Showing papers on "Polarimetry published in 1990"

Radar polarimetry for geoscience applications

Abstract: The present volume on radar polarimetry for geoscience applications discusses wave properties and polarization, scattering matrix representation for simple targets, scattering models for point and distributed targets, polarimetric scatterometer systems and measurements, polarimetric radar system design, and polarimetric SAR applications. Attention is given to plane waves in a lossless homogeneous medium-wave polarization, polarization synthesis and response, and coordinate system transformations. Topics addressed include high- and low-frequency scattering, rough-surface scattering models, radiative transfer theory and deficiencies thereof, solutions for the radiative transfer equation, and a radiative transfer model for a forest canopy. Also discussed are network analyzer-based polarimetric scatterometers, calibration of polarimetric scatterometers, synthesized polarization response of distributed targets, and measurement of the propagation parameters of a forest canopy.

Radar polarimetry for geoscience applications

Abstract: The present volume on radar polarimetry for geoscience applications discusses wave properties and polarization, scattering matrix representation for simple targets, scattering models for point and distributed targets, polarimetric scatterometer systems and measurements, polarimetric radar system design, and polarimetric SAR applications. Attention is given to plane waves in a lossless homogeneous medium-wave polarization, polarization synthesis and response, and coordinate system transformations. Topics addressed include high- and low-frequency scattering, rough-surface scattering models, radiative transfer theory and deficiencies thereof, solutions for the radiative transfer equation, and a radiative transfer model for a forest canopy. Also discussed are network analyzer-based polarimetric scatterometers, calibration of polarimetric scatterometers, synthesized polarization response of distributed targets, and measurement of the propagation parameters of a forest canopy.

Calibration of polarimetric radar systems with good polarization isolation

Abstract: A practical technique is proposed for calibrating single-antenna polarimetric radar systems using a metal sphere plus any second target with a strong cross-polarized radar cross section. This technique assumes perfect isolation between antenna ports. It is shown that all magnitudes and phases (relative to one of the like-polarized linear polarization configurations) of the radar transfer function can be calibrated without knowledge of the scattering matrix of the second target. Comparison of the values measured (using this calibration technique) for a tilted cylinder in the X-band with theoretical values shows agreement within +or-0.3 dB in magnitude and +or-5 degrees in phase. The radar overall cross-polarization isolation was 25 dB. The technique is particularly useful for calibrating a radar under field conditions, because it does not require the careful alignment of calibration targets. >

Polarimetric SAR calibration experiment using active radar calibrators

Abstract: Active radar calibrators are used to derive both the amplitude and phase characteristics of a multichannel polarimetric synthetic aperture radar (SAR) from the complex image data. Results are presented from an experiment carried out using the NASA/JPL DC-8 aircraft SAR over a calibration site at Goldstone, California. As part of the experiment, polarimetric active radar calibrators (PARCs) with adjustable polarization signatures were deployed. Experimental results demonstrate that the PARCs can be used to calibrate polarimetric SAR images successfully. Restrictions on the application of the PARC calibration procedure are discussed. >

A convenient technique for polarimetric calibration of single-antenna radar systems

Abstract: A practical technique for calibrating single-antenna polarimetric radar systems is introduced. This technique requires only a single calibration target such as a conducting sphere or a trihedral corner reflector to calibrate the radar system, both in amplitude and phase, for all linear polarization configurations. By using a metal sphere, which is orientation independent, error in calibration measurement is minimized while simultaneously calibrating the crosspolarization channels. The antenna system and two orthogonal channels (in free space) are modeled as a four-port passive network. Upon using the reciprocity relations for the passive network and assuming the crosscoupling terms of the antenna to be equal, the crosstalk factors of the antenna system and the transmit and receive channel imbalances can be obtained from measurement of the backscatter from a metal sphere. For an X-band radar system with cross polarization isolation of 25 dB, comparison of values measured for a sphere and a cylinder with theoretical values shows agreement within 0.4 dB in magnitude and 5 degrees in phase. An effective polarization isolation of 50 dB is achieved using this calibration technique. >

Phase calibration of imaging radar polarimeter Stokes matrices

Abstract: It is shown that the Stokes matrices measured by an imaging radar polarimeter provide enough information for the accurate phase calibration of the observed polarimetric characteristics of a surface. This is important because it allows the data to be reduced in volume in an operational synthetic aperture radar correlator with no prior knowledge of the conditions at the surface, and the end user can later select the particular region where he or she is comfortable with making an assumption regarding the relative phases of the hh and nu nu signals. No ground calibration equipment is necessary, as all important parameters are derived from the data themselves. >

Motional Stark effect polarimetry for a current profile diagnostic in DIII‐D

Abstract: Motional Stark effect produces large net linear polarization of Hα emission from neutral beams in tokamaks. Measurement of the polarization direction permits determination of the local magnetic field pitch angle. Design of a single point, spatially scannable, high‐sensitivity polarimeter installed on DIII‐D is described. Excellent signal‐to‐noise ratio with good temporal and spatial resolution was obtained in preliminary measurements of magnetic field pitch angle.

