scholarly journals Image Simulation for Mingantu Ultrawide Spectral Radioheliograph in the Decimetre Wave Range

2015 ◽  
Vol 32 ◽  
Author(s):  
Jing Du ◽  
Yihua Yan ◽  
Wei Wang ◽  
Donghao Liu
Keyword(s):  
Inner Mongolia ◽  
Dynamic Range ◽  
Signal To Noise Ratio ◽  
Frequency Resolution ◽  
The Sun ◽  
Image Simulation ◽  
Time Space ◽  
Wide Range ◽  
Wave Range ◽  
Imaging Performance

AbstractThe MUSER is a solar-dedicated radio interferometric array, which will observe the Sun over a wide range of radio frequencies (0.4–15 GHz), and make high time, space and frequency resolution images of the Sun simultaneously. MUSER is located in Mingantu Station in Inner Mongolia of China, which is about 400 kilometres away from Beijing. MUSER consists of two arrays: MUSER-I and MUSER-II. MUSER-I contains 40 antennas with 4.5-m aperture operating at 400 MHz to 2 GHz. MUSER-II contains 60 antennas with 2-m aperture operating at 2 to 15 GHz. Currently, MUSER has already been established and entered into the stage of test observation. This work is focus on the imaging performance of MUSER-I. This paper introduces MUSER-I briefly, presents the analysis of the array configurations, and evaluates the image quality mainly using the dynamic range, fidelity index, and the peak signal-to-noise ratio, also make some actual solar model simulations with CASA, the results will be shown below.

scholarly journals Radio imaging-spectroscopy observations of the Sun in decimetric and centimetric wavelengths

2012 ◽  
Vol 8 (S294) ◽  
pp. 489-494 ◽  
Author(s):  
Yihua Yan ◽  
Wei Wang ◽  
Fei Liu ◽  
Lihong Geng ◽  
Zhijun Chen ◽  
...  
Keyword(s):  
Radio Emission ◽  
Solar Flares ◽  
Inner Mongolia ◽  
Imaging Spectroscopy ◽  
Current Status ◽  
The Sun ◽  
Radio Imaging ◽  
Time Space ◽  
Decimetric Wave ◽  
Wave Range

AbstractTo address fundamental processes in the solar eruptive phenomena it is important to have imaging-spectroscopy over centimetric-decimetric wave range. The Chinese Spectral Radioheliograph (CSRH) in 0.4-15 GHz range with high time, space and frequency resolutions is being constructed to achieve this goal. The perspectives to open new observational windows on solar flares and CMEs will be achieved by mapping the radio emission from unstable electron populations during the basic processes of energy release. CSRH is located in a radio quiet region in Inner Mongolia of China. The array of CSRH-I in 0.4-2.0 GHz with 40 4.5m antennas has been established and starts test observations. The 60 2m antennas for array of CSRH-II in 2-15 GHz have been mounted and assembled. The progress and current status of CSRH are introduced.

scholarly journals Detectivity optimization to detect of ultraweak light fluxes with an EM-CCD as binary photon counter array

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Ibtissame Khaoua ◽  
Guillaume Graciani ◽  
Andrey Kim ◽  
François Amblard
Keyword(s):  
Dynamic Range ◽  
Signal To Noise Ratio ◽  
Photon Counting ◽  
Detection Methods ◽  
Strong Nonlinearity ◽  
Wide Range ◽  
Depth Analysis ◽  
Spatially Extended ◽  
Extended Sources ◽  
Photon Counting Mode

AbstractFor a wide range of purposes, one faces the challenge to detect light from extremely faint and spatially extended sources. In such cases, detector noises dominate over the photon noise of the source, and quantum detectors in photon counting mode are generally the best option. Here, we combine a statistical model with an in-depth analysis of detector noises and calibration experiments, and we show that visible light can be detected with an electron-multiplying charge-coupled devices (EM-CCD) with a signal-to-noise ratio (SNR) of 3 for fluxes less than $$30\,{\text{photon}}\,{\text{s}}^{ - 1} \,{\text{cm}}^{ - 2}$$ 30 photon s - 1 cm - 2 . For green photons, this corresponds to 12 aW $${\text{cm}}^{ - 2}$$ cm - 2 ≈ $$9{ } \times 10^{ - 11}$$ 9 × 10 - 11 lux, i.e. 15 orders of magnitude less than typical daylight. The strong nonlinearity of the SNR with the sampling time leads to a dynamic range of detection of 4 orders of magnitude. To detect possibly varying light fluxes, we operate in conditions of maximal detectivity $${\mathcal{D}}$$ D rather than maximal SNR. Given the quantum efficiency $$QE\left( \lambda \right)$$ Q E λ of the detector, we find $${ \mathcal{D}} = 0.015\,{\text{photon}}^{ - 1} \,{\text{s}}^{1/2} \,{\text{cm}}$$ D = 0.015 photon - 1 s 1 / 2 cm , and a non-negligible sensitivity to blackbody radiation for T > 50 °C. This work should help design highly sensitive luminescence detection methods and develop experiments to explore dynamic phenomena involving ultra-weak luminescence in biology, chemistry, and material sciences.

