Showing papers on "Polarimetry published in 1998"

Polarimetric SAR interferometry

Abstract: The authors examine the role of polarimetry in synthetic aperture radar (SAR) interferometry. They first propose a general formulation for vector wave interferometry that includes conventional scalar interferometry as a special case. Then, they show how polarimetric basis transformations can be introduced into SAR interferometry and applied to form interferograms between all possible linear combinations of polarization states. This allows them to reveal the strong polarization dependency of the interferometric coherence. They then solve the coherence optimization problem involving maximization of interferometric coherence and formulate a new coherent decomposition for polarimetric SAR interferometry that allows the separation of the effective phase centers of different scattering mechanisms. A simplified stochastic scattering model for an elevated forest canopy is introduced to demonstrate the effectiveness of the proposed algorithms. In this way, they demonstrate the importance of wave polarization for the physical interpretation of SAR interferograms. They investigate the potential of polarimetric SAR interferometry using results from the evaluation of fully polarimetric interferometric shuttle imaging radar (SIR)-C/X-SAR data collected during October 8-9, 1994, over the SE Baikal Lake Selenga delta region of Buriatia, Southeast Siberia, Russia.

Polarimetric SAR interferometry

Abstract: In this paper, we examine the role of polarimetry in synthetic aperture radar (SAR) interferometry. We first propose a general formulation for vector wave interferometry that includes conventional scalar interferometry as a special case. Then, we show how polarimetric basis transformations can be introduced into SAR interferometry and applied to form interferograms between all possible linear combinations of polarization states. This allows us to reveal the strong polarization dependency of the interferometric coherence. We then solve the coherence optimization problem involving maximization of interferometric coherence and formulate a new coherent decomposition for polarimetric SAR interferometry that allows the separation of the effective phase centers of different scattering mechanisms. A simplified stochastic scattering model for an elevated forest canopy is introduced to demonstrate the effectiveness of the proposed algorithms. In this way, we demonstrate the importance of wave polarization for the physical interpretation of SAR interferograms. We investigate the potential of polarimetric SAR interferometry using results from the evaluation of fully polarimetric interferometric shuttle imaging radar (SIR)-C/X-SAR data collected during October 8-9, 1994, over the SE Baikal Lake Selenga delta region of Buriatia, Southeast Siberia, Russia.

Design, performance, and applications of a coherent ultra-wideband random noise radar

Abstract: Ram M. NarayananYi XuPaul D. HoffmeyerUniversity of Nebraska—LincolnCenter for Electro-OpticsDepartment of Electrical EngineeringLincoln, Nebraska 68588-0511E-mail: rnarayanan@unl.eduJohn O. CurtisU.S. Army Waterways Experiment StationEnvironmental LaboratoryVicksburg, Mississippi 39180-6199Abstract. A novel coherent ultra-wideband radar system operating inthe 1- to 2-GHz frequency range has been developed recently at theUniversity of Nebraska. The radar system transmits white Gaussiannoise. Detection and localization of buried objects is accomplished bycorrelating the reflected waveform with a time-delayed replica of thetransmitted waveform. Broadband dual-polarized log-periodic antennasare used for transmission and reception. A unique signal-processingscheme is used to inject coherence into the system by frequency trans-lation of the ultrawideband signal by a coherent 160-MHz phase-lockedsource prior to performing heterodyne correlation. The system coher-ence allows the extraction of a target’s polarimetric amplitude and phasecharacteristics. This paper describes the unique design features of theradar system, develops the theoretical foundations of noise polarimetry,provides experimental evidence of the polarimetric and resolution capa-bilities of the system, and demonstrates results obtained in subsurfaceprobing applications.

Broadband Division-of-Amplitude Polarimeter Based on Uncoated Prisms

Abstract: A broadband division-of-amplitude polarimeter (DOAP) is presented. It can provide the real-time measurement of any state of polarization of light, described by its Stokes vector, in large spectral windows. The light is split first into two beams by a prism and then into four beams by means of any polarizer device that will separate the two linear orthogonal states of polarization. Finally, the Stokes vector is directly deduced from the four measured intensities. To avoid interference effects, the splitting of light into four beams is induced only by refractive-index contrast effects between semi-infinite media that are weakly dependent on the wavelength. An experimental setup working from 0.4 to 2 mum is described. It provides similar sensitivities for all the states of polarization, and its characteristics are constant, on a scale of a few percent, within the spectral window. Calibrations performed at 458 and 633 nm display good agreement between theoretical and experimental values. The accuracy of the prism DOAP, evaluated by measurement of the Stokes vector produced by a rotating Glan polarizer, is better than 1%. An infrared extension of this polarimeter is also presented.

