short-term variations. These variations are most prominent in the nighttime season (phase 1X), when eclipses are accompanied by offset changes as large as 1 nT. Eclipses are followed by a recovery period as long as 12 hours where the offsets continue to change as temperatures stabilize. Understanding and compensating for these changes will become critical during Phase 2 of the mission in 2017, when the nightside will become the focus of MMS science. Although there is no direct correlation between offset and temperature, the offsets are seen for the period of any given week to be well-characterized as function of instrument temperature. Using this property, a new calibration method has been developed that has proven effective in compensating for temperature-dependent offsets during phase 1X of the MMS mission and also promises to further refine calibration quality during the dayside season.
Toward improved calibration of hydrologic models: Combining the strengths of manual and automatic methods
NASA Astrophysics Data System (ADS)
Boyle, Douglas P.; Gupta, Hoshin V.; Sorooshian, Soroosh
2000-12-01
Automatic methods for model calibration seek to take advantage of the speed and power of digital computers, while being objective and relatively easy to implement. However, they do not provide parameter estimates and hydrograph simulations that are considered acceptable by the hydrologists responsible for operational forecasting and have therefore not entered into widespread use. In contrast, the manual approach which has been developed and refined over the years to result in excellent model calibrations is complicated and highly labor-intensive, and the expertise acquired by one individual with a specific model is not easily transferred to another person (or model). In this paper, we propose a hybrid approach that combines the strengths of each. A multicriteria formulation is used to "model" the evaluation techniques and strategies used in manual calibration, and the resulting optimization problem is solved by means of a computerized algorithm. The new approach provides a stronger test of model performance than methods that use a single overall statistic to aggregate model errors over a large range of hydrologie behaviors. The power of the new approach is illustrated by means of a case study using the Sacramento Soil Moisture Accounting model.
NASA Astrophysics Data System (ADS)
Chen, Yuanpei; Wang, Lingcao; Li, Kui
2017-10-01
Rotary inertial navigation modulation mechanism can greatly improve the inertial navigation system (INS) accuracy through the rotation. Based on the single-axis rotational inertial navigation system (RINS), a self-calibration method is put forward. The whole system is applied with the rotation modulation technique so that whole inertial measurement unit (IMU) of system can rotate around the motor shaft without any external input. In the process of modulation, some important errors can be decoupled. Coupled with the initial position information and attitude information of the system as the reference, the velocity errors and attitude errors in the rotation are used as measurement to perform Kalman filtering to estimate part of important errors of the system after which the errors can be compensated into the system. The simulation results show that the method can complete the self-calibration of the single-axis RINS in 15 minutes and estimate gyro drifts of three-axis, the installation error angle of the IMU and the scale factor error of the gyro on z-axis. The calibration accuracy of optic gyro drifts could be about 0.003°/h (1σ) as well as the scale factor error could be about 1 parts per million (1σ). The errors estimate reaches the system requirements which can effectively improve the longtime navigation accuracy of the vehicle or the boat.
Lu, Dan; Ricciuto, Daniel; Walker, Anthony; ...
2017-02-22
Calibration of terrestrial ecosystem models is important but challenging. Bayesian inference implemented by Markov chain Monte Carlo (MCMC) sampling provides a comprehensive framework to estimate model parameters and associated uncertainties using their posterior distributions. The effectiveness and efficiency of the method strongly depend on the MCMC algorithm used. In this study, a Differential Evolution Adaptive Metropolis (DREAM) algorithm was used to estimate posterior distributions of 21 parameters for the data assimilation linked ecosystem carbon (DALEC) model using 14 years of daily net ecosystem exchange data collected at the Harvard Forest Environmental Measurement Site eddy-flux tower. The DREAM is a multi-chainmore » method and uses differential evolution technique for chain movement, allowing it to be efficiently applied to high-dimensional problems, and can reliably estimate heavy-tailed and multimodal distributions that are difficult for single-chain schemes using a Gaussian proposal distribution. The results were evaluated against the popular Adaptive Metropolis (AM) scheme. DREAM indicated that two parameters controlling autumn phenology have multiple modes in their posterior distributions while AM only identified one mode. The calibration of DREAM resulted in a better model fit and predictive performance compared to the AM. DREAM provides means for a good exploration of the posterior distributions of model parameters. Lastly, it reduces the risk of false convergence to a local optimum and potentially improves the predictive performance of the calibrated model.« less
A Quantitative Comparison of Calibration Methods for RGB-D Sensors Using Different Technologies
Villena-Martínez, Víctor; Fuster-Guilló, Andrés; Azorín-López, Jorge; Saval-Calvo, Marcelo; Mora-Pascual, Jeronimo; Garcia-Rodriguez, Jose; Garcia-Garcia, Alberto
2017-01-01
RGB-D (Red Green Blue and Depth) sensors are devices that can provide color and depth information from a scene at the same time. Recently, they have been widely used in many solutions due to their commercial growth from the entertainment market to many diverse areas (e.g., robotics, CAD, etc.). In the research community, these devices have had good uptake due to their acceptable level of accuracy for many applications and their low cost, but in some cases, they work at the limit of their sensitivity, near to the minimum feature size that can be perceived. For this reason, calibration processes are critical in order to increase their accuracy and enable them to meet the requirements of such kinds of applications. To the best of our knowledge, there is not a comparative study of calibration algorithms evaluating its results in multiple RGB-D sensors. Specifically, in this paper, a comparison of the three most used calibration methods have been applied to three different RGB-D sensors based on structured light and time-of-flight. The comparison of methods has been carried out by a set of experiments to evaluate the accuracy of depth measurements. Additionally, an object reconstruction application has been used as example of an application for which the sensor works at the limit of its sensitivity. The obtained results of reconstruction have been evaluated through visual inspection and quantitative measurements. PMID:28134826
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.
Calibration method for carbon dioxide sensors to investigate direct methanol fuel cell efficiency
NASA Astrophysics Data System (ADS)
Stähler, M.; Burdzik, A.
2014-09-01
Methanol crossover is a process in direct methanol fuel cells which causes significant reduction of cell efficiency. Methanol permeates through the membrane electrode assembly and reacts at the cathode with oxygen to form carbon dioxide. This process is undesirable because it does not generate electric energy, but rather only increases heat production. Different procedures have been used for the investigation of this crossover. One method uses the detection of carbon dioxide in the exhaust gas of the cathode by means of a carbon dioxide sensor. This technique is inexpensive and enables real-time measurements but its disadvantage is the low accuracy. This paper demonstrates a simple method to generate gas mixtures for the calibration of the sensor in order to increase the accuracy. The advantages of this technique consist in the fact that only the existing devices of a direct methanol fuel cell test rig are needed and that the operator can adjust the carbon dioxide concentration for the calibration process. This is important for dealing with nonlinearities of the sensor. A detailed error analysis accompanies the experiments. At the end it is shown that the accuracy of the determined Faraday efficiency can be improved by using the presented calibration technique.
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.more » 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.« less
A calibration method for lateral forces for use with colloidal probe force microscopy cantilevers
NASA Astrophysics Data System (ADS)
Quintanilla, M. A. S.; Goddard, D. T.
2008-02-01
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, 20μm glass beads and UO3 agglomerates attached to silicon tapping mode cantilevers were used to test the method against substrates including glass, cleaved mica, and UO2 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.
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.
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.
High accuracy position response calibration method for a micro-channel plate ion detector
NASA Astrophysics Data System (ADS)
Hong, R.; Leredde, A.; Bagdasarova, Y.; Fléchard, X.; García, A.; Müller, P.; Knecht, A.; Liénard, E.; Kossin, M.; Sternberg, M. G.; Swanson, H. E.; Zumwalt, D. W.
