Showing papers on "Polarimetry published in 1994"
TL;DR: In this paper, the symmetry of polametric scattering and emission coefficients of media with reflection symmetry was investigated, and the authors showed that the symmetry can be obtained for media with the following properties:
Abstract: This paper investigates the symmetry of polametric scattering and emission coefficients of media with reflection symmetry.
108 citations
TL;DR: There exists a basic difference between these two matrices that seems to have been overlooked by a number of researchers, resulting in a great deal of confusion, and an attempt is made to clarify this point and to present the basic relationships of radar polarimetry in a compact form.
Abstract: This paper is concerned with the notions of the Mueller matrix and the Kennaugh (or Stokes scattering) matrix, that are commonly used in the field of radar polarimetry. Although these two matrices are quite similar, there exists a basic difference between them that seems to have been overlooked by a number of researchers, resulting in a great deal of confusion. An attempt is made to clarify this point and to present the basic relationships of radar polarimetry in a compact form. >
85 citations
TL;DR: The phase difference and the product of two complex Gaussian signals are important parameters in the study of interferometry and polarimetry as discussed by the authors, and to reduce statistical variations, polarimetric and inte...
Abstract: The phase difference and the product of two complex Gaussian signals are important parameters in the study of interferometry and polarimetry. To reduce statistical variations, polarimetric and inte...
84 citations
TL;DR: A novel interferometric polarimeter capable of mapping a spatiotemporal change in the state of polarization (SOP) of light is described and successful experiments are demonstrated by generating an elliptically polarized beam whose SOP varies in space and time.
Abstract: A novel interferometric polarimeter capable of mapping a spatiotemporal change in the state of polarization (SOP) of light is described. The polarimeter has a reference beam of light with two orthogonal linearly polarized components that interfere with the counterpart components of an elliptically polarized signal beam. The resultant interference pattern is recorded by a computer by the use of a wideband metal-oxide semiconductor video camera. The interference pattern reduces to the ellipticity and azimuth of the ellipse at an instant of time, by which the spatiotemporal change in the SOP is mapped. No optical elements are used for the control of polarization in the polarimeter, and this allows for the mapping of a rapid change in the SOP. Successful experiments are demonstrated by generating an elliptically polarized beam whose SOP varies in space and time.
52 citations
Patent•
29 Jul 1994
TL;DR: In this paper, a polarimetric Doppler weather radar system is proposed, which allows measurement of linear orthogonal polarIMetric variables without a switch by using simultaneous transmission of horizontally and vertically polarized waves.
Abstract: A polarimetric Doppler weather radar system which allows measurement of linear orthogonal polarimetric variables without a switch by using simultaneous transmission of horizontally and vertically polarized waves. This is accomplished by splitting the transmitted power into two waveguides and combining them with an orthomode coupler at the antenna feed. Thus, in general the transmitted polarization is elliptical but with equal amount of power in horizontal and vertical polarization. On reception, the power is divided, at the orthomode coupler, into linear horizontal and vertical components. These components are processed and combined to yield Doppler and polarimetric information about storm structure.
49 citations
TL;DR: In this paper, a technique was described which makes use of the high magnetic resolution in this spectral range to remove instrumental polarization from observed StokesQ, U, and V line profiles.
Abstract: Full Stokes polarimetry is obtained using the National Solar Observatory Vacuum Tower Telescope at Sacramento Peak while observing the magnetically sensitive infrared Fei line at wavelength of 1.56μ. A technique is described which makes use of the high magnetic resolution in this spectral range to remove instrumental polarization from observed StokesQ, U, andV line profiles.
43 citations
11 Aug 1994-Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment
TL;DR: In this article, a number of different Mott polarimeter designs are described that illustrate the wide range of operating energies (∼ 150 eV to 150 keV) and geometries that can be used in such instruments.
Abstract: Electron spin polarization analysis adds a valuable dimension to studies involving synchrotron radiation. Electron polarimeters based on Mott scattering are particularly attractive for use in this application because they provide good efficiency and analyzing power, they are relatively simple to implement experimentally and the physical basis of their operation is well understood. A number of different Mott polarimeter designs are described that illustrate the wide range of operating energies (∼ 150 eV to 150 keV) and geometries that can be used in such instruments. Potential sources of systematic error that can limit measurement accuracies are addressed together with techniques for polarimeter calibration.