scholarly journals Consistent and accurate estimation of stellar parameters from HARPS-N Spectroscopy using Deep Learning

2021 ◽  
Vol 2 ◽  
Author(s):  
Frederik Boe Hüttel ◽  
Line Katrine Harder Clemmensen
Keyword(s):  
Signal To Noise Ratio ◽  
Rotational Velocity ◽  
High Accuracy ◽  
Data Driven ◽  
Accurate Estimation ◽  
The Sun ◽  
Signal To Noise ◽  
Wide Range ◽  
Processing Steps ◽  
Astrophysical Research

Consistent and accurate estimation of stellar parameters is of great importance for information retrieval in astrophysical research. The parameters span a wide range from effective temperature to rotational velocity. We propose to estimate the stellar parameters directly from spectral signals coming from the HARPS-N spectrograph pipeline before any spectrum-processing steps are applied to extract the 1D spectrum. We propose an attention-based model to estimate the stellar parameters, which estimate both mean and uncertainty of the stellar parameters through estimation of the parameters of a Gaussian distribution. The estimated distributions create a basis to generate data-driven Gaussian confidence intervals for the estimated stellar parameters. We show that residual networks and attention-based models can estimate the stellar parameters with high accuracy for low Signal-to-noise ratio (SNR) compared to previous methods. With an observation of the Sun from the HARPS-N spectrograph, we show that the models can estimate stellar parameters from real observational data.

scholarly journals Laboratory verification of Fast & Furious phase diversity: Towards controlling the low wind effect in the SPHERE instrument

2018 ◽  
Vol 615 ◽  
pp. A34 ◽  
Author(s):  
M. J. Wilby ◽  
C. U. Keller ◽  
J.-F. Sauvage ◽  
K. Dohlen ◽  
T. Fusco ◽  
...  
Keyword(s):  
Real Time ◽  
Closed Loop ◽  
Dynamic Range ◽  
Signal To Noise Ratio ◽  
Wind Effect ◽  
Wind Speeds ◽  
Phase Diversity ◽  
Expected Performance ◽  
Wide Range ◽  
Predictive Simulations

Context. The low wind effect (LWE) refers to a characteristic set of quasi-static wavefront aberrations seen consistently by the SPHERE instrument when dome-level wind speeds drop below 3 ms−1. The LWE produces bright low-order speckles in the stellar point-spread function (PSF), which severely limit the contrast performance of SPHERE under otherwise optimal observing conditions. Aims. In this paper we propose the Fast & Furious (F&F) phase diversity algorithm as a viable software-only solution for real-time LWE compensation, which would utilise image sequences from the SPHERE differential tip-tilt sensor (DTTS) and apply corrections via reference slope offsets on the AO system’s Shack-Hartmann wavefront sensor. Methods. We evaluated the closed-loop performance of F&F on the MITHIC high-contrast test-bench, under conditions emulating LWE-affected DTTS images. These results were contrasted with predictive simulations for a variety of convergence tests, in order to assess the expected performance of an on-sky implementation of F&F in SPHERE. Results. The algorithm was found to be capable of returning LWE-affected images to Strehl ratios of greater than 90% within five iterations, for all appropriate laboratory test cases. These results are highly representative of predictive simulations, and demonstrate stability of the algorithm against a wide range of factors including low image signal-to-noise ratio (S/N), small image field of view, and amplitude errors. It was also found in simulation that closed-loop stability can be preserved down to image S/N as low as five while still improving overall wavefront quality, allowing for reliable operation even on faint targets. Conclusions. The Fast & Furious algorithm is an extremely promising solution for real-time compensation of the LWE, which can operate simultaneously with science observations and may be implemented in SPHERE without requiring additional hardware. The robustness and relatively large effective dynamic range of F&F also make it suitable for general wavefront optimisation applications, including the co-phasing of segmented ELT-class telescopes.