2016-11-01
We have developed a position response calibration method for a micro-channel plate (MCP) detector with a delay-line anode position readout scheme. Using an in situ calibration mask, an accuracy of 8 μm and a resolution of 85 μm (FWHM) have been achieved for MeV-scale α particles and ions with energies of ∼10 keV. At this level of accuracy, the difference between the MCP position responses to high-energy α particles and low-energy ions is significant. The improved performance of the MCP detector can find applications in many fields of AMO and nuclear physics. In our case, it helps reducing systematic uncertainties in a high-precision nuclear β-decay experiment.
Sigalov, A B; Isaeva, N V; Bezruchkina, S V
1993-01-01
The authors have investigated the possibility of using various albumin preparations as calibrators in measurements of human blood serum total protein by the biuret method. Analysis of Precinorm U and Precipath U reference sera has demonstrated that use of various albumin preparations as calibrators may result in significant deviations (as much as 27%) of the resultant values from the due ones.
Calibration of EBT2 film by the PDD method with scanner non-uniformity correction.
Chang, Liyun; Chui, Chen-Shou; Ding, Hueisch-Jy; Hwang, Ing-Ming; Ho, Sheng-Yow
2012-09-21
The EBT2 film together with a flatbed scanner is a convenient dosimetry QA tool for verification of clinical radiotherapy treatments. However, it suffers from a relatively high degree of uncertainty and a tedious film calibration process for every new lot of films, including cutting the films into several small pieces, exposing with different doses, restoring them back and selecting the proper region of interest (ROI) for each piece for curve fitting. In this work, we present a percentage depth dose (PDD) method that can accurately calibrate the EBT2 film together with the scanner non-uniformity correction and provide an easy way to perform film dosimetry. All films were scanned before and after the irradiation in one of the two homemade 2 mm thick acrylic frames (one portrait and the other landscape), which was located at a fixed position on the scan bed of an Epson 10 000XL scanner. After the pre-irradiated scan, the film was placed parallel to the beam central axis and sandwiched between six polystyrene plates (5 cm thick each), followed by irradiation of a 20 × 20 cm² 6 MV photon beam. Two different beams on times were used on two different films to deliver a dose to the film ranging from 32 to 320 cGy. After the post-irradiated scan, the net optical densities for a total of 235 points on the beam central axis on the films were auto-extracted and compared with the corresponding depth doses that were calculated through the measurement of a 0.6 cc farmer chamber and the related PDD table to perform the curve fitting. The portrait film location was selected for routine calibration, since the central beam axis on the film is parallel to the scanning direction, where non-uniformity correction is not needed (Ferreira et al 2009 Phys. Med. Biol. 54 1073-85). To perform the scanner non-uniformity calibration, the cross-beam profiles of the film were analysed by referencing the measured profiles from a Profiler™. Finally, to verify our method, the films were
Gómez-Valdés, Jorge A; Quinto-Sánchez, Mirsha; Menéndez Garmendia, Antinea; Veleminska, Jana; Sánchez-Mejorada, Gabriela; Bruzek, Jaroslav
2012-09-10
Sex estimation is the first step for biological profile reconstruction of an unknown skeleton (archaeological or contemporary) and consequently for positive identification of skeletal remains recovered from forensic settings. Several tools have been developed using different osseous structures. With the intention to provide an objective method comparison, we reported the analysis of three different methods (visual, metric and geometric morphometrics) for sex assessment of the greater sciatic notch. One hundred and thirty pelvic bones (45.4% females and 54.6% males) from the National Autonomous University of Mexico Skeletal Collection pertaining to the contemporary Mexican population were analyzed. We used the ROC-analysis to test between desired false positive thresholds (1-specificity) and expected true positive rates (sensitivity) in order to predict the best approach to sex assessment. The comparison of the area under the ROC-curves shows significant differences among visual and metric methods. At the same time, the analysis suggested that higher morphological variation among the sexes is independent of the methodological approach. The results indicate that the metric (angle), with a high percent of indeterminate cases (34.6%), and visual, with 26.2% of the cases allocated as intermediate cases, were poorly accurate; we cannot recommend these techniques for sexing an unknown specimen. On the other hand, the geometric morphometrics approach improves sex estimation in 82.3% of correctly classified individuals with more than 95% of posterior probability. In addition to the method comparison, the major sexual variation of the greater sciatic notch was determined to be located on its posterior border. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.
In-situ Calibration Methods for Phased Array High Frequency Radars
NASA Astrophysics Data System (ADS)
Flament, P. J.; Flament, M.; Chavanne, C.; Flores-vidal, X.; Rodriguez, I.; Marié, L.; Hilmer, T.
2016-12-01
the presence of reflecting structures (buildings, fences), or possibly fractal nature of the wavefronts; (e) amplitudes lack stability in time and azimuth to be usable as a-priori calibrations, confirming the accepted method of re-normalizing amplitudes by the signal of nearby cells prior to beam-forming.
An efficient surrogate-based simulation-optimization method for calibrating a regional MODFLOW model
NASA Astrophysics Data System (ADS)
Chen, Mingjie; Izady, Azizallah; Abdalla, Osman A.
2017-01-01
Simulation-optimization method entails a large number of model simulations, which is computationally intensive or even prohibitive if the model simulation is extremely time-consuming. Statistical models have been examined as a surrogate of the high-fidelity physical model during simulation-optimization process to tackle this problem. Among them, Multivariate Adaptive Regression Splines (MARS), a non-parametric adaptive regression method, is superior in overcoming problems of high-dimensions and discontinuities of the data. Furthermore, the stability and accuracy of MARS model can be improved by bootstrap aggregating methods, namely, bagging. In this paper, Bagging MARS (BMARS) method is integrated to a surrogate-based simulation-optimization framework to calibrate a three-dimensional MODFLOW model, which is developed to simulate the groundwater flow in an arid hardrock-alluvium region in northwestern Oman. The physical MODFLOW model is surrogated by the statistical model developed using BMARS algorithm. The surrogate model, which is fitted and validated using training dataset generated by the physical model, can approximate solutions rapidly. An efficient Sobol' method is employed to calculate global sensitivities of head outputs to input parameters, which are used to analyze their importance for the model outputs spatiotemporally. Only sensitive parameters are included in the calibration process to further improve the computational efficiency. Normalized root mean square error (NRMSE) between measured and simulated heads at observation wells is used as the objective function to be minimized during optimization. The reasonable history match between the simulated and observed heads demonstrated feasibility of this high-efficient calibration framework.
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.
NASA Astrophysics Data System (ADS)
Luo, Jing; Liu, Dong; Bi, Lei; Zhang, Kejun; Tang, Peijun; Xu, Peituo; Su, Lin; Yang, Liming
2018-01-01
A new method is proposed to calibrate the gain ratio for polarization lidars in this paper, which involves a half-wave plate (HWP) placed immediately upstream of the polarizing beam splitter (PBS) in the receiver of polarization lidars. Gain ratio can be determined by rotating the HWP by 45° without key assumptions. The calibration results of this new method are independent of the monitored atmosphere as well as the system errors related to the components that are upstream of the HWP. Both theoretical calculations in the framework of the Mueller-Stokes formalism and experimental measurements are carried out to validate the calibration method.
NASA Technical Reports Server (NTRS)
Doelling, David R.; Bhatt, Rajendra; Scarino, Benjamin R.; Gopalan, Arun; Haney, Conor O.; Minnis, Patrick; Bedka, Kristopher M.
