Showing papers on "Polarimetry published in 2013"

Principles and Applications of Dual-Polarization Weather Radar. Part I: Description of the Polarimetric Radar Variables

Abstract: The United States Weather Surveillance Radar-1988 Doppler (WSR-88D) radar network