179,746 research outputs found
Demodulation of Spatial Carrier Images: Performance Analysis of Several Algorithms Using a Single Image
http://link.springer.com/article/10.1007%2Fs11340-013-9741-6#Optical full-field techniques have a great importance in modern experimental mechanics. Even if they are reasonably spread among the university laboratories, their diffusion in industrial companies remains very narrow for several reasons, especially a lack of metrological performance assessment. A full-field measurement can be characterized by its resolution, bias, measuring range, and by a specific quantity, the spatial resolution. The present paper proposes an original procedure to estimate in one single step the resolution, bias and spatial resolution for a given operator (decoding algorithms such as image correlation, low-pass filters, derivation tools ...). This procedure is based on the construction of a particular multi-frequential field, and a Bode diagram representation of the results. This analysis is applied to various phase demodulating algorithms suited to estimate in-plane displacements.GDR CNRS 2519 âMesures de Champs et Identification en MĂ©canique des Solide
Gaia on-board metrology: basic angle and best focus
The Gaia payload ensures maximum passive stability using a single material,
SiC, for most of its elements. Dedicated metrology instruments are, however,
required to carry out two functions: monitoring the basic angle and refocusing
the telescope. Two interferometers fed by the same laser are used to measure
the basic angle changes at the level of as (prad, micropixel), which is
the highest level ever achieved in space. Two Shack-Hartmann wavefront sensors,
combined with an ad-hoc analysis of the scientific data are used to define and
reach the overall best-focus. In this contribution, the systems, data analysis,
procedures and performance achieved during commissioning are presentedComment: 18 pages, 14 figures. To appear in SPIE proceedings 9143-30. Space
Telescopes and Instrumentation 2014: Optical, Infrared, and Millimeter Wav
On-the-fly Data Assessment for High Throughput X-ray Diffraction Measurement
Investment in brighter sources and larger and faster detectors has
accelerated the speed of data acquisition at national user facilities. The
accelerated data acquisition offers many opportunities for discovery of new
materials, but it also presents a daunting challenge. The rate of data
acquisition far exceeds the current speed of data quality assessment, resulting
in less than optimal data and data coverage, which in extreme cases forces
recollection of data. Herein, we show how this challenge can be addressed
through development of an approach that makes routine data assessment automatic
and instantaneous. Through extracting and visualizing customized attributes in
real time, data quality and coverage, as well as other scientifically relevant
information contained in large datasets is highlighted. Deployment of such an
approach not only improves the quality of data but also helps optimize usage of
expensive characterization resources by prioritizing measurements of highest
scientific impact. We anticipate our approach to become a starting point for a
sophisticated decision-tree that optimizes data quality and maximizes
scientific content in real time through automation. With these efforts to
integrate more automation in data collection and analysis, we can truly take
advantage of the accelerating speed of data acquisition
Circular polarization measurement in millimeter-wavelength spectral-line VLBI observations
This paper considers the problem of accurate measurement of circular
polarization in imaging spectral-line VLBI observations in the lambda=7 mm and
lambda=3 mm wavelength bands. This capability is especially valuable for the
full observational study of compact, polarized SiO maser components in the
near-circumstellar environment of late-type, evolved stars. Circular VLBI
polarimetry provides important constraints on SiO maser astrophysics, including
the theory of polarized maser emission transport, and on the strength and
distribution of the stellar magnetic field and its dynamical role in this
critical circumstellar region. We perform an analysis here of the data model
containing the instrumental factors that limit the accuracy of circular
polarization measurements in such observations, and present a corresponding
data reduction algorithm for their correction. The algorithm is an enhancement
of existing spectral line VLBI polarimetry methods using autocorrelation data
for calibration, but with innovations in bandpass determination,
autocorrelation polarization self-calibration, and general optimizations for
the case of low SNR, as applicable at these wavelengths. We present an example
data reduction at mm and derive an estimate of the predicted
accuracy of the method of m_c < 0.5% or better at lambda=7 mm and m_c < 0.5-1%
or better at lambda=3 mm. Both the strengths and weaknesses of the proposed
algorithm are discussed, along with suggestions for future work.Comment: 23 pages, 13 figure
Quality criteria benchmark for hyperspectral imagery
Hyperspectral data appear to be of a growing interest
over the past few years. However, applications for hyperspectral
data are still in their infancy as handling the significant size of
the data presents a challenge for the user community. Efficient
compression techniques are required, and lossy compression,
specifically, will have a role to play, provided its impact on remote
sensing applications remains insignificant. To assess the data
quality, suitable distortion measures relevant to end-user applications
are required. Quality criteria are also of a major interest
for the conception and development of new sensors to define their
requirements and specifications. This paper proposes a method to
evaluate quality criteria in the context of hyperspectral images.
The purpose is to provide quality criteria relevant to the impact
of degradations on several classification applications. Different
quality criteria are considered. Some are traditionnally used in
image and video coding and are adapted here to hyperspectral
images. Others are specific to hyperspectral data.We also propose
the adaptation of two advanced criteria in the presence of different
simulated degradations on AVIRIS hyperspectral images. Finally,
five criteria are selected to give an accurate representation of the
nature and the level of the degradation affecting hyperspectral
data
- âŠ