2016-01-01
Consistent cross-sensor Advanced Very High Resolution Radiometer (AVHRR) calibration coefficients are determined using desert, polar ice, and deep convective cloud (DCC) invariant Earth targets. The greatest AVHRR calibration challenge is the slow orbit degradation of the host satellite, which precesses toward a terminator orbit. This issue is solved by characterizing the invariant targets with NOAA-16 AVHRR observed radiances that have been referenced to the Aqua Moderate Resolution Imaging Spectrometer (MODIS) calibration using simultaneous nadir overpass (SNO) observations. Another benefit of the NOAA-16 invariant target-modeled reflectance method is that, because of the similarities among the AVHRR spectral response functions, a smaller spectral band adjustment factor is required than when establishing calibrations relative to a non-AVHRR reference instrument. The sensor- and band-specific calibration uncertainties, with respect to the calibration reference, are, on average, 2 percent and 3 percent for channels 1 and 2, respectively. The uncertainties are smaller for sensors that are in afternoon orbits, have longer records, and spend less time in terminator conditions. The multiple invariant targets referenced to Aqua MODIS (MITRAM) AVHRR calibration coefficients are evaluated for individual target consistency, compared against Aqua MODIS/AVHRR SNOs, and selected published calibration gains. The MITRAM and SNO relative calibration biases mostly agree to within 1 percent for channels 1 and 2, respectively. The individual invariant target and MITRAM sensor relative calibration biases are mostly consistent to within 1 percent and 2 percent for channels 1 and 2, respectively. The differences between the MITRAM and other published calibrations are mostly attributed to the reference instrument calibration differences.
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
On a calibration of a reaction rate model for explosive by a DSD-informed method
NASA Astrophysics Data System (ADS)
Yoo, Sunhee; Rumchik, Chad; Stewart, Scott
2017-06-01
The theory of detonation shock dynamics (DSD) applies to a model of an explosive with a specified reactant equation of state (EOS), products EOS, and a reaction rate law for reaction progress variable for the change from reactants to products. Given the assumed forms for the EOS, closure for the components and reaction rate law, a ``DSD-informed'' calibration uses experimental shock Hugnoiot data, plane shock initiation data, and shock curvature data and or diameter effect data. It has been found that DSD-informed reactive flow models are predictive of experimentally observed shock dynamics over a wide-range of conditions, once determined. This paper discusses how to calibrate the EOS and reaction rate of Ignition & Growth (I&G) coupled with the reactive flow model. Previous methods of calibration generated a detonation shock speed, curvature relation (D-kappa) from theory and compared with an experimentally determined D-kappa relation. Our new procedure generates a shock shape across a rate stick from theory and compares it with shock shapes obtained from experiments. The procedure is carried out based on the sensitivity of completion term in the I&G model to D-kappa relation and of the reactant equation of state to the local shock shape at wall in a cylindrical explosive.
Vibration detection and calibration method used to remote sensing optical camera
NASA Astrophysics Data System (ADS)
Li, Qi; Dong, Wende; Xu, Zhihai; Feng, Huajun
2013-09-01
In order to obtain sharp remote sensing images, the image stabilization technology of space camera and the remote sensing image restoration technology are usually used now. Vibration detection is the key to realize these technologies: an image stabilization system needs the displacement vector derived from vibration detection to drive the compensation mechanism; and the remote sensing image restoration technology needs the vibration displacement vector to construct the point spread function (PSF). Vibration detection not only can be used to improve image quality of panchromatic camera, infrared cameras and other optical camera, also is motion compensation basis of satellite radar equipment. In this paper we have constructed a vibration measuring method based on Fiber optic gyro (FOG). FOG is a device sensitive to angular velocity or angular displacement. High-precision FOG can be used to measure the jitter angle of the optic axis of a space camera fixed on satellite platform. According to the measured data, the vibration displacement vector of the imaging plane can be calculated. Consequently the vibration data provide a basis for image stabilization of space camera and restoration of remote sensing images. We simulated the vibration of a space camera by using a piezoelectric ceramic deflection platform, and calibrated vibration measurement by using laser beam and a high-speed linear array camera. We compared the feedback output of the deflection platform, the FOG measured data and the calibrated data of the linear array camera, and obtained a calibration accuracy better than 1.5 μrad.
A blind fragile watermarking method for 3D models based on geometric properties of triangles
NASA Astrophysics Data System (ADS)
Molaei, Amir Masoud; Ebrahimnezhad, Hossein; Sedaaghi, Mohammad Hossein
2013-12-01
In this paper, a blind fragile watermarking method is presented for 3D triangular mesh models. In the proposed algorithm, watermark data displace medians of the mark triangle instead of embedding them into the vertices, based on the method which is explained. The displacement leads to a new triangle. The proposed method embeds data into the middle of three sides of mark triangle in spherical coordinates. It is performed by fixing one component of the center of neighboring vertices to mark triangle by small and controlled changes. It also increases the number of mark triangles in their selection process and thereby it increases the embedding capacity. The proposed method is invariant to affine transformation including translation, rotation and uniform scaling, due to the use of the normalization process before the embedding and also detection stages. Simulation results show that the proposed method has higher embedding capacity compared to the similar algorithms with the capability of detecting destructive attacks. [Figure not available: see fulltext.
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
NASA Astrophysics Data System (ADS)
Cepeda, J.; Lacasse, S.; Nadim, F.
2014-12-01
The evaluation of runout is a key aspect in hazard and risk assessments of highly mobile landslides, which frequently cause significant loss of life and property. Both, empirical methods and numerical models can be used for predicting runout behavior, with preference for the latter when estimates of the spatial distribution and time evolution of landslide depths and velocities are required, as in the calculation of expected losses and the design of mitigation works. The input material parameters for numerical models can be directly measured in very few situations due to scale problems or to rheologies not being reproducible in experimental conditions. In most cases, these parameters need to be calibrated by back-analyses where runout simulations are fitted to field observations (footprint, maximum velocities, final depths, etc.). This fitting has normally been performed by comparing the observed and simulated runout area visually and only in few cases quantitative comparisons have been made, but still based only in the planimetric area. The present contribution proposes a new method for quantitatively calibrating material parameters in numerical models for landslide runout prediction. The basis for the procedure is the application of classification statistics to observed runout variables (e.g., planimetric area, depths, velocities) and sets of simulations obtained from a range of input material parameters and rheological models. A first version of the method was put forward recently. This consisted in calculating discrete classifiers for a single landslide and performing simulations for a deterministic set of input variables. The method herein presented is a generalized formulation that allows addressing the following situations: (a) calibration for a set of landslide cases; (b) stochastic input variables; (c) multiple rheologies; and (d) uncertainty in the observed runout variables. The generalized procedure is illustrated with case studies of highly mobile
A three-step calibration method for tri-axial field sensors in a 3D magnetic digital compass
NASA Astrophysics Data System (ADS)
Zhu, Xiaoning; Zhao, Ta; Cheng, Defu; Zhou, Zhijian
2017-04-01
In a 3D magnetic compass, it is important to calibrate the tri-axial magnetometers and accelerometers so the compass will provide accurate heading and attitude information. Previous researchers have used two methods to calibrate these two field sensors separately, i.e. the classic independent ellipsoid fitting method and the independent dot product invariant method, respectively. Both methods are easy to use, and no highly accurate, external equipment is required. However, self-calibration with ellipsoid fitting has the disadvantage that it interfuses an orthogonal matrix, and the dot product invariant method requires the use of pre-calibrated internal field sensors, which may be unavailable in many cases. In this paper, we have introduced and unified an error model of two tri-axial field sensors. Accordingly, the orthogonal matrix caused by ellipsoid fitting was mathematically proved to be the combination of two sources, the mounting misalignment and the rotation misalignment. Moreover, a new method, which we call optimal resultant vector, was proposed to further calibrate multi-sensor systems on the basis of ellipsoid fitting and dot product invariant methods, establishing a new, three-step calibration method. The superiority of the proposed method over the state-of-the-art approaches were demonstrated by simulations and a 3D compass experiment.
