scholarly journals Analysis of non-thermal velocities in the solar corona

2004 ◽  
Vol 22 (8) ◽  
pp. 3055-3062 ◽  
Author(s):  
L. Contesse ◽  
S. Koutchmy ◽  
C. Viladrich
Keyword(s):  
Solar Corona ◽  
Emission Line ◽  
Signal To Noise Ratio ◽  
Central Line ◽  
Line Of Sight ◽  
Polar Regions ◽  
Full Line ◽  
Coronal Line ◽  
Signal To Noise ◽  
Line Widths

Abstract. We describe new ground-based spectroscopic observations made using a 40-cm aperture coronagraph over a whole range of radial distances (up to heights of 12' above the limb) and along four different heliocentric directions N, E, S and W. The analysis is limited to the study of the brightest forbidden emission line of Fe XIV at 530.3nm, in order to reach the best possible signal-to-noise ratio. To make the results statistically more significant, the extracted parameters are averaged over the whole length of the slit, and measurements are repeated fives times at each position; the corresponding dispersions in the results obtained along the slit are given. Central line profile intensities and full line widths (FWHM) are plotted and compared to measurements published by other authors closer to the limb. We found widths and turbulent (non-thermal) velocities of significantly higher values above the polar regions, especially when a coronal hole is present along the line of sight. We do not see a definitely decreasing behaviour of widths and turbulent velocities in equatorial directions for larger radial distances, as reported in the literature, although lower values are measured compared to the values in polar regions. The variation in the high corona is rather flat and a correlation diagram indicates that it is different for different regions and different radial distances. This seems to be the first analysis of the profiles of this coronal line, up to large heights above the limb for both equatorial and polar regions.

scholarly journals Low-latency time-of-flight non-line-of-sight imaging at 5 frames per second

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Ji Hyun Nam ◽  
Eric Brandt ◽  
Sebastian Bauer ◽  
Xiaochun Liu ◽  
Marco Renna ◽  
...  
Keyword(s):  
Signal To Noise Ratio ◽  
Time Of Flight ◽  
Motion Blur ◽  
Line Of Sight ◽  
Low Latency ◽  
Imaging Method ◽  
Signal To Noise ◽  
Array Detectors ◽  
Noise Ratio ◽  
Non Line Of Sight

AbstractNon-Line-Of-Sight (NLOS) imaging aims at recovering the 3D geometry of objects that are hidden from the direct line of sight. One major challenge with this technique is the weak available multibounce signal limiting scene size, capture speed, and reconstruction quality. To overcome this obstacle, we introduce a multipixel time-of-flight non-line-of-sight imaging method combining specifically designed Single Photon Avalanche Diode (SPAD) array detectors with a fast reconstruction algorithm that captures and reconstructs live low-latency videos of non-line-of-sight scenes with natural non-retroreflective objects. We develop a model of the signal-to-noise-ratio of non-line-of-sight imaging and use it to devise a method that reconstructs the scene such that signal-to-noise-ratio, motion blur, angular resolution, and depth resolution are all independent of scene depth suggesting that reconstruction of very large scenes may be possible.

scholarly journals Computed Spectral Line Variations for Oblique Nonradial Pulsators

1986 ◽  
Vol 90 ◽  
pp. 234-234
Author(s):  
Dietrich Baade ◽  
Werner W. Weiss
Keyword(s):  
Spectral Line ◽  
Observational Data ◽  
Rotation Axis ◽  
Signal To Noise Ratio ◽  
Line Of Sight ◽  
Pulsation Velocity ◽  
Line Profiles ◽  
Signal To Noise ◽  
Velocity Amplitude ◽  
Mode Order

AbstractSpectral line profiles are computed for nonradially pulsating CP2 stars. For a range which currently is thought to be typical for these stars, the influence of six parameters on the line profiles is considered: mode order ℓ and degree m, pulsation velocity amplitude, the angle between the rotation and pulsation axis, the angle between the rotation axis and the line-of-sight, and the phase angle of the rotation. In view of the expected low signal-to-noise ratio of observational data it is investigated to what extent easily measurable, simple quantities can still be useful in discriminating between different modes.

