scholarly journals Polarimetry of Saturnian satellite Enceladus

2015 ◽  
Vol 5 (1) ◽  
pp. 29-32 ◽  
Author(s):  
S. Zaitsev ◽  
N. Kiselev ◽  
V. Rosenbush ◽  
S. Kolesnikov ◽  
D. Shakhovskoy
Keyword(s):  
Light Scattering ◽  
Phase Angle ◽  
Linear Polarization ◽  
Spectral Band ◽  
Crimean Astrophysical Observatory ◽  
Angle Dependence ◽  
Phase Angles ◽  
Saturnian Satellite

We present results of polarimetric observations of Saturn's moon Enceladus carried out from April 14, 2010 to April 13, 2013 in WR spectral band (550-750 nm). We used 2.6-m telescope equipped with a one-channel photoelectric photometer-polarimeter (Crimean Astrophysical Observatory). The measurements were performed at phase angles ranging from 1.65° to 5.71°. The phase-angle dependence of linear polarization of Enceladus was obtained using the results of our observations. Results obtained are discussed in terms of existing models of light scattering by regolith surfaces.

scholarly journals Light Scattering as a Clue to Cometary Dust Structure

2005 ◽  
Vol 13 ◽  
pp. 498-500 ◽  
Author(s):  
A. Chantal Levasseur-Regourd ◽  
E. Hadamcik ◽  
J. Lasue
Keyword(s):  
Light Scattering ◽  
Physical Properties ◽  
Phase Angle ◽  
Linear Polarization ◽  
Dust Structure ◽  
Cometary Dust ◽  
Microgravity Conditions

AbstractThe linear polarization of comets depends upon the cometary dust physical properties, as well as upon the phase angle and the wavelength. The observed similarities and discrepancies provide drastic constraints on the physical properties of the dust. A series of measurements of light scattering properties on clouds of particles and of the aggregates they form under microgravity conditions should allow the interpretation of the observations in terms of physical properties of the dust.

scholarly journals Phase-angle dependence of colour ratios and potential implications for lunar remote sensing

2020 ◽  
Vol 644 ◽  
pp. A30
Author(s):  
Yazhou Yang ◽  
Pei Ma ◽  
Le Qiao ◽  
Hao Zhang ◽  
Weidong Jin ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Particle Size ◽  
Phase Angle ◽  
Remote Sensing Data ◽  
Target Surface ◽  
Phase Dependence ◽  
Imaging Device ◽  
Angle Dependence ◽  
Solar Phase ◽  
Phase Angles

Context. The colour-ratio technique has been widely used in mapping planetary surfaces, but its solar phase-angle dependence is not well understood. Understanding the phase-angle dependence of the colour ratio would enhance our abilities in interpreting planetary remote sensing data. Aims. We aim to investigate the dependence of the colour ratio indices on mineralogy, phase angle, particle size, and the degree of simulated space weathering. Methods. We measured the multi-band (i.e. 458, 633, 750, and 905 nm) and multi-angle reflectance spectra of four typical lunar-type minerals with different particle sizes using a custom multi-angular imaging device. Results. The colour ratio does have a phase-angle dependence that is more sensitive to the mineralogy and wavelength and less sensitive to particle size distribution. Conclusions. The combined analysis of the colour ratio and its phase dependence can improve efficiency in mapping the lunar surface. With a prior knowledge of the phase behaviours of colour ratios of specific lunar-type minerals, an optimised colour ratio at certain phase angles can be found to efficiently distinguish the composition of a target surface.

scholarly journals Scattering Properties of Cometary Dust Based on Polarimetric Data

1991 ◽  
Vol 126 ◽  
pp. 249-252
Author(s):  
Sonoyo Mukai ◽  
Tadashi Mukai ◽  
Sen Kikuchi
Keyword(s):  
Linear Polarization ◽  
Phase Function ◽  
Mie Scattering ◽  
Mixing Ratio ◽  
Small Particles ◽  
Cometary Dust ◽  
Maximum Polarization ◽  
Large Particles ◽  
Lower Maximum ◽  
Phase Angles

AbstractReferring to the dust model in Mukai and Mukai(1990), where the scattering by large rough particles and Mie scattering by small particles are taken into account, a phase function of linear polarization of several comets is examined, especially in a region of phase angles α near a maximum polarization. A lower maximum polarization observed in comet Austin(1989c1) than those in comets West(1975n) and P/Halley leads a speculation that a mixing ratio of rough scattering to Mie scattering in comet Austin increases from a sun-comet distance r of 0.6 AU to 1.2 AU. This implies that a shortage of large particles in comet Austin occured in r <1 AU.