Submillimeter Array Polarimetry with Hertz

Abstract: We describe the characteristics of the 350 μm polarimeter Hertz learned from laboratory tests and recent observations at the Caltech Submillimeter Observatory. Hertz contains a pair of 32 element arrays with 18'' pixel spacing and 20'' resolution. The instrument has been improved since initial observations in 1994 and 1995; the detector noise is now below the sky background noise. In excellent weather conditions on Mauna Kea, the noise-equivalent flux density (NEFD) for the measurement of polarized flux is 3-4 Jy Hz-1/2. The subtraction of correlated sky noise accomplished by the two-array design is crucial for achieving this performance. A method for analysis of our polarization data in the presence of the correlated noise is described. The instrumental polarization of Hertz is less than 0.5% across the detector array. Systematic errors in the measurement of polarization are less than 0.2%. We present a 350 μm polarization map of Sgr B2 with 140 detections at greater than 3 σ significance. For our current database of all 350 μm polarization measurements, the median polarization is 1.1%.

A fully polarimetric optical time-domain reflectometer

Abstract: We report the implementation of the first fully polarization sensitive optical time domain reflectometer (POTDR). This nondestructive measurement technique, requiring access to one fiber end only, enables the determination of both the linear and twist induced circular birefringence distribution along the fiber. This information, combined with a knowledge of the mode coupling length, enables the evaluation of the polarization mode dispersion (PMD) properties of fibers and optical cables exhibiting both types of birefringence, as well as identifying fiber sections with and without twist. The POTDR, which has a spatial resolution of 0.3 m, could also be used for monitoring the birefringence properties of fibers at the manufacturing stage, leading to optimization of fabrication techniques to minimize PMD.

Polarization diversity active imaging

Abstract: We present the concept of a Polarization Diversity Active Imager operating at (lambda) equals 810 nm. Each pixel of the image is encoded by the polarization degree Pd (0% < Pd < 100%) given by its Mueller Matrix. The measurement of the Mueller matrices is obtained using the Dual Rotation Retarder Technique. A theoretical analysis and an experimental validation of this technique are presented. The device is operating in a monostatic configuration, using a semiconductor laser ((lambda) equals 810 nm) to illuminate the target and a telescope to create the image on a CCD matrix. The experiment is controlled by a computer that drives the rotation of the retarders, the digitalization and the encoding of the image. The measured intensity and polarization images are compared and the information contained in the polarization degree are analyzed. Dual images (intensity-polarization) of different targets are presented, showing the experimental validation of the technique. The application of this active imager to the detection and the decamouflage of target buried in the background (same albedo but different polarization degree) is proposed.

Polarimetric analysis and modeling of multifrequency SAR signatures from Gulf Stream fronts

Abstract: Using airborne synthetic aperture radar data from the 1990 Gulf Stream Experiment, this paper investigates the polarization and wavelength dependence of radar signatures for narrow fronts with converging flows occurring within the Gulf Stream. The signal-to-background ratios of the cross-polarization backscatter return from a convergent front were found much higher than those of copolarization returns, when the flight path is crossing the front. However, a second convergent front, imaged at 45/spl deg/, showed that the signal-to-background ratios are nearly equal for co- and cross-polarizations. A polarimetric procedure, which has been successfully used to measure terrain slopes and to generate elevation maps, is applied to the convergent front to explain the polarization and imaging geometry dependence of these radar responses. A theoretical modeling of radar modulation using an ocean wave model and a composite-Bragg scattering model, which incorporates the effect of breaking waves, was developed. Calculations with the model agree reasonably well with the radar measurements at various polarizations for three radar frequencies: P-band (68 cm in wavelength), L-band (24 cm), and C-band (5.7 cm).