On Filter Observations of Coronal Structures in the Light of FeX 6374 Å Emission Line

1994 ◽  
Vol 144 ◽  
pp. 575-578
Author(s):  
F. I. Guetman ◽  
I. S. Kim ◽  
A. Bücher ◽  
C. A. Druzhinin ◽  
J.-C. Noëns ◽  
...  
Keyword(s):  
Comparative Analysis ◽  
Solar Corona ◽  
Emission Line ◽  
Interference Filter ◽  
Spectral Interval ◽  
Coronal Line ◽  
Interference Filters ◽  
Coronal Structures

AbstractThe red coronal line of Fe X (6374 Å) seems to be extremely suitable for filter observations due to reduced sky scattering in this spectral interval and absence of blending by Fraunhofer lines. Comparative analysis of location of Hαstructures in colour and black-white pictures of the solar corona of July 11, 1991 was carried out. A conclusion was made that care should be taken when interference filters are used for the red corona observations. Non-ideal monochromatization of present-day existing interference filters may be responsible for some ”false“ red and white coronal structures which belong to Hαprominence emission. Estimations of parameters of an interference filter for the reliable red coronal observations are presented.

scholarly journals A global climatology of stratospheric OClO derived from GOMOS measurement

2013 ◽  
Vol 6 (2) ◽  
pp. 3511-3543
Author(s):  
C. Tétard ◽  
D. Fussen ◽  
F. Vanhellemont ◽  
C. Bingen ◽  
E. Dekemper ◽  
...  
Keyword(s):  
Near Infrared ◽  
Signal To Noise Ratio ◽  
Equatorial Region ◽  
Optical Absorption Spectroscopy ◽  
Polar Regions ◽  
Signal To Noise ◽  
Spectral Window ◽  
Stellar Occultation ◽  
Noise Ratio ◽  
Window Selection

Abstract. The Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument on board the European platform ENVISAT was dedicated to the study of the atmosphere of the Earth using the stellar occultation technique. The spectral range of the GOMOS spectrometer extends from the UV to the near infrared, allowing for the retrieval of species such as O3, NO2, NO3, H2O, O2, air density, aerosol extinction and OClO. Nevertheless, OClO can not be retrieved using a single GOMOS measurement because of the weak signal-to-noise ratio and the small optical thickness associated with this molecule. We present here the method used to detect this molecule by using several GOMOS measurements. It is based on a two-step approach. First, several co-located measurements are combined in a statistical way to build an averaged measurement with a higher signal-to-noise ratio. Then, a Differential Optical Absorption Spectroscopy (DOAS) method is applied to retrieve OClO slant column densities. The statistics of the sets of GOMOS measurements used to build the averaged measurement and the spectral window selection are analyzed. The obtained retrievals are compared to results from two balloon-borne instruments. It appears that the inter-comparisons of OClO are generally satisfying. Then, two nighttime climatologies of OClO slant column densities based on GOMOS averaged measurements are presented. The first depicts annual global pictures of OClO from 2003 to 2011. From this climatology, the presence of an OClO layer in the equatorial region at about 35 km is confirmed and strong concentrations of OClO in both polar regions are observed, a sign of chlorine activation. The second climatology is a monthly time series. It clearly shows the chlorine activation of the lower stratosphere during winter. Moreover the equatorial OClO layer is observed during all the years without any significant variations. Finally, the anti-correlation between OClO and NO2 is highlighted. This very promising method, applied on GOMOS measurements, allowed us to build the first nighttime climatology of OClO.

scholarly journals Dichotomy of radio loud and radio quiet quasars in four dimensional eigenvector one (4DE1) parameter space

2019 ◽  
Vol 15 (S356) ◽  
pp. 351-354
Author(s):  
Shimeles Terefe ◽  
Ascensión del Olmo ◽  
Paola Marziani ◽  
Mirjana Pović
Keyword(s):  
Emission Line ◽  
Parameter Space ◽  
Signal To Noise Ratio ◽  
High Redshift ◽  
Emission Lines ◽  
Signal To Noise ◽  
Broad Emission ◽  
Broad Emission Line ◽  
Two Populations ◽  
Calar Alto

