scholarly journals The contribution of atmospheric aerosols to the Martian opposition effect

1971 ◽  
Vol 40 ◽  
pp. 166-169
Author(s):  
Jaylee M. Mead
Keyword(s):  
Atmospheric Aerosols ◽  
Mie Scattering ◽  
The Other ◽  
Spherical Particles ◽  
Refractive Indices ◽  
Opposition Effect ◽  
Absorbing Materials ◽  
Small Phase ◽  
Ice Water ◽  
Phase Angles

Mie scattering calculations have been made for atmospheric aerosols having various indices of refraction to determine their possible contribution to a Martian opposition effect, such as that reported by O'Leary in 1967. Neither substances with a real index between 1.20 and 1.50, such as ice, water, or solid CO2, nor highly absorbing materials, such as limonite, can produce the observed effect. Submicron-sized spherical particles with refractive indices of 1.55 to 2.00 do, on the other hand, exhibit a marked increase in reflectivity at small phase angles and might be responsible for the enhanced brightness at the shorter wavelengths.

Saturn rings: divisions, gaps and ringlets from ground-based telescopes

1984 ◽  
Vol 75 ◽  
pp. 147-154 ◽  
Author(s):  
Audouin Dollfus
Keyword(s):  
Phase Angle ◽  
Volume Density ◽  
Light Curves ◽  
High Magnification ◽  
Density Dependent ◽  
Opposition Effect ◽  
Small Phase ◽  
Saturn's Rings ◽  
Phase Angles ◽  
Zero Phase

ABSTRACTThe high magnification visual telescopic observation of Saturn’s rings exhibits divisions, gaps and bright sub-rings. B. Lyot gave a first description of these features. Later, with still more resolving telescopes, we improved the analysis of the ring features. Some gaps and concentric bright or dark sub-rings are phase angle dependent; the steep luminance peaks of their light curves around zero phase angle are volume-density dependent (opposition effect); the overall result produces changes in the shapes and intensities of these features at small phase angles, which are analysed.

scholarly journals Longitudinal variations, the opposition effect and monochromatic albedos for Mars

1971 ◽  
Vol 40 ◽  
pp. 141-155
Author(s):  
William M. Irvine ◽  
James C. Higdon ◽  
Susan J. Ehrlich
Keyword(s):  
Phase Curve ◽  
Central Meridian ◽  
Opposition Effect ◽  
Small Phase ◽  
Longitudinal Variations ◽  
The Mean ◽  
Phase Angles ◽  
Narrow Bands ◽  
Zero Phase ◽  
Phase Phase

Observations of Mars previously reported in 10 narrow bands between 3150 Å and 1.06 μ and in UBV are analyzed for brightness variations which correlate with longitude of the central meridian. Such an effect is found for λ ≥ 5000 Å, with some evidence for such a correlation at λ = 4570 Å. The data are then corrected to the mean (over longitude) brightness and a linear phase curve fitted to those observations with phase angle i ≥ 15°. An opposition effect (anomalous brightening at small phase angles) is found for wavelengths λ ≤ 5500 Å, in contrast to a result previously reported. The magnitude at zero phase, phase coefficient, and monochromatic albedo are computed for Mars as a function of wavelength.

scholarly journals Opposition effect on S-type asteroid (25143) Itokawa

2018 ◽  
Vol 616 ◽  
pp. A178 ◽  
Author(s):  
Mingyeong Lee ◽  
Masateru Ishiguro
Keyword(s):  
Linear Increase ◽  
Clear Correlation ◽  
Slope Parameter ◽  
Sample Return ◽  
Opposition Effect ◽  
Imaging Camera ◽  
Small Phase ◽  
Solar System Bodies ◽  
Sample Return Mission ◽  
Phase Angles

Aims. The opposition effect has been detected on solar system bodies such as asteroids and comets. Two mechanisms have been proposed to explain the effect: the shadow-hiding opposition effect (SHOE) and the coherent backscattering opposition effect (CBOE). The Hayabusa asteroid sample return mission provides a unique opportunity to investigate the opposition effect on disk-resolved images of the S-type asteroid (25413) Itokawa at very small phase angles α. Methods. We made use of the data taken at α = 0.°04–2.°54 using the Asteroid Multi-band Imaging Camera (AMICA) on UT 2005 October 13. Comparing sets of two images taken at different phase angles, we derived the opposition slope parameter (SOE) that characterizes a linear increase in the reflectance I∕F per unit phase angle. Results. We found that (i) SOE is less dependent on the incidence and emission angles; (ii) the reflectance increases nonlinearly toward the opposition at small angles with α ≲ 1.°4, showing a good correlation between mean I∕F and SOE; and (iii) SOE becomes nearly constant at α ≳ 1.°4 and shows no clear correlation between I∕F and SOE. Conclusions. From these results, we conjecture that CBOE is dominant at α ≲ 1.°4, while SHOE is dominant at α ≳ 1.°4.