Polarization effects of seawater and underwater targets.

Abstract: In underwater optical imaging using pulsed laser radiation the vector nature of the electromagnetic wave can be used to produce polarization contrast. We have analyzed different polarimetric transformations of light pulses through seawater on immersed targets and defined optimum conditions for using polarization parameters.

Linear polarization of radiation from oblique and conical shocks

Abstract: A simple model for synchrotron radio emission from oblique and conical shock waves is described, and the polarization properties are examined, assuming that the magnetic field in plasma upstream from the shock is random in direction. Such structures have been suggested as the origin of radio emission from the knots in radio jets that emerge from active nuclei, particularly on VLBI scales. It is found that conical shock waves in jets of circular cross section can yield polarized radiation with electric vector either parallel or perpendicular to the jet axis. The results provide insight into the extent to which conical shock waves might account for the polarization structures of jets in BL Lac objects and quasars that have been revealed by recent VLBI polarimetry. 13 refs.

Optimal Processing of Polarimetric Synthetic-Aperture Radar Imagery

Abstract: The Advanced Detection Technology Sensor can detect, discriminate, and classify stationary ground targets—during the day or night—even through cloud cover, fog, smoke, dust, or rain. The sensor is a coherent, fully polarimetric, 35-GHz syntheticaperture radar (SAR) with a resolution of 1 ft × 1 ft. And, to minimize SAR speckle while preserving image resolution, it uses the polarimetric whitening filter, our recently developed method for processing fully polarimetric data into SAR imagery. The Advanced Detection Technology Sensor (ADTS) is a fully polarimetric, 35-GHz synthetic-aperture radar. The polarimetric capability of the radar is used to enhance the quality of the imagery taken from a small aircraft; the synthetic aperture permits data to be processed to a resolution of 1 ft by 1 ft at a slant range of 7 km. The sensor was developed to provide a high-quality database of clutter and targetin-clutter imagery, and to perform stationary-target detection, discrimination, and

Digital array scanned interferometers for astronomy

Abstract: Investigations are reported of digital array scanned interferometers (DASI) with silicon CCD array detectors to define the operational capabilities of a mapping (polarimetric) spectrometer for astronomical applications based on these instruments. For spectral mapping, spatially resolved spectra using a cylindrical lens to image in the interferometers's redundant coordinate are given. The signal-to-noise characteristics of the Fourier transformed data are demonstrated with regard to the effects of a rectangular sampling function, spectral multiplexing and the pixel-to-pixel variation of the CCD array. These data indicate that DASIs can offer simple, versatile (polarization) mapping spectrometers suitable for spectral mapping observations from the ultraviolet to the infrared of extended sources at variable spatial resolution, particularly where long term stable operation is essential, as for spacecraft instruments.

A polarimetric spectral imager using acousto-optic tunable filters

Abstract: We report laboratory and telescopic observations with a polarimetric spectral imager based on an acousto-optic tunable filter (AOTF) where we demonstrate simultaneous acquisition of orthogonally polarized images at a spectral resolving power on the order of 103 and at a Rayleigh criterion spatial resolution of 100 line pairs per mm. This matches the spatial resolution of most digital arrays. An AOTF is shown to be usable as a fast shutter with a contrast of over 104 on a sub-millisecond time scale while providing an high transmittance of about 75% (both polarizations summed) when illuminated by white light. The polarization contrast between the orthogonally polarized images exceeds 104 across the field of view, permitting accurate measurement of the polarization parameters of incident light. These characteristics are now being used in a program of high spatial resolution imaging in narrow spectral bands. Some peculiarities and limitations of AOTFs are indicated.

Polarization Variability among Wolf-Rayet Stars. VI. Linear Polarimetry of the Eclipsing Binary V444 Cygni

Abstract: Precision broad-band blue light monitoring in linear polarization of the bright Cygnus W-R + O system V444 Cyg is reported. Analysis of the data yields an orbital inclination i = 78.5 deg, in good agreement with previous estimates based on polarimetry and on the analysis of light curves. In addition, V444 Cyg shows rapid polarimetric modulation around phase 0.5, when the O star companion eclipses the scattering electrons located primarily in the dense inner W-R wind. Simple modeling of the polarization eclipse based on a spherical electron envelope around the W-R star yields a satisfactory fit to the data. This model also supports the small value of the W-R core radius previously proposed by other authors. 35 refs.

