MLD's and the phase angle, alpha.
Alpha phase angle effect /angle between narrow band masker and tonal signal/ on binaural detection, discussing experiments failure
Jeffress, L. A.↗
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(abstract) Observation by Clementine of a Hugh Opposition Surge on the Moon at Very Small Solar Phase Angles
The Clementine mission enabled the first quantative observations of the Moon at very small solar phase angles. It is well established from Earth-based observations that the Moon exhibits a non-linear increase in brightness as its face becomes fully illuminated to a terrestrial observer. Because the models of the opposition effect are sensitive indicators of surfical compaction state and particle size, observations at small solar phase angles are important to obtain. A recent model for optical coherent backscatter seeks to explain a narrow opposition spike at very small phase angles (< 1 degree) seen on several icy satellites , including Europa, Icarus 90, and Oberon . Over 90 images of the Moon's surface at phase angles less than 0.5(deg) (the minimum phase angle observable from Earth due to the Moon's angular size) were obtained by the Clementine spacecraft. Our analysis of these images shows the moon exhibits a surge in brightness of approximately 20% below 0.25(deg), comparable to the values observed on icy satellites. No color dependence was detected in the lunar phase curve below 2 degrees.
partical size icy satellites Europa Icarus 90 Ober↗
NEAs: Phase Angle Dependence of Asteroid Class and Diameter from Observational Studies
We will discuss the results of a planned observation campaign of Near Earth Asteroids (NEAs), 1999 CU3, 2002 GM2, 2002 FG7, and 3691 Bede with instruments on the United Kingdom Infrared Telescope (UKIRT) from 15-Mar-2015 to 28-April 2015 UT. We will study the phase-angle dependence of the reflectance and thermal emission spectra. Recent publications reveal that the assignment of the asteroid class from visible and near-IR spectroscopy can change with phase angle for NEAs with silicate-bearing minerals on their surfaces (S-class asteroids) (Thomas et al. 2014, Icarus 228, 217; Sanchez et al. 2012 Icarus 220, 36). Only three of the larger NEAs have been measured at a dozen phase angles and the trends are not all the same, so there is not yet enough information to create a phase-angle correction. Also, the phase angle effect is not characterized well for the thermal emission including determination of the albedo and the thermal emission. The few NEAs were selected for our study amongst many possible targets based on being able to observe them through a wide range of phase angles, ranging from less than about 10 degrees to greater than 45 degrees over the constrained date range. The orbits of NEAs often generate short observing windows at phase angles higher than 45 deg (i.e., whizzing by Earth and/or close to dawn or dusk). Ultimately, lowering the uncertainty of the translation of asteroid class to meteorite analog and of albedo and size determinations are amongst our science goals. On a few specific nights, we plan to observe the 0.75-2.5 micron spectra with IRTF+SpeX for comparison with UKIRT data including 5-20 micron with UKIRT+UIST/Michelle to determine as best as possible the albedos. To ensure correct phasing of spectroscopic data, we augment with TRAPPIST-telescope light curves and R-band guider image data. Our observations will contribute to understanding single epoch mid-IR and near-IR measurements to obtain albedo, size and IR beaming parameters (the outcomes of thermal models) and asteroid spectral class.
phase-angle↗
Visible spectral reflectance measurements /0.33-1.1 microns/ of the Galilean satellites at many orbital phase angles
One hundred eighty-seven reflectance spectra (0.33-1.10 microns) of the Galilean satellites have been obtained. Solar phase angle color correction coefficients were derived and the spectra corrected to a solar phase of 6 deg. Solar phase angle coefficients beyond 0.55 micron are presented for the first time. The spectra as a function of orbital phase angle are presented in the form of images to display hemispheric spectral variations. Io and Europa are redder on their trailing hemispheres while Callisto is redder on its leading hemisphere. Ganymede shows small longitudinal color variations despite the complex albedo structure visible in Voyager images. Comparisons of these data with previous measurements reveal that most differences can be attributed to the solar calibration. Reflectance measurements of Io at 0.73 micron observed 8.5 years apart show a 6% global reflectance decrease. However, it is difficult to unambiguously attribute this particular decrease in reflectance to a change in Io's surface composition.