40 citations
TL;DR: The first measurements and scientific observations of the solar photosphere obtained with a new two-dimensional polarimeter based on piezoelastic modulators and synchronous demodulation in a CCD imager is presented.
Abstract: We present the first measurements and scientific observations of the solar photosphere obtained with a new two-dimensional polarimeter based on piezoelastic modulators and synchronous demodulation in a CCD imager. This instrument, which is developed for precision solar-vector polarimetry, contains a specially masked CCD that has every second row covered with an opaque mask. During exposure the charges are shifted back and forth between covered and light-sensitive rows synchronized with the modulation. In this way Stokes I and one of the other Stokes parameters can be recorded. Since the charge shifting is performed at frequencies well above the seeing frequencies and both polarization states are measured with the same pixel, highly sensitive and accurate polarimetry is achieved. We have tested the instrument in laboratory conditions as well as at three solar telescopes.
40 citations
TL;DR: A calibration algorithm is proposed that circumvents all of the problems of external calibration of polarimetric synthetic aperture radars and is shown that the radar distortion parameters and effective illumination area can be obtained from a homogeneous distributed target with a known differential Mueller matrix.
Abstract: Existing methods for external calibration of polarimetric synthetic aperture radars (SAR) are all based on point targets with known scattering matrices. The quantity of interest in radar measurement of distributed targets is the backscattering coefficient, which is different from the radar cross section (RCS) formulated for point targets. Therefore, in order to infer the backscattering cross section of a distributed target from a point target rigorously, the polarimetric ambiguity function of the SAR (unknown) is needed for the computation of the effective illumination area. In existing methods the illumination area is approximated by the area of a pixel. The second problem is the uncertainty in the RCS of point calibration targets. The large physical size of the point targets and their interaction with the background produce uncertainties in the measurement of the calibration targets. The third problem with existing methods arises from the application of the calibration algorithm to individual pixels. The measured response of a distributed target by a SAR is the convolution of the actual radar reflectivity of the target with the ambiguity function of the SAR. Thus, the statistics derived from individual pixels is influenced by the ambiguity function and the measurement becomes system dependent. In this paper a calibration algorithm is proposed that circumvents all of the mentioned problems. It is shown that the radar distortion parameters and effective illumination area can be obtained from a homogeneous distributed target with a known differential Mueller matrix. The distortion parameters are then used in an algorithm to provide the calibrated differential Mueller matrix for the other homogeneous targets in the image. This algorithm is tested for the JPL L- and C-band SAR using four different distributed targets measured with polarimetric scatterometers. >
37 citations
TL;DR: In this article, a near-infrard (10 microns-2.5 microns) camera was used at the Canada-France-Hawaii Telescope and at the Observatoire du Mont Megantic 1.6 m telescope.
Abstract: A near-infrard (10 microns-2.5 microns) camera in use at the Canada-France-Hawaii Telescope and at the Observatoire du Mont Megantic 1.6 m telescope is described. The camera is based on a NICMOS3 256X256 HgCdTe array detector. While it is used for broad-band imaging and polarimetry through the standard J, H, and K filters, a distinguishing feature of its design is the use of circular variable filters for spectral line imaging in regions of strong continuum emission. The control system was designed to minimize overhead and be simple to use and to maintain. The performance of the instrument is described and illustrated with images of the H2 emission from the Cepheus A star formation region and a K-band image of the environment of the quasar 3C 345.
36 citations
TL;DR: The polarimetric calibration of the Delft Atmospheric Research Radar with a rotatable dihedral corner reflector is performed and the experimental results and the calibration procedure are presented.
