Electron Densities in Solar Prominences

1994 ◽  
Vol 144 ◽  
pp. 381-383
Author(s):  
J. E. Wiik ◽  
P. Heinzel ◽  
B. Schmieder
Keyword(s):  
Optical Thickness ◽  
Field Of View ◽  
Line Of Sight ◽  
Two Dimensional ◽  
Line Profiles ◽  
Quiescent Prominence ◽  
Electron Densities ◽  
Solar Prominences ◽  
Thickness Variations ◽  
Limiting Values

AbstractObservations of a quiescent prominence made with the MSDP spectrograph at the Pic du Midi Observatory provided Hαline profiles in each pixel of a 2D field of view. Comparing the absolute observed intensities with values derived from NLTE computations, we estimated the range ofelectron densitiesNe≈ 1 – 5 × 1010cm−3,source functionsS/Ic≈ 0.07 – 0.12, andoptical thicknessτ ≈ 0.3 – 8.0 within the observed prominence. Two dimensional maps of the electron densities are presented assuming two limiting values of the geometrical thickness along the line-of-sight. It is shown that if we consider geometrical thickness variations within a factor of about four, the electron density will be determined to within a factor of two, just by measuring the Hαline intensity.

Spectroscopy of a Solar Prominence with the Narrow-Bandpass Filter

1994 ◽  
Vol 144 ◽  
pp. 343-344
Author(s):  
P. Rudawy
Keyword(s):  
Optical Thickness ◽  
Large Scale ◽  
Bandpass Filter ◽  
Solar Limb ◽  
Physical Parameters ◽  
Two Dimensional ◽  
Line Profiles ◽  
Solar Prominence ◽  
Quiescent Prominence ◽  
Made In

AbstractObservations and analysis of a quiescent prominence above the solar limb are presented. The set of quasi-monochromatic images of the prominence made in a few wavelengths of Hα, Hβand D3lines have been used for reconstruction of the coarse line profiles. Two-dimensional maps of the main physical parameters of the prominence matter-macroscopic and turbulent velocities, electron temperature, density and optical thickness have been constructed. Presented method of low-resolution spectroscopy is useful for investigations of the variety of large-scale solar phenomena.

scholarly journals Prominence Emission Lines Observed With SUMER and Two Ground-based Telescopes

1998 ◽  
Vol 167 ◽  
pp. 196-200
Author(s):  
C.R. de Boer ◽  
G. Stellmacher ◽  
E. Wiehr
Keyword(s):  
Optical Thickness ◽  
Emission Lines ◽  
Two Dimensional ◽  
Quiescent Prominence ◽  
Euv Emission ◽  
Ionization Temperature ◽  
Balmer Lines ◽  
Higher Temperature ◽  
Line Widths ◽  
Emission Ratios

AbstractTwo sets of H, He, and Ca+ emission lines were observed in a quiescent prominence simultaneously with the VTT and the Gregory telescope on Tenerife. At the same time, SUMER took two scans of low-ionized EUV emission lines.The emission ratios of Ca+–to–Balmer lines from ground vary little in the prominence, indicating a largely constant gas-pressure. In contrast, the ratio of He–to–Balmer from the ground shows the (known) increase toward the prominence borders, indicating higher temperature there. Similarly, the two-dimensional distributions of the ratios S IV/N II and C III/He I show pronounced bright prominence rims.The reduced He 537Å and He 584Å line widths are 2.6 and 3.6 times larger, respectively, than those of He D3 and He 3888Å. Explaining this by the optical thickness yields τ0 = 104 and τ0 = 2 · 105 for the two EUV lines. The total He 584 emission amounts to 13 watt/m2 ster in the main prominence body where the D3 line yields 4 watt/m2 ster; existing models, however, predict a factor 0.18.The widths of simultaneously observed optical lines with different atomic weights yield thermal and non-thermal broadening parameters of Tkin ≈ 8000 K and 2.5 < ξ < 6.5 km/s. The EUV lines, however, show line widths which correspond to much higher temperatures and non-thermal velocities. Assuming for each ion the corresponding ionization temperature, the line widths require non-thermal velocities of 15–40 km/s which is similar to values for the quiet corona.

Structuring, Motions and Shapes of Corona Emission Line Profiles

1994 ◽  
Vol 144 ◽  
pp. 421-426
Author(s):  
N. F. Tyagun
Keyword(s):  
Emission Line ◽  
Filling Factor ◽  
Direct Relationship ◽  
Coronal Plasma ◽  
Line Of Sight ◽  
Line Profiles ◽  
The Difference ◽  
Yellow Line ◽  
Red Line

AbstractThe interrelationship of half-widths and intensities for the red, green and yellow lines is considered. This is a direct relationship for the green and yellow line and an inverse one for the red line. The difference in the relationships of half-widths and intensities for different lines appears to be due to substantially dissimilar structuring and to a set of line-of-sight motions in ”hot“ and ”cold“ corona regions.When diagnosing the coronal plasma, one cannot neglect the filling factor - each line has such a factor of its own.