Mcfadden, L. A.↗
Phase-Angle Dependence of Determinations of Diameter, Albedo, and Taxonomy: A Case Study of NEO 3691 Bede
Parameters important for NEO risk assessment and mitigation include Near-Earth Object diameter and taxonomic classification, which translates to surface composition. Diameters of NEOs are derived from the thermal fluxes measured by WISE, NEOWISE, Spitzer Warm Mission and ground-based telescopes including the IRTF and UKIRT. Diameter and its coupled parameters Albedo and IR beaming parameter (a proxy for thermal inertia and/or surface roughness) are dependent upon the phase angle, which is the Sun-target-observer angle. Orbit geometries of NEOs, however, typically provide for observations at phase angles greater than 20 degrees. At higher phase angles, the observed thermal emission is sampling both the day and night sides of the NEO. We compare thermal models for NEOs that exclude (NEATM) and include (NESTM) night-side emission. We present a case study of NEO 3691 Bede, which is a higher albedo object, X (Ec) or Cgh taxonomy, to highlight the range of H magnitudes for this object (depending on the albedo and phase function slope parameter G), and to examine at different phase angles the taxonomy and thermal model fits for this NEO. Observations of 3691 Bede include our observations with IRTF+SpeX and with the 10 micrometer UKIRT+Michelle instrument, as well as WISE and Spitzer Warm mission data. By examining 3691 Bede as a case study, we highlight the interplay between the derivation of basic physical parameters and observing geometry, and we discuss the uncertainties in H magnitude, taxonomy assignment amongst the X-class (P, M, E), and diameter determinations. Systematic dependencies in the derivation of basic characterization parameters of H-magnitude, diameter, albedo and taxonomy with observing geometry are important to understand. These basic characterization parameters affect the statistical assessments of the NEO population, which in turn, affects the assignment of statistically-assessed basic parameters to discovered but yet-to-be-fully-characterized NEOs.
Albedo and taxonomy↗
Cassini CIRS Observations of Thermal Differences in Saturn's Main Rings with Increasing Phase Angle
Radial scans of main rings obtained at a variety of phase angles, local times and ring opening angles. Circular focal plane 1 slowly scanned across rings. Radial resolution approx. 2500 km. Temperatures decrease with increasing phase angle for all main rings. Rough estimate of particle spin period for B ring particle is P > 1.8 hours
CIRS↗
Size estimates of Titan's aerosols based on Voyager high-phase-angle images
Limits on the physical properties of the scattering haze near the top of Titan's atmosphere are derived from data obtained from seven high-phase-angle images from Voyager 1 and 2. From the ratio of the intensities observed at two different high phase angles, an estimate can be made of the forward-scattering lobe of the single-scattering phase function. Comparing the forward-scattering estimate with diffraction lobes from particles of different radii, it is concluded that the average radius of the particles found in the upper few tenths of an optical depth exceeds 0.19 micron. Judging from data observed at four different phase angles, the haze particles probably have a refractive index near 1.6 and a mean size of about 0.5 micron, if the widths of their diffraction peaks are close to those for equal-volume spheres. However, the highly polarizing nature of the particles over a broad wavelength-bandpass (Tomasko and Smith, 1982; West et al, 1983) combined with their forward-scattering behavior makes it very unlikely that the particles are spherical. The nonsphericity contributes to the uncertainty about the radii of the particles, but it is thought that the average radius is several tenths of a micron.
Rages, K.↗
Phase-angle controller for Stirling engines
An actuator includes a restraint link adapted to be connected with a pivotal carrier arm for a force transfer gear interposed between the crankshaft for an expander portion of a Stirling engine and a crankshaft for the displacer portion of the engine. The restraint link is releasably trapped hydraulic fluid for selectively establishing a phase angle relationship between the crankshaft. A second embodiment incorporates a hydraulic coupler for use in varying the phase angle of gear-coupled crank fpr a Stirling engine whereby phase angle changes are obtainable.