Abstract: Based on the existing mathematical formalisms of radar polarimetry, it is necessary to perform accurate and diversified polarimetric measurements in the real world to thoroughly investigate signature definition, identification, and classification of radar targets. For this study the Delft Atmospheric Research Radar (DARR) is used. This ground-based polarimetric FM-CW radar operates in the S-band. The purpose of the present paper is the polarimetric calibration of the DARR. Among the passive reflectors, a rotatable dihedral corner reflector is a suitable calibration object. It enables one to measure different scattering matrices with only one reflector. One alignment must be performed and the scattering matrices are measured at the same range. By measuring several scattering matrices, the accuracy of the calibration result can be estimated. A measurement campaign with a rotatable dihedral corner reflector was therefore performed. The experimental results and the calibration procedure are presented in this paper. >
08 Aug 1994
TL;DR: An original unsupervised classification procedure, based around neural networks with competitive architecture, is proposed, based on the study of the sensitivity of the synaptic coefficients of the network for segmentation and clustering of different Earth terrain components within a full polarimetric SAR image.
Abstract: Classification of Earth terrain components within a full polarimetric SAR image is one of the most important applications of radar polarimetry in remote sensing. An original unsupervised classification procedure, based around neural networks with competitive architecture, is proposed in this paper. This process, based on the study of the sensitivity of the synaptic coefficients of the network, is applied to the full polarimetric SAR images of San Francisco Bay (NASA/JPL 1988) for segmentation and clustering of different Earth terrain components. Then, an identification procedure, based on polarimetric decomposition theorems is presented from which a new approach to the interpretation of different scattering mechanisms is obtained after clustering. >
TL;DR: In this article, an ultrawideband radar system is described which has the capability of making pulse-to-pulse polarimetric measurements of the dynamic water features responsible for radar backscatter from the sea.
Abstract: An ultrawideband radar system is described which has the capability of making pulse-to-pulse polarimetric measurements of the dynamic water features responsible for radar backscatter from the sea. The fast risetime voltage step produced by a Tektronix time-domain reflectometer (TDR) is used to excite a 6-12-GHz amplifier, producing a short (15 cm) radar pulse, A pair of 2- to 18-GHz antennas and appropriate pulse-to-pulse transmit and receive switching capability allows the collection of four consecutive equivalent-time-sampled pulses, one for each combination of the linear transmit and receive antenna polarizations. A polarimetric scattering matrix is then obtained at a sequence of frequencies across the 6-12-GHz band through the Fourier transform of each of the four waveforms and the application of an ultrawideband, polarimetric calibration procedure. The effect of motion on the computed scattering matrix is discussed and quantified, as this is an important consideration for polarimetric investigations of the water features responsible for radar sea scatter, A technique is then presented which compensates for the effects of target translation during the sampling interval. Scattering measurements of several rigid targets and of small breaking waves in a wave tank are used to illustrate the unique capabilities of this system and its applicability to sea scatter studies. >
TL;DR: In this paper, a non-coherent X-band polarimetric radar was used to discriminate between liquid and solid hydrometeors and to identify the areas of strong ground clutter contamination.
Abstract: Combined measurements of differential reflectivity and cross-correlation coefficient between linear copolar components of weather radar returns have been obtained with a noncoherent X-band polarimetric meteorological radar. In examining these data, special attention is devoted to the problem of discrimination between liquid and solid hydrometeors and to identification of the areas of strong ground-clutter contamination. Furthermore, polarization parameters of backscattered signals are used to locate updrafts.
14 Sep 1994
TL;DR: In this paper, a new type of imaging polarimeter for fast and orientation independent measurement of birefringent fine structures is proposed, implemented as a polarized light microscope incorporating a precision universal compensator made of two electro-optic modulators.
Abstract: A new type of imaging polarimeter for fast and orientation independent measurement of birefringent fine structures is proposed. The new imaging polarimeter was implemented as a polarized light microscope incorporating a precision universal compensator made of two electro-optic modulators. A video camera and computer-assisted image analysis system provide fast measurements of optical anisotropy (retardance magnitude and azimuth) in the specimen at ALL POINTS of the image constituting the field of view. The images document fine structural and molecular organization within a thin optical section of the specimen. The sensitivity of the current instrument is 0.1 nm of specimen retardance, measured in 0.43 seconds at all 640 X 480 image points. Examples of measurements of birefringent fine structures are presented.
TL;DR: In this paper, a new microscope was developed that integrates laser scanning microscopy with polarization modulation polarimetry, which allows quantitative characterization of the molecular orientation and the degree of order through characterization of optical anisotropy.