Simultaneous scattering matrix measurement through signal coding

Abstract: A method making use of signal coding for simultaneous measurement of all four elements of a target scattering matrix with a polarimetric radar is studied. The method is based on a simultaneous transmission of two orthogonal signals on two orthogonal polarization channels. The four elements of the scattering matrix are retrieved on reception by correlating the signal on each polarization channel with both orthogonal signals. Although the method increases the radar system complexity, it potentially overcomes the limitations of the measurement accuracy introduced by the fast polarization switch and may also improve both polarization and Doppler processing of radar signals. >

On the performance of polarimetric target detection algorithms

Abstract: The performance of six polarimetric target detection algorithms is analyzed. The detection performance of the optimal polarimetric detector (OPD), the identity-likelihood-ratio-test (ILRT), the polarimetric whitening filter (PWF), the single-polarimetric-channel detector, the span detector, and the power maximization synthesis (PMS) detector is compared. Results for both probabilistic and deterministic targets in the presence of complex-Gaussian clutter are presented. The results of these studies indicate that the PWF and the ILRT typically achieve near optimal performance. Each remaining detection algorithm typically yields performance that is degraded compared to the performance of the OPD, the PWF, and the ILRT. >

A state-of-the-art review in radar polarimetry and its applications in remote sensing

Abstract: The authors assess the state of the art, focusing on their own contributions. Covered areas are the electromagnetic inverse problem in radar polarimetry, coherent polarization radar theory, partially coherent polarization radar theory, vector (polarization) inverse scattering approaches, the polarimetric matched filter approach, polarimetric Doppler radar applications in meteorology and oceanography, and image fidelity in microwave vector diffraction tomographic imaging. >

Multiple scattering effects on the transmission and reflection of millimeter pulse waves in rain

Abstract: Numerical solutions of the vector two-frequency radiative transfer equation are obtained to investigate the effects of multiple scattering on pulse propagation in rain. Only the case of circularly polarized incident wave is treated. First, the shape and magnitude of transmitted incoherent pulses in co- and cross-polarized channels are compared with those of the incident pulses, and the effect of multiple scattering on communication quality is discussed. Next, the shape and magnitude of the reflected pulses in the main polarization channel are compared with those calculated by the conventional radar equation, and the difference of the two results is examined. In backward scattering, the radar returns of spherical raindrops in the cross-polarized channel given by the multiple scattering calculations are often comparable to those obtained by the first-order calculations for Pruppacher-Pitter-shaped distorted raindrops. The multiple scattering effect on the polarimetric interpretation of cross-polarized radar returns from distorted raindrops is discussed.

Millipol, a millimeter/submillimeter wavelength polarimeter: instrument, operation, and calibration

Abstract: An instrument capable of measuring the polarization characteristics of weakly polarized, cold dust at millimeter and submillimeter wavelengths is presented in detail. The operation and calibration of this polarimeter at a wavelength of 1300 microns, configured for the NRAO 12-meter telescope, are discussed. Deep observations of Jupiter using this instrument revealed a main-beam instrumental polarization at, or below, the 0.2 percent level. Lunar limb observations revealed a sidelobe polarization sensitivity, in the range 0.25 percent - 1.0 percent. Further, through these efforts the nonthermal polarized flux from Jupiter at a level of about 0.04 percent of the thermal flux has been detected. Astronomical polarization measurements to 0.03 percent are possible, limited by the uncertainties in the instrumental polarization. This instrument has been primarily employed to measure and map magnetic-field directions in the very optically opaque cores of massive molecular clouds.

The Stellar X-ray Polarimeter - A focal plane polarimeter for the Spectrum X-Gamma mission

Abstract: This paper describes an X-ray polarimeter that will be flown on the Spectrum X-Gamma mission. The instrument exploits three distinct physical processes to measure polarization: Bragg reflection from a graphite crystal, Thomson scattering from a metallic lithium target, and photoemission from a cesium iodide photocathode. These three methods allow polarization measurements over an energy band from 0.3 to 12 keV. The polarimeter will make possible sensitive measurements of several hundred known X-ray sources. X-ray polarization measurements will make it possible to constrain the geometry of gas flow in X-ray binaries, identify nonthermal emission in supernova remnants, test current models for X-ray emission in radio pulsars, determine the radiation mechanisms in active galactic nuclei, and search for inertial frame dragging (Lense-Thirring effect) around the putative black hole in Cygnus X-1.