scholarly journals Nature of Dust Grains in the Atmosphere of Comet Ashbrook

1980 ◽  
Vol 90 ◽  
pp. 259-262 ◽  
Author(s):  
O. V. Dobrovolsky ◽  
N. N. Kiselev ◽  
G. P. Chernova ◽  
F. A. Tupieva ◽  
N. V. Narizhnaja
Keyword(s):  
Dust Grains ◽  
Opposition Effect ◽  
Small Phase ◽  
Phase Angles ◽  
Anomalous Polarization

Anomalous polarization at small phase angles is confirmed as a common feature of dusty cometary atmospheres. The opposition effect is detected and interpreted as evidence of similarity between grains covering interplanetary, cometary and asteroidal surfaces. The prevailing radii of dust grains in the comet's atmosphere are estimated to be 0.15-0.19 μm.

scholarly journals Phase-curve analysis of comet 67P/Churyumov-Gerasimenko at small phase angles

2019 ◽  
Vol 630 ◽  
pp. A11
Author(s):  
N Masoumzadeh ◽  
L Kolokolova ◽  
C Tubiana ◽  
M. R. El-Maarry ◽  
S Mottola ◽  
...  
Keyword(s):  
Phase Angle ◽  
Textural Properties ◽  
Phase Ratio ◽  
Phase Curve ◽  
Model Parameters ◽  
Study Phase ◽  
Opposition Effect ◽  
Small Phase ◽  
Phase Angles ◽  
Comet 67P

Aims. The Rosetta-OSIRIS images acquired at small phase angles in three wavelengths during the fly-by of the spacecraft on 9–10 April 2016 provided a unique opportunity to study the opposition effect on the surface of comet 67P/Churyumov-Gerasimenko (67P). Our goal is to study phase curves of the nucleus at small phase angles for a variety of surface structures to show the differences in their opposition effect and to determine which surface properties cause the differences. Methods. We used OSIRIS NAC images that cover the Ash-Khepry-Imhotep region to extract the phase curve, that is, the reflectance of the surface as a function of phase angle. We selected six regions of interest (ROIs) and derived the phase curves for each ROI. We fit a linear-exponential function to the phase curves. The resulting model parameters were then interpreted by spectrophotometric, geomorphological, and phase-ratio analyses, and by investigating the influence of structural and textural properties of the surface. Results. We find evidence for the opposition effect (deviation of the phase curve from linear behavior) in phase curves for all areas. We found an anticorrelation between the phase ratio and reflectance in a small phase angle range. This provides evidence for the shadow-hiding effect. We conclude that the decrease in the slope of the phase ratio versus reflectance indicates a decrease in the proportion of shadowed regions and reduces the contribution of the shadow-hiding effect. Large uncertainties in the determination of the opposition effect parameters with respect to wavelength do not allow us to conclusively claim coherent backscattering in the opposition effect phenomenon. Based on the two analyses, we conclude that the opposition effect of comet 67P in the Ash-Khepry-Imhotep region is mainly affected by shadow-hiding.

Mathematical modelling of remote detection of molecular air pollutants

1987 ◽  
Vol 52 (6) ◽  
pp. 1397-1406
Author(s):  
František Zrcek ◽  
Milan Horák
Keyword(s):  
Atmospheric Aerosols ◽  
Air Pollutants ◽  
Complex Refractive Index ◽  
Mie Scattering ◽  
Heat Emission ◽  
Remote Detection ◽  
Radiation Absorption ◽  
Variable Concentration ◽  
Lidar Equation ◽  
Optical Pathway

A model of remote detection of molecular air pollutants is devised based on the lidar equation. The various kinds of interaction of radiation with matter, viz. absorption, induced fluorescence, and Raman scattering, are taken into account; detection of either scattered or reflected signal is considered. The reflection is assumed to be either axial, using a retroreflector, or omnidirectional from a field target. Based on this model, an algorithm was set up for simulation of the different variants of the experiment, making allowance for a generally variable concentration of the compound along the optical pathway of the light beam. The basic atmospheric processes, viz. radiation absorption by the backround, heat emission, turbulence, and the effect of atmospheric aerosols, are treated, and the last of them is found to play the major role. Aerosols are looked upon as a source of the Mie scattering and they are described by distribution equations with respect to the particle size and the complex refractive index. The variable concentration of the aerosol along the optical pathway and the simultaneous effect of a higher numberof aerosol types are included.