Abstract: To image the orientational order in a broad class of biological and manufactured materials, a new microscope has been developed that integrates laser scanning microscopy with polarization modulation polarimetry. Polarimetry allows quantitative characterization of the molecular orientation and the degree of order through characterization of optical anisotropy. Combined with laser scanning microscopy, it is used here to image the anisotropy with high spatial resolution, sensitivity, and speed. The design of the microscope is presented; and the vast improvement in sensitivity achieved using PM-LSM over conventional polarization microscopy is illustrated by imaging the linear dichroism of ultrathin Langmuir–Blodgett polymer films. PM-LSM allows imaging of the magnitude and orientation of linear dichroism in films as thin as three molecular layers (~66 A) at high resolution by rastering a diffraction limited spot of laser light across the sample. The rate of image acquisition is over 2000 pixels/s, two to three orders of magnitude faster than the previous methods of imaging optical anisotropy.
01 Jan 1994
TL;DR: When a ray of electromagnetic radiation strikes a flat surface at an angle, the ray may be bent upward (reflected) or bend downward (refracted) as illustrated in Fig. 27.1.
Abstract: When a ray of electromagnetic radiation strikes a flat surface at an angle, the ray may be bent upward (reflected) or bend downward (refracted) as illustrated in Fig. 27.1. Notice that the ray does not go straight through the material.
TL;DR: This paper compares the mathematics of the two disciplines and it is shown that Kennaugh's optimum polarizations can be derived in the context of optical polarimetry, which always employs a local right-handed coordinate system.
Abstract: The fields of radar and optical polarimetry are compared. Both fields have defined scattering matrices that describe the coherent scattering of monochromatic electric fields. This paper compares the mathematics of the two disciplines and it is then shown that Kennaugh's optimum polarizations can be derived in the context of optical polarimetry, which always employs a local right-handed coordinate system. In addition, a novel definition of the receive copolar polarization state is given: that polarization state that results when a plane wave is reflected by a specular surface. The resulting mathematics when this definition is used in termed specular null polarization theory. It is shown that this new definition facilitates the analysis of backscatterers by focusing on those polarization state changes that are only due to the scatterer. >
Journal Article•
TL;DR: In this paper, the covariance matrix is used to transform the radar data obtained with ±45° linear polarization states to conventional radar parameters measured at horizontal and vertical polarization states, assuming a diagonal propagation matrix and a reciprocal scattering matrix with nonzero crosspolar terms.
Abstract: Equations are derived for transforming radar data obtained with ±45° linear polarization states to conventional radar parameters measured at horizontal and vertical polarization states. The derivation is based on the covariance matrix and assumes a diagonal propagation matrix and a reciprocal scattering matrix with nonzero cross-polar terms. Time series data gathered during the summers of 1990 and 1992 with the German Aerospace Research Establishment (DLR) C-band polarimetric radar, POLDIRAD, located in Oberpfaffenhofen, Germany, are used to validate the polarization transformation method. Data collected in two convective precipitation shafts are analyzed and the resulting signatures are microphysically interpreted. The analysis and the presented data validate the polarization transformation method derived here under the assumption of a diagonal propagation matrix.
29 Sep 1994
TL;DR: A high resolution Mueller matrix imaging polarimetry test bed has been constructed and calibrated that has unique capabilities for characterizing optoelectronic devices, such as liquid crystal modulators, PLZT modulators and surface emitting lasers as discussed by the authors.
Abstract: A high resolution Mueller matrix imaging polarimetry test bed has been constructed and calibrated that has unique capabilities for characterizing optoelectronic devices, such as liquid crystal modulators, PLZT modulators, quantum well modulators, and surface emitting lasers. Similarly, the instrument can perform end-to-end measurements on optoelectronic systems including optical computers, interconnects, and correlators. It addresses, at the systems level, the need for incorporating polarimetric analysis and measurement techniques into the design, alignment, and testing of photonics technologies. The polarimeter maps the polarization altering characteristics of optical devices and optical systems, producing means of the retardance, the diattenuation, and the depolarization. The polarization mappings may be obtained across individual pixels or across large pixel arrays. The data sets provide a wealth of information not otherwise accessible for characterizing device uniformity, operating parameters, angular bandwidth, as well as identifying non-ideal polarization characteristics.
