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Results for “PHASE ANGLE”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

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.↗
NASA NTRS1992

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.↗
DOE OSTI2025

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↗
NASA NTRS1974

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.↗
NASA NTRS1988

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.↗
NASA NTRS1980

Preliminary results of polarimetry and photometry of Titan at large phase angles from Pioneer 11

The imaging photopolarimeter (IPP) aboard the Pioneer 11 spacecraft measured the linear polarization of the integrated disk of Titan in red and blue light at a variety of phase angles from 15 to 97 deg. The large polarization (54%) measured in blue light at 90 deg phase constrains the size of the aerosols near the top of Titan's atmosphere to have radii smaller than about 0.09 microns if they have a refractive index of 2.0. The polarization at 90 deg phase in red light is smaller (41%) and implies that the optical thickness of the layer of small aerosols is about 0.6 above an effectively depolarizing surface. The shape of the polarization versus phase curve in blue light suggests increasing particle size with increasing depth into the atmosphere. The limb darkening of Titan was measured at 28 deg phase by using the imaging mode of the IPP. The limb darkening observed in both colors is reasonably consistent with that given by the scattering models derived from the polarization observations.

Tomasko, M. G.↗
NASA NTRS1991

Laboratory photometric measurement of particulate soils out to very large phase angles

In the present study, the objectives were to develop the laboratory methods and tools to conduct photometric observations of dark particulate samples over a large range of phase angles and to demonstrate whether forward scattering behavior can be seen in a surface constructed of low albedo material. The researchers also examined the adequacy of various model formulations of P (alpha) to describe the effective scattering properties of their sample.

Helfenstein, Paul↗
NASA NTRS1978

Photometry and polarimetry of Jupiter at large phase angles. I - Analysis of imaging data of a prominent belt and a zone from Pioneer 10

Photopolarimetric observations of a prominent bright zone and a dark belt of Jupiter in red and blue light are analyzed which were performed by Pioneer 10 at phase angles of 12, 23, 34, 109, 120, 127, and 150 deg. Geometric and photometric reductions of the imaging data are described, the instrument sensitivity at various times is evaluated, and the data are referred to an absolute scale. The observations are analyzed in detail by comparing the data with results of radiative-transfer calculations for specific scattering models of Jupiter's atmosphere. These models include those with a vertical structure consisting of a layer of Rayleigh-scattering gas above a semiinfinite mixture of cloud particles and gas, those having a small quantity of aerosols in the gas above either the diffuse cloud in a reflecting-scattering model or the top cloud of a two-cloud-layer model, those in which a forward-scattering haze is mixed uniformly with gas, and those containing dust layers. It is found that in both the belt and the zone in red as well as blue light, cloud phase functions are required which provide both strong forward scattering and some backscattering.

Tomasko, M. G.↗
DOE OSTI2018

Validation of gyrokinetic simulations with measurements of electron temperature fluctuations and density-temperature phase angles on ASDEX Upgrade

Measurements of turbulent electron temperature fluctuation amplitudes, $δT_e⊥/T_e$, frequency spectra, and radial correlation lengths, $L_r(T_{e⊥}$), have been performed at ASDEX Upgrade using a newly upgraded Correlation ECE diagnostic in the range of scales $k_⊥<1.4 cm^{-1}, k_r < 3.5 cm^{-1} (k_⊥ρ_s < 0.28$ and $k_rρ_s < 0.7$). The phase angle between turbulent temperature and density fluctuations, α nT , has also been measured by using an ECE radiometer coupled to a reflectometer along the same line of sight. These quantities are used simultaneously to constrain a set of ion-scale non-linear gyrokinetic turbulence simulations of the outer core ( ρ tor = 0.75) of a low density, electron heated L-mode plasma, performed using the gyrokinetic simulation code, GENE. The ion and electron temperature gradients were scanned within uncertainties. It is found that gyrokinetic simulations are able to match simultaneously the electron and ion heat flux at this radius within the experimental uncertainties. The simulations were performed based on a reference discharge for which $δT_{e⊥}/T_e$ measurements were available, and $L_r(T_{e⊥}$) and α nT were then predicted using synthetic diagnostics prior to measurements in a repeat discharge. While temperature fluctuation amplitudes are overestimated by >50% for all simulations within the sensitivity scans performed, good quantitative agreement is found for $L_r(T_{e⊥}$) and α nT . Finally, a validation metric is used to quantify the level of agreement of individual simulations with experimental measurements, and the best agreement is found close to the experimental gradient values.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1980

Photometry of Saturn at large phase angles

In the present paper, the single-scattering phase function of Saturn's aerosols is determined from the vertical structure of Saturn's atmosphere, derived in a previous analysis, and Pioneer's imaging photometry of bright and dark zones on Saturn in red and blue light. The single-scattering phase function is well represented by a combination of two Henyey-Greenstein functions. Moderately forward scattering functions fit well both in red and blue light, although a definite difference between the two colors is found.

Tomasko, M. G.↗
NASA NTRS1992

High-phase-angle observations of Neptune at 2650 and 7500 A - Haze structure and particle properties

An analysis is conducted of spatially resolved Voyager 2 Photopolarimeter Subsystem (PPS) observations at 2650 and 7500 A. The continuum absorber that is tropospherically abundant, if confined to the region below the methane haze layer, indicates an optical depth for that layer no greater than 0.8; models in which this optical depth is as large as 3.0 yield too much limb darkening, in the case where the continuum absorber is mixed with both the methane haze and deeper clouds. Tropospheric aerosols are noted to have phase functions with shallow backward lobes.

Pryor, Wayne R.↗