CALCULATION OF THE DEPENDENCE OF THE DISTANCE TO THE LOCATED OBJECT FROM THE CORNER POSITION OF THE VEHICLE LINE

2018 ◽  
pp. 14-18
Author(s):  
V. V. Artyushenko ◽  
A. V. Nikulin
Keyword(s):  
Real Time ◽  
Statistical Physics ◽  
Angular Position ◽  
Three Dimensional ◽  
Line Of Sight ◽  
Two Dimensional ◽  
Radar Station ◽  
Flight Mode ◽  
Vector Algebra ◽  
Analytical Expressions

To simulate echoes from the earth’s surface in the low flight mode, it is necessary to reproduce reliably the delayed reflected sounding signal of the radar in real time. For this, it is necessary to be able to calculate accurately and quickly the dependence of the distance to the object being measured from the angular position of the line of sight of the radar station. Obviously, the simplest expressions for calculating the range can be obtained for a segment or a plane. In the text of the article, analytical expressions for the calculation of range for two-dimensional and three-dimensional cases are obtained. Methods of statistical physics, vector algebra, and the theory of the radar of extended objects were used. Since the calculation of the dependence of the range of the object to the target from the angular position of the line of sight is carried out on the analytical expressions found in the paper, the result obtained is accurate, and due to the relative simplicity of the expressions obtained, the calculation does not require much time.

Towards Finding the Optimum Position in the Visual Field for a Head Worn Display Used for Task Guidance with Non-registered Graphics

2021 ◽  
Vol 5 (1) ◽  
pp. 1-26
Author(s):  
Georgianna Lin ◽  
Malcolm Haynes ◽  
Sarthak Srinivas ◽  
Pramod Kotipalli ◽  
Thad Starner
Keyword(s):  
Visual Field ◽  
Order Picking ◽  
Field Of View ◽  
Line Of Sight ◽  
Single Task ◽  
Horizontal Field ◽  
Optimum Position ◽  
Preference Task ◽  
Task Efficiency ◽  
Task Guidance

Where should a HWD be placed in a user's visual field? We present two studies that compare comfort, preference, task efficiency and accuracy for various HWD positions. The first study offsets a 9.2° horizontal field-of-view (FOV) display temporally (toward the ear) from 0° to 30° in 10° steps. 30° proves too uncomfortable while 10° is the most preferred position for a simple button-pushing game, corroborating results from previous single-task reading experiments. The second experiment uses a Magic Leap One to compare 10° x 10° FOV interfaces centered at line-of-sight, temporally offset 15° (center-right), inferiorly offset 15° (bottom-center), and offset in both directions (bottom-right) for an order picking task. The bottom-right position proved worst in terms of accuracy and several subjective metrics when compared to the line-of-sight position.

scholarly journals Statistical comparison of the observed and synthetic hydrogen Lyman line profiles in solar prominences

2010 ◽  
Vol 514 ◽  
pp. A43 ◽  
Author(s):  
S. Gunár ◽  
P. Schwartz ◽  
B. Schmieder ◽  
P. Heinzel ◽  
U. Anzer
Keyword(s):  
Line Profiles ◽  
Statistical Comparison ◽  
Solar Prominences

scholarly journals Subtraction of Bright Point Sources from Synthesis Images of the Epoch of Reionization

2011 ◽  
Vol 28 (1) ◽  
pp. 46-57 ◽  
Author(s):  
B. Pindor ◽  
J. S. B. Wyithe ◽  
D. A. Mitchell ◽  
S. M. Ord ◽  
R. B. Wayth ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Dynamic Range ◽  
Low Frequency ◽  
Neutral Hydrogen ◽  
Galactic Nuclei ◽  
Point Sources ◽  
Field Of View ◽  
Bright Point ◽  
Line Of Sight ◽  
Diffuse Background

AbstractBright point sources associated with extragalactic active galactic nuclei and radio galaxies are an important foreground for low-frequency radio experiments aimed at detecting the redshifted 21-cm emission from neutral hydrogen during the epoch of reionization. The frequency dependence of the synthesized beam implies that the sidelobes of these sources will move across the field of view as a function of observing frequency, hence frustrating line-of-sight foreground subtraction techniques. We describe a method for subtracting these point sources from dirty maps produced by an instrument such as the MWA. This technique combines matched filters with an iterative centroiding scheme to locate and characterize point sources in the presence of a diffuse background. Simulations show that this technique can improve the dynamic range of epoch-of-reionization maps by 2—3 orders of magnitude.

scholarly journals Simulation study for the Stratospheric Inferred Winds (SIW) sub-millimeter limb sounder

