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NASA NTRS1992

Extrapolation procedures in Mott electron polarimetry

In standard Mott electron polarimetry using thin gold film targets, extrapolation procedures must be used to reduce the experimentally measured asymmetries A to the values they would have for scattering from single atoms. These extrapolations involve the dependent of A on either the gold film thickness or the maximum detected electron energy loss in the target. A concentric cylindrical-electrode Mott polarimeter, has been used to study and compare these two types of extrapolations over the electron energy range 20-100 keV. The potential systematic errors which can result from such procedures are analyzed in detail, particularly with regard to the use of various fitting functions in thickness extrapolations, and the failure of perfect energy-loss discrimination to yield accurate polarizations when thick foils are used.

Gay, T. J.↗
NASA NTRS1991

Imaging radar polarimetry - A review

The authors present a tutorial review of the broad sweep of topics relating to imaging radar polarimetry, ranging from mathematical foundations to hardware and from implementation approaches to signal processing and calibration. The authors examine current developments in sensor technology and implementation for recording polarimetric measurements, and describe techniques and areas of application for this form of remotely sensed data. Those aspects of ground signal processing and calibration peculiar to the polarimetric signals are addressed. Several of the currently operating instruments and some of the implementations planned for future use are discussed.

Zebker, Howard A.↗
NASA NTRS1992

High-resolution space-shuttle polarimetry for farm crop classification

A significant advance is reported in imaging the polarimetry of a terrestrial area of earth located along the Mississippi River near New Madrid, Missouri. Color imagery was obtained with twin Hasselblad cameras with mutually perpendicular polarization analyzers. Digitization of the imagery in three colors (red, green, and blue) was accomplished at the Johnson Space Center Video Digital Analysis System Laboratory, Houston, Texas. A ground resolution of 80-90 m was achieved in the high-resolution imagery. Percent polarization was superior to photometry for recognition and characterization of farm crops such as rice, milo, cotton, and soybeans and of fallow areas. Statistical analyses of the percent-polarization data permit a unique classification of crops. Atmospheric effects may be deduced. Space-shuttle window distortion and viewing angle-sun geometry must be taken into account in analyzing the data.

Egan, Walter G.↗
NASA NTRS1993

Ultraviolet polarimetry and spectroscopy of the BL Lacertae object PKS 2155-304

HST and Faint Object Spectrograph spectropolarimetry is presented for the BL Lac object PKS 2155-304; attention is given to the wavelength dependence of the UV linear polarization in a BL Lac object. The UV polarimetry yields evidence that the UV polarized flux is generated by the synchrotron mechanism responsible for optical polarization. Both the UV and optical emission are produced in the same region of the source.

Allen, Richard G.↗
NASA NTRS1994

COBE DIRBE near-infrared polarimetry of the zodiacal light: Initial results

This Letter describes near-infrared polarimetry of the zodiacal light at 2.2 micrometers, measured with the Diffuse Infrared Background Experiment (DIRBE) aboard the Cosmic Background Explorer (COBE) spacecraft. The polarization is due to scattering of sunlight. The polarization vector is perpendicular to the scattering plane, and its observed amplitude on the ecliptic equator at an elongation of 90 deg and ecliptic longitude of 10 deg declines from 12.0 +/- 0.4% at 1.25 micrometers to 8.0 +/- 0.6% at 3.5 micrometers (cf. 16% in the visible); the principal source of uncertainty is photometric noise due to stars. The observed near-infrared colors at this location are redder than Solar, but at 3.5 micrometers this is due at least in part to the thermal emission contribution from the interplanetary dust. Mie theory calculations show that both polarizations and colors are important in constraining models of interplanetary dust.

Berriman, G. B.↗
NASA NTRS1994

OH/IR stars near the Galactic Center: Pulsation periods, luminosities, and polarimetry

17 stars in the direction of the Galactic Center, 15 of which are OH/IR stars, have been monitored at infrared wavelengths over a period of nearly eight years. Pulsation periods, bolometric luminosities, and light curves for 14 OH/IR stars are presented. The Galactic Center OH/IR stars range in luminosity between M(sub Bol) = -4.5 to M(sub Bol) = -6, implying main sequence progenitors with masses less than 3 solar mass. When compared to optically visible long period variables in the Large Magellanic Cloud (LMC) with similar bolometric luminosities, the Galactic Center OH/IR stars have pulsation periods on average 30% longer. This shift to longer periods is consistent with the current picture of late asymptotic giant branch evolution, placing the OH/IR stars in a phase immediately following the optically visible Mira variable phase during which the star dramatically increases its mass loss rate, becoming invisible at optical wavelength. Infrared polarimetry of 11 of the stars is also presented. The polarization for all of the stars is consistent with purely interstellar polarization, with little evidence for a significant intrinsic component. When compared to OH/IR stars in the galactic plane, the Galactic Center OH/IR stars appear similar in photometric characteristics, except none of the Galactic Center OH/IR stars shows the extremely thick dust shells or very high intrinsic polarization found in the more extreme galactic plane OH/IR stars.

