24,300 research outputs found
Signal-to-noise properties of correlation plenoptic imaging with chaotic light
Correlation Plenoptic Imaging (CPI) is a novel imaging technique, that
exploits the correlations between the intensity fluctuations of light to
perform the typical tasks of plenoptic imaging (namely, refocusing out-of-focus
parts of the scene, extending the depth of field, and performing 3D
reconstruction), without entailing a loss of spatial resolution. Here, we
consider two different CPI schemes based on chaotic light, both employing ghost
imaging: the first one to image the object, the second one to image the
focusing element. We characterize their noise properties in terms of the
signal-to-noise ratio (SNR) and compare their performances. We find that the
SNR can be significantly higher and easier to control in the second CPI scheme,
involving standard imaging of the object; under adequate conditions, this
scheme enables reducing by one order of magnitude the number of frames for
achieving the same SNR.Comment: 12 pages, 3 figure
Source Reconstruction as an Inverse Problem
Inverse Problem techniques offer powerful tools which deal naturally with
marginal data and asymmetric or strongly smoothing kernels, in cases where
parameter-fitting methods may be used only with some caution. Although they are
typically subject to some bias, they can invert data without requiring one to
assume a particular model for the source. The Backus-Gilbert method in
particular concentrates on the tradeoff between resolution and stability, and
allows one to select an optimal compromise between them. We use these tools to
analyse the problem of reconstructing features of the source star in a
microlensing event, show that it should be possible to obtain useful
information about the star with reasonably obtainable data, and note that the
quality of the reconstruction is more sensitive to the number of data points
than to the quality of individual ones.Comment: 8 pages, 3 figures. To be published in "Microlensing 2000, A New Era
of Microlensing Astrophysics", eds., J.W. Menzies and P.D. Sackett, ASP
Conference Serie
Examples of current radar technology and applications, chapter 5, part B
Basic principles and tradeoff considerations for SLAR are summarized. There are two fundamental types of SLAR sensors available to the remote sensing user: real aperture and synthetic aperture. The primary difference between the two types is that a synthetic aperture system is capable of significant improvements in target resolution but requires equally significant added complexity and cost. The advantages of real aperture SLAR include long range coverage, all-weather operation, in-flight processing and image viewing, and lower cost. The fundamental limitation of the real aperture approach is target resolution. Synthetic aperture processing is the most practical approach for remote sensing problems that require resolution higher than 30 to 40 m
Active microwave sensor technology, chapter 5
The relationship between surface properties and echo characteristics, as determined by radar technology, is discussed; echo enhancement to reduce measurement uncertainty was included. Feasibility data, suggested baseline functional descriptions of various types of active microwave sensors, and examples of existing radar techniques are summarized. Data manage and measurement processes are also covered
Better than a lens -- Increasing the signal-to-noise ratio through pupil splitting
Lenses are designed to fulfill Fermats principle such that all light
interferes constructively in its focus, guaranteeing its maximum concentration.
It can be shown that imaging via an unmodified full pupil yields the maximum
transfer strength for all spatial frequencies transferable by the system.
Seemingly also the signal-to-noise ratio (SNR) is optimal. The achievable SNR
at a given photon budget is critical especially if that budget is strictly
limited as in the case of fluorescence microscopy. In this work we propose a
general method which achieves a better SNR for high spatial frequency
information of an optical imaging system, without the need to capture more
photons. This is achieved by splitting the pupil of an incoherent imaging
system such that two (or more) sub-images are simultaneously acquired and
computationally recombined. We compare the theoretical performance of split
pupil imaging to the non-split scenario and implement the splitting using a
tilted elliptical mirror placed at the back-focal-plane (BFP) of a fluorescence
widefield microscope
Analysis of Quasi-Cyclic LDPC codes under ML decoding over the erasure channel
In this paper, we show that Quasi-Cyclic LDPC codes can efficiently
accommodate the hybrid iterative/ML decoding over the binary erasure channel.
We demonstrate that the quasi-cyclic structure of the parity-check matrix can
be advantageously used in order to significantly reduce the complexity of the
ML decoding. This is achieved by a simple row/column permutation that
transforms a QC matrix into a pseudo-band form. Based on this approach, we
propose a class of QC-LDPC codes with almost ideal error correction performance
under the ML decoding, while the required number of row/symbol operations
scales as , where is the number of source symbols.Comment: 6 pages, ISITA1
Active feedback of a Fabry-Perot cavity to the emission of a single InAs/GaAs quantum dot
We present a detailed study of the use of Fabry-Perot (FP) cavities for the
spectroscopy of single InAs quantum dots (QDs). We derive optimal cavity
characteristics and resolution limits, and measure photoluminescence linewidths
as low as 0.9 GHz. By embedding the QDs in a planar cavity, we obtain a
sufficiently large signal to actively feed back on the length of the FP to lock
to the emission of a single QD with a stability below 2% of the QD linewidth.
An integration time of approximately two seconds is found to yield an optimum
compromise between shot noise and cavity length fluctuations.Comment: 7 pages, 3 figure
A New Method for Generation of Soundings from Phase-Difference Measurements
A desirable feature of bathymetric sonar systems is the production of statistically independent soundings allowing a system to achieve its full capability in resolution and object detection. Moreover gridding algorithms such as the Combined Uncertainty Bathymetric Estimator (CUBE) rely on the statistical independence of soundings to properly estimate depth and discriminate outliers. Common methods of filtering to mitigate uncertainty in the signal processing of both multibeam and phase-differencing sidescan systems (curve fitting in zero-crossing detections and differential phase filtering respectively) can produce correlated soundings. Here we propose an alternative method for the generation of soundings from differential phase measurements made by either sonar type to produce statistically independent soundings. The method extracts individual, non-overlapping and unfiltered, phase-difference measurements (from either sonar type) converting these to sonar-relative receive angle, estimates their uncertainty, fixes the desired depth uncertainty level and combines these individual measurements into an uncertainty-weighted mean to achieve the desired depth uncertainty, and no more. When the signal to noise ratio is sufficiently high such that the desired depth uncertainty is achieved with an individual measurement, bathymetric estimates are produced at the sonar’s full resolution capability. When multiple measurements are required, the filtering automatically adjusts to maintain the desired uncertainty level, degrading the resolution only as necessary. Because no two measurements contribute to a single reported sounding, the resulting estimated soundings are statistically independent and therefore better resolve adjacent objects, increase object detectability and are more suitable for statistical gridding methodologies
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