2011-08-15
map the pixels showing the damaged area to the model using a ray-tracing like procedure. Our method uses something we developed called “ quaternion ...with CAD models via quaternion optimization,” which will be presented at the annual meeting in August 2011 in San Diego. 5. Extraction and...Stiller, P. F., “Aligning images with CAD models via quaternion optimization,” Mathematical Methods in Pattern and Image Analysis, SPIE, San Diego
Kumar, Sudhir; Srinivasan, P; Sharma, S D
2010-06-01
A cylindrical graphite ionization chamber of sensitive volume 1002.4 cm(3) was designed and fabricated at Bhabha Atomic Research Centre (BARC) for use as a reference dosimeter to measure the strength of high dose rate (HDR) (192)Ir brachytherapy sources. The air kerma calibration coefficient (N(K)) of this ionization chamber was estimated analytically using Burlin general cavity theory and by the Monte Carlo method. In the analytical method, calibration coefficients were calculated for each spectral line of an HDR (192)Ir source and the weighted mean was taken as N(K). In the Monte Carlo method, the geometry of the measurement setup and physics related input data of the HDR (192)Ir source and the surrounding material were simulated using the Monte Carlo N-particle code. The total photon energy fluence was used to arrive at the reference air kerma rate (RAKR) using mass energy absorption coefficients. The energy deposition rates were used to simulate the value of charge rate in the ionization chamber and N(K) was determined. The Monte Carlo calculated N(K) agreed within 1.77 % of that obtained using the analytical method. The experimentally determined RAKR of HDR (192)Ir sources, using this reference ionization chamber by applying the analytically estimated N(K), was found to be in agreement with the vendor quoted RAKR within 1.43%. Copyright 2009 Elsevier Ltd. All rights reserved.
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.
Investigation of methods for calibration of classifier scores to probability of disease
NASA Astrophysics Data System (ADS)
Chen, Weijie; Sahiner, Berkman; Samuelson, Frank; Pezeshk, Aria; Petrick, Nicholas
2015-03-01
Classifier scores in many diagnostic devices, such as computer-aided diagnosis systems, are usually on an arbitrary scale, the meaning of which is unclear. Calibration of classifier scores to a meaningful scale such as the probability of disease is potentially useful when such scores are used by a physician or another algorithm. In this work, we investigated the properties of two methods for calibrating classifier scores to probability of disease. The first is a semiparametric method in which the likelihood ratio for each score is estimated based on a semiparametric proper receiver operating characteristic model, and then an estimate of the probability of disease is obtained using the Bayes theorem assuming a known prevalence of disease. The second method is nonparametric in which isotonic regression via the pool-adjacent-violators algorithm is used. We employed the mean square error (MSE) and the Brier score to evaluate the two methods. We evaluate the methods under two paradigms: (a) the dataset used to construct the score-to-probability mapping function is used to calculate the performance metric (MSE or Brier score) (resubstitution); (b) an independent test dataset is used to calculate the performance metric (independent). Under our simulation conditions, the semiparametric method is found to be superior to the nonparametric method at small to medium sample sizes and the two methods appear to converge at large sample sizes. Our simulation results also indicate that the resubstitution bias may depend on the performance metric and, for the semiparametric method, the resubstitution bias is small when a reasonable number of cases (> 100 cases per class) are available.
Verification of Geometric Model-Based Plant Phenotyping Methods for Studies of Xerophytic Plants.
Drapikowski, Paweł; Kazimierczak-Grygiel, Ewa; Korecki, Dominik; Wiland-Szymańska, Justyna
2016-06-27
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.
NASA Technical Reports Server (NTRS)
1991-01-01
This report describes progress made during the period July 1991 to December 1991 on the tasks identified in the technical proposals for the subject grant. The plans for further effort on each of the tasks are outlined. The computer implementation of the method of analysis under development is referred to in this document as NLPAN. These tasks included: (1) implementation of continuation methods; (2) dynamic analysis capability; (3) additional boundary condition options for the panel ends; (4) transverse pressure loading; (5) second-order displacement fields; and (6) results for an i-stiffened panel with a complex cross section.
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.
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.
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 .
Olch, Arthur J; Whitaker, Matthew L
2010-08-01
Dosimetry using film, CR, electronic portal imaging, or other 2D detectors requires calibration of the raw image data to obtain dose. Typically, a series of known doses are given to the detector, the raw signal for each dose is obtained, and a calibration curve is created. This calibration curve is then applied to the measured raw signals to convert them to dose. With the advent of IMRT, film dosimetry for quality assurance has become a routine and labor intensive part of the physicist's day. The process of calibrating the film or other 2D detector takes time and additional film or images for performing the calibration, and comes with its own source of errors. This article studies a new methodology for the relative dose calibration of 2D imaging detectors especially useful for IMRT QA, which relies on the treatment plan dose image to provide the dose information which is paired with the raw QA image data after registration of the two images (plan-based calibration). Validation of the accuracy and robustness of the method is performed on ten IMRT cases performed using EDR2 film with conventional and plan-based calibration. Also, for each of the ten cases, a 5 mm registration error was introduced and the Gamma analysis was reevaluated. In addition, synthetic image tests were performed to test the limits of the method. The Gamma analysis is used as a measure of dosimetric agreement between plan and film for the clinical cases and a dose difference metric for the synthetic cases. The QA image calibrated by the plan-based method was found to more accurately match the treatment plan doses than the conventionally calibrated films and also to reveal dose errors more effectively when a registration error was introduced. When synthetic acquired images were systematically studied, localized and randomly placed dose errors were correctly identified without excessive falsely passing or falsely failing pixels, unless the errors were concentrated in a majority of pixels in a
Solution of the equations for one-dimensional, two-phase, immiscible flow by geometric methods
NASA Astrophysics Data System (ADS)
Ivan, Boronin; Andrey, Shevlyakov
2016-12-01
Buckley-Leverett equations describe non viscous, immiscible, two-phase filtration, which is often of interest in modelling of oil production. For many parameters and initial conditions, the solutions of these equations exhibit non-smooth behaviour, namely discontinuities in form of shock waves. In this paper we obtain a novel method for the solution of Buckley-Leverett equations, which is based on geometry of differential equations. This method is fast, accurate, stable, and describes non-smooth phenomena. The main idea of the method is that classic discontinuous solutions correspond to the continuous surfaces in the space of jets - the so-called multi-valued solutions (Bocharov et al., Symmetries and conservation laws for differential equations of mathematical physics. American Mathematical Society, Providence, 1998). A mapping of multi-valued solutions from the jet space onto the plane of the independent variables is constructed. This mapping is not one-to-one, and its singular points form a curve on the plane of the independent variables, which is called the caustic. The real shock occurs at the points close to the caustic and is determined by the Rankine-Hugoniot conditions.
Geometric Methods for ATR: Shape Spaces, Metrics, Object/Image Relations, and Shapelets
2007-09-30
and only if Kr - 4 C L r - 3 C H r - l C r This fact and the incidence relations given in Theorem I, §5, Chapter VII of Hodge and Pedoe [4] give us our...Springer-Verlag, 1992. 4. W.V.D. Hodge and D. Pedoe , Methods of Algebraic Geometry, nos. 1, 2, and 3, in Mathematical Library Series, Cambridge...and Pedoe [5] give us our object-image relations. Theorem 2.4. Let Pi = (xi, yi, zi), 1 < i < r be an object configuration with corresponding matrix M
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.
Non-uniformity correction for division of focal plane polarimeters with a calibration method.
Zhang, Junchao; Luo, Haibo; Hui, Bin; Chang, Zheng
2016-09-10
Division of focal plane polarimeters are composed of nanometer polarization elements overlaid upon a focal plane array (FPA) sensor. The manufacturing flaws of the polarization grating and each detector in the FPA having a different photo response can introduce non-uniformity errors when reconstructing the polarization image without correction. A new calibration method is proposed to mitigate non-uniformity errors in the visible waveband. We correct non-uniformity in the form of a vector. The correction matrix and offset vector are calculated for the following correction. The performance of the proposed method is compared with state-of-the-art techniques by employing simulated data and real scenes. The experimental results showed that the proposed method can effectively mitigate non-uniformity errors and achieve better visual results.