AbstractRecent work has shown that it is possible to systematize quasars (QSOs) spectral diversity in 4DE1 parameter space. The spectra contained in most of the surveys have low signal to noise ratio which fed the impression that all QSO’s are spectroscopically similar. Exploration of 4DE1 parameter space gave rise to the concept of two populations of QSOs that present important spectroscopic differences. We aim to quantify broad emission line differences between radio quiet and radio loud sources by exploiting more complete samples of QSO with spectral coverage in Hβ, MgII and CIV emission lines. We used a high redshift sample (0.35 < z < 1) of strong radio emitter QSOs observations from Calar Alto Observatory in Spain.

scholarly journals OClO slant column densities derived from GOMOS averaged transmittance measurements

2013 ◽  
Vol 6 (11) ◽  
pp. 2953-2964 ◽  
Author(s):  
C. Tétard ◽  
D. Fussen ◽  
F. Vanhellemont ◽  
C. Bingen ◽  
E. Dekemper ◽  
...  
Keyword(s):  
Near Infrared ◽  
Signal To Noise Ratio ◽  
Arctic Region ◽  
Equatorial Region ◽  
The Arctic ◽  
Optical Absorption Spectroscopy ◽  
Polar Regions ◽  
Signal To Noise ◽  
Spectral Window ◽  
Noise Ratio

Abstract. The Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument on board the European platform ENVISAT (ENVironment SATellite) was dedicated to the study of the of Earth's atmosphere using the stellar occultation technique. The spectral range of the GOMOS spectrometer extends from the UV (ultra violet) to the near infrared, allowing for the retrieval of species such as O3, NO2, NO3, H2O, O2, air density, aerosol extinction and OClO. Nevertheless, OClO cannot be retrieved using a single GOMOS measurement because of the weak signal-to-noise ratio and the small optical thickness associated with this molecule. We present here the method used to detect this molecule by using several GOMOS measurements. It is based on a two-step approach. First, several co-located measurements are combined in a statistical way to build an averaged measurement with a higher signal-to-noise ratio; then, a differential optical absorption spectroscopy (DOAS) method is applied to retrieve OClO slant column densities (SCD). The statistics of the sets of GOMOS measurements used to build the averaged measurement and the spectral window selection are analyzed. The obtained retrievals are compared to results from two balloon-borne instruments. It appears that the inter-comparisons of OClO are generally satisfying (relative differences are about 15–60%). Two nighttime climatologies of OClO based on GOMOS averaged measurements are presented. The first depicts annual global pictures of OClO from 2003 to 2011. From this climatology, the presence of an OClO SCD peak in the equatorial region at about 35 km is confirmed and strong OClO SCD in both polar regions are observed (more than 1016 cm−2 in the Antarctic region and slightly less in the Arctic region), a sign of chlorine activation. The second climatology is a monthly time series. It clearly shows the chlorine activation of the lower stratosphere during winter. Moreover the equatorial OClO SCD peak is observed during all years without any significant variations. This very promising method, applied on GOMOS measurements, allowed us to build the first nighttime climatology of OClO using limb-viewing instruments.

scholarly journals Capacity Bounds for Dense Massive MIMO in a Line-of-Sight Propagation Environment

Sensors ◽  
2020 ◽  
Vol 20 (2) ◽  
pp. 520 ◽  
Author(s):  
Felipe A. P. de Figueiredo ◽  
Claudio F. Dias ◽  
Eduardo R. de Lima ◽  
Gustavo Fraidenraich
Keyword(s):  
Probability Density Function ◽  
Probability Density ◽  
Density Function ◽  
Signal To Noise Ratio ◽  
Base Station ◽  
Line Of Sight ◽  
High Signal ◽  
Signal To Noise ◽  
Sum Capacity ◽  
Base Station Antennas

The use of large-scale antenna arrays grants considerable benefits in energy and spectral efficiency to wireless systems due to spatial resolution and array gain techniques. By assuming a dominant line-of-sight environment in a massive multiple-input multiple-output scenario, we derive analytical expressions for the sum-capacity. Then, we show that convenient simplifications on the sum-capacity expressions are possible when working at low and high signal-to-noise ratio regimes. Furthermore, in the case of low and high signal-to-noise ratio regimes, it is demonstrated that the Gamma probability density function can approximate the probability density function of the instantaneous channel sum-capacity as the number of served devices and base station antennas grows, respectively. A second important demonstration presented in this work is that a Gamma probability density function can also be used to approximate the probability density function of the summation of the channel’s singular values as the number of devices increases. Finally, it is important to highlight that the presented framework is useful for a massive number of Internet of Things devices as we show that the transmit power of each device can be made inversely proportional to the number of base station antennas.