Jones, Terry Jay↗
NASA NTRS1996

Wideband Interferometric Sensing and Imaging Polarimetry

Wideband Interferometric Sensing and Imaging Polarimetry (WISIP) has become an important, indispensible tool in wide area military surveillance and global environmental monitoring of the terrestrial and planetary covers. It enables dynamic, real time optimal feature extraction of significant characteristics of desirable targets and/or target sections with simultaneous suppression of undesirable background clutter and propagation path speckle at hitherto unknown clarity and never before achieved quality. WISIP may be adopted to the detection, recognition, and identification (DRI) of any stationary, moving or vibrating targets or distributed scatterer segments versus arbitrary stationary, dynamical changing and/or moving geo-physical/ecological environments, provided the instantaneous 2x2 phasor and 4x4 power density matrices for forward propagation/backward scattering, respectively, can be measured with sufficient accuracy. For example, the DRI of stealthy, dynamically moving inhomogeneous volumetric scatter environments such as precipitation scatter, the ocean/sea/lake surface boundary layers, the littoral coastal surf zones, pack ice and snow or vegetative canopies, dry sands and soils, etc. can now be successfully realized. A comprehensive overview is presented on how these modern high resolution/precision, complete polarimetric co-registered signature sensing and imaging techniques, complemented by full integration of novel navigational electronic tools, such as DGPS, will advance electromagnetic vector wave sensing and imaging towards the limits of physical realization. Various examples utilizing the most recent image data take sets of airborne, space shuttle, and satellite imaging systems demonstrate the utility of WISIP.

Verdi, James Salvatore↗
NASA NTRS1999

Far-Infrared Polarimetry of Galactic Clouds from the Kuiper Airborne Observatory

In this paper we present a complete summary of the data obtained with the far-infrared polarimeter, Stokes, in flights of the Kuiper Airborne Observatory. We have observed 12 Galactic clouds and have made over 1100 individual measurements at 100 micrometer and 60 micrometer. The median P for all of the 60 micrometer and 100 micrometer measurements is 3.6% and 2.6% respectively. We also present flux maps obtained simultaneously with the polarimetry.

Dotson, Jessie L.↗
NASA NTRS2002

Infrared Imaging Polarimetry of Comets

This paper presents a final report on the observation of comets using infrared imaging polarimetry. A theoretical program to model the observations is also presented.

Jones, Terry Jay↗
NASA NTRS2003

High-Sensitivity X-ray Polarimetry with Amorphous Silicon Active-Matrix Pixel Proportional Counters

Photoelectric X-ray polarimeters based on pixel micropattern gas detectors (MPGDs) offer order-of-magnitude improvement in sensitivity over more traditional techniques based on X-ray scattering. This new technique places some of the most interesting astronomical observations within reach of even a small, dedicated mission. The most sensitive instrument would be a photoelectric polarimeter at the focus of 2 a very large mirror, such as the planned XEUS. Our efforts are focused on a smaller pathfinder mission, which would achieve its greatest sensitivity with large-area, low-background, collimated polarimeters. We have recently demonstrated a MPGD polarimeter using amorphous silicon thin-film transistor (TFT) readout suitable for the focal plane of an X-ray telescope. All the technologies used in the demonstration polarimeter are scalable to the areas required for a high-sensitivity collimated polarimeter. Leywords: X-ray polarimetry, particle tracking, proportional counter, GEM, pixel readout

Black, J. K.↗
NASA NTRS2004

The X-ray Polarimetry Explorer (XPE)

We present details of a Thomson scattering polarimeter suitable for a small-explorer- class mission. Termed XPE, for X-Ray Polarimetry Explorer, the instrument consists of a beryllium scattering cone surrounded by an annular multiwire proportional counter which registers the energy and position of scattered source photons. The polarimeter is sensitive over an energy range of 7-27 keV and will achieve 3% minimum detectable polarization of Her X-1 in a 1/2-day observation, and cover a 30-target core observation program, at the same sensitivity level, in approximately 8 months.

