19,737 research outputs found
Interferometry-based modal analysis with finite aperture effects
We analyze the effects of aperture finiteness on interferograms recorded to
unveil the modal content of optical beams in arbitrary basis using generalized
interferometry. We develop a scheme for modal reconstruction from
interferometric measurements that accounts for the ensuing clipping effects.
Clipping-cognizant reconstruction is shown to yield significant performance
gains over traditional schemes that overlook such effects that do arise in
practice. Our work can inspire further research on reconstruction schemes and
algorithms that account for practical hardware limitations in a variety of
contexts
Generalized linear sampling method for elastic-wave sensing of heterogeneous fractures
A theoretical foundation is developed for active seismic reconstruction of
fractures endowed with spatially-varying interfacial condition
(e.g.~partially-closed fractures, hydraulic fractures). The proposed indicator
functional carries a superior localization property with no significant
sensitivity to the fracture's contact condition, measurement errors, and
illumination frequency. This is accomplished through the paradigm of the
-factorization technique and the recently developed Generalized
Linear Sampling Method (GLSM) applied to elastodynamics. The direct scattering
problem is formulated in the frequency domain where the fracture surface is
illuminated by a set of incident plane waves, while monitoring the induced
scattered field in the form of (elastic) far-field patterns. The analysis of
the well-posedness of the forward problem leads to an admissibility condition
on the fracture's (linearized) contact parameters. This in turn contributes
toward establishing the applicability of the -factorization method,
and consequently aids the formulation of a convex GLSM cost functional whose
minimizer can be computed without iterations. Such minimizer is then used to
construct a robust fracture indicator function, whose performance is
illustrated through a set of numerical experiments. For completeness, the
results of the GLSM reconstruction are compared to those obtained by the
classical linear sampling method (LSM)
Finding Structural Information of RF Power Amplifiers using an Orthogonal Non-Parametric Kernel Smoothing Estimator
A non-parametric technique for modeling the behavior of power amplifiers is
presented. The proposed technique relies on the principles of density
estimation using the kernel method and is suited for use in power amplifier
modeling. The proposed methodology transforms the input domain into an
orthogonal memory domain. In this domain, non-parametric static functions are
discovered using the kernel estimator. These orthogonal, non-parametric
functions can be fitted with any desired mathematical structure, thus
facilitating its implementation. Furthermore, due to the orthogonality, the
non-parametric functions can be analyzed and discarded individually, which
simplifies pruning basis functions and provides a tradeoff between complexity
and performance. The results show that the methodology can be employed to model
power amplifiers, therein yielding error performance similar to
state-of-the-art parametric models. Furthermore, a parameter-efficient model
structure with 6 coefficients was derived for a Doherty power amplifier,
therein significantly reducing the deployment's computational complexity.
Finally, the methodology can also be well exploited in digital linearization
techniques.Comment: Matlab sample code (15 MB):
https://dl.dropboxusercontent.com/u/106958743/SampleMatlabKernel.zi
Multiwavelength active optics Shack-Hartmann sensor for seeing and turbulence outer scale monitoring
Real-time seeing and outer scale estimation at the location of the focus of a
telescope is fundamental for the adaptive optics systems dimensioning and
performance prediction, as well as for the operational aspects of instruments.
This study attempts to take advantage of multiwavelength long exposure images
to instantaneously and simultaneously derive the turbulence outer scale and
seeing from the full-width at half-maximum (FWHM) of seeing-limited images
taken at the focus of a telescope. These atmospheric parameters are commonly
measured in most observatories by different methods located away from the
telescope platform, and thus differing from the effective estimates at the
focus of a telescope, mainly because of differences in pointing orientation,
height above the ground, or local seeing bias (dome contribution). Long
exposure images can either directly be provided by any multiwavelength
scientific imager or spectrograph, or alternatively from a modified active
optics Shack-Hartmann sensor (AOSH). From measuring simultaneously the AOSH
sensor spot point spread function FWHMs at different wavelengths, one can
estimate the instantaneous outer scale in addition to seeing. Although AOSH
sensors are specified to measure not spot sizes but slopes, real-time r0 and L0
measurements from spot FWHMs can be obtained at the critical location where
they are needed with major advantages over scientific instrument images:
insensitivity to the telescope field stabilization, and being continuously
available. Assuming an alternative optical design allowing simultaneous
multiwavelength images, AOSH sensor gathers all the advantages for real-time
seeing and outer scale monitoring. With the substantial interest in the design
of extremely large telescopes, such a system could have a considerable
importance.Comment: Accepted for publication in A&A. arXiv admin note: text overlap with
arXiv:1201.233
Generalized Inpainting Method for Hyperspectral Image Acquisition
A recently designed hyperspectral imaging device enables multiplexed
acquisition of an entire data volume in a single snapshot thanks to
monolithically-integrated spectral filters. Such an agile imaging technique
comes at the cost of a reduced spatial resolution and the need for a
demosaicing procedure on its interleaved data. In this work, we address both
issues and propose an approach inspired by recent developments in compressed
sensing and analysis sparse models. We formulate our superresolution and
demosaicing task as a 3-D generalized inpainting problem. Interestingly, the
target spatial resolution can be adjusted for mitigating the compression level
of our sensing. The reconstruction procedure uses a fast greedy method called
Pseudo-inverse IHT. We also show on simulations that a random arrangement of
the spectral filters on the sensor is preferable to regular mosaic layout as it
improves the quality of the reconstruction. The efficiency of our technique is
demonstrated through numerical experiments on both synthetic and real data as
acquired by the snapshot imager.Comment: Keywords: Hyperspectral, inpainting, iterative hard thresholding,
sparse models, CMOS, Fabry-P\'ero
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