Least-squares decomposition with time–space constraint for denoising microseismic data

2020 ◽  
Vol 222 (3) ◽  
pp. 1864-1880
Author(s):  
Yangkang Chen ◽  
Wei Chen ◽  
Yufeng Wang ◽  
Min Bai
Keyword(s):  
Least Squares ◽  
Signal To Noise Ratio ◽  
Random Noise ◽  
Microseismic Data ◽  
Smoothness Constraint ◽  
Time Space ◽  
Wide Range ◽  
The Stability ◽  
And Inversion

SUMMARY Microseismic data are usually of low signal-to-noise ratio (SNR), which makes it difficult to utilize the microseismic waveforms for imaging and inversion. We develop a useful denoising algorithm based on a non-stationary least-squares decomposition model to enhance the quality of microseismic signals. The microseismic signals are assumed to be represented by a superposition of several smoothly variable components. We construct a least-squares inverse problem to solve for the the smooth components. We constrain the least-squares inversion via both time and space constraints. The temporal smoothness constraint is applied to ensure the stability when calculating the non-stationary autoregression coefficients. The space-smoothness constraint is applied to extract the spatial correlation among multichannel microseismic traces. The new algorithm is validated via several synthetic and real microseismic data and are proved to be effective. Comparison with the state-of-the-art algorithms demonstrates that the proposed method is more powerful in suppressing random noise of a wide range of levels than its competing methods.

scholarly journals A photometric search for ‘5-min’ oscillations in the components of Alpha Centauri and two other double stars

1988 ◽  
Vol 123 ◽  
pp. 253-254
Author(s):  
L. A. Balona ◽  
F. Marang
Keyword(s):  
Small Amplitude ◽  
Signal To Noise Ratio ◽  
Broad Band ◽  
Double Star ◽  
The Other ◽  
The Sun ◽  
Star System ◽  
Signal To Noise ◽  
Double Stars ◽  
Wide Range

The discovery of global solar 5-min oscillations has prompted the search for such oscillations in other stars. The main problem in detecting these variations is their expected small amplitude (in the sun it is less than 1 m/s in velocity and 10−6 in integrated light). Two recent studies by Fossat et al. (1984) and Noyes et al. (1984) have suggested that the 5-min oscillations in α Cen and ε Eri may have been detected.We attempted to detect these oscillations by means of conventional broad-band photometry in the components of three double star systems (α Cen, HR4677 and HR5568). We selected these stars because they cover a wide range of spectral types (F2V to M2V). It was hoped that there may be a region where the pulsation amplitudes are particularly large. By using one component of a double star system to correct for transparency variations in the other, we also expected to obtain a larger signal-to-noise ratio.

An Over 120dB Dynamic Range Linear Response Single Exposure CMOS Image Sensor with Two-stage Lateral Overflow Integration Trench Capacitors

2020 ◽  
Vol 2020 (7) ◽  
pp. 143-1-143-6 ◽  
Author(s):  
Yasuyuki Fujihara ◽  
Maasa Murata ◽  
Shota Nakayama ◽  
Rihito Kuroda ◽  
Shigetoshi Sugawa
Keyword(s):  
Linear Response ◽  
Dynamic Range ◽  
Signal To Noise Ratio ◽  
Cmos Image Sensor ◽  
Image Sensor ◽  
Signal To Noise ◽  
Single Exposure ◽  
Two Stage ◽  
Noise Ratio ◽  
Maximum Signal

This paper presents a prototype linear response single exposure CMOS image sensor with two-stage lateral overflow integration trench capacitors (LOFITreCs) exhibiting over 120dB dynamic range with 11.4Me- full well capacity (FWC) and maximum signal-to-noise ratio (SNR) of 70dB. The measured SNR at all switching points were over 35dB thanks to the proposed two-stage LOFITreCs.

Much Ado about (Practically) Nothing

2010 ◽  
Author(s):  
David Fisher
Keyword(s):  
Energy Source ◽  
Atomic Nucleus ◽  
The Sun ◽  
Scientific Journals ◽  
Rare Gases ◽  
Important Work ◽  
The Earth ◽  
Wide Range ◽  
Life On Mars ◽  
The Universe