Phase-angle dependence study of modulated e.s.r. and ENDOR signals from coal samples

Fuel ◽  
1986 ◽  
Vol 65 (11) ◽  
pp. 1588-1593 ◽  
Author(s):  
Kaoru Shibata ◽  
Chester Alexander ◽  
Ichiro Miyagawa
Keyword(s):  
Phase Angle ◽  
Angle Dependence

scholarly journals Attention and Temporal Expectations Modulate Power, Not Phase, of Ongoing Alpha Oscillations

2015 ◽  
Vol 27 (8) ◽  
pp. 1573-1586 ◽  
Author(s):  
Rosanne M. van Diepen ◽  
Michael X Cohen ◽  
Damiaan Denys ◽  
Ali Mazaheri
Keyword(s):  
Phase Angle ◽  
Phase Locking ◽  
Auditory Target ◽  
Alpha Power ◽  
Visual Condition ◽  
Top Down ◽  
Alpha Oscillations ◽  
Alpha Oscillation ◽  
Sensory Cortices ◽  
Phase Angles

The perception of near-threshold visual stimuli has been shown to depend in part on the phase (i.e., time in the cycle) of ongoing alpha (8–13 Hz) oscillations in the visual cortex relative to the onset of that stimulus. However, it is currently unknown whether the phase of the ongoing alpha activity can be manipulated by top–down factors such as attention or expectancy. Using three variants of a cross-modal attention paradigm with constant predictable stimulus onsets, we examined if cues signaling to attend to either the visual or the auditory domain influenced the phase of alpha oscillations in the associated sensory cortices. Importantly, intermixed in all three experiments, we included trials without a target to estimate the phase at target presentation without contamination from the early evoked responses. For these blank trials, at the time of expected target and distractor onset, we examined (1) the degree of the uniformity in phase angles across trials, (2) differences in phase angle uniformity compared with a pretarget baseline, and (3) phase angle differences between visual and auditory target conditions. Across all three experiments, we found that, although the cues induced a modulation in alpha power in occipital electrodes, neither the visual condition nor the auditory cue condition induced any significant phase-locking across trials during expected target or distractor presentation. These results suggest that, although alpha power can be modulated by top–down factors such as attention and expectation, the phase of the ongoing alpha oscillation is not under such control.

scholarly journals Spectral Sizing of a Coarse Spectral Resolution Satellite Sensor for XCO<sub>2</sub>

2019 ◽  
Author(s):  
Jonas Simon Wilzewski ◽  
Anke Roiger ◽  
Johan Strandgren ◽  
Jochen Landgraf ◽  
Dietrich G. Feist ◽  
...  
Keyword(s):  
Light Scattering ◽  
Spectral Resolution ◽  
Spectral Band ◽  
Ground Truth ◽  
Resolving Power ◽  
Total Carbon ◽  
Band Selection ◽  
Co2 Absorption ◽  
Absorption Bands ◽  
Satellite Sensor

Abstract. Verifying anthropogenic carbon dioxide (CO2) emissions globally is essential to inform about the progress of institutional efforts to mitigate man-made climate forcing. To monitor localized emission sources, spectroscopic satellite sensors have been proposed that operate on the CO2 absorption bands in the shortwave-infrared (SWIR) spectral range with ground resolution as fine as a few tens to about a hundred meters. When designing such sensors, fine ground resolution requires a trade-off towards coarse spectral resolution in order to achieve sufficient noise performance. Since fine ground resolution also implies limited ground coverage, such sensors are envisioned to fly in fleets of satellites, requiring low-cost and simple design, e.g. by restricting the spectrometer to a single spectral band. Here, we use measurements of the Greenhouse Gases Observing Satellite (GOSAT) to evaluate the spectral resolution and spectral band selection of a prospective satellite sensor with fine ground resolution. To this end, we degrade GOSAT SWIR spectra of the CO2 bands at 1.6 (SWIR-1) and 2.0 μm (SWIR-2) to coarse spectral resolution, and we evaluate retrievals of the column-averaged dry-air mole-fractions of CO2 (XCO2) by comparison to ground-truth provided by the Total Carbon Column Observing Network (TCCON) and by comparison to global native GOSAT retrievals with native spectral resolution and spectral band selection. Coarsening spectral resolution from GOSAT's native resolving power of > 20,000 to the range of 700 to a few thousand makes the scatter of differences between the SWIR-1 and SWIR-2 retrievals and TCCON increase moderately. For resolving powers of 1,600 (SWIR-1) and 1,200 (SWIR-2), the scatter increases from 2.4 ppm (native) to 3.0 ppm for SWIR-1 and 3.3 ppm for SWIR-2. Coarser spectral resolution yields only marginally worse performance than the native GOSAT configuration in terms of station-to-station variability and geophysical parameter correlations for the TCCON-GOSAT differences. Comparing the SWIR-1 and SWIR-2 configurations to native GOSAT retrievals on the global scale, however, reveals that the coarse resolution SWIR-1 and SWIR-2 configurations suffer from some spurious correlations with geophysical parameters that characterize the light-scattering properties of the scene such as particle amount, size, height and surface albedo. Overall, the SWIR-1 and SWIR-2 configurations with resolving powers of 1,600 and 1,200 show promising performance for future sensor design in terms of random error sources while residual errors induced by light-scattering along the lightpath need to be investigated further. Due to the stronger CO2 absorption bands in SWIR-2 than in SWIR-1, the former has the advantage that measurement noise propagates less into the retrieved XCO2 and that some retrieval information on particle scattering properties is accessible.

