Showing papers on "Polarimetry published in 1987"

Imaging radar polarization signatures: Theory and observation

Abstract: Radar polarimetry theory is reviewed, and comparison between theory and experimental results obtained with an imaging radar polarimeter employing two orthogonally polarized antennas is made. Knowledge of the scattering matrix permits calculation of the scattering cross section of a scatterer for any transmit and receive polarization combination, and a new way of displaying the resulting scattering cross section as a function of polarization is introduced. Examples of polarization signatures are presented for several theoretical models of surface scattering, and these signatures are compared with experimentally measured polarization signatures. The coefficient of variation, derived from the polarization signature, may provide information regarding the amount of variation in scattering properties for a given area.

Imaging radar polarimetry from wave synthesis

Abstract: A new approach is reported to the measurement of the complete polarization signature of each resolution element in an image implemented with an airborne synthetic aperture radar system. Signals recorded on one data pass from orthogonal linearly polarized antennas are utilized. The signals are combined in a data processor to synthesize any desired combination of transmit and receive polarizations. The technique permits measurement of the complex, multichannel reflectivity of a scene on a single aircraft pass and to late reprocess the data to provide multiple image maps, with each representing the backscattered energy from the scene measured with a different combination of observational transmit and recieve polarizations. The resulting polarization signature measurements indicate optimum polarizations for observations of certain classes of objects and give insight into the identification of dominant scattering mechanisms for each kind of object. The mathematical model for polarization synthesis is summarized, and some theoretical polarization measurements are illustrated for several types of targets. The overall radar system implementation is described in detail. Some analyses of data acquired on three aircraft flights are presented. The technique has been applied to mapping and differentiation of lava flows and to differentiation of forested and clear-cut areas.

Rotating waveplates as polarization modulators for Stokes polarimetry of the sun: evaluation of seeing-induced crosstalk errors

Abstract: A formalism for estimating the crosstalk error among Stokes I,Q,U,V introduced by seeing-induced image motion is presented. This formalism is applied to several modulation schemes for polarization involving rotating waveplates, and it is evaluated using an observed power spectrum of image motion obtained from the Vacuum Tower Telescope at the National Solar Observatory/Sunspot. It is shown that rotating waveplates offer an acceptable alternative for measurements of absorption line polarization of features observed on the solar disk, provided the detection can be carried out at video frame rates or faster.

Interpretation of the Polarimetric Co-Polarization Phase Tern in Radar Images Obtained with the JPL Airborne L-Band SAR System

Abstract: The utilization of both polarimetric amplitude and relative phase terms of the polarization scattering matrix [S] given for each pixel, is pursued for polarimetric SAR imagery interpretation. The existing amplitude-only backscattering approaches hitherto used are extended and modified to accommodate the interpretation of information contained in the amplitude and/or phase terms. Both a vector radiative transfer model for surface versus volume scattering from rough terrain with and without vegetation canopy and a high-frequency electrical curvature model for perfectly conducting surfaces are examined to come up with theoretical models that out-perform other hitherto known approaches. The developed models agree with the excellent polarimetric SAR imagery recently obtained with the JPL CV-990 dual-polarization L-band (1.225 GHz) SAR system. Recommendations are made on how to further perfect the system for integration in the SIR-C and other future polarimetric SIR-SAR systems.

Four-channel polarimeter for time-resolved ellipsometry

Abstract: A new four-channel partial polarimeter was designed for use in time-resolved ellipsometry measurements. The device outputs four parallel, equispaced beams from a single input beam. By detecting and digitizing the intensities of these four beams, the intensity, as well as two of the three elements of the reduced Stokes vector can be determined. Since there are no moving parts to the polarimeter, time resolution is limited only by the response time of the photodetectors and the digitizers. The linear array of output beams is ideal for streak-camera detection, yielding a potential time resolution of ~1 psec. A beam splitter is described that separates the input beam into two beams, which are parallel to the input beam and whose polarizations are nearly the same as the input beam. In addition, the polarimeter is achromatic, operating in the wavelength region from 220 to 1100 nm.