There are eight columns in the Periodic Table. The eighth column is comprised of the rare gases, so-called because they are the rarest elements on earth. They are also called the inert or noble gases because, like nobility, they do no work. They are colorless, odorless, invisible gases which do not react with anything, and were thought to be unimportant until the early 1960s. Starting in that era, David Fisher has spent roughly fifty years doing research on these gases, publishing nearly a hundred papers in the scientific journals, applying them to problems in geophysics and cosmochemistry, and learning how other scientists have utilized them to change our ideas about the universe, the sun, and our own planet. Much Ado about (Practically) Nothing will cover this spectrum of ideas, interspersed with the author's own work which will serve to introduce each gas and the important work others have done with them. The rare gases have participated in a wide range of scientific advances-even revolutions-but no book has ever recorded the entire story. Fisher will range from the intricacies of the atomic nucleus and the tiniest of elementary particles, the neutrino, to the energy source of the stars; from the age of the earth to its future energies; from life on Mars to cancer here on earth. A whole panoply that has never before been told as an entity.

Modal frequencies of bridges from GNSS (GPS) monitoring data: Experimental, statistical evidence

2021 ◽  
Vol 17 (1-2) ◽  
pp. 3-14
Author(s):  
Stathis C. Stiros ◽  
F. Moschas ◽  
P. Triantafyllidis
Keyword(s):  
Signal To Noise Ratio ◽  
Vertical Axis ◽  
Bridge Monitoring ◽  
Low Snr ◽  
True Value ◽  
Gps Satellites ◽  
Wide Range ◽  
Spectral Peaks ◽  
Monitoring Survey ◽  
True Frequency

GNSS technology (known especially for GPS satellites) for measurement of deflections has proved very efficient and useful in bridge structural monitoring, even for short stiff bridges, especially after the advent of 100 Hz GNSS sensors. Mode computation from dynamic deflections has been proposed as one of the applications of this technology. Apart from formal modal analyses with GNSS input, and from spectral analysis of controlled free attenuating oscillations, it has been argued that simple spectra of deflections can define more than one modal frequencies. To test this scenario, we analyzed 21 controlled excitation events from a certain bridge monitoring survey, focusing on lateral and vertical deflections, recorded both by GNSS and an accelerometer. These events contain a transient and a following oscillation, and they are preceded and followed by intervals of quiescence and ambient vibrations. Spectra for each event, for the lateral and the vertical axis of the bridge, and for and each instrument (GNSS, accelerometer) were computed, normalized to their maximum value, and printed one over the other, in order to produce a single composite spectrum for each of the four sets. In these four sets, there was also marked the true value of modal frequency, derived from free attenuating oscillations. It was found that for high SNR (signal-to-noise ratio) deflections, spectral peaks in both acceleration and displacement spectra differ by up to 0.3 Hz from the true value. For low SNR, defections spectra do not match the true frequency, but acceleration spectra provide a low-precision estimate of the true frequency. This is because various excitation effects (traffic, wind etc.) contribute with numerous peaks in a wide range of frequencies. Reliable estimates of modal frequencies can hence be derived from deflections spectra only if excitation frequencies (mostly traffic and wind) can be filtered along with most measurement noise, on the basis of additional data.

scholarly journals A System-Agnostic, Adaptable and Extensible Animal Support Cradle System for Cardio-Respiratory-Synchronised, and Other, Multi-Modal Imaging of Small Animals

Tomography ◽  
2021 ◽  
Vol 7 (1) ◽  
pp. 39-54
Author(s):  
Veerle Kersemans ◽  
Stuart Gilchrist ◽  
Philip Danny Allen ◽  
Sheena Wallington ◽  
Paul Kinchesh ◽  
...  
Keyword(s):  
Scientific Data ◽  
Cardiac Monitoring ◽  
Small Animals ◽  
Maintenance System ◽  
Wide Range ◽  
Set Up ◽  
Animal Handling ◽  
Imaging Performance ◽  
Significant Effort

Standardisation of animal handling procedures for a wide range of preclinical imaging scanners will improve imaging performance and reproducibility of scientific data. Whilst there has been significant effort in defining how well scanners should operate and how in vivo experimentation should be practised, there is little detail on how to achieve optimal scanner performance with best practices in animal welfare. Here, we describe a system-agnostic, adaptable and extensible animal support cradle system for cardio-respiratory-synchronised, and other, multi-modal imaging of small animals. The animal support cradle can be adapted on a per application basis and features integrated tubing for anaesthetic and tracer delivery, an electrically driven rectal temperature maintenance system and respiratory and cardiac monitoring. Through a combination of careful material and device selection, we have described an approach that allows animals to be transferred whilst under general anaesthesia between any of the tomographic scanners we currently or have previously operated. The set-up is minimally invasive, cheap and easy to implement and for multi-modal, multi-vendor imaging of small animals.

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