scholarly journals Terrestrial Planet Optical Phase Curves. I. Direct Measurements of the Earth

2021 ◽  
Vol 163 (1) ◽  
pp. 5
Author(s):  
Roderick De Cock ◽  
Timothy A. Livengood ◽  
Daphne M. Stam ◽  
Carey M. Lisse ◽  
Tilak Hewagama ◽  
...  
Keyword(s):  
Phase Angle ◽  
Terrestrial Planet ◽  
Wavelength Dependence ◽  
Deep Impact ◽  
Spectral Filters ◽  
Optical Phase ◽  
The Earth ◽  
Direct Measurements ◽  
Phase Angles ◽  
Geometric Albedo

Abstract NASA’s EPOXI mission used the Deep Impact spacecraft to observe the disk-integrated Earth as an analog to terrestial exoplanets’ appearance. The mission took five 24 hr observations in 2008–2009 at various phase angles (57.°7–86.°4) and ranges (0.11–0.34 au), of which three equatorial (E1, E4, E5) and two polar (P1, North and P2, South). The visible data taken by the HRIV instrument ranges from 0.3 to 1.0 μm, taken trough seven spectral filters that have spectral widths of about 100 nm, and which are centered about 100 nm apart, from 350 to 950 nm. The disk-integrated, 24 hr averaged signal is used in a phase angle analysis. A Lambertian-reflecting, spherical planet model is used to estimate geometric albedo for every observation and wavelength. The geometric albedos range from 0.143 (E1, 950 nm) to 0.353 (P2, 350 nm) and show wavelength dependence. The equatorial observations have similar values, while the polar observations have higher values due to the ice in view. Therefore, equatorial observations can be predicted for other phase angles, but (Earth-like) polar views (with ice) would be underestimated.

scholarly journals Blue, white, and red ocean planets

2019 ◽  
Vol 626 ◽  
pp. A129 ◽  
Author(s):  
V. J. H. Trees ◽  
D. M. Stam
Keyword(s):  
Phase Angle ◽  
Surface Albedo ◽  
Color Change ◽  
Water Flux ◽  
Angular Distance ◽  
Total Flux ◽  
Degree Of Polarization ◽  
Reflected Light ◽  
Phase Functions ◽  
Phase Angles

Context. An exoplanet’s habitability will depend strongly on the presence of liquid water. Flux and/or polarization measurements of starlight that is reflected by exoplanets could help to identify exo-oceans. Aims. We investigate which broadband spectral features in flux and polarization phase functions of reflected starlight uniquely identify exo-oceans. Methods. With an adding-doubling algorithm, we computed total fluxes F and polarized fluxes Q of starlight that is reflected by cloud-free and (partly) cloudy exoplanets, for wavelengths from 350 to 865 nm. The ocean surface has waves composed of Fresnel reflecting wave facets and whitecaps, and scattering within the water body is included. Results. Total flux F, polarized flux Q, and degree of polarization P of ocean planets change color from blue, through white, to red at phase angles α ranging from ~134° to ~108° for F, and from ~123° to ~157° for Q, with cloud coverage fraction fc increasing from 0.0 (cloud-free) to 1.0 (completely cloudy) for F, and to 0.98 for Q. The color change in P only occurs for fc ranging from 0.03 to 0.98, with the color crossing angle α ranging from ~88° to ~161°. The total flux F of a cloudy, zero surface albedo planet can also change color, and for fc = 0.0, an ocean planet’s F will not change color for surface pressures ps ≿ 8 bars. Polarized flux Q of a zero surface albedo planet does not change color for any fc. Conclusions. The color change of P of starlight reflected by an exoplanet, from blue, through white, to red with increasing α above 88°, appears to identify a (partly) cloudy exo-ocean. The color change of polarized flux Q with increasing α above 123° appears to uniquely identify an exo-ocean, independent of surface pressure or cloud fraction. At the color changing phase angle, the angular distance between a star and its planet is much larger than at the phase angle where the glint appears in reflected light. The color change in polarization thus offers better prospects for detecting an exo-ocean.

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.

Dynamic Simulation and Analysis of Different Phase Synchronous Rotor Mixing Process

2013 ◽  
Vol 561 ◽  
pp. 279-284
Author(s):  
Xue Jie Mu ◽  
Xing Wei Li ◽  
Na Duan
Keyword(s):  
Dynamic Simulation ◽  
Phase Angle ◽  
Mixing Process ◽  
Two Phase ◽  
Mixing Effect ◽  
Phase Angles ◽  
Better Than

Contrast and analysis of the influence that synchronous rotor mixer’s two phase angles 90° and 180° to the mixing effect using special visco-elasticity fluid software--Polyflow. The results show that 90° phase angle rotor could promote compound mixing, and improve mixing rubber’s uniformity, and its mixing effect is better than synchronous rotor with 180° phase angle.

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