Mcdougal, A. R.↗
The Coherent Backscattering Opposition Effect: Measurements at Very Small Phase Angles
This oral presentation explains that measurements of the opposition surge (the nonlinear increase in reflectance seen in particulate materials when observed at small phase angles) are the first ever made using the JPL long-arm goniometer, which permits very small phase angle measuremnets to be made.
long-arm goniometer phase angles coherent backscat↗
Analysis of hydrogen maser frequency drift due to possible drifts in load VSWR and phase angle of reflection coefficient
Theoretical equations are derived for calculating the effects of local VSWR and reflection coefficient phase angle drifts on hydrogen maser frequency stability. Sample calculations made for a typical JPL maser show that under special load conditions, a VSWR drift of 0.000075/h or phase angle drive of 0.01 deg/h can produce a frequency drift of (10 to the -14th power f sub 0) Hz/h where f sub 0 is the maser frequency of approximately 1.42 x 10 to the 9th power Hz.
Beatty, R. W.↗
An Analysis of Neptune's Stratospheric Haze Using High-Phase-Angle Voyager Images
We have inverted high-phase-angle Voyager images of Neptune to determine the atmospheric extinction coefficient as a function of altitude and the scattering phase function at a reference altitude. Comparisons between theoretical model and observations help separate the contributions from molecular Rayleigh and aerosol scattering and help determine the variation of the aerosol size, concentration, and scattering properties with altitude. Further comparisons between models and data allow us to place constraints on the location and composition of the hazes, the concentration and downward flux of certain condensible hydrocarbon gases, the eddy diffusion coefficient in the lower stratosphere, and the thermal profile in parts of Neptune's stratosphere. We find that a distinct stratospheric haze layer exists near 12(sub -1, sup +1) mbar in Neptune's lower stratosphere, most probably due to condensed ethane. The derived stratospheric haze production rate of 1.0(sub -0.3, sup +0.2) x 10(exp -15) g cm(exp -2) sec(exp -1) is substantially lower than photochemical model predictions. Evidence for hazes at higher altitudes also exists. Unlike the situation on Uranus, large particles (0.08-0.11 microns) may be present at high altitudes on Neptune (e.g., near 0.5 mbar), well above the region in which we expect the major hydrocarbon species to condense. Near 28 mbar, the mean particle size is about 0.13(sub -0.02, sup +0.02) microns with a concentration of 5(sub -3, sup +3) particles cm(exp -3). The cumulative haze extinction optical depth above 15 mbar in the clear filter is approx. 3 x 10(exp -3), and much of this extinction is due to scattering rather than absorption; thus, if our limb-scan sites are typical, the hazes cannot account for the stratospheric temperature inversion on Neptune and may not contribute significantly to atmospheric heating. We compare the imaging results with the results from other observations, including those of the Voyager Photopolarimeter Subsystem, and discuss differences between Neptune and Uranus.
Moses, Julianne I.↗
Variation of lunar sodium emission intensity with phase angle
We report new measurements of the sodium emission intensity seen in a line of sight just above the surface of the Moon. These data show a strong dependence on lunar phase. The emission intensity decreases from a maximum around first quarter (phase angle 90 deg) to very small values near full Moon (phase angle 0 deg). This suggests that the rate of sodium vapor production from the lunar surface is largest at the subsolar point and becomes small near the terminator. However, the sodium emission near full Moon falls below that which would be expected for solar photon-driven processes. Since the solar wind flux decreases substantially when the Moon enters the Earth's magnetotail near full Moon, while the global solar photon flux is undiminished, we suggest that solar wind sputtering is the dominant process for sodium production.
Potter, A. E.↗
Limb darkening of two latitudes of Jupiter at phase angles of 34 and 109 deg
The imaging photopolarimeter aboard Pioneer 10 produced hundreds of red and blue images of Jupiter covering a wide range of phase angles and having good linearity and signal-to-noise characteristics. In this preliminary analysis the limb darkening across two of the red images (at phase angles of about 34 and 109 deg) in both a prominent dark belt and a bright zone are compared with multiple-scattering models. Of the simple models tried, the smallest deviations from the observations result for ones consisting of a thin absorbing layer above a semiinfinite atmosphere of particles scattering according to the Henyey-Greenstein phase function. The asymmetry parameter for the best fits to both the belt and the zone data is in the range g = 0 to 0.25, corresponding to particles small in comparison with the wavelength of red light. The phase integral derived from the models lies in the range of about 1.5 to 1.6, implying a substantial internal heat source for Jupiter.