scholarly journals PROCESSING JUMP POINT OF LIDAR DETECTION DATA AND INVERSING THE AEROSOL EXTINCTION COEFFICIENT

2019 ◽  
Vol XLII-3/W9 ◽  
pp. 227-232
Author(s):  
H. L. Zhang ◽  
H. Zhao ◽  
Y. P. Liu ◽  
X. K. Wang ◽  
C. Shu
Keyword(s):  
Atmospheric Aerosols ◽  
Extinction Coefficient ◽  
Interpolation Method ◽  
Linear Interpolation ◽  
Mie Scattering ◽  
Inversion Method ◽  
Aerosol Extinction ◽  
Detection Range ◽  
Long Time ◽  
Aerosol Extinction Coefficient

Abstract. For a long time, the research of the optical properties of atmospheric aerosols has aroused a wide concern in the field of atmospheric and environmental. Many scholars commonly use the Klett method to invert the lidar return signal of Mie scattering. However, there are always some negative values in the detection data of lidar, which have no actual meaning，and which are jump points. The jump points are also called wild value points and abnormal points. The jump points are refered to the detecting points that are significantly different from the surrounding detection points, and which are not consistent with the actual situation. As a result, when the far end point is selected as the boundary value, the inversion error is too large to successfully invert the extinction coefficient profile. These negative points are jump points, which must be removed in the inversion process. In order to solve the problem, a method of processing jump points of detection data of lidar and the inversion method of aerosol extinction coefficient is proposed in this paper. In this method, when there are few jump points, the linear interpolation method is used to process the jump points. When the number of continuous jump points is large, the function fitting method is used to process the jump points. The feasibility and reliability of this method are verified by using actual lidar data. The results show that the extinction coefficient profile can be successfully inverted when different remote boundary values are chosen. The extinction coefficient profile inverted by this method is more continuous and smoother. The effective detection range of lidar is greatly increased using this method. The extinction coefficient profile is more realistic. The extinction coefficient profile inverted by this method is more favorable to further analysis of the properties of atmospheric aerosol. Therefore, this method has great practical application and popularization value.

scholarly journals Analysis of transmission characteristics of non-line-of-sight ultraviolet light under complex channel conditions

2021 ◽  
Vol 336 ◽  
pp. 01012
Author(s):  
Xuan Zheng ◽  
Yanfeng Tang ◽  
Jingyi Du
Keyword(s):  
Ultraviolet Light ◽  
Path Loss ◽  
Mie Scattering ◽  
Spherical Particles ◽  
Dust Particles ◽  
Line Of Sight ◽  
Communication Link ◽  
Communication Quality ◽  
Long Distance ◽  
Non Line Of Sight

Using the multiple scattering model of non-line-of-sight ultraviolet light to simulate and analyze the atmospheric channel characteristics in the complex environment of haze and dust. The Mie scattering theory and T matrix method are used to analyze the path loss of spherical particles and non-spherical particles with particle concentration at different communication distances. The results show that when the communication distance is less than 50 meters, the communication quality under severe haze is the best, and for long-distance communication, the path loss under severe haze increases almost proportionally. In the non-line-of-sight ultraviolet light communication link, the higher the concentration of dust particles, the better the communication quality of the non-line-of-sight ultraviolet light communication transmission. Analysis of the scattering coefficient of spherical particles is significantly greater than that of non-spherical particles.

scholarly journals Clusters Formed by Dumbbell-like One-Patch Particles Confined in Thin Systems

2021 ◽  
Author(s):  
Masahide Sato
Keyword(s):  
Monte Carlo ◽  
Monte Carlo Simulations ◽  
Particle Interaction ◽  
Three Dimensional ◽  
The Other ◽  
Spherical Particles ◽  
Dimensionless Distance ◽  
Large Island ◽  
Cluster Shape

Abstract Performing isothermal-isochoric Monte Carlo simulations, I examine the types of clusters that dumbbell-like one–patch particles form in thin space between two parallel walls, assuming that each particle is synthesized through the merging of two particles, one non-attracting and the other attracting for which, for example, the inter-particle interaction is approximated by the DLVO model. The shape of these dumbbell-like particles is controlled by the ratio of the diameters q of the two spherical particles and by the dimensionless distance l between them. Using a modified Kern–Frenkel potential, I examine the dependence of the cluster shape on l and q. Large island-like clusters are created when q < 1. With increasing q, the clusters become chain-like. When q increases further, elongated clusters and regular polygonal clusters are created. In hte simulations, the cluster shape becomes three-dimensional with increasing l because the thickness of the thin system increases proportionally to l.

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