Reflection and transmission of light by a layer with a large optical thickness

1979 ◽  
Vol 30 (5) ◽  
pp. 646-653
Author(s):  
�. P. Zege ◽  
O. V. Bushmakova ◽  
I. L. Katsev ◽  
N. V. Konovalov
Keyword(s):  
Optical Thickness ◽  
Reflection And Transmission ◽  
Large Optical Thickness

scholarly journals Active Regions at Millimeter Wavelengths and the Measurement of Magnetic Fields

1971 ◽  
Vol 43 ◽  
pp. 642-651 ◽  
Author(s):  
M. R. Kundu
Keyword(s):  
Magnetic Fields ◽  
Electron Density ◽  
Optical Thickness ◽  
Background Radiation ◽  
Active Regions ◽  
Brightness Temperatures ◽  
Millimeter Wavelengths ◽  
Solar Active Regions ◽  
Large Optical Thickness ◽  
Filamentary Material

Some properties of solar active regions at 9 and 3.5 mm wavelengths are discussed. The regions have excess brightness temperatures of up to 1000 and 700K at 9 and 3.5 mm wavelengths respectively. The background radiation at 3.5 mm is often seen to be ‘absorbed’ in regions closely coincident with Hα dark filaments on the disk. Interpretation of this ‘absorption’ as due to the large optical thickness of the overlying filamentary material leads to an estimate of electron density in the filaments. The active regions at millimeter wavelengths show almost one-to-one correspondence with the Ca-plage regions as well as with the regions of longitudinal magnetic fields on Mt. Wilson magnetograms. A comparison of the mm-λ maps with the magnetograms ‘smoothed’ with the beams of mm observations shows this correspondence in a striking manner. This relationship suggests the possibility of measuring chromospheric magnetic fields from the measurement of polarization at millimeter wavelengths.

scholarly journals Contrails of Small and Very Large Optical Depth

2010 ◽  
Vol 67 (9) ◽  
pp. 3065-3073 ◽  
Author(s):  
David Atlas ◽  
Zhien Wang
Keyword(s):  
High Resolution ◽  
Optical Depth ◽  
Optical Thickness ◽  
Extinction Coefficient ◽  
Ice Water Content ◽  
Lower Height ◽  
Equivalent Distance ◽  
Ice Water ◽  
Large Optical Thickness ◽  
Clear Atmosphere

Abstract This work deals with two kinds of contrails. The first comprises a large number of optically thin contrails near the tropopause. They are mapped geographically using a lidar to obtain their height and a camera to obtain azimuth and elevation. These high-resolution maps provide the local contrail geometry and the amount of optically clear atmosphere. The second kind is a single trail of unprecedentedly large optical thickness that occurs at a lower height. The latter was observed fortuitously when an aircraft moving along the wind direction passed over the lidar, thus providing measurements for more than 3 h and an equivalent distance of 620 km. It was also observed by Geostationary Operational Environmental Satellite (GOES) sensors. The lidar measured an optical depth of 2.3. The corresponding extinction coefficient of 0.023 km−1 and ice water content of 0.063 g m−3 are close to the maximum values found for midlatitude cirrus. The associated large radar reflectivity compares to that measured by ultrasensitive radar, thus providing support for the reality of the large optical depth.

scholarly journals On the Detection of Binary Be Stars

1976 ◽  
Vol 70 ◽  
pp. 401-415 ◽  
Author(s):  
R. S. Polidan
Keyword(s):  
Low Temperature ◽  
Optical Thickness ◽  
Spectroscopic Investigation ◽  
Promising Method ◽  
Be Stars ◽  
Binary Nature ◽  
Photometric Observations ◽  
Be Star ◽  
Large Optical Thickness

Possible methods for detecting the presence of a cool companion to a Be star are discussed. Photometric observations are shown to be incapable of detecting companions in all but the most extreme cases. Spectroscopic investigation is also unlikely to yield many new discoveries. It, however, remains the most promising method for the detection of binary Be stars. The four known binary Be stars are also discussed.Infrared calcium triplet emission in Be stars is discussed in detail. The lines are shown to originate in a region of large optical thickness and low temperature (T ~ 5000 K). The possible connection between the presence of calcium triplet emission and binary nature is briefly discussed.

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