104,596 research outputs found
Parametric spectral analysis: scale and shift
We introduce the paradigm of dilation and translation for use in the spectral
analysis of complex-valued univariate or multivariate data. The new procedure
stems from a search on how to solve ambiguity problems in this analysis, such
as aliasing because of too coarsely sampled data, or collisions in projected
data, which may be solved by a translation of the sampling locations.
In Section 2 both dilation and translation are first presented for the
classical one-dimensional exponential analysis. In the subsequent Sections 3--7
the paradigm is extended to more functions, among which the trigonometric
functions cosine, sine, the hyperbolic cosine and sine functions, the Chebyshev
and spread polynomials, the sinc, gamma and Gaussian function, and several
multivariate versions of all of the above.
Each of these function classes needs a tailored approach, making optimal use
of the properties of the base function used in the considered sparse
interpolation problem. With each of the extensions a structured linear matrix
pencil is associated, immediately leading to a computational scheme for the
spectral analysis, involving a generalized eigenvalue problem and several
structured linear systems.
In Section 8 we illustrate the new methods in several examples: fixed width
Gaussian distribution fitting, sparse cardinal sine or sinc interpolation, and
lacunary or supersparse Chebyshev polynomial interpolation
Constructing A Flexible Likelihood Function For Spectroscopic Inference
We present a modular, extensible likelihood framework for spectroscopic
inference based on synthetic model spectra. The subtraction of an imperfect
model from a continuously sampled spectrum introduces covariance between
adjacent datapoints (pixels) into the residual spectrum. For the high
signal-to-noise data with large spectral range that is commonly employed in
stellar astrophysics, that covariant structure can lead to dramatically
underestimated parameter uncertainties (and, in some cases, biases). We
construct a likelihood function that accounts for the structure of the
covariance matrix, utilizing the machinery of Gaussian process kernels. This
framework specifically address the common problem of mismatches in model
spectral line strengths (with respect to data) due to intrinsic model
imperfections (e.g., in the atomic/molecular databases or opacity
prescriptions) by developing a novel local covariance kernel formalism that
identifies and self-consistently downweights pathological spectral line
"outliers." By fitting many spectra in a hierarchical manner, these local
kernels provide a mechanism to learn about and build data-driven corrections to
synthetic spectral libraries. An open-source software implementation of this
approach is available at http://iancze.github.io/Starfish, including a
sophisticated probabilistic scheme for spectral interpolation when using model
libraries that are sparsely sampled in the stellar parameters. We demonstrate
some salient features of the framework by fitting the high resolution -band
spectrum of WASP-14, an F5 dwarf with a transiting exoplanet, and the moderate
resolution -band spectrum of Gliese 51, an M5 field dwarf.Comment: Accepted to ApJ. Incorporated referees' comments. New figures 1, 8,
10, 12, and 14. Supplemental website: http://iancze.github.io/Starfish
Joint Demosaicing and Super-Resolution Imaging from a Set of Unregistered Aliased Images
We present a new algorithm that performs demosaicing and super-resolution jointly from a set of raw images sampled with a color filter array. Such a combined approach allows us to compute the alignment parameters between the images on the raw camera data before interpolation artifacts are introduced. After image registration, a high resolution color image is reconstructed at once using the full set of images. For this, we use normalized convolution, an image interpolation method from a nonuniform set of samples. Our algorithm is tested and compared to other approaches in simulations and practical experiments
The SAMI Galaxy Survey: Cubism and covariance, putting round pegs into square holes
We present a methodology for the regularization and combination of sparse sampled and irregularly gridded observations from fibre-optic multiobject integral field spectroscopy. The approach minimizes interpolation and retains image resolution on combining subpixel dithered data. We discuss the methodology in the context of the Sydney-AAO multiobject integral field spectrograph (SAMI) Galaxy Survey underway at the Anglo-Australian Telescope. The SAMI instrument uses 13 fibre bundles to perform high-multiplex integral field spectroscopy across a 1° diameter field of view. The SAMI Galaxy Survey is targeting ~3000 galaxies drawn from the full range of galaxy environments. We demonstrate the subcritical sampling of the seeing and incomplete fill factor for the integral field bundles results in only a 10 per cent degradation in the final image resolution recovered. We also implement a new methodology for tracking covariance between elements of the resulting data cubes which retains 90 per cent of the covariance information while incurring only a modest increase in the survey data volume
Continuous Plasma density measurement in TJ-II infrared interferometer-Advanced signal processing based on FPGAs
This work presents the behavioral simulation in an FPGA of a novel processing system for measuring line average electronic density in the TJ-II stellarator diagnostic, Infra-Red Two-Color Interferometer. Line average electronic density is proportional to phase difference between probing and reference signals of the interferometer, as the Appleton–Hartree cold plasma model states. The novelty of the approach is the development of a real time measuring system where research work has been carried out in two ways: a new interpolation algorithm and the implementation of a new specific processor on an FPGA.
The main goal of this new system is to measure line plasma electronic density for several channels in real time, also it will be useful to eliminate intermediate mixing frequency stages (the output signals coming from the interferometer are going to be directly sampled) and finally to generate real time density signals for control purposes in TJ-II and in other diagnostics. This device is intended to be the new data acquisition-processing system for the future six channel infrared interferometer that requires at least 14 input signals. The knowledge acquired could be useful in the design of W7-X and ITER IR-interferometer data acquisition and processing systems
TESTING THE PERFORMANCE OF DIFFERENT SPATIAL INTERPOLATION TECHNIQUES ON MAPPING SHORT DATASERIES OF PRECIPITATION PROPRETIES
patial interpolation, in the context of spatial analysis, can be defined as the derivation of new data from already known information, a technique frequently used to predict and quantify spatial variation of a certain property or parameter. In this study we compared the performance of Inverse Distance Weighted (IDW), Ordinary Kriging and Natural Neighbor techniques, applied in spatial interpolation of precipitation parameters (pH, electrical conductivity and total dissolved solids). These techniques are often used when the area of interest is relatively small and the sampled locations are regularly spaced. The methods were tested on data collected in Iasi city (Romania) between March – May 2013. Spatial modeling was performed on a small dataset, consisting of 7 sample locations and 13 different known values of each analyzed parameter. The precision of the techniques used is directly dependent on sample density as well as data variation, greater fluctuations in values between locations causing a decrease in the accuracy of the methods used. To validate the results and reveal the best method of interpolating rainfall characteristics, leave-one – out cross-validation approach was used. Comparing residues between the known values and the estimated values of pH, electrical conductivity and total dissolved solids, it was revealed that Natural Neighbor stands out as generating the smallest residues for pH and electrical conductivity, whereas IDW presents the smallest error in interpolating total dissolved solids (the parameter with the highest fluctuations in value)
- …