Showing papers on "Polarimetry published in 1977"

System and method of fluorescence polarimetry

Abstract: A system and method for measurement of the polarization of fluorescence A laser source provides a collimated linearly polarized beam of high intensity and small cross-section A relatively small number of optical components are employed to minimize spurious fluorescence and spurious polarization which usually occurs from most optical materials A photodetector provides an electrical signal in response to and representative of fluorescence polarization and is processed to directly produce first and second signals representing the difference and sum components of the polarization equation, the ratio of these components being directly provided without need for division computation

6. The Nature of Asteroid Surfaces, from Optical Polarimetry

Abstract: Telescopic observations of the polarization of light by asteroids are interpreted on the basis of a systematic polarimetric analysis of terrestrial, meteoritic and lunar samples. Laboratory measurements were made using samples with different surface textures, and scanning electron microscope pictures were used to investigate the influence of microtexture and crystalline structure. It is demonstrated that asteioid surfaces do not accumulate thick regolithic layers of micro-fragments, as do the Moon and Mercury. This is because the majority of debris ejected by impacts are lost, due to the low gravitational escape velocity from these bodies. However, asteroids are not bare rocks, but are coated with a thin layer of adhesive debris. This coating apparently has the composition of the body itself. The fact that there is no indication of significant maturation by space weathering suggests that the dust which coats the surface of asteroids is frequently replaced by further impacts. Asteroids may be classified polarimetrically in several groups: those in group C are made of very dark material and behave like carbonaceous chondrites, or very dark Fe-rich basalts; Those in group S correspond to silicates and stony meteorites. A third group represented by Asteroid 21 Lutetia and 16 Psyche may be metallic.

Polarimetry of satellite surfaces

Abstract: Available polarization observations of the satellites are reviewed, and the question of what information about satellite surfaces such observations contain is discussed critically. For satellites with negligible atmospheres, polarization measurements should provide useful information on surface texture and on the opacity of the surface materials. However, they are unlikely to yield specific compositional information. For Titan, the only satellite known to have an extensive atmosphere, polarimetry indicates the presence of optically thick clouds; it should be possible to deduce the cloud particle characteristics from such data, especially if more extensive observations, covering the full range of available phase angles and wavelengths, are obtained.

A Spectrum Scanning Stokes Polarimeter

Abstract: A photoelectric polarimeter for measuring solar spectral line profiles in all four Stokes parameters has been built and operates on a 40 cm coronagraph in a joint project with Sacramento Peak Observatory. A description of the optical and electronic systems and the calibration scheme is presented. Performance parameters determined from observations are also given. The polarimeter package consisting of a pair of KDP's, a quarter wave plate, and a polarizing beam splitter is located at the prime focus of the coronograph. Modulation of the KDP's encodes polarization information into intensity signals that are electronically detected. The scanning of the spectrum, accomplished by rotating the grating, permits Stokes line profiles to be recorded on magnetic tape for processing. The instrument can be used to scan any line from 3900 to 7000A with a spectral resolution of .01A. Polarizations as small as .001 percent are detectable. The polarimeter and observing system are computer controlled.

Optical polarimetry of particulate surfaces

Abstract: Reflection polarimetry is a remote-sensing tool sensitive to the refractive index and microtexture of solid surfaces. Mechanisms producing linear polarization within a rough, porous, or particulate surface are discussed, and laboratory techniques for precise measurements are described in some detail. Polarimetry of atmosphereless solar-system bodies provides valuable indications of albedo for objects too small and distant for direct diameter determinations, and reveals that even quite small asteroids and satellites have particulate surfaces

Polarization-Dependent Light-Scattering Measurements Using An Electro-Optical Modulator-Based Instrument

Abstract: We have developed an instrument which permits the direct measurement of all sixteen ele-ments of the 4 x 4 phase matrix. This is accomplished using four electro -optic modulatorsto modulate the polarization of the incident and scattered light. Synchronous detectionis then used to measure each of the sixteen individual matrix elements. The instrument andbrief theory of its operation will be discussed, along with possible applications.IntroductionThe determination of the complete light scattering properties, including all polariza-tion effects, of a light scattering medium has received little experimental attention.We have knowledge of only three instruments, other than our own, which have been construc-ted for this purpose. Of these, only ours makes use of polarization modulation. The other three use conventional polarizers and quarter -wave plates to effect the measurements.It is this difference which makes our instrument superior.To facilitate the discussion of polarized light, it is convenient to use the Stokes

High-Resolution Spectropolarimetry: A New Atmospheric Remote Sensor

Abstract: Polarimetry within a spectral line or band is proposed as a new atmospheric remote sensor, particularly for clouds and hazes. The limitations of conventional absorption/emission spectroscopy and photopolarimetry are discussed. The selective formation and behavior of intensity and polarization lines is analyzed under a variety of atmospheric and scattering conditions. The technique, limitations and advantages of Fourier Transform Spectroscopy are reviewed as a prelude to the proposed approach. Experimental results obtained at the telescope for the planet Venus are presented as evidence for the existence, behavior and effects of line polarization. Fourier Transform Spectropolarimetry provides means for separating the effects of scattering from those of absorption, probing the internal properties of clouds and hazes, and studying the detailed wavelength dependence of polarization with variable spectral resolutions from low to high.

Polarimeter measures sea state characteristics using emitted infrared radiation

Abstract: An infrared polarimeter, capable of operating between 1 and 12 micrometers wavelength has been used to measure the polarization of emitted radiation from the sea The observed polarization at 106 micrometers from a smooth sea was found to be positive, indicating the dominance of reflected infrared sky radiation over the emitted With the appearance of waves, the percent polarization increased, as expected, for a zenith angle well above the Brewster angle for water This is qualitatively in accordance with a model presented to explain the behavior Initial analyses indicate that the polarized components of the sea's emitted and reflected radiation are affected by type and direction of waves, angle of viewing, and foam The effects of variations in these parameters require further delineation The infrared polarimetric technique appears to be a novel new passive method for remote monitoring of waves

Photometry and Polarimetry of the Solar Corona of 30 June 1973

Abstract: The High Altitude Observatory's coronal camera successfully photographed the 30 June 1973 eclipse (from the National Science Foundation Eclipse Expedition Camp at Loiyengalani, Kenya) for the purpose of acquiring white light photometry, polarization, and high resolution, radially-graded filtered pictures of the inner corona. The method of reduction, its strengths and weaknesses, and suggestions for improvements are discussed. A comparison of our coronal camera observations is made with other ground-based observations of Koutchmy, Hansen, and Saito (and Moriyama), the rocket observations of Koomen, the aircraft observations of Keller and the ATM Skylab observations of Poland and Munro. Generally excellent agreement in white light photometry and polarimetry of the North Polar coronal region is most encouraging, while the discrepancies in other regions should provide insights into instrumental limitations or directions for future refinements.