Scattering from breaking gravity waves without wind

Abstract: Scattering experiments from breaking gravity waves conducted at a wave tank facility at small grazing angles in the absence of wind are analyzed. Breaking gravity waves are studied using a fully plane polarimetric horizontal (HH), vertical (VV), vertically transmitted and horizontally received polarization (VH), and horizontally transmitted and vertically received polarization (HV) pulse-chirped X-band (8.5-9.6 GHz) radar in conjunction with optical instruments: the plane polarimetric optical specular event detector (OSED) and side-looking camera (SLC). Spatially and temporally resolved radar backscatter has been measured and temporally correlated to the data obtained from the optical diagnostics. The experiments yield the following results: (1) enhanced scattering compared to Bragg scattering levels occurs throughout the evolutionary process of wave-breaking, i.e., the radar scatters strongly from both the unbroken and broken surfaces; (2) an explanation is found for the observation that the scatterer Doppler frequency is slightly less than the Doppler frequency corresponding to the fundamental wave phase speed; (3) a representative non-Bragg cross section of a breaking wave can be obtained; and (4) a breaking wave surface is found to be an efficient depolarizer.

Nanometer scale polarimetry studies using a near-field scanning optical microscope.

Abstract: We describe a new technique that incorporates polarization modulation into near-field scanning optical microscopy (NSOM) for nanometer scale polarimetry studies. By using this technique, we can quantitatively measure the optical anisotropy of materials with both the high sensitivity of dynamic polarimetry and the high spatial resolution of NSOM. The magnitude and relative orientation of linear birefringence or linear dichroism are obtained simultaneously. To demonstrate the sensitivity and resolution of the microscope, we map out stress-induced birefringence associated with submicrometer defects at the fusion boundaries of SrTiO3 bicrystals. Features as small as 150 nm were imaged with a retardance sensitivity of ∼3 × 10-3 rad.

Polarized CO emission from molecular clouds

Abstract: Linearly polarized, non-masing, rotational lines have been detected for the first time in the interstellar medium. This effect occurs in molecular clouds with a magnetic field, and traces the field direction, offering an alternative technique to dust emission polarimetry. The line polarization mechanism is similar to that in masers, but with lower degrees of polarization (~1%). We have detected the effect towards the Galactic Centre and its surrounding `2 pc ring', and in the molecular clouds S140 and DR21 (tentatively), in the lines CO J=2-1 and J=3-2, and 13CO J=2-1. The deduced magnetic field directions agree well with previous dust polarimetry results, confirming that the line polarization is a real effect. This new technique will be useful in sources that are too faint for dust polarimetry, and can also be used to investigate 3-dimensional morphology of magnetic fields, where the velocity structure of the clouds is known.

A comparison of different polarization schemes for the radar sensing of precipitation

Abstract: The equations of the radar covariances and cross covariances for linear vertical and horizontal polarization, slant linear +45° and −45° polarization, and left-hand and right-hand circular polarization are presented for a model medium containing spheroidal particlesThis model takes into account the distribution of canting angles but assumes the uniformity of the distribution function along the propagation path Assuming the particles to be locally equioriented, equations for the intrinsic differential reflectivity and the mean canting angle are derived Furthermore, for particles having the same orientations throughout the region of precipitation, the total differential phase shift is obtained Reflectivity and depolarization ratios are also considered A comparison of the three polarization schemes from a theoretical point of view is made and illustrated with data from the DLR C band Doppler and polarimetric weather radar Since the DLR radar did not record the magnitude of the covariances and cross covariances, the comparison is only partially complete The data confirm the theoretical prediction that depolarization is stronger in circular and slant linear polarization than in linear horizontal/vertical polarization

A Compton backscattering polarimeter for measuring longitudinal electron polarization

Abstract: Compton backscattering polarimetry provides a fast and accurate method to measure the polarization of an electron beam in a storage ring. Since the method is non-destructive, the polarization of the electron beam can be monitored during internal target experiments. For this reason, a Compton polarimeter has been constructed at NIKHEF to measure the polarization of the longitudinally polarized electrons which can be stored in the AmPS ring. The design and results of the polarimeter, the first Compton polarimeter to measure the polarization of a stored longitudinally polarized electron beam directly, are presented in this paper.