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.
Local-geometric-projection method for noise reduction in chaotic maps and flows
NASA Astrophysics Data System (ADS)
Cawley, Robert; Hsu, Guan-Hsong
1992-09-01
We describe a method for noise reduction in chaotic systems that is based on projection of the set of points comprising an embedded noisy orbit in openRd toward a finite patchwork of best-fit local approximations to an m-dimensional surface M'⊂openRd, m<=d. We generate the orbits by the delay coordinate construction of Ruelle and Takens [N. H. Packard et al., Phys. Rev. Lett. 45, 712 (1980); F. Takens, in Dynamical Systems and Turbulence, Warwick, 1980, edited by D. A. Rand and L.-S. Young (Springer, Berlin, 1981)] from time series v(t), which in an experimental situation we would assume to have come, together with additional high-dimensional background noise, from an underlying dynamical system ft: M-->M existing on some low m-dimensional manifold M. The surface M' in openRd is the assumed embedded image of M. We give results of systematic studies of linear (tangent plane) projection schemes. We describe in detail the basic algorithm for implementing these schemes. We apply the algorithm iteratively to known map and flow time series to which white noise has been added. In controlled studies, we measure the signal-to-noise ratio improvements, iterating nM times until a stable maximum δM is achieved. We present extensive results for δM and nM for a wide range of values of embedding trial dimension d, projection dimension k, number of nearest-neighbor points for local approximation ν, embedding delay Δ, sampling interval ΔT, initial noise amplitude scrN, and trajectory length N. We give results for very low and very high noise amplitudes 0%<=scrN<=100%. We develop an empirical method for estimating the initial noise level for a given experimental time series, and for the optimal choice of algorithm parameters to achieve peak reduction. We present interesting results of application of the noise-reduction algorithm to a chaotic time series produced from a periodically driven magnetoelastic ribbon experiment on the control of chaos. Two noteworthy elements of the
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. Copyright © 2014 Elsevier B.V. All rights reserved.
NASA Astrophysics Data System (ADS)
Sadoc, Jean-François; Mosseri, Rimy
1999-10-01
This book shows how the concept of geometrical frustration can be used to elucidate the structure and properties of nonperiodic materials such as metallic glasses, quasicrystals, amorphous semiconductors and complex liquid crystals. Examples and idealized models introduce geometric frustration, illustrating how it can be used to identify ordered and defective regions in real materials. The book goes on to show how these principles can also be used to model physical properties of materials, in particular specific volume, melting, the structure factor and the glass transition. Final chapters consider geometric frustration in periodic structures with large cells and quasiperiodic order. Appendices give all necessary background on geometry, symmetry and tilings. The text considers geometrical frustration at different scales in many types of materials and structures, including metals, amorphous solids, liquid crystals, amphiphiles, cholisteric systems, polymers, phospholipid membranes, atomic clusters, and quasicrystals. This book will be of great interest to researchers in condensed matter physics, materials science and structural chemistry, as well as mathematics and structural biology.
Beyond bilateral symmetry: geometric morphometric methods for any type of symmetry
2011-01-01
Background Studies of symmetric structures have made important contributions to evolutionary biology, for example, by using fluctuating asymmetry as a measure of developmental instability or for investigating the mechanisms of morphological integration. Most analyses of symmetry and asymmetry have focused on organisms or parts with bilateral symmetry. This is not the only type of symmetry in biological shapes, however, because a multitude of other types of symmetry exists in plants and animals. For instance, some organisms have two axes of reflection symmetry (biradial symmetry; e.g. many algae, corals and flowers) or rotational symmetry (e.g. sea urchins and many flowers). So far, there is no general method for the shape analysis of these types of symmetry. Results We generalize the morphometric methods currently used for the shape analysis of bilaterally symmetric objects so that they can be used for analyzing any type of symmetry. Our framework uses a mathematical definition of symmetry based on the theory of symmetry groups. This approach can be used to divide shape variation into a component of symmetric variation among individuals and one or more components of asymmetry. We illustrate this approach with data from a colonial coral that has ambiguous symmetry and thus can be analyzed in multiple ways. Our results demonstrate that asymmetric variation predominates in this dataset and that its amount depends on the type of symmetry considered in the analysis. Conclusions The framework for analyzing symmetry and asymmetry is suitable for studying structures with any type of symmetry in two or three dimensions. Studies of complex symmetries are promising for many contexts in evolutionary biology, such as fluctuating asymmetry, because these structures can potentially provide more information than structures with bilateral symmetry. PMID:21958045
Self-calibration method of the bias of a space electrostatic accelerometer.
Qu, Shao-Bo; Xia, Xiao-Mei; Bai, Yan-Zheng; Wu, Shu-Chao; Zhou, Ze-Bing
2016-11-01
The high precision space electrostatic accelerometer is an instrument to measure the non-gravitational forces acting on a spacecraft. It is one of the key payloads for satellite gravity measurements and space fundamental physics experiments. The measurement error of the accelerometer directly affects the precision of gravity field recovery for the earth. This paper analyzes the sources of the bias according to the operating principle and structural constitution of the space electrostatic accelerometer. Models of bias due to the asymmetry of the displacement sensing system, including the mechanical sensor head and the capacitance sensing circuit, and the asymmetry of the feedback control actuator circuit are described separately. According to the two models, a method of bias self-calibration by using only the accelerometer data is proposed, based on the feedback voltage data of the accelerometer before and after modulating the DC biasing voltage (V b ) applied on its test mass. Two types of accelerometer biases are evaluated separately using in-orbit measurement data of a space electrostatic accelerometer. Based on the preliminary analysis, the bias of the accelerometer onboard of an experiment satellite is evaluated to be around 10 -4 m/s 2 , about 4 orders of magnitude greater than the noise limit. Finally, considering the two asymmetries, a comprehensive bias model is analyzed. A modified method to directly calibrate the accelerometer comprehensive bias is proposed.
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.
NASA Astrophysics Data System (ADS)
Suryoputro, Nugroho; Suhardjono, Soetopo, Widandi; Suhartanto, Ery
2017-09-01
In calibrating hydrological models, there are generally two stages of activity: 1) determining realistic model initial parameters in representing natural component physical processes, 2) entering initial parameter values which are then processed by trial error or automatically to obtain optimal values. To determine a realistic initial value, it takes experience and user knowledge of the model. This is a problem for beginner model users. This paper will present another approach to estimate the infiltration parameters in the tank model. The parameters will be approximated by the runoff coefficient of rational method. The value approach of infiltration parameter is simply described as the result of the difference in the percentage of total rainfall minus the percentage of runoff. It is expected that the results of this research will accelerate the calibration process of tank model parameters. The research was conducted on the sub-watershed Kali Bango in Malang Regency with an area of 239,71 km2. Infiltration measurements were carried out in January 2017 to March 2017. Analysis of soil samples at Soil Physics Laboratory, Department of Soil Science, Faculty of Agriculture, Universitas Brawijaya. Rainfall and discharge data were obtained from UPT PSAWS Bango Gedangan in Malang. Temperature, evaporation, relative humidity, wind speed data was obtained from BMKG station of Karang Ploso, Malang. The results showed that the infiltration coefficient at the top tank outlet can be determined its initial value by using the approach of the coefficient of runoff rational method with good result.
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
2015-07-28
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.
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.