Polarimetry: the characterisation of polarisation effects in EM scattering

Abstract: This thesis is concerned with the development of a general theory for the characterisation of polarimetric scattering problems. Traditionally, two main approaches have been used in the literature: the first based on measurement of the coherent scattering matrix (Jones calculus) and the second on measurement of the wave Stokes parameters (Mueller calculus). This thesis contains three main developments which extend and complement the published work in this area: 1) The representation of nonsymmetric scattering matrices on the Poincare sphere, using an extension of the fork analysis first introduced by Kennaugh. 2) The construction of a geometry based on the Lorentz , transformation for analysing, on the Poincare sphere. The interaction of partially polarised waves with single targets. 3) The reformulation of polarisation scattering problems in terms of a target spinor and associated coherency matrix. This leads to the construction of a target sphere in 6 dimensions analogous to the Poincare sphere in 3 dimensions. This new formulation also leads to the development of a decomposition theorem for dynamic targets based on the eigenvectors of the coherency matrix. This decomposition is more fundamental than that used by Huynen and the two are compared and contrasted. In order to demonstrate main features of the new theory and to highlight its importance to experimental polarimetry, a laser based optical polarimeter was constructed. Results for the measured coherency Matrix obtained for transmission through quarter and half wave plates are presented and analysed using the target spinor theory.

Features in Saturn's rings

Abstract: A systematic, uniform search of Voyage 2 photopolarimeter system (PSS) data set for all significant features of Saturn's rings is described. On August 25, 1981, the PSS observed the occultation of the star Delta Scorpii by the rings of Saturn, and the timing of the data taking was rapid enough that the spatial resolution in the radial direction in the ring plane was better than 100 m. Tabular information and figures for 216 significant features that were found are presented.

Fiber birefringence measurements with an external stress method and heterodyne polarization detection

Abstract: Precise birefringence measurements on polarization maintaining fibers have been obtained with external pressure scanning along the fiber axis. Output detection has been performed through heterodyne interferometric polarimetry, which allows the use of a simplified technique (avoiding pressure modulation and fiber eigenaxis search). Beat-length evaluation is achieved directly through multiple counting of periodical variations of the two radio-frequency output signals provided by the polarimeter. A theoretical model for the behavior of the fiber output polarization on the Poincare' sphere, as a function of pressure scanning, has been developed and experimentally tested and the results are in good agreement with the theory.

A polarimetric model for the recovery of the high-frequency scattering centers from bistatic-monostatic scattering matrix data

Abstract: The objective of this investigation is to develop multistatic electromagnetic identification/discrimination algorithms using the complete polarimetric scattering data. At high frequencies the electromagnetic scattering from a complex object is modeled by certain scattering centers. The high-frequency (physical optics) bistatic and monostatic scattering matrix properties of a flat plate model of such a scattering center are developed in detail. For the complex target representations, the single scattering center results can be extended to two and three scattering center models. It is suggested that the knowledge of the locations and the local geometries of these scattering centers can be useful in developing identification and pattern recognition algorithms.

Fourier Transform Polarimetry

Abstract: Electromagnetic radiation propagates through homogeneous isotropic media without change in polarization state. Reflection or transmission through an interface at other than normal incidence, however, does result in a change of polarization state, as does propagation through anisotropic media. Ellipsometry is the art of measurement of the polarization state of fully polarized light, and hence of the measurement of the properties of materials and interfaces to transform fully polarized light. The information sought in the case of transmission through anisotropic materials is the differential dispersion and differential absorption spectra, while from reflection studies, most commonly it is the thickness and optical constants of one or more overlayers. In this paper, we address all of these in connection with Fourier transform UV-VIS and IR spectroscopy of polymers, but in addition, a section on emission spectra, which in general involves making measurements on partially polarized light, has been included, hence the choice of the more general term “polarimetry” over “ellipsometry”.