Physical optics analysis of the field backscattered by a depolarising trihedral corner reflector

Abstract: A physical optics (PO) model is developed to analyse the backscattering properties of an anisotropically loaded trihedral corner reflector, which can be obtained from the conventional triangular one by corrugating one of its interior faces. In such a way it can present a dihedral-like polarisation response over a wide angular range in both azimuth and elevation, thus making it particularly attractive for use in polarimetric radar systems as a location marker for radar navigation, and as a ground reference target in remote sensing applications. In fact, it can be designed to return elliptically or circularly polarised waves with the same handedness as the incident ones, and to rotate the polarisation of linearly polarised incident waves by 90°. The proposed model treats the corrugated surface as an anisotropic impedance boundary condition (IBC). Moreover, it evaluates in explicit form both the illuminating electric field related to the direct, singly and doubly reflected rays incident on each corner face and the shape of the corresponding illuminated patches. This allows a closed form evaluation of the related PO backscattering integrals, which produces a very fast computer code also suitable for non-powerful computers.

A three-intensity technique for polarizer-sample-analyser photometric ellipsometry and polarimetry

Abstract: This work presents a novel three-intensity-measurement technique to determine the ellipsometric parameters and in a polarizer-sample-analyser photometric ellipsometer. This technique can be employed to correct the azimuthal misalignment of the analyser with respect to the plane of incidence. By performing two sets of measurements with this technique with the polarizer's azimuth at and , respectively, we can simultaneously determine the azimuthal deviation of the polarizer and further improve the ellipsometric measurements. Applying this technique in the transmission mode allows us to obtain the phase retardation and the optical axis of a waveplate at the same time.

Effect of molecular concentrations in tissue-simulating phantoms on images obtained using diffuse reflectance polarimetry

Abstract: We have investigated the possibility of using diffuse reflectance polarimetry to detect changes caused by different molecular compounds and concentrations in tissue-simulating phantoms The effects of glucose, β-alanine and l-lysine at different concentrations in turbid media have been investigated separately This approach is based on the effect of optical properties on the polarization state of light The results show that this method has potential for determining changes in molecular concentrations in highly scattering biological media from polarization images

Visible stokes polarimetric imager

Abstract: A visible Stokes polarimetric imager (80) that separately and contemporaneously measures each of the four separate Stokes polarization parameters of a visible light beam reflected from a scene. The imager (80) includes a compound prism assembly (50) including five prism elements (52-58). The reflected beam from the scene is collected by an input lens (84) in the imager (80), and is directed to the prism assembly (50) at a certain location. The prism elements (52-58) split the beam (82) into four separate beams (62-68) of substantially equal intensity that are emitted from the prism assembly (50) in different directions. Four separate polarimetric filters (86) and imaging devices (88) are positioned relative to the prism assembly (50) to separately receive each of the four beams (62-68) emitted from the prism assembly (50). One of the filters (86) is a neutral density filter, one of the filters only passes light that is plane polarized in the vertical direction, one of the filters only passes light as plane polarized light oriented 45° from the vertical. The last filter only passes light that is circular polarized. Thus, each of the four imaging devices (88) measures the light intensity reflected from the scene for each of the four Stokes parameters. A processing system (102) aligns and processes the video frames of data from each of the imaging devices (88) so that the relative intensity in each of the four polarized directions can be determined for each location in the scene.

A fabry-perot cavity for compton polarimetry

Abstract: A new kind of Compton polarimeter using a resonant Fabry—Pe« rot cavity as a power buildup for the photon beam is proposed. A prototype of such a cavity is described, along with the results obtained in terms of source to be used in a Compton scattering polarimeter. ( 1998 Elsevier Science B.V. All rights reserved.

Real-time and full polarimetric FM-CW radar and its application to the classification of targets

Abstract: The Sinclair scattering matrix plays a decisive role in radar polarimetry. For realization of a real-time and full polarimetric radar, there are some technical problems associated with hardware implementations. Since the FM-CW radar system is suitable for short-range sensing applications, we modified an FW-CW radar to a real-time and polarimetric system by adding a PIN diode-switching circuitry for antenna polarization changes. A parallel operation scheme in the signal processing and the radar control is employed in a personal computer, which enables 44 snapshots for acquiring scattering matrices and displays the polarimetric target classification results along 43 radar ranges per second. In this paper, we present the hardware design of the system and its fundamental application to the classification of targets using the three-component decomposition theorem.