Methods for Calibrating Basin-Wide Hydroacoustic Propagation in the Indian Ocean
Blackman, D; de Groot-Hedlin, C; Orcutt, J A
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 ofmore » 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.« less
NASA Astrophysics Data System (ADS)
Zhang, Liqiong; Cui, Yuanyuan; Zhang, Feng
2017-11-01
Hardness testing is widely used for characterizing the mechanical properties of materials. However, the measured hardness values in hardness measurements are strongly influenced by the geometrical parameters of diamond hardness indenters. In the most severe case, the geometrical error of the diamond indenter, Rockwell hardness measurements in particular, leads to be about 50% hardness measurement uncertainty. It has been generally recognized for many years that the geometry of diamond indenters must be calibrated or verified before use to correct the hardness value for each indenter and improve the hardness measurement uncertainty. The contact-based calibration methods and the contactless based optical measuring methods are two typical ways to calibrate the geometrical form of an indenter at present. The contact-based calibration methods characterized by large measurement range of tens of mm with nanometer resolution, has a time-consuming measurement process, the contactless based optical measuring methods have become a general trend. In this work, an optical measuring system, which employs the combination of an interferometric microscope and a profile projection technique, is presented to measure and calibrate the geometrical parameters of Rockwell and Vickers diamond hardness indenters in National Institute of Metrology of China. Initial experiments demonstrated that the angle and axis angle measurement of indenter are achieved with accuracy of 0.1°, the straightness deviation of Rockwell indenters is less than 2μm, the radius measurement uncertainty of the tip of Rockwell indenters is better than 5μm.
A novel method for absolute calibration of intracellular pH indicators.
Eisner, D A; Kenning, N A; O'Neill, S C; Pocock, G; Richards, C D; Valdeolmillos, M
1989-03-01
In this paper we present methods to measure intracellular pH (pHi) with fluorescent indicators. These methods are based on the change in intracellular pH following the addition of weak acids and weak bases to the extracellular medium. The first method requires that the fluorescence of the indicator is proportional to the change in pHi that follows the addition of a weak acid or weak base to the extra-cellular medium. The second is a null method which uses a mixture of weak acid and weak base that does not change the fluorescent signal. This null method can be used in situations in which the fluorescent signal is a monotonic but non-linear function of pH. The first method depends upon four assumptions. (i) That only the uncharged forms of the weak acids and bases cross the surface membrane. (ii) That the pKa is the same inside and outside the cell. (iii) That the buffering power is constant. (iv) That there is no significant pH regulation on the time scale of the change in pHi. The null method only requires the first two assumptions. We have made estimates of pHi in four different cell types and compared the results obtained with these methods with those obtained from other methods of pHi calibration.
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
The research on calibration methods of dual-CCD laser three-dimensional human face scanning system
NASA Astrophysics Data System (ADS)
Wang, Jinjiang; Chang, Tianyu; Ge, Baozhen; Tian, Qingguo; Yang, Fengting; Shi, Shendong
2013-09-01
In this paper, on the basis of considering the performance advantages of two-step method, we combines the stereo matching of binocular stereo vision with active laser scanning to calibrate the system. Above all, we select a reference camera coordinate system as the world coordinate system and unity the coordinates of two CCD cameras. And then obtain the new perspective projection matrix (PPM) of each camera after the epipolar rectification. By those, the corresponding epipolar equation of two cameras can be defined. So by utilizing the trigonometric parallax method, we can measure the space point position after distortion correction and achieve stereo matching calibration between two image points. Experiments verify that this method can improve accuracy and system stability is guaranteed. The stereo matching calibration has a simple process with low-cost, and simplifies regular maintenance work. It can acquire 3D coordinates only by planar checkerboard calibration without the need of designing specific standard target or using electronic theodolite. It is found that during the experiment two-step calibration error and lens distortion lead to the stratification of point cloud data. The proposed calibration method which combining active line laser scanning and binocular stereo vision has the both advantages of them. It has more flexible applicability. Theory analysis and experiment shows the method is reasonable.
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.
NASA Astrophysics Data System (ADS)
Singh, Veena D.; Daharwal, Sanjay J.
2017-01-01
Three multivariate calibration spectrophotometric methods were developed for simultaneous estimation of Paracetamol (PARA), Enalapril maleate (ENM) and Hydrochlorothiazide (HCTZ) in tablet dosage form; namely multi-linear regression calibration (MLRC), trilinear regression calibration method (TLRC) and classical least square (CLS) method. The selectivity of the proposed methods were studied by analyzing the laboratory prepared ternary mixture and successfully applied in their combined dosage form. The proposed methods were validated as per ICH guidelines and good accuracy; precision and specificity were confirmed within the concentration range of 5-35 μg mL- 1, 5-40 μg mL- 1 and 5-40 μg mL- 1of PARA, HCTZ and ENM, respectively. The results were statistically compared with reported HPLC method. Thus, the proposed methods can be effectively useful for the routine quality control analysis of these drugs in commercial tablet dosage form.
Singh, Veena D; Daharwal, Sanjay J
2017-01-15
Three multivariate calibration spectrophotometric methods were developed for simultaneous estimation of Paracetamol (PARA), Enalapril maleate (ENM) and Hydrochlorothiazide (HCTZ) in tablet dosage form; namely multi-linear regression calibration (MLRC), trilinear regression calibration method (TLRC) and classical least square (CLS) method. The selectivity of the proposed methods were studied by analyzing the laboratory prepared ternary mixture and successfully applied in their combined dosage form. The proposed methods were validated as per ICH guidelines and good accuracy; precision and specificity were confirmed within the concentration range of 5-35μgmL-1, 5-40μgmL-1 and 5-40μgmL-1of PARA, HCTZ and ENM, respectively. The results were statistically compared with reported HPLC method. Thus, the proposed methods can be effectively useful for the routine quality control analysis of these drugs in commercial tablet dosage form. Copyright © 2016 Elsevier B.V. All rights reserved.
Toman, Blaza; Nelson, Michael A; Bedner, Mary
2017-06-01
Chemical measurement methods are designed to promote accurate knowledge of a measurand or system. As such, these methods often allow elicitation of latent sources of variability and correlation in experimental data. They typically implement measurement equations that support quantification of effects associated with calibration standards and other known or observed parametric variables. Additionally, multiple samples and calibrants are usually analyzed to assess accuracy of the measurement procedure and repeatability by the analyst. Thus, a realistic assessment of uncertainty for most chemical measurement methods is not purely bottom-up (based on the measurement equation) or top-down (based on the experimental design), but inherently contains elements of both. Confidence in results must be rigorously evaluated for the sources of variability in all of the bottom-up and top-down elements. This type of analysis presents unique challenges due to various statistical correlations among the outputs of measurement equations. One approach is to use a Bayesian hierarchical (BH) model which is intrinsically rigorous, thus making it a straightforward method for use with complex experimental designs, particularly when correlations among data are numerous and difficult to elucidate or explicitly quantify. In simpler cases, careful analysis using GUM Supplement 1 (MC) methods augmented with random effects meta analysis yields similar results to a full BH model analysis. In this article we describe both approaches to rigorous uncertainty evaluation using as examples measurements of 25-hydroxyvitamin D3 in solution reference materials via liquid chromatography with UV absorbance detection (LC-UV) and liquid chromatography mass spectrometric detection using isotope dilution (LC-IDMS).
NASA Astrophysics Data System (ADS)
Toman, Blaza; Nelson, Michael A.; Bedner, Mary
2017-06-01
Chemical measurement methods are designed to promote accurate knowledge of a measurand or system. As such, these methods often allow elicitation of latent sources of variability and correlation in experimental data. They typically implement measurement equations that support quantification of effects associated with calibration standards and other known or observed parametric variables. Additionally, multiple samples and calibrants are usually analyzed to assess accuracy of the measurement procedure and repeatability by the analyst. Thus, a realistic assessment of uncertainty for most chemical measurement methods is not purely bottom-up (based on the measurement equation) or top-down (based on the experimental design), but inherently contains elements of both. Confidence in results must be rigorously evaluated for the sources of variability in all of the bottom-up and top-down elements. This type of analysis presents unique challenges due to various statistical correlations among the outputs of measurement equations. One approach is to use a Bayesian hierarchical (BH) model which is intrinsically rigorous, thus making it a straightforward method for use with complex experimental designs, particularly when correlations among data are numerous and difficult to elucidate or explicitly quantify. In simpler cases, careful analysis using GUM Supplement 1 (MC) methods augmented with random effects meta analysis yields similar results to a full BH model analysis. In this article we describe both approaches to rigorous uncertainty evaluation using as examples measurements of 25-hydroxyvitamin D3 in solution reference materials via liquid chromatography with UV absorbance detection (LC-UV) and liquid chromatography mass spectrometric detection using isotope dilution (LC-IDMS).