Study of Multilayered X-UV Polarizers and Consequence of the Use of Partially Polarized Light on Absolute Reflectivity Measurements

Abstract: An X-UV polarimeter with a rotating 45° angle of incidence multilayer as polarizer has been built and used to measure the polarization rates of the 154A and 304A light after monochromators. Due to the good polarization of the synchrotron source, polarization rates around of 70% have been measured.

Two-wavelength interferometric fiber temperature sensor

Abstract: Temperature sensing using single-mode fibers has been demonstrated using both Michelson and Mach-Zehnder fiber interferometers and by polarization mode interference in a single-fiber polarimetric configuration.1,3 In the latter approach the sensitivity is a function of the dependence of the fiber birefringence on temperature, which, for thermally stressed high-birefringence fibers, can be strong. In general, however, the overall sensitivity of the polarimetric approach is less than that exhibited by the interferometric configurations. Due to this high sensitivity, the intrinsic unambiguous sensing range of the interferometric technique is small. A range of demodulation techniques, such as pseudoheterodyne detection, has been developed in recent years, which allows the total phase excursion of the interferometer to be electronically tracked. The use of such processing techniques, however, only partially alleviates the ambiguity problem associated with the interferometric transfer function as the absolute measurand value cannot be determined when the sensor is initialized.

Imaging radar polarimetry - A status report

Abstract: The development of imaging radar polarimetry at JPL is considered. Advances in the correlation of polarimetric SAR and in the synthesis of arbitrary polarization are discussed. The capabilities of the polarization workstation are described. Various applications for polarimetric SAR data include: the identification of scatter, the evaluation of scattering theories, the measurement of the roughness of geologic targets, the classification of forest stands, and the characterization of trees within a particular stand. The development and testing of the DC-8 SAR and the SIR-C system are examined.

Charge-Coupled-Device-Based Imaging Polarimeter For Astronomy

Abstract: Using a thinned, three-phase Texas Instruments 800 X800 CCD (T1 3PCCD) and inexpensive plastic Polaroid material, we have constructed an imaging polarimeter for astronomical data collection. A unique method of image shifting, shuttering, and Polaroid rotation enables us to circumvent the sky transmission fluctuations that normally plague polarimetry. The method is possible only because of the exceedingly low dark current and exceedingly high charge-transfer efficiency of this CCD. Our observations of standard polarimetry stars have verified the operation of our imaging polarimeter and have demonstrated that polarimetry can be accurately performed below the 1% polarization level with well-behaved CCDs.

Five-colour (UBVRI) polarimetry of H 0139-68 = BL Hydri.

Abstract: On rapporte les observations simultanees de la polarisation lineaire et circulaire dans la bande UBVRI de la binaire magnetique BL Hydri. On en deduit les parametres geometriques inclinaison de l'axe de rotation et colatitude du pole magnetique, la hauteur et la largeur de la region d'emissions

FM-CW Radar Remote Sensing of Hydrometeors,

Abstract: : In order to investigate phenomena influencing co-polar attenuation and cross-polar discrimination along earth-space satellite paths and terrestrial radio links at frequencies above 10 GHz, the number density, geometry, and orientation of hydrometeors (rain, snow, hail, melting particles etc.) along the path have to be characterized. This paper describes the modelling of the melting process, the dielectric properties of melting particles, and fall velocity behavior of hydrometeors for Doppler velocity computation with vertically pointing radars. Attention is paid to backward scattering of ellipsoidal hydrometeors for radar polarimetry computations at arbitrary elevation angles, and to forward scattering of spherical hydrometeors for attenuation computations at high frequencies. The multi-parameter FM-CW radar systems of Delft University of Technology is able to measure the polarization properties and Doppler velocity spectra of hydrometeors with high resolution in range and reflectivity level. Preliminary results obtained with this radar system are shown, indicating the capabilities of combined Doppler- and polarimetry measurements for classification of hydrometers along a satellite path.