Analysis Of Interferometric Data Research Articles

Interferometric Data Analysis of Convective Heat Transfer under a Downward-Facing Horizontal Circular Plate

Interferometric Data Analysis of Convective Heat Transfer under a Downward-Facing Horizontal Circular Plate

DoG-HiT: A novel VLBI multiscale imaging approach

Context. Reconstructing images from very long baseline interferometry (VLBI) data with a sparse sampling of the Fourier domain (uv-coverage) constitutes an ill-posed deconvolution problem. It requires application of robust algorithms, maximizing the information extraction from all of the sampled spatial scales, and minimizing the influence of the unsampled scales on image quality. Aims. We develop a new multiscale wavelet deconvolution algorithm, DoG-HiT, for imaging sparsely sampled interferometric data, which combines the difference of Gaussian (DoG) wavelets and hard image thresholding (HiT). Based on DoG-HiT, we propose a multistep imaging pipeline for analysis of interferometric data. Methods. DoG-HiT applies the compressed sensing approach to imaging by employing a flexible DoG wavelet dictionary, which is designed to adapt smoothly to the uv-coverage. It uses closure properties as data fidelity terms only, initially, and performs nonconvex, nonsmooth optimization by an amplitude-conserving and total-flux-conserving, hard thresholding splitting. DoG-HiT calculates a multiresolution support as a side product. The final reconstruction is refined through self-calibration loops and imaging with amplitude and phase information applied for the multiresolution support only. Results. We demonstrate the stability of DoG-HiT, and benchmark its performance against image reconstructions made with the CLEAN and regularized maximum-likelihood (RML) methods using synthetic data. The comparison shows that DoG-HiT matches the super-resolution achieved by the RML reconstructions and surpasses the sensitivity to extended emission reached by CLEAN. Conclusions. The application of regularized maximum likelihood methods, outfitted with flexible multiscale wavelet dictionaries, to imaging of interferometric data, matches the performance of state-of-the art convex optimization imaging algorithms and requires fewer prior and user-defined constraints.

GASP. XXII. The Molecular Gas Content of the JW100 Jellyfish Galaxy at z ∼ 0.05: Does Ram Pressure Promote Molecular Gas Formation?

Abstract Within the GASP survey, aimed at studying the effect of ram pressure stripping on star formation quenching in cluster galaxies, we analyze here ALMA observations of the jellyfish galaxy JW100. We find an unexpected large amount of molecular gas (∼2.5 × 1010 ), 30% of which is located in the stripped gas tail out to ∼35 kpc from the galaxy center. The overall kinematics of the molecular gas is similar to the one shown by the ionized gas, but for clear signatures of double components along the stripping direction detected only out to 2 kpc from the disk. The line ratio r 21 has a clumpy distribution and in the tail can reach large values (≥1), while its average value is low (0.58 with a 0.15 dispersion). All these evidence strongly suggest that the molecular gas in the tail is newly born from stripped H i gas or newly condensed from stripped diffuse molecular gas. The analysis of interferometric data at different scales reveals that a significant fraction (∼40%) of the molecular gas is extended over large scales (≥8 kpc) in the disk, and this fraction becomes predominant in the tail (∼70%). By comparing the molecular gas surface density with the star formation rate surface density derived from the Hα emission from MUSE data, we find that the depletion time on 1 kpc scale is particularly large (5–10 Gyr) both within the ram-pressure-disturbed region in the stellar disk and in the complexes along the tail.

PSInSAR analysis in urban areas: a case study in the Arno coastal plain (Italy

The Permanent Scatterer Interferometry (PSI) has been used to detect the land subsidence of the Arno coastal plain, in particular within the urban area of the city of Pisa. Two satellite PSInSAR dataset (ERS 1/2 and Envisat) were used to quantify the spatial evolution of ground displacements. A set of 92 geotechnical borehole was also analyzed to relate the measured displacements with the local stratigraphic asset. Furthermore, the results of the interferometric data analysis were compared with the urban development, from1978 to 2013, of the eastern part of Pisa. The PSInSAR data show that the city of Pisa is divided in two sectors with different subsidence rates: the south - western part, with null or very small movements, and the eastern part that shows a general lowering with maximum velocities of 5 mm/yr. In the eastern part, single or small groups of buildings recorded subsidence rates higher than 15 mm/yr. Through the analysis of the temporal evolution and magnitude of the subsidence rates recorded by several buildings in these areas, the importance of the urbanization as an accelerating factor for the consolidation process have been demonstrated.