The Accuracy of the Fixed Parameter Method of Item Bank Calibration.
ERIC Educational Resources Information Center
Forster, Fred; Karr, Chad
This study investigates two fixed parameter models for calibrating test items for an item bank under local school district control. Mathematics, reading, and language tests administered to students (Grades 7-9) provided the criterion information. Model I used calibrations from the Northwest Evaluation Association Item Bank to calibrate new items…
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…
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.
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.
Calibration method for lumbosacral dimensions in wearable sensor system of lumbar alignment.
Tsuchiya, Yoshio; Kusaka, Takashi; Tanaka, Takayuki; Matsuo, Yoshikazu; Oda, Makoto; Sasaki, Tsukasa; Kamishima, Tamotsu; Yamanaka, Masanori
2015-01-01
Anteflexion of the spine is essential for many physical activities in everyday life. However, this motion places the lumbar disks under heavy load due to changes in the shape of the lumbar spine and can lead to low back pain. With the aim of reducing low back pain, here we developed a wearable sensor system that can estimate lumbosacral alignment and lumbar load by measuring the shape of the lumbar skin when the lumbosacral alignment changes. In addition, we used this system to measure the parameters of anteflexion and studied the change in dimensions of the lumbar spine from changes in posture. By determining the dimensions of the lumbosacral spine on an X-ray image, a lumbosacral dimensions calibration method based on body surface area and height was developed. By using this method, lumbosacral alignment and lumbar load could be accurately estimated using the wearable sensor system.
NASA Astrophysics Data System (ADS)
Yun, Yong-Huan; Li, Hong-Dong; Wood, Leslie R. E.; Fan, Wei; Wang, Jia-Jun; Cao, Dong-Sheng; Xu, Qing-Song; Liang, Yi-Zeng
2013-07-01
Wavelength selection is a critical step for producing better prediction performance when applied to spectral data. Considering the fact that the vibrational and rotational spectra have continuous features of spectral bands, we propose a novel method of wavelength interval selection based on random frog, called interval random frog (iRF). To obtain all the possible continuous intervals, spectra are first divided into intervals by moving window of a fix width over the whole spectra. These overlapping intervals are ranked applying random frog coupled with PLS and the optimal ones are chosen. This method has been applied to two near-infrared spectral datasets displaying higher efficiency in wavelength interval selection than others. The source code of iRF can be freely downloaded for academy research at the website: http://code.google.com/p/multivariate-calibration/downloads/list.
Sikorska, Ewa; Gliszczyńska-Swigło, Anna; Insińska-Rak, Małgorzata; Khmelinskii, Igor; De Keukeleire, Denis; Sikorski, Marek
2008-04-21
The study demonstrates an application of the front-face fluorescence spectroscopy combined with multivariate regression methods to the analysis of fluorescent beer components. Partial least-squares regressions (PLS1, PLS2, and N-way PLS) were utilized to develop calibration models between synchronous fluorescence spectra and excitation-emission matrices of beers, on one hand, and analytical concentrations of riboflavin and aromatic amino acids, on the other hand. The best results were obtained in the analysis of excitation-emission matrices using the N-way PLS2 method. The respective correlation coefficients, and the values of the root mean-square error of cross-validation (RMSECV), expressed as percentages of the respective mean analytic concentrations, were: 0.963 and 14% for riboflavin, 0.974 and 4% for tryptophan, 0.980 and 4% for tyrosine, and 0.982 and 19% for phenylalanine.
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
Lin, Shyh-Tsong; Yeh, Sheng-Lih; Chiu, Chi-Shang; Huang, Mou-Shan
2011-10-24
A calibrator utilizing a low-coherent light source straightness interferometer and a compensation method is introduced for straightness measurements in this paper. Where the interference pattern, which is modulated by an envelope function, generated by the interferometer undergoes a shifting as the Wolaston prism of the interferometer experiences a lateral displacement, and the compensation method senses the displacement by driving the prism back to the position to restore the pattern. A setup, which is with a measurement sensitivity of 36.6°/μm, constructed for realizing the calibrator is demonstrated. The experimental results from the uses of the setup reveal that the setup is with a measurement resolution and stability of 0.019 and 0.08 μm, respectively, validate the calibrator, and confirm the calibrator's applicability of straightness measurements and advantage of extensible working distance. © 2011 Optical Society of America
New methods of data calibration for high power-aperture lidar.
Guan, Sai; Yang, Guotao; Chang, Qihai; Cheng, Xuewu; Yang, Yong; Gong, Shaohua; Wang, Jihong
2013-03-25
For high power-aperture lidar sounding of wide atmospheric dynamic ranges, as in middle-upper atmospheric probing, photomultiplier tubes' (PMT) pulse pile-up effects and signal-induced noise (SIN) complicates the extraction of information from lidar return signal, especially from metal layers' fluorescence signal. Pursuit for sophisticated description of metal layers' characteristics at far range (80~130km) with one PMT of high quantum efficiency (QE) and good SNR, contradicts the requirements for signals of wide linear dynamic range (i.e. from approximate 10(2) to 10(8) counts/s). In this article, Substantial improvements on experimental simulation of Lidar signals affected by PMT are reported to evaluate the PMTs' distortions in our High Power-Aperture Sodium LIDAR system. A new method for pile-up calibration is proposed by taking into account PMT and High Speed Data Acquisition Card as an Integrated Black-Box, as well as a new experimental method for identifying and removing SIN from the raw Lidar signals. Contradiction between the limited linear dynamic range of raw signal (55~80km) and requirements for wider acceptable linearity has been effectively solved, without complicating the current lidar system. Validity of these methods was demonstrated by applying calibrated data to retrieve atmospheric parameters (i.e. atmospheric density, temperature and sodium absolutely number density), in comparison with measurements of TIMED satellite and atmosphere model. Good agreements are obtained between results derived from calibrated signal and reference measurements where differences of atmosphere density, temperature are less than 5% in the stratosphere and less than 10K from 30km to mesosphere, respectively. Additionally, approximate 30% changes are shown in sodium concentration at its peak value. By means of the proposed methods to revert the true signal independent of detectors, authors approach a new balance between maintaining the linearity of adequate signal (20
Calibration problems with the viscosity measurement of liquid metallurgical slags
NASA Astrophysics Data System (ADS)
Heller, H. P.; Schürmann, M.; Scholl, K.; Haustein, N.; Lychatz, B.; Falkus, J.
2017-01-01
The viscosity of slag is an important characteristic of liquid slags regarding its lubricating effect and mass transfer. For measurement, however, they exhibit considerable differences in the values reported. Therefore, the rotation method, mostly used for high temperatures areas, is investigated regarding the impacts of any geometric inaccuracies. Furthermore, problems in the centering and use of calibration slags are discussed. It appears that, with the use of a more precise rheometer with air bearing, an error of less than +/- 3 % is possible in compliance with geometric critical values and online monitoring of the central operations. The verification was carried out with a blast furnace slag, which is also proposed as a calibration slag.