Ramsey, Brian↗
NASA NTRS1993

Imaging Radar Polarimetry

In this paper, we review the state of the art in imaging radar polarimetry, examine current developments in sensor technology and implementation for recording polarimetric measurements, and describe techniques and areas of application for the new remote sensing data.

radars fixed-polarization antenna digital data rec↗
NASA NTRS2008

An Imaging X-Ray Polarimetry Mission

Technical progress both in x-ray optics and in polarization-sensitive x-ray detectors, which our groups have pioneered, enables a scientifically powerful - yet inexpensive - dedicated mission for imaging x-ray polarimetry. Such a mission is sufficiently sensitive to measure x-ray (linear) polarization for a broad range of cosmic sources --- particularly those involving neutron stars, stellar black holes, and supermassive black holes (active galactic nuclei). We describe the technical elements, discuss a mission concept, and synopsiz:e the important physical and astrophysical questions such as mission would address.

Weisskopf, Martin C.↗
NASA NTRS2008

An Imaging X-Ray Polarimetry Mission

Technical progress both in x-ray optics and in polarization-sensitive x-ray detectors, which our groups have pioneered, enables a scientifically powerful---yet inexpensive---dedicated mission for imaging x-ray polarimetry. Such a mission is sufficiently sensitive to measure x-ray (linear) polarization for a broad range of cosmic sources --particularly those involving neutron stars, stellar black holes, and supermassive black holes (active galactic nuclei). We describe the technical elements, discuss a mission concept, and synopsize the important physical and astrophysical questions such a mission would address.

Weisskopf, Martin C.↗
NASA NTRS2008

Diagnosing the Structure of the HD 163296 Protoplanetary Disk Via Coronagraphic Imaging Polarimetry

Coronagraphic imaging polarimetry is a high contrast imaging technique which can diagnose both the spatial distribution and size distribution of dust grains which comprise primordial protoplanetary disks. It can therefore be a useful tool to test our understanding of how the structure of young disks evolves through the era of gas giant planet formation. We report our initial analysis of the H-band polarized and total intensity of the nearby Herbig Ae star HD 163296, and characterize the morphology of the scattered light disk in the context of previous optical HST coronagraphic imagery. Our observations were obtained as part of a multi-epoch campaign designed to diagnose and correlate the behavior of the inner and outer regions of select protoplanetary disks. This campaign will help test recent suggestions (Sitko et al. 2008; Wisniewski et al. 2008) that that HD 163296 dis experiences the novel phenomenon of time-variable self-shadowing, whereby occasional changes in the scale height of the inner disk wall induces changes in the illumination of the outer disk.

Kowalski, Adam F.↗
NASA NTRS2009

X-Ray Polarimetry: Historical Remarks and Other Considerations

We briefly discuss the history of X-ray polarimetry for astronomical applications including a guide to the appropriate statistics. We also provide an introduction to some of the new techniques discussed in more detail elsewhere in these proceedings. We conclude our discussion with our concerns over adequate ground calibration, especially with respect to unpolarized beams, and at the system level.

Weisskopf, Martin C.↗
NASA NTRS2010

Active Galaxy Unification in the Era of X-Ray Polarimetry

Active galactic nuclei (AGNs), Seyfert galaxies, and quasars are powered by luminous accretion and often accompanied by winds that are powerful enough to affect the AGN mass budget, and whose observational appearance bears an imprint of processes that are happening within the central parsec around the black hole (BH). One example of such a wind is the partially ionized gas responsible for X-ray and UV absorption (warm absorbers). Here, we show that such gas will have a distinct signature when viewed in polarized X-rays. Observations of such polarization can test models for the geometry of the flow and the gas responsible for launching and collimating it. We present calculations that show that the polarization depends on the hydrodynamics of the flow, the quantum mechanics of resonance-line scattering, and the transfer of polarized X-ray light in the highly ionized moving gas. The results emphasize the three-dimensional nature of the wind for modeling spectra. We show that the polarization in the 0.1-10 keV energy range is dominated by the effects of resonance lines. We predict a 5%-25% X-ray polarization signature of type-2 objects in this energy range. These results are generalized to flows that originate from a cold torus-like structure, located approximately 1 pc from the BH, which wraps the BH and is ultimately responsible for the apparent dichotomy between type 1 and type 2 AGNs. Such signals will be detectable by future dedicated X-ray polarimetry space missions, such as the NASA Gravity and Extreme Magnetism Small Explorer SMEX, "GEMS" Swank et al. (2008).

Dorodnitsyn, A.↗