K-band polarimetry of seven high-redshift radio galaxies

Abstract: ABSTRA C T We present the results of K-band imaging polarimetry of seven 3CR radio galaxies with 0:7 < z < 1:2. We find strong evidence for polarization in three sources: 3C 22, 3C 41 and 3C 114. Of these, 3C 41 shows strong evidence of having a quasar core the infrared light of which is scattered by dust. We also find some evidence for polarization in 3C 54 and in 3C 356. The two point-like sources (3C 22 and 3C 41) and the barely-elongated 3C 54 appear to have of order 10 per cent of their K-band flux contributed by scattered light from the active nucleus. We conclude that scattered nuclear light can form a significant component of the near-infrared light emitted by high-redshift radio galaxies, and discuss models in which the scattering particles are electrons and dust grains.

Advanced polarimetric subsurface FM-CW radar

Abstract: The subsurface radar suffers from two typical problems, i.e., strong clutter from surface and severe wave attenuation in the underground. This paper presents a unique countermeasure to these problems using a polarimetric FM-CW radar and an equivalent sensitivity time control (STC) technique. The authors apply the polarimetric filtering principle to suppress surface clutter either in the Co-pol channel or in the X-pol channel of synthetic aperture radar, yielding to polarimetric enhanced target image. This technique works when the surface clutter and target have different polarization properties. Moreover, they use an equivalent STC technique specially suited for FM-CW radar for a deep object sounding to compensate wave attenuation within the ground. These techniques contribute to a significant improvement of the radar performance and the detection image contrast, although the detection of the target is in general a much more complicated topic. The field experiments were carried out to show the usefulness of the method. Some detection results are presented.

Near-infrared imaging polarimetry of Cygnus A

Abstract: Original article can be found at: www3.interscience.wiley.com Copyright Blackwell Publishing / Royal Astronomical Society. DOI: 10.1046/j.1365-8711.1998.01586.x [Full text of this article is not available in the UHRA]

Beam folding optics system and method of use with application in ellipsometry and polarimetry

Abstract: Disclosed is an electromagnetic beam directing system and method which enables changing the direction of propagation of a beam of electromagnetic radiation without significantly changing the phase angle between orthogonal components therein. Two pairs of mirrors are oriented to form two orthogonally related planes such that phase shift entered to an electromagnetic beam by interaction with the first pair of mirrors is canceled by interaction with the second pair.

Toward precision polarimetry of dense polarized 3He targets

Abstract: We describe several new measurement and analysis techniques used to determine the polarization of the 3He target in a recently completed measurement of the neutron spin structure function g 1n at SLAC (E-154). The polarization was determined using two independent methods. The first method used a standard technique of Adiabatic Fast Passage, calibrated by a measurement of Boltzmann polarization in a sample of water. We describe several systematic effects affecting this calibration procedure. The second method used a shift of the Rb Zeeman resonance frequency due to the polarization of 3He. Implementation and calibration of this technique are discussed in detail. Finally, the density of 3He in the cell was measured using two independent methods, one of them based on the pressure broadening of Rb D1 and D2 lines due to 3He.