01 Jun 1994
TL;DR: The PICNIC as discussed by the authors is a near IR camera equipped with the 2D array detector NICMOS-3 manufactured by Rockwell and employs a four aspherical metal mirror system for reimaging optics.
Abstract: We constructed a near IR camera PICNIC equipped with the 2D array detector NICMOS-3 manufactured by Rockwell. Employing a four aspherical metal mirror system for reimaging optics, PICNIC is an IR imager distinguished with high throughput and small chromatic aberration. In addition to normal imaging mode, the camera has a prism spectroscopy mode and a polarimetry mode. A direct view prism, which can be optionally inserted in front of the camera, make it possible to obtain multiobject low resolution spectroscopy in the wavelength range from 1 to 2.5 micrometers at resolving power of approximately 50. Linear polarization can be measured with combination of the filters and/or the prism. We realized user-friendly operating environment as well as automated observation.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
14 Sep 1994
TL;DR: In this paper, a computer-controlled polarimeter was constructed to detect residual birefringence induced by residual stresses in GaAs, GaP and Si, which is suitable for quick investigation of large area wafers, since the data are acquired from a dense (256 X 256) network of points giving a reasonable spatial resolution.
Abstract: A computer-controlled polarimeter has been constructed. A wafer up to 6' in dia. is placed in a parallel beam of light between two sheet linear polarizers, whose transmission axes are set at 45 degree(s) and are simultaneously rotated by a stepper motor versus the immobile wafer. Four images of the wafer grabbed in the video frame grabber's memory at four incremented angles of the polarizer' transmission axes are then analyzed by a suitable procedure to yield tree maps: birefringence, the principal azimuth and transmission. The retardation error is usually smaller than 4 X 10 -3 radians, whereas that of the principal azimuth and transmission of a degree and of a percent, respectively. The four images are grabbed within 3 - 4 seconds (10 such averaging cycles--if necessary--consumes less than 50 seconds), and the maps are calculated within 6 - 7 seconds including corrections for background birefringence and transmission. The polarimeter is suitable for quick investigation of large-area wafers, since the data are acquired from a dense (256 X 256) network of points giving a reasonable spatial resolution. In this work some results of investigations of birefringence induced by residual stresses in GaAs, GaP and Si are presented.
15 Feb 1994
TL;DR: The Wide Field Imaging Survey Polarimeter (WISPolarimeter) as discussed by the authors was designed for ultraviolet polarimetry and was used in the WISP flight to explore the Pleiades reflection nebula.
Abstract: Two sounding rockets payloads under development at the Space Astronomy Laboratory are intended to explore different forms of ultraviolet astronomical polarimetry as a follow-up to the successful mission of the Wisconsin Ultraviolet Photo-Polarimeter Experiment (WUPPE). The unknown territory of diffuse-object ultraviolet polarimetry is to be explored by the Wide- Field Imaging Survey Polarimeter (WISP). WISP is a quite unusual integrated fast telescope/polarimeter optimized for the wavelengths 135 - 260 nm. The first WISP flight is scheduled for Fall 1993, targeting the Pleiades reflection nebula. Just in its early development is another sounding rocket payload, the Far-Ultraviolet Spectropolarimeter. This instrument is to have a resolution of better than 0.1 nm and a spectral coverage from 105 to 145 nm. It will consist of a 0.4 m parabolic primary with polarimetric optics at the prime focus and a far ultraviolet spectrometer. The polarimetric analyzer will be a thin stressed-LiF waveplate, followed by a diamond Brewster-angle polarizer.
15 Feb 1994
TL;DR: In this article, the response of some possible configurations with different thickness of plastic scintillator, CsI and CaF2, was computed by means of MCNP code.
Abstract: Scattering polarimetry is based on the detection of photons scattered by a target at angles close to 90 degree(s). For Astrophysical purposes in the hard X-ray band, where a large collecting area is needed and optics are ineffective, we suggest to produce a large array of very thin detectors made of scintillating fibers read by optical fibers. We computed, by means of MCNP code the response of some possible configurations with different thickness of plastic scintillator, CsI and CaF2.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.