2018 ◽  
Author(s):  
Philippe Baron ◽  
Donal Murtagh ◽  
Patrick Eriksson ◽  
Jana Mendrok ◽  
Satoshi Ochiai ◽  
...  
Keyword(s):  
Simulation Study ◽  
Spectral Band ◽  
Chemical Species ◽  
Field Of View ◽  
Emission Lines ◽  
Horizontal Wind ◽  
Line Of Sight ◽  
Heterodyne Receiver ◽  
Vertical Field ◽  
Wind Measurements

Abstract. Stratospheric Inferred Winds (SIW) is a Swedish mini sub-millimeter limb sounder selected for the 2nd InnoSat platform launch planned near 2022. It is intended to fill the altitude gap between 30–70 km in atmospheric wind measurements and also aims at pursuing the limb observations of temperature and key atmospheric constituents between 10–90 km when current satellite missions are probably stopped. Line-of-sight winds are retrieved from the Doppler shift of the emission lines introduced by 5 the wind field. Observations will be performed with two antennas pointing toward the limb with perpendicular directions to reconstruct the 2-D horizontal wind vector. Each antenna has a vertical field of view of 5 km. The chosen spectral band near 655 GHz contains a dense group of strong O3 lines suitable for exploiting the small wind information in stratospheric spectra. Using both sidebands of the heterodyne receiver, a large number of chemical species will be measured including O3-isopotologues, H2O, HDO, HCl, ClO, N2O, HNO3, NO, NO2, HCN, CH3CN and HO2. This paper presents the simulation study for assessing the measurement performances. The line-of-sight winds are retrieved between 30–90 km with the best sensitivity between 35–70 km where the precision (1-sigma) is 5–10 m s−1 for a single scan. Similar performances can be obtained during day and night conditions except in the lower mesosphere where the photo-dissociation of O3 in day-time reduces the sensitivity by 50 % near 70 km. Profiles of O3, H2O and temperature are retrieved with a high precision up to 50 km (

A survey on stereo vision-based autonomous navigation for multi-rotor MUAVs

Robotica ◽  
2018 ◽  
Vol 36 (8) ◽  
pp. 1225-1243 ◽  
Author(s):  
Jose-Pablo Sanchez-Rodriguez ◽  
Alejandro Aceves-Lopez
Keyword(s):  
Unmanned Aerial Vehicles ◽  
Stereo Vision ◽  
Autonomous Navigation ◽  
Three Dimensional ◽  
Field Of View ◽  
Line Of Sight ◽  
Onboard Computer ◽  
Low Weight ◽  
Vision Based Navigation ◽  
Difficult Challenge

SUMMARYThis paper presents an overview of the most recent vision-based multi-rotor micro unmanned aerial vehicles (MUAVs) intended for autonomous navigation using a stereoscopic camera. Drone operation is difficult because pilots need the expertise to fly the drones. Pilots have a limited field of view, and unfortunate situations, such as loss of line of sight or collision with objects such as wires and branches, can happen. Autonomous navigation is an even more difficult challenge than remote control navigation because the drones must make decisions on their own in real time and simultaneously build maps of their surroundings if none is available. Moreover, MUAVs are limited in terms of useful payload capability and energy consumption. Therefore, a drone must be equipped with small sensors, and it must carry low weight. In addition, a drone requires a sufficiently powerful onboard computer so that it can understand its surroundings and navigate accordingly to achieve its goal safely. A stereoscopic camera is considered a suitable sensor because of its three-dimensional (3D) capabilities. Hence, a drone can perform vision-based navigation through object recognition and self-localise inside a map if one is available; otherwise, its autonomous navigation creates a simultaneous localisation and mapping problem.

FOV constrained guidance law for nonstationary nonmaneuvering target interception with any impact angle

2021 ◽  
pp. 095441002110468
Author(s):  
Nikhil Kumar Singh ◽  
Sikha Hota
Keyword(s):  
Kinematic Model ◽  
Angular Spectrum ◽  
Impact Angle ◽  
Field Of View ◽  
Two Dimensional ◽  
Proportional Navigation ◽  
Guidance Law ◽  
Real World Applications ◽  
Target Interception ◽  
Impact Angles

This paper presents the nonstationary nonmaneuvering target interception with all possible desired impact angles in a two-dimensional (2D) aerial engagement scenario, where the target can move in any direction. The paper also considers the field-of-view (FOV) constraint for designing the guidance law so that the target is always visible while following the missile trajectory in the entire engagement time, which makes it feasible for real world applications. The guidance law is based on the pure proportional navigation (PPN) to achieve any impact angle of the entire angular spectrum. The proposed guidance law is then simulated for intercepting a nonstationary nonmaneuvering target using a kinematic model of a missile to demonstrate the efficacy of the presented scheme. A comparison with the related work existing in the literature has also been added to establish the superiority of the present work.

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