Improved beta (local beta >1) and density in electron cyclotron resonance heating on the RT-1 magnetosphere plasma

This study reports the recent progress in improved plasma parameters of the RT-1 device. Increased input power and the optimized polarization of electron cyclotron resonance heating (ECRH) with an 8.2 GHz klystron produce a significant increase in electron beta, which is evaluated by an equilibrium analysis of the Grad–Shafranov equation. The peak value of the local electron beta βe is found to exceed 1. In the high-beta and high-density regime, the density limit is observed for H, D and He plasmas. The line-averaged density is close to the cutoff density for 8.2 GHz ECRH. When the filling gas pressure is increased, the density limit still exists even in the low-beta region. This result indicates that the density limit is caused by the cutoff density rather than the beta limit. From the analysis of interferometer data, we found that inward diffusion causes a peaked density profile beyond the cutoff density.

How serious can the stealth bias be in gravitational wave parameter estimation?

The upcoming direct detection of gravitational waves will open a window to probing the strong-field regime of general relativity (GR). As a consequence, waveforms that include the presence of deviations from GR have been developed (e.g. in the parametrized post-Einsteinian approach). TIGER, a data analysis pipeline which builds Bayesian evidence to support or question the validity of GR, has been written and tested. In particular, it was shown recently that data from the LIGO and Virgo detectors will allow to detect deviations from GR smaller than can be probed with Solar System tests and pulsar timing measurements or not accessible with conventional tests of GR. However, evidence from several detections is required before a deviation from GR can be confidently claimed. An interesting consequence is that, should GR not be the correct theory of gravity in its strong field regime, using standard GR templates for the matched filter analysis of interferometer data will introduce biases in the gravitational wave measured parameters with potentially disastrous consequences on the astrophysical inferences, such as the coalescence rate or the mass distribution. We consider three heuristic possible deviations from GR and show that the biases introduced by assuming GR's validity manifest in various ways. The mass parameters are usually the most affected, with biases that can be as large as $30$ standard deviations for the symmetric mass ratio, and nearly one percent for the chirp mass, which is usually estimated with sub-percent accuracy. We conclude that statements about the nature of the observed sources, e.g. if both objects are neutron stars, depend critically on the explicit assumption that GR it the right theory of gravity in the strong field regime.

A 189 MHz, 2400 deg2POLARIZATION SURVEY WITH THE MURCHISON WIDEFIELD ARRAY 32-ELEMENT PROTOTYPE

We present a Stokes I, Q and U survey at 189 MHz with the Murchison Widefield Array 32-element prototype covering 2400 square degrees. The survey has a 15.6 arcmin angular resolution and achieves a noise level of 15 mJy/beam. We demonstrate a novel interferometric data analysis that involves calibration of drift scan data, integration through the co-addition of warped snapshot images and deconvolution of the point spread function through forward modeling. We present a point source catalogue down to a flux limit of 4 Jy. We detect polarization from only one of the sources, PMN J0351-2744, at a level of 1.8 \pm 0.4%, whereas the remaining sources have a polarization fraction below 2%. Compared to a reported average value of 7% at 1.4 GHz, the polarization fraction of compact sources significantly decreases at low frequencies. We find a wealth of diffuse polarized emission across a large area of the survey with a maximum peak of ~13 K, primarily with positive rotation measure values smaller than +10 rad/m^2. The small values observed indicate that the emission is likely to have a local origin (closer than a few hundred parsecs). There is a large sky area at 2^h30^m where the diffuse polarized emission rms is fainter than 1 K. Within this area of low Galactic polarization we characterize the foreground properties in a cold sky patch at $(\alpha,\delta) = (4^h,-27^\circ.6)$ in terms of three dimensional power spectra

Spatio-temporal analysis of ground deformation occurring near Rice Lake, Saskatchewan, and observed by Radarsat-2 DInSAR during 2008–2011

We present ground deformation maps for the southern Saskatchewan region between Rice Lake and the City of Saskatoon measured by Radarsat-2 Differential Interferometric Synthetic Aperture Radar (DInSAR) during 2008–2011. We acquired and processed Radarsat-2 data from two different tracks (Multi-Look Fine beam and one Standard beam) and performed advanced interferometric analysis that revealed ground deformation with a maximum line-of-sight rate close to 10 cm per year. Decomposition of ascending and descending, line-of-sight images into horizontal (mainly east–west) and vertical components revealed the presence of localized horizontal motion with a maximum absolute rate of 4 cm per year and subsidence with a maximum rate of −10 cm per year. These results suggested that simple line-of-sight time series analysis of interferometric data acquired in single geometry is insufficient for capturing a complete pattern of ground deformation and can be misleading in the presence of both horizontal and vertical components of deformation.