Acousto-optic spectrometer/polarimeter

Abstract: An acousto-optic spectrometer/polarimeter for analyzing an incident broad-band beam including an acousto-optic tunable filter (AOTF) for separating the incident broad-band beam into a diffracted extraordinary narrow-band beam, a diffracted ordinary narrow-band beam, and at least one undiffracted broad-band beam; first, second and third detectors respectively positioned to respectfully receive at least a portion of the diffracted extraordinary narrow-band beam, the diffracted ordinary narrow broad-band beam and the at least one undiffracted broad-band beam, and to respectively provide first, second and third signals based thereon; a subtracter for providing a polarimeter output by taking the difference between the first and the second signals; and an adder for providing a spectrometer output by adding the first and the second signals. The acousto-optic spectrometer/polarimeter according to the present invention allows broad-band imaging, spectroscopy and polarimetry to be performed simultaneously and through the same optical aperture.

A polarimetric radar calibration technique with insensitivity to target orientation

Abstract: A convenient polarimetric radar calibration technique is presented and used to calibrate an X band polarimetric radar The technique uses a distortion matrix model for the errors introduced by the transmitter and receiver, and it is applicable to any polarimetric radar system where the concept of an invariant distortion matrix is valid A sphere and two arbitrary passive targets are used to calibrate the radar with respect to the unknown polarization transmitted when the v-polarized channel is energized The unknown transmitted polarization is then recovered by measuring any nondepolarizing target Because knowledge of the scattering matrices for the two arbitrary targets is not required, the technique is insensitive to errors in the orientation of calibration targets Experimental results are presented, and they indicate magnitude and relative phase measurement errors of less than 02 dB and 2°, respectively

Optical polarimetric sensor for blood glucose measurement

Abstract: Preliminary results for an optical polarimetry system which could be used as a sensor to monitor in vivo glucose concentrations are presented. Polarization retaining optical fibers make it feasible to transport coherent light to and from the sensing site. A bidirectional technique increases the sensitivity of the system for a given path length. Preliminary in vitro results show the ability of the system to monitor glucose levels. The first result shows the linearity of the polarization rotation of light with blood glucose levels. In a second experiment, it was verified that the polarization preserving fiber allows for the transference of linear polarized light with enough intensity, after coupling, to be detected at the output. The bidirectional technique for increasing the sensitivity is verified. >

Determination of the characteristic polarization states of the target scattering matrix [S(AB)] for the coherent, monostatic, and reciprocal propagation space

Abstract: A problem originating in radar polarimetry is considered for which the radar target is to be characterized by its coherent polarization state properties, given complete coherent backscattering scattering matrix data sets at one frequency and for one target aspect angle. For the monostatic reciprocal case, it is shown that there exist in total five pairs of characteristic polarization states. These include the orthogonal cross-polarization null and copolarization maximum state pairs and the orthogonal cross polarization maximum state pairs, as well as a newly identified pair, the orthogonal cross-polarization saddle point extrema which are normal to the plane spanned by the other four pairs. With this complete and unique mathematical description of Huynen's polarization fork concept, it is now possible to study the polarimetric radar target optimization problem more rigorously.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Incorporation of polarimetric radar images into multisensor data sets

Abstract: A technique is presented for registering polarimetric synthetic aperture radar (SAR) data to other aircraft and spaceborne data sets. Resampling is done on the full Stokes matrix, allowing full polarization synthesis on the coregistered data set. Analysis of data acquired over Pisgah Crater in the Mojave Desert, CA, as part of the Mojave Field Experiment shows that the resampling does not seriously affect the pedestal heights of polarization signatures or estimates of RMS heights for smooth to moderately rough surfaces. >

Applications and Limitations of Polarimetry

Abstract: Applications of optical polarimetry are reviewed, and limitations of polarimetry are discussed in the context of information content and error management of polarimetry applications Polarimetric measurement techniques are categorized as spectral or nonspectral, active or passive, monostatic or bistatic, and whether or not measurements of the complete Stokes vector or Mueller matrix are made Specific examples from the literature of passive polarimetry, laser polarimetry, and spectropolarimetry are discussed© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering Downloading of the abstract is permitted for personal use only

Basic equations of radar polarimetry and its solutions: the characteristic radar-polarization states for the coherent and partially polarized cases

Abstract: A comprehensive overview of the basic principles of radar polarimetry is presented. The relevant fundamental field equations are first provided in order to introduce the polarization state formulations of electromagnetic waves in the frequency domain, including the Jones and the Stokes vector formalism and its presentation on the Poincare sphere and on relevant map projections. In the next step, the scattering matrices (S) and (M) are given together with change of polarization bases transformation operators, and the optimal polarization states are determined for the coherent and partially coherent cases.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.