3,596,801 research outputs found
Partial polarizer filter
A birefringent filter module comprises, in seriatum. (1) an entrance polarizer, (2) a first birefringent crystal responsive to optical energy exiting the entrance polarizer, (3) a partial polarizer responsive to optical energy exiting the first polarizer, (4) a second birefringent crystal responsive to optical energy exiting the partial polarizer, and (5) an exit polarizer. The first and second birefringent crystals have fast axes disposed + or -45 deg from the high transmitivity direction of the partial polarizer. Preferably, the second crystal has a length 1/2 that of the first crystal and the high transmitivity direction of the partial polarizer is nine times as great as the low transmitivity direction. To provide tuning, the polarizations of the energy entering the first crystal and leaving the second crystal are varied by either rotating the entrance and exit polarizers, or by sandwiching the entrance and exit polarizers between pairs of half wave plates that are rotated relative to the polarizers. A plurality of the filter modules may be cascaded
Optimization of a field-widened Michelson interferometer
This paper considers the optical design of a wide-angle fixed-path Michelson interferometer consisting of
two arm glasses and an air gap. It is shown that this configuration can be optimized to give (a) extra large
fringes (over 50° in diameter) over a range of wavelength, (b) a path difference nearly independent of wavelength,
or (c) a path difference specified differently at two different wavelengths for observing a pair of doublets.
Specific examples refer to the airglow wavelengths of 557.7, 630.0, 732.0 nm and others, and to a path difference of 4.5 cm. The properties of different glass combinations are discussed
Operators manual for the magnetograph program (section 2)
This manual for use of the magnetograph program describes: (1) black box use of the programs; (2) the magtape data formats used; (3) the adjustable control parameters in the program; and (4) the algorithms. With no adjustments on the control parameters this program may be used purely as a black box. For optimal use, however, the control parameters may be varied. The magtape data formats are of use in adopting other programs to look at raw data or final magnetograph data
A solar magnetic and velocity field measurement system for Spacelab 2: The Solar Optical Universal Polarimeter (SOUP)
The Solar Optical Universal Polarimeter (SOUP) flew on the shuttle mission Spacelab 2 (STS-51F) in August, 1985, and collected historic solar observations. SOUP is the only solar telescope on either a spacecraft or balloon which has delivered long sequences of diffraction-limited images. These movies led to several discoveries about the solar atmosphere which were published in the scientific journals. After Spacelab 2, reflights were planned on the shuttle Sunlab mission, which was cancelled after the Challenger disaster, and on a balloon flights, which were also cancelled for funding reasons. In the meantime, the instrument was used in a productive program of ground-based observing, which collected excellent scientific data and served as instrument tests. Given here is an overview of the history of the SOUP program, the scientific discoveries, and the instrument design and performance
Balltracking: an highly efficient method for tracking flow fields
We present a method for tracking solar photospheric flows that is highly efficient, and demonstrate it using high resolution MDI continuum images. The method involves making a surface from the photospheric granulation data, and allowing many small floating tracers or balls to be moved around by the evolving granulation pattern. The results are tested against synthesised granulation with known flow fields and compared to the results produced by Local Correlation tracking (LCT). The results from this new method have similar accuracy to those produced by LCT. We also investigate the maximum spatial and temporal resolution of the velocity field that it is possible to extract, based on the statistical properties of the granulation data. We conclude that both methods produce results that are close to the maximum resolution possible from granulation data. The code runs very significantly faster than our similarly optimised LCT code, making real time applications on large data sets possible. The tracking method is not limited to photospheric flows, and will also work on any velocity field where there are visible moving features of known scale length
The quiet Sun's magnetic flux estimated from CaIIH bright inter-granular G-band structures
We determine the number density and area contribution of small-scale
inter-granular calcium-II bright G-band structures in images of the quiet Sun
as tracers of kilo-Gauss magnetic flux-concentrations.
In a 149" x 117" G-band image of the disk center at the activity minimum,
7593 small inter-granular structures ['IGS']were segmented with the
`multiple-level tracking' pattern recognition algorithm ['MLT_4']. The
scatter-plot of the continuum versus the G-band brightness shows the known
magnetic and non-magnetic branches. These branches are largely disentangled by
applying an intrinsic Ca-II excess criterion. The thus obtained 2995 structures
contain 1152 G-band bright points ['BP'] and 1843 G-band faint points ['FP'].
They show a tendency of increasing size with decreasing G-band excess, as
expected from the `hot wall' picture. Their Ca-H and G-band brightness are
slightly related, resembling the known relation of Ca-II and magnetic field
strength. The magnetic flux density of each individual BP and FP is estimated
from their G-band brightness according to MHD-model calculations.
The entity of BP and FP covers the total field-of-view ['FOV'] with a number
density of 0.32/Mm^2 and a total area contribution of 2.0%. Their individual
calibrations yield a mean flux density of 20 Mx/cm^2 in the entire FOV and 13
Mx/cm^2 for inter-network regions
Discriminant analysis of solar bright points and faculae I. Classification method and center-to-limb distribution
While photospheric magnetic elements appear mainly as Bright Points (BPs) at
the disk center and as faculae near the limb, high-resolution images reveal the
coexistence of BPs and faculae over a range of heliocentric angles. This is not
explained by a "hot wall" effect through vertical flux tubes, and suggests that
the transition from BPs to faculae needs to be quantitatively investigated. To
achieve this, we made the first recorded attempt to discriminate BPs and
faculae, using a statistical classification approach based on Linear
Discriminant Analysis(LDA). This paper gives a detailed description of our
method, and shows its application on high-resolution images of active regions
to retrieve a center-to-limb distribution of BPs and faculae. Bright "magnetic"
features were detected at various disk positions by a segmentation algorithm
using simultaneous G-band and continuum information. By using a selected sample
of those features to represent BPs and faculae, suitable photometric parameters
were identified in order to carry out LDA. We thus obtained a Center-to-Limb
Variation (CLV) of the relative number of BPs and faculae, revealing the
predominance of faculae at all disk positions except close to disk center (mu >
0.9). Although the present dataset suffers from limited statistics, our results
are consistent with other observations of BPs and faculae at various disk
positions. The retrieved CLV indicates that at high resolution, faculae are an
essential constituent of active regions all across the solar disk. We speculate
that the faculae near disk center as well as the BPs away from disk center are
associated with inclined fields
Communicating Energy
http://deepblue.lib.umich.edu/bitstream/2027.42/108428/1/lntitle_1366909410.pd
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