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NASA NTRS1989

Detection of elliptical polarization and mode splitting in discrete Schumann resonance excitations

Elliptical polarization and mode splitting have been detected in the magnetic component of discrete, well defined Schumann resonance excitations. These ELF excitations, which are large electromagnetic transients of approximately 1 s duration, are called Q-bursts and typically occur every few minutes. They are believed to be the signature of the impulsive excitation of the earth-ionosphere cavity by ultra-large lightning currents. In this paper the magnetic polarization and spectral characteristics of four large Q-bursts are examined in detail using a new analysis technique. Two events display right-hand polarization and two display left-hand polarization. The theoretical polarization properties of the central and side multiplets of the Schumann resonances are used to define a local orthogonal coordinate system in the measurement frame in which these components may be separated. Maximum entropy spectrums computed separately for what are identified to be the central and side multiplets in this coordinate system show distinctly different eigenfrequencies for the lowest mode near 7.5 Hz. For the limited number of cases examined the magnitude of the line splitting detected using this technique is roughly 1.4-1.8 Hz, larger by nearly a factor of two than theoretical or observed values of the splitting previously reported. The frequencies of the side multiplets may lie either above or below the frequency of the central multiplet.

Sentman, D. D.↗

NASA NTRS1990

New observations and a photographic atlas of polar-ring galaxies

A photographic atlas of polar-ring galaxies and related objects is presented. The atlas includes kinematically confirmed polar-ring galaxies (category A), good candidates based on their morphological appearance (category B), possible candidates (category C), and possibly related objects (category D). New photometric and kinematic observations are reported for several galaxies in the catalog, including observations that show that UGC 7576 and UGC 9796 ( = II ZW 73) are S0 galaxies with polar rings. Roughly 0.5 percent of all nearby S0 galaxies appear to have polar rings. When corrected for various selection effects (e.g., nonoptimal viewing orientation, possible dimming, or limited lifetime of the ring) the percentage increases to about 5 percent of S0 galaxies which have, or have had a polar ring.

Whitmore, Bradley C.↗

NASA NTRS1991

Circular polarization in 1612 MHz OH maser emission from OH/IR stars

In order to study the incidence of circular polarization in the 1612 MHz OH emission from envelopes of OH/IR stars, the Arecibo radio telescope was used to obtain high-resolution, high signal-to-noise 1612 MHz spectra in both circular polarizations for several OH/IR stars. The method of Troland and Heiles (1982) was used to estimate the intensities of magnetic fields in the envelopes. The fields appear to have complex structures, and intensities on the order of 1-100 microG. The spectra are weakly polarized, probably as a result of weakly polarized emission from individual emitting elements. Integration over the Stokes parameter V yields nonzero results for three of the stars, suggesting that another polarizing mechanism (in addition to simple Zeeman splittings) is at work.

Zell, Philip↗

NASA NTRS1991

Polar faculae - 1906-1990

The numbers of faculae at the sun's poles have been estimated from white-light images obtained at the Mount Wilson Observatory during 1970-1990 and have been combined with previous measurements extending back to 1906 when the observations began. The combined measurements now span four complete 22 year cycles and show the following: (1) the numbers of north and south polar faculae were about 50 percent larger around sunspot minimum in 1986 than in 1976, but were still smaller than some of the very large numbers that occurred near sunspot minima in earlier cycles; (2) in 1974, the number of south polar faculae exhibited a short-lived increase which coincided with the arrival of a surge of trailing-polarity flux at the pole, suggesting that similar poleward surges may have been responsible for previously unexplained bursts of faculae such as the one that occurred at the south pole in 1959; and (3) the numbers of polar faculae have been highly correlated with the Wilcox Solar Observatory polar field strengths since these magnetic measurements began in 1976.

Sheeley, N. R., Jr.↗

NASA NTRS1991

Thermal and albedo mapping of the north and south polar regions of Mars

The first maps of the thermal properties of the north and south polar region of Mars are presented. The maps complete the mapping of the entire planet. The maps for the north polar region were derived from Viking Infrared Thermal Mapper (IRTM) observations obtained from 10 Jun. to 30 Sep. 1978. This period corresponds to the early summer season in the north, when the north residual water ice cap was exposed, and the polar surface temperatures were near their maximum. The maps in the south were derived from observations obtained between 24 Aug. to 23 Sep. 1977. This period corresponds to the late summer season in the south, when the seasonal polar cap had retreated to close to its residual configuration, and the second global dust storm of 1977 had largely subsided. The major results concerning the following topics are summarized: (1) surface water ice; (2) polar dune material; and (3) dust deposits.

Paige, D. A.↗

NASA NTRS1991

Observations of the Earth in polarized light from the US Space Shuttle

During the four American Space Shuttle missions of year 1985, the crewmembers took pictures of the Earth in polarized light. Different problems were encountered in the quantitative use of the data: induced polarization by the shuttle window, lack of calibration correction of the window polarization and enveloped in flight calibration methods. The analysis of the selected data first confirmed the previous observation over snow and sand. A low polarization on these surfaces was observed. On the other hand, the measurements show the potentiability of the polarization for agricultural inventory. Contamination of the atmosphere is well characterized.