Tomasko, M. G.↗
Interaction types and their like-polarization phase-angle difference signatures
The JPL Airborne Synthetic Aperture Radar (AIRSAR) measures the full polarimetric properties of scene objects. AIRSAR data contain a complete set of magnitudes (for all linearly-polarized combinations (viz., VV, HH, and CS (cross Polarization))) and phase-angle differences (for all pairs of linearly-polarized components) for each image pixel. Radar images users have been greatly interested in the like-polarization (LK) phase-angle difference parameter, delta phi(sub LK). Usually, it is associated with the type of interaction between microwaves and scene-object scattering-elements. One value of delta phi(sub LK) is said to be produced by a dominant single scattering (or reflection) event, and another value is said to be the result of a dominant double-scattering (or double reflection) event. these are often called 'single bounce' and 'double bounce' interaction signatures, respectively. There appears to be a significant amount of confusion about how the interaction processes produce the characteristic values of delta phi(sub LK) and about what value of delta phi(sub LK) should be associated with each specific type. This issue is addressed.
Paris, Jack F.↗
Design of a correlation reflectometer radiometer diagnostic and measurements of the electron density–temperature cross-phase angle in the H-mode pedestal with small edge localized modes at ASDEX Upgrade
This work presents the hardware design and first results from a newly commissioned correlation reflectometer radiometer diagnostic that measures the cross-phase angle between electron density and temperature fluctuations in ASDEX Upgrade plasmas. This diagnostic employs cross correlations between signals measured by a tunable, continuous wave, perpendicular incidence, fluctuation reflectometer, and a 24-channel radiometer sharing the same line of sight. Novel measurements in the pedestal of a helium H-mode plasma with small edge localized modes show changes in the cross-phase angle between the electron density and temperature fluctuations from ∼90° to 120°, suggesting changes in the properties of the turbulence driving transport in the plasma edge.
70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
Voltage transients due to phase angle switching of speed control power for a Brayton cycle alternator
Voltage transients due to phase angle switching of speed control power for Brayton cycle alternator examined by computerized simulation
Bainbridge, R. C.↗
Optical polarization measurements of the Jupiter atmosphere at 103 deg phase angle
The first measurements have been made of the linear polarization of sunlight scattered by the Jupiter atmosphere at phase angles greater than 12 deg, using the imaging photopolarimeter on Pioneer 10. The data are of high accuracy, in spite of several problems in the instrument. The polarization is positive at 440 nm. There is no direct evidence for spherical particles in the Jupiter clouds. Using a simple model of Rayleigh scattering above a Lambertian cloud layer, a unique fit is found to the observed intensity and polarization at each point on the planet. The resulting Rayleigh optical depths, if they are attributed to molecular scattering alone (i.e., no aerosols above the cloud tops), can be converted into physical altitudes of the cloud tops. The first results suggest that the north tropical zone, parts of the equatorial zone, and the red spot are all elevated regions.
Coffeen, D. L.↗
Spectrogoniometer for measuring planetary surface materials at small phase angles
This paper describes an instrument, termed spectrogoniometer, which was designed to measure the bidirectional reflectance properties of planetary surface analogs at very small phase angles. By using a pellicle beam splitter, a highly collimated laser light source, and a carefully aligned apparatus it was possible to measure the reflectance properties of geologic samples under any viewing geometry: the angles of incidence and emission ranging from 0 to 90 deg, and the azimuthal angle ranging from 0 to 360 deg. The results on the effect of porosity are demonstrated by comparing measurements on a compact sample (with a void space of 25 percent) and a fluffy sample (with a void space of 90 percent). The fluffy sample exhibited a 30-percent increase in intensity between 10 and 0 deg, whereas the compact sample exhibited only a 20-percent increase.
Buratti, Bonnie J.↗