Approximating Shadowed Rician Model to Other Simpler Models

2016 ◽  
Vol 7 (1) ◽  
pp. 1-29
Author(s):  
Wassim Yassin Aljuneidi ◽  
Yasser M Jaamour ◽  
Khaldoun Khorzom
Keyword(s):  
Standard Deviation ◽  
Wireless Channels ◽  
Numerical Solutions ◽  
Signal To Noise Ratio ◽  
Critical Issue ◽  
Line Of Sight ◽  
Small Scale ◽  
Signal To Noise ◽  
Real Time Applications ◽  
Probability Density Function Pdf

Shadowed Rician model is considered to be the most appropriate that is used to characterize the impairments seen in wireless channels, which suffer Line-Of-Sight (LOS) shadowing and small-scale fading. In this model, the Probability Density Function (PDF) of the Signal to Noise Ratio (SNR) per symbol needs numerical solutions to be evaluated. More than that, for some values of the fading parameters, the numerical solution converging too slowly, and so needs too much time to be evaluated. This is considered as a problem in real time applications where delay is a critical issue. In this paper, the authors present and prove approximations for Shadowed Rician model according to the values of the fading parameters, which are the Rice factor and the Shadowing standard deviation. With the proposed approximation, the required PDF could be written in intervals which make it easier to calculate at parameters values that causes slow converging.

scholarly journals Characterizing Spectral Channels of Visible Emission Line Coronagraph of Aditya-L1

2021 ◽  
Vol 8 ◽  
Author(s):  
Ritesh Patel ◽  
A. Megha ◽  
Arpit Kumar Shrivastav ◽  
Vaibhav Pant ◽  
M. Vishnu ◽  
...  
Keyword(s):  
Emission Line ◽  
Signal To Noise Ratio ◽  
Scattered Light ◽  
Plasma Temperature ◽  
Slit Width ◽  
Field Of View ◽  
Visible Emission ◽  
Line Profiles ◽  
Signal To Noise ◽  
Spectral Channels

Aditya-L1 is India’s first solar mission with the Visible Emission Line Coronagraph (VELC), which consists of three spectral channels taking high-resolution spectroscopic observations of the inner corona up to 1.5 Rʘ at 5,303, 7,892, and 10,747 Å. In this work, we present a strategy for the slit width optimization of the VELC using synthetic line profiles by taking into account the instrument characteristics and coronal conditions for log(T) varying from 6 to 6.5. The synthetic profiles are convolved with simulated instrumental scattered light and noise to estimate the signal-to-noise ratio (SNR), which will be crucial to designing the future observation plans. We find that the optimum slit width for VELC turns out to be 50 μm, providing sufficient SNR for observations in different solar conditions. We also analyzed the effect of plasma temperature on the SNR at different heights in the VELC field of view for the optimized slit width. We also studied the expected effect of the presence of a CME on the spectral channel observations. This analysis will help to plan the scientific observations of VELC in different solar conditions.

FeXIV Line Emission Polarization of the July 11, 1991 Solar Corona

1994 ◽  
Vol 144 ◽  
pp. 541-547
Author(s):  
J. Sýkora ◽  
J. Rybák ◽  
P. Ambrož
Keyword(s):  
High Resolution ◽  
Solar Corona ◽  
Emission Line ◽  
Solar Eclipse ◽  
White Light ◽  
Preliminary Analysis ◽  
Line Emission ◽  
Total Solar Eclipse ◽  
Degree Of Polarization ◽  
High Resolution Images

AbstractHigh resolution images, obtained during July 11, 1991 total solar eclipse, allowed us to estimate the degree of solar corona polarization in the light of FeXIV 530.3 nm emission line and in the white light, as well. Very preliminary analysis reveals remarkable differences in the degree of polarization for both sets of data, particularly as for level of polarization and its distribution around the Sun’s limb.

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