Roger, Jean-Claude↗

NASA NTRS1992

Sunlight penetration through the Martian polar caps: Effects on the thermal and frost budgets

An energy balance model of the seasonal polar caps on Mars is modified to include penetration of solar radiation into and through the ice. Penetration of solar radiation has no effect on subsurface temperature or total frost sublimation if seasonal ice overlies a dust surface. An effect is noted for seasonal ice which overlies the residual polar caps. For the case of an exposed water-ice residual polar cap, the temperature at depth is calculated to be up to several degrees warmer and the calculated lifetime of seasonal CO2 frost is slightly lower when penetration of sunlight is properly treated in the model. For the case of a residual polar cap which is perennially covered by CO2 frost, the calculated lifetime of seasonal CO2 frost is very slightly increased as a result of sunlight penetration through the ice. Hence, penetration of sunlight into the ice helps to stabilize the observed dichotomy in the residual polar caps on Mars, although it is a small effect.

Lindner, Bernhard Lee↗

NASA NTRS1991

On the elliptical polarization of Jupiter's decametric radio emission

The origin of the 100 percent elliptical polarization of Jupiter's decametric radio emission is investigated. The transfer of polarized radiation when coupling of the Stokes parameters is important is studied, and it is found, in agreement with earlier authors, that the density in and near the source region must be so low that the polarization remains fixed along the ray path. The polarization of the cyclotron maser radiation in these circumstances is determined, and it is found that the dispersion relation of the rarefied plasma composed of energetic, anisotropic electrons is like that in the vacuum. It is also found that the growth rate is sufficient to saturate the maser and account for the observed brightness temperature. Possible sources of plasma in and near the source region in Jupiter's inner, polar magnetosphere are considered.

Melrose, D. B.↗

NASA NTRS1991

Polarization of the impulsive signals observed in the nightside ionosphere of Venus

The impulsive plasma wave bursts detected by the Pioneer Venus Orbiter electric field detector in the nightside ionosphere of Venus have been attributed to atmospheric lightning. However, it has also been argued that the wave bursts are generated locally by plasma instabilities. The waves associated with local instabilities are most probably electrostatic in nature, while lightning-generated waves should be whistler mode waves, at least at the lowest frequencies. It is shown that for typical ionospheric parameters the whistler mode wave electric field should be polarized predominantly perpendicular to the ambient magnetic field. It is shown that the 100-Hz waves are polarized perpendicular to the ambient magnetic field provided the data are restricted to those intervals in which the magnetic field is sufficiently far from horizontal to allow vertical propagation within the whistler mode resonance cone. The 100-Hz waves detected outside of the resonance cone are polarized parallel to the magnetic field, as are the waves at higher frequency. The waves consequently fall into two classes: whistler mode waves which are most likely due to atmospheric lightning, and a mode that is polarized parallel to the ambient field. This latter mode may be analogous to the anomalous parallel polarized wave fields detected in the terrestrial ionosphere above thunderstorms.

Strangeway, R. J.↗

NASA NTRS1992

The complete polarization state of a storm of millisecond bursts from Jupiter

Normal bursts with right-hand (RH) elliptical polarization, millisec S-bursts with RH elliptical polarization, and S-bursts with left-hand (LH) elliptical polarization, are presently observed in an extended storm of decametric radiation from Jupiter's Io-related source, 'Io-B'. This radiation was 100 percent elliptically polarized at all frequencies in the 14-31 MHz range measured. For an 80-min period, there was a mixture of RH and LH elliptically polarized S bursts in the 14-20 MHz range. An examination of the origin of a Faraday-rotation difference between RH and LH elliptical bursts suggests that some Faraday rotation occurs in the Io torus; this was traversed more centrally by the LH bursts from the southern auroral zone than the HH bursts from the northern auroral zone.

Dulk, G. A.↗

NASA NTRS1991

The photoelectric effect from CsI by polarized soft X-rays

Studies of the polarization dependence of the photoelectric effect produced by soft X-rays from CsI indicate that the geometrical effects in these experiments can often mimic the polarization signature. This paper presents a detailed calculation of these geometrical effects that are produced when the X-ray beam is not precisely aligned on a rotatable plane photocathode. The experimentally observed geometrical effects were used to precisely determine the realignment of the incident beam of polarized X-rays on a rotatable photocathode. The results allow determinations of the true polarization dependence of the photoemission from CsI. It is shown that the photoelectric effect in CsI depends on the polarization state of the X-rays.

Shaw, Ping S.↗

NASA NTRS1992

Sunlight penetration through the Martian polar caps - Effects on the thermal and frost budgets

An energy balance model of the seasonal polar caps on Mars is modified to include penetration of solar radiation into and through the ice. Penetration of solar radiation has no effect on subsurface temperature or total frost sublimation if seasonal ice overlies a dust surface. An effect is noted for seasonal ice which overlies the residual polar caps. For the case of an exposed water-ice residual polar cap, the temperature at depth is calculated to be up to several degrees warmer, and the calculated lifetime of seasonal CO2 frost is slightly lower when penetration of sunlight is properly treated in the model. For the case of a residual polar cap which is perennially covered by CO2 frost, the calculated lifetime of seasonal CO2 frost is very slightly increased as a result of sunlight penetration through the ice. Hence, penetration of sunlight into the ice helps to stabilize the observed dichotomy in the residual polar caps on Mars, although it is a small effect.