Hot circumstellar material resolved aroundβ Pic with VLTI/PIONIER

We aim at resolving the circumstellar environment around beta Pic in the near-infrared in order to study the inner planetary system (< 200 mas, i.e., ~4 AU). Precise interferometric fringe visibility measurements were obtained over seven spectral channels dispersed across the H band with the four-telescope VLTI/PIONIER interferometer. Thorough analysis of interferometric data was performed to measure the stellar angular diameter and to search for circumstellar material. We detected near-infrared circumstellar emission around beta Pic that accounts for 1.37% +/- 0.16% of the near-infrared stellar flux and that is located within the field-of-view of PIONIER (i.e., ~200 mas in radius). The flux ratio between this excess and the photosphere emission is shown to be stable over a period of 1 year and to vary only weakly across the H band, suggesting that the source is either very hot (> 1500 K) or dominated by the scattering of the stellar flux. In addition, we derived the limb-darkened angular diameter of beta Pic with an unprecedented accuracy (theta_LD= 0.736 +/- 0.019 mas). The presence of a small H-band excess originating in the vicinity of beta Pic is revealed for the first time thanks to the high-precision visibilities enabled by VLTI/PIONIER. This excess emission is likely due to the scattering of stellar light by circumstellar dust and/or the thermal emission from a yet unknown population of hot dust, although hot gas emitting in the continuum cannot be firmly excluded.

Inversion of Wrapped Differential Interferometric SAR Data for Fault Dislocation Modeling

The differential synthetic aperture radar interferometry (DInSAR) technique has dramatically boosted the application of remote sensing in many geophysical disciplines, particularly tectonics. Coseismic interferograms have provided, in many cases, “images of earthquakes,” showing the surface displacement due to the deep fault dislocation. Aside from being visually appealing, such interferograms are of fundamental importance for the analysis, by means of appropriate dislocation models, of the geometrical and kinematic characteristics of the fault, which are also parameters of key interest for earthquake risk management. This paper provides a contribution in the general framework of the integration of dislocation models in DInSAR processing. In particular, with reference to coseismic interferograms, it proposes a technique that allows the direct inversion of wrapped interferograms for dislocation model analysis. This option makes it possible to avoid the critical and error-prone processing step of phase unwrapping, carried out in the classical analysis of interferometric data. Examples of inversion of real data, relevant to the 1999 Athens and Izmit earthquakes, demonstrate the feasibility and the advantages of this data processing approach.

Extraction of phase derivative data from interferometer images using a continuous wavelet transform to determine two-dimensional refractive index profiles

Two-dimensional refractive index profiles of ion exchanged channel waveguides in glass have been obtained from the analysis of interferometer data. To obtain depth data, a shallow bevel is produced in the glass by polishing. The refractive index profile information that is contained within the derivative of the phase data is extracted directly using a continuous wavelet transform algorithm. The algorithm used to characterize and smooth the wavelet ridge is discussed in detail.

Software holography: interferometric data analysis for the challenges of next generation observatories

Next generation radio observatories such as the Murchison Widefield Array (MWA), the Long Wavelength Array (LWA), the LOw Frequency ARray (LOFAR), the Combined Array for Research Millimeter-wave Astronomy (CARMA) and the Square Kilometer Array (SKA) provide a number of challenges for interferometric data analysis. These challenges include heterogeneous arrays, direction-dependent instrumental gain, and refractive and scintillating atmospheric conditions. From the analysis perspective, this means that calibration solutions cannot be described using a single complex gain per antenna. In this paper, we use the optimal map-making formalism developed for cosmic microwave background analyses to extend traditional interferometric radio analysis techniques – removing the assumption of a single complex gain per antenna and allowing more complete descriptions of the instrumental and atmospheric conditions. Due to the similarity with holographic mapping of radio antenna surfaces, we call this extended analysis approach software holography. The resulting analysis algorithms are computationally efficient, unbiased and optimally sensitive. We show how software holography can be used to solve some of the challenges of next generation observations, and how more familiar analysis techniques can be derived as limiting cases.

Reducing Binary Star Data from Long-Baseline Interferometers

AbstractProcessing long-baseline interferometry data presents a unique set of complications: How does one derive relative astrometry from interferometric data? How can 1-D interferometric results be used to solve a 2-D orbit? How can baseline-only solutions be combined with historical data and how should interferometric data be published so that they can be combined with archived data? What new techniques for interferometers are coming on line? This paper contains a brief review of interferometric data analysis in the context of binary star astrometry.