Hyperspectral imaging polarimeter in the infrared

Abstract: The Space Dynamics Laboratoiy at Utah State University is building an infrared Hyperspectral ImagingPolarimeter (HIP). Designed for high spatial and spectral resolution polarimeiry ofbackscattered sui1ight from cloud topsin the 2.7 im water band, it will fly aboard the Flying Infrared Signatures Technology Aircraft (FISTA)1, an Air Force KC-135. It is a proof-of-concept sensor, combining hyperspectral pushbroom imaging with high speed, solid state polarimetiy,using as many off-the-shelf components as possible, and utilizing an optical breadboard design for rapid prototyping. It isbased around a 256x320 window selectable InSb camera, a solid-state Ferro-electric Liquid Ciystal (FLC) polarimeter, anda transmissive diffraction grating.Keywords: optical remote sensing; hyperspectral; imaging spectrometer; imaging polanmeter, polarimetry; polarizationmeasurement, radiometric calibration. 1. INTRODUCTION The linear polarization characteristics (degree and angle) of sunlight backscattered from cloud tops can yield a wealth ofinfonnation about the phase ofthe particles in the cloud, whether they are ice ciystals, water droplets, or a mixture2.Measurements in the wings ofthe 2.7 m water band should be especially fruitful, since at certain wavelengths in this band,photons that have undergone a single scattering should dominate the backscattered photons. At these (yet undetermined)wavelengths, the degree ofpolarization should be maximized, and the information contained in this polarization should bemore readily analyzed. Information about the phase ofthe cloud particles has a number ofpotential scientific applications.Determination ofthe glaciation characteristics and altitudes ofclouds via passive remote sensing would be of particularinterest to aviation, weather prediction, and the global climate modeling community, among others.One ofthe purposes ofthe HIP sensor is to determine the precise wavelengths at which the single scattered photonsdominate, and to evaluate the data analysis algorithms that will be required to determine the cloud particle phaseinformation. In order to do this a hyperspectral sensor that will split the 2.5 pm to 3.5

Multichannel imaging for wideband wide-angle polarimetric synthetic aperture radar

Abstract: In this paper we introduce multi-channel techniques to compensate for effects of antenna shading and crosstalk in wideband, wide-angle full polarization radar imaging We model the systems as a 2D integral operator that includes the transmit pulse function, receive and transmit antenna transfer functions, and response from scattering objects Existing imaging algorithms provide an approximate inversion of this integral operator, without compensation for the effect of antenna transfer functions Thus, standard processing results in image quality diminished by the inherent variation of the antenna response--in magnitude, phase and polarization--across a large band of frequencies and wide range of aspect angles We propose three inversion techniques for this integral operator, to improve polarization purity and to achieve localized point spread functions The first technique uses a local approximation to the system model, and propose a conceptually simple method for the inversion The other two techniques propose inversion methods for the exact system model in different transform domains The result is imagery with improved polarization purity and a more localized point spread function

Rainfall rate measurement with a polarimetric radar at an attenuated wavelength

Abstract: Among the many ways investigated for radar estimation of rainfall, polarimetric methods are the most promising. However most polarimetric algorithms are degraded by attenuation by precipitation and clouds and by calibration error. A new method was recently proposed in which the differential polarimetric attenuation is used to perform an accurate rain rate measurement. The method is independent of the radar calibration and of the attenuation by undetected clouds. This algorithm is also usable as a qualitative hail detector, as well as a detector of anomalous propagation. The goal of the paper is to describe the results of the first experimental implementation of this method using the 35 GHz RABELAIS radar, as attenuated radar, and the 3 GHz CAMRa radar as a reference. We show that the proposed algorithm is stable and enables us to retrieve the actual rain rate even from an observed signal attenuated by more than 30 dB. The results are insensitive to the value used for the power coefficient of the Z(R) relation.

Measurement of the linear polarization of Parametric X-radiation

Abstract: The linear polarization of Parametric X-radiation (PXR) produced by 80.5 MeV electrons in a 13 μm thick silicon single crystal has been analyzed by means of a novel method of polarimetry exploiting directional information of the photoeffect in a charge coupled device consisting of 1.3×10 6 square pixels of 6.8 μm. The experiment was carried out at the Darmstadt superconducting linear accelerator S-DALINAC providing a low-emittance electron beam. The linear polarization of the (2 2 0) reflection observed in eight narrow angular bins between 20 ∘ and 21 ∘ with respect to the electron beam direction is consistent with complete local linear polarization. The orientation of the polarization plane, within measurement errors of typically 10 ∘ , varies over the diffraction pattern in such a way as to be expected from kinematical theory. The result of this experiment is in contradiction to the only other PXR polarization measurement performed so far.

On the use of polarization modulation in combined interferometry and polarimetry

Abstract: The combination of interferometry and polarimetry using modulation of the input polarization is considered. For this case an expression for the interferometric phase is derived showing the presence of an additional time-varying term with respect to the case without modulation. It is found that for finite plasma birefringence the additional term is always important even if a linear input polarization is used, in contrast to the case where birefringence is zero. If the contribution of the additional term is eliminated by filtering, a consequence is a loss of time resolution on the interferometric measurement.