Lindner, Bernhard L.↗

NASA NTRS1993

Device For Perception Of Polarization

Polarized image viewed through rotating polarizing filter appears to pulsate. Optical device enables human observer to perceive polarization of light. Used alone for viewing in real time and/or in conjunction with video or movie camera to record for subsequent detailed quantitative analysis of polarization in scene. Device used in remote sensing to classify portions of scenes according to polarization characteristics, to enhance viewing through atmosphere and oceans and to enhance contrasts. Used to monitor oilspill from air and detect changes in soil moisture and to map wetlands, among many other possible civilian and military applications.

Whitehead, Victor S.↗

NASA NTRS1992

Polarization effects and multipolarization SAR

Imaging radar polarimeters are usually implemented using a Synthetic Aperture Radar (SAR) approach to give a high resolution image in two dimensions: range and azimuth. For each pixel in the image a polarimetric SAR gives sufficient information to characterize the polarimetric scattering properties of the imaged area (or target) as seen by the radar. Using a polarimetric SAR system as opposed to a single-polarization SAR system provides significantly more information about the target scattering mechanisms and allows better discrimination between different types of surfaces. In these notes a brief overview of SAR polarimetry is offered. The notes are intended as a text to accompany a lecture on SAR polarimetry as part of an AGARD-NATO course. Covered in the notes are the following: the polarization properties of electromagnetic waves; the concepts of radar scattering and measuring radar backscatter with a SAR; polarization synthesis; scattering matrix, Stokes matrix, and covariance matrix representations of polarimetric SAR data; polarization signature plots; design and calibration of polarimetric SAR systems; polarization filtering for target detection; fitting a simple model to polarimetric SAR measurements of naturally occurring features; and supervised classification of polarimetric SAR data.

Freeman, Anthony↗

NASA NTRS1992

Polarization cancellation in the two-component winds from Wolf-Rayet stars

In this paper we explore the possibility that there can be at least partial cancellation of the equatorial disk polarization as a result of scattering from the electrons that are present in the strong polar wind of WR stars. In order to achieve the cancellation necessary to explain the wavelength-dependent polarization, the polar wind must have a mass-loss rate that is near the maximum that is supported by radiation-driven wind theory. In addition, we find that it is possible to derive important new information regarding the relative column masses of the polar and equatorial winds.

Taylor, M.↗

NASA NTRS1992

Dynamical polar wind and its response to kinetic ion heating

The effect of the kinetic ion heating of the polar wind on the dynamic expansion of the polar wind outflow is investigated by incorporating the kinetic ion heating effect into a time-dependent hydrodynamic polar wind model in which the polar wind O(+) and H(+) continuity and momentum equations are solved in a flux tube from ionospheric to magnetospheric altitudes. Two limiting cases were considered: (1) preferential O(+) escape and (2) preferential H(+) heating. It was found that ion heating does not have much effect on the escape of H(+) ions because of the limiting nature of the H(+) escape fluxes. However, O(+) heating can substantially increase the upward O(+) pressure gradient in the heating region, indicating that O(+) heating is a viable explanation for the unexpectedly large O(+) fluxes frequently observed in the polar magnetosphere.

Chen, Margaret W.↗

NASA NTRS1993

On the negative polarization of light scattered by subwavelength regolithic grains

Recent laboratory polarimetric measurements of light scattering by layers of alumina grains of different size are used to examine the relevance of the Wolff & Dollfus (1990) theory of negative polarization, which has been developed to describe light scattering by regolithic grains of arbitrary size. It is demonstrated that, while reproducing satisfactorily the main polarization characteristics of light scattering by grains much greater than the wavelength, this theory does not describe the negative polarization of light measured by Geake & Geake (1990) for subwavelength-sized grains. The smallest grains exhibit a polarization feature that may be called the 'polarization opposition effect'. This feature requires an alternative explanation and may be due to the so-called weak localization of photons in discrete random media.

Kolokolova, L. O.↗

NASA NTRS1992

Polarization sensitivity analysis of an earth remote sensing instrument - The MODIS-N phase B study

Polarization analysis software that employs Jones matrix formalism to calculate the polarization sensitivity of an instrument design was developed at Hughes Danbury Optical Systems. The code is capable of analyzing the full ray bundle at its angles of incidence for each optical surface. Input is based on the system ray trace and the thin film coating design at each surface. The MODIS-N (Moderate Resolution Imaging Spectrometer) system is used to demonstrate that it is possible to meet stringent requirements on polarization insensitivity associated with planned remote sensing instruments. Analysis indicates that a polarization sensitivity less than or equal to 2 percent was achieved in all desired spectral bands at all pointing angles, per specification. Polarization sensitivities were as high as 10 percent in similar remote sensing instruments.

Waluschka, E.↗