Optimal detection of burst events in gravitational wave interferometric observatories

We consider the problem of detecting a burst signal of unknown shape. We introduce a statistic which generalizes the excess power statistic proposed by Flanagan and Hughes and extended by Anderson et al. The statistic we propose is shown to be optimal for arbitrary noise spectral characteristic, under the two hypotheses that the noise is Gaussian, and that the prior for the signal is uniform. The statistic derivation is based on the assumption that a signal affects only affects N samples in the data stream, but that no other information is a priori available, and that the value of the signal at each sample can be arbitrary. We show that the proposed statistic can be implemented combining standard time-series analysis tools which can be efficiently implemented, and the resulting computational cost is still compatible with an on-line analysis of interferometric data. We generalize this version of an excess power statistic to the multiple detector case, also including the effect of correlated noise. We give full details about the implementation of the algorithm, both for the single and the multiple detector case, and we discuss exact and approximate forms, depending on the specific characteristics of the noise and on the assumed length of the burst event. As a example, we show what would be the sensitivity of the network of interferometers to a delta-function burst.

Interferometric data analysis based on Markov nonlinear filtering methodology.

For data processing in conventional phase shifting interferometry, Fourier transform, and least-squares-fitting techniques, a whole interferometric data series is required. We propose a new interferometric data processing methodology based on a recurrent nonlinear procedure. The signal value is predicted from the previous step to the next step, and the prediction error is used for nonlinear correction of an a priori estimate of the parameters phase, visibility, or frequency of interference fringes. Such a recurrent procedure is correct on the condition that the noise component be a Markov stochastic process realization. The accuracy and stability of the recurrent Markov nonlinear filtering algorithm were verified by computer simulations. It was discovered that the main advantages of the proposed methodology are dynamic data processing, phase error minimization, and high noise immunity against the influence of non-Gaussian noise correlated with the signal and the automatic solution of the phase unwrapping problem.

Search techniques for gravitational waves from black-hole ringdowns

Of all the astronomical sources of gravitational radiation, the ringdown waveform arising from a small perturbation of a spinning black hole is perhaps the best understood: for the late stages of such a perturbation, the waveform is simply an exponentially damped sinusoid. Searching interferometric gravitational wave antenna data for these should be relatively easy. In this paper, I present the results of a single-filter search for ringdown waveforms arising from a 50 solar mass black hole with $98%$ of its maximum spin angular momentum using data from the Caltech 40-m prototype interferometer. This search illustrates the techniques that may be used in analyzing data from future kilometer-scale interferometers and describes some of the difficulties present in the analysis of interferometer data. Most importantly, it illustrates the use of coincident events in the output of two independent interferometers (here simulated by 40-m data at two different times) to substantially reduce the spurious event rate. Such coincidences will be essential tools in future gravitational wave searches in kilometer-scale interferometers.

Automated fringe analysis in diffusivity measurements by sandwich holography

An image processing system to analyze interference patterns, related to the measurement of diffusion coefficient of liquid binary mixtures by sandwich holography, is proposed. Basic image processing tools are used and a specific software has been developed to perform an automated analysis of interferometric data. An example of application of this electrooptical method to the measurement of the diffusion coefficient of LiBr is reported

A poststatistics steering technique for MST radar applications

A new interferometric data analysis procedure equivalent to software beam synthesis and scanning is introduced. It is shown that the self‐ and cross‐spectra of interferometric multiple‐receiver signals can be linearly combined to obtain the self‐ and cross‐spectra of radar returns from selected viewing directions within the two‐way radar beam pattern.

A computer-controlled submillimeter Fourier spectrometer

A system for submillimeter-wave Fourier transform spectroscopy (FTS) has been automated for the measurement of the power absorption coefficient of liquids in the wavenumber range 10-400 cm/sup -1/. The interferometer is interfaced with a RM380Z Research Machines microcomputer. Software and hardware have been developed to automate the process of collecting and storing the data. Some points of relevance to the analysis of interferometric data are reviewed including the use of phase modulation, the resolution of spectra computed using the discrete Fourier transform, and the necessity of proper optical filtering in spectrometers which use Fourier transform techniques. Spectra measured using the FTS system described have been compared with results obtained using a tunable submillimeter laser and a good agreement was found between the two sets of data. >

Functional Group Analysis of Interferometric Data from Gas Chromatography Fourier Transform Infrared Spectroscopy

A method is presented for the direct analysis of interferometric data from gas chromatography Fourier transform infrared spectroscopy (GC/FTIR). A synthetic interferogram is initially produced which represents the characteristic absorption features of a particular functional group or compound class. A zero displacement correlation is performed between this test interferogram and each sample interferogram from the GC data. The presence of the desired functionality in the GC effluent is indicated by a small value of the resulting cumulative sum. A “correlogram” which emulates the response from a chemically specific GC detector is obtained by plotting the cumulative sum from each sample correlation. Synthetic interferograms representing infrared absorption bands which are truly specific for a particular functionality yield the best results.