NASA Astrophysics Data System (ADS)
Jin, Yue; Liu, Bilin; Li, Jianhua; Chen, Xinjun
2017-10-01
The hard tissues of squid can provide important information for species identification. In this study, we used statolith and beak to identify three squid species including Uroteuthis duvaucelii, Loliolus beka, and U. edulis in the South China Sea. Because of the highly overlapping habitat and similar body morphology of the three squid species, we explored four different ways to identify them, by using statolith, upper beak, lower beak and a combination of statolith and beak. An outline geometric morphometric method and stepwise discriminant analysis were used to evaluate the most suitable method for the identification. We found that the combination of statolith and beak had the highest cross validation rate that was 75.0%, 87.5% and 88.7% for U. duvaucelii, L. beka and U. edulis, respectively. Using two beaks had similar results and the lowest cross validation rate was 60.0%, 50.0%, and 73.7% for the upper beak, 46.9%, 58.5% and 75.3% for the lower beak of U. duvaucelii, L. beka and U. edulis, respectively. Analyzing with the statolith had moderate cross validation which was 72.2%, 80.0%, and 87.7% for U. duvaucelii, L. beka and U. edulis, respectively. From the results it is suggested when the entire body of a squid is available, a combination of statolith and beak should be used for the identification. When only one hard tissue is available, species identification can be subjected to large errors.
Lee, Won-Joon; Wilkinson, Caroline M; Hwang, Hyeon-Shik; Lee, Sang-Mi
2015-05-01
Accuracy is the most important factor supporting the reliability of forensic facial reconstruction (FFR) comparing to the corresponding actual face. A number of methods have been employed to evaluate objective accuracy of FFR. Recently, it has been attempted that the degree of resemblance between computer-generated FFR and actual face is measured by geometric surface comparison method. In this study, three FFRs were produced employing live adult Korean subjects and three-dimensional computerized modeling software. The deviations of the facial surfaces between the FFR and the head scan CT of the corresponding subject were analyzed in reverse modeling software. The results were compared with those from a previous study which applied the same methodology as this study except average facial soft tissue depth dataset. Three FFRs of this study that applied updated dataset demonstrated lesser deviation errors between the facial surfaces of the FFR and corresponding subject than those from the previous study. The results proposed that appropriate average tissue depth data are important to increase quantitative accuracy of FFR. © 2015 American Academy of Forensic Sciences.
NASA Astrophysics Data System (ADS)
Zhang, Q.; Xie, H.; Liu, Z.; Dai, X.
2018-03-01
Characterization of residual stress around thermal grown oxide (TGO) is important for understanding the spallation failure of thermal barrier coatings (TBCs). Cr3+ photoluminescence piezo-spectroscopy (CPLPS) is a nondestructive method for measuring the in-plane residual stress in the TGO layer. However, using CPLPS it is hard to evaluate the out-of-plane residual stress around TGO. Here, we adopted the micro-slotting method combined with geometric phase analysis (GPA) for measuring the in-plane and out-of-plane stresses around TGO, with measured areas of 6 × 4 µm2. In the experiment, a grating and a slot were milled on the specimen surface using focused ion beam, and GPA was applied to analyze the grating structure before and after the slot milling for calculating the released displacement field. Then finite element analysis was used to infer the residual stress in the direction vertical to the micro-slot. Two experiments were performed on the in-service TBC specimen. The first experiment presented the in-plane compression in the TGO, while the second experiment presented the out-of-plane tension at the crest of the TGO/BC interface, thus validating the theoretical analysis.
Martin-de-Las-Heras, Stella; Tafur, Daniel; Bravo, Manuel
2014-07-01
To develop a quantitative method to compare 3D overlays from dental casts with experimental bitemarks by using geometric morphometric analysis. Thirteen upper and lower dental casts and corresponding simulated bitemarks were 3D-scanned to generate comparison overlays with DentalPrint software(©). This study considered the inter-canine distance and four incisal angles. A matrix was created to compare all possible combinations of matches and non-matches between models and bites, i.e. 169 combinations (13 models × 13 bites), of which 13 were true matches. For each combination, the percentage difference was calculated between the variables in the model and the same variables in the bitemark. Logistic regression was used to obtain a predictive model (algorithm) for a match, calculating the discriminative values (area under the ROC curve, sensitivity and specificity) for each measure and for the logistic model. Statistically significant discriminative power was found for all single (angle or distance) and combined (logistic model) variables, with lower 95% CI limits > 0.50 for areas under the ROC curves and sensitivity/specificity values > 50% in both maxilla and mandible. This quantitative method has sufficient discriminative power to be utilized in forensic cases.
Abdolmaleki, Azizeh; Ghasemi, Jahan B; Shiri, Fereshteh; Pirhadi, Somayeh
2015-01-01
Data manipulation and maximum efficient extraction of useful information need a range of searching, modeling, mathematical, and statistical approaches. Hence, an adequate multivariate characterization is the first necessary step in investigation and the results are interpreted after multivariate analysis. Multivariate data analysis is capable of not only large dataset management but also interpret them surely and rapidly. Application of chemometrics and cheminformatics methods may be useful for design and discovery of new drug compounds. In this review, we present a variety of information sources on chemometrics, which we consider useful in different fields of drug design. This review describes exploratory analysis (PCA), classification and multivariate calibration (PCR, PLS) methods to data analysis. It summarizes the main facts of linear and nonlinear multivariate data analysis in drug discovery and provides an introduction to manipulation of data in this field. It handles the fundamental aspects of basic concepts of multivariate methods, principles of projections (PCA and PLS) and introduces the popular modeling and classification techniques. Enough theory behind these methods, more particularly concerning the chemometrics tools is included for those with little experience in multivariate data analysis techniques such as PCA, PLS, SIMCA, etc. We describe each method by avoiding unnecessary equations, and details of calculation algorithms. It provides a synopsis of the method followed by cases of applications in drug design (i.e., QSAR) and some of the features for each method.
Monitoring the VIIRS ocean color band calibration using the Rayleigh scattering method
NASA Astrophysics Data System (ADS)
Wang, Wenhui; Cao, Changyong
2014-11-01
Post-launch monitoring of radiometric accuracy and stability of VIIRS (Visible Infrared Imaging Radiometer Suite) Solar Reflective Bands (RSB) at high gain stage (HGS) is essential for ocean color applications. This study investigates the absolute radiometric calibration accuracy of VIIRS bands M1-M5 at HGS using selected clear-sky dark ocean surfaces where top of atmosphere (TOA) signal is dominated by Rayleigh scattering. Vicarious gains were estimated using ratios between satellite observed and radiative transfer model simulated TOA reflectance. VIIRS TOA reflectance was simulated using 6SV (Second Simulation of a Satellite Signal in the Solar Spectrum - Vector, version 1.1). Input parameters required by the 6SV, including atmospheric profiles, wind speed and direction, aerosol optical thickness, and chlorophyll-a concentration, were obtained from the NASA Modern-Era Retrospective Analysis for Research and Applications reanalysis products, VIIRS aerosol optical thickness product, and previous studies. The Rayleigh scattering method developed in this study was applied to June to August 2014 VIIRS observations over six oceanic sites. Preliminary results indicated that the 3-month averaged vicarious gain for bands M1, M2, and M5 are close to 1. Relatively larger vicarious gains were observed in the other two bands, especially in band M4. The Rayleigh scattering calibration results generally agree with results from the VIIRS deep convective clouds time series analysis.
Calibration method for accurate optical measurement of thickness profile for the paper industry
NASA Astrophysics Data System (ADS)
Graeffe, Jussi
2009-06-01
Online measurement of paper thickness profile is essential in paper production. For decades paper thickness has been measured online with sensors that are contacting the web on both sides. In 2005 a new optical online paper thickness gauge was introduced which only contacts the web on the other side. The sensor is based on a laser triangulation sensor and a magnetic sensor, and it determines the paper thickness from the difference of the two measurements. For calibration of the two sensors, a robust concept has been developed which utilizes the measured object and takes place in the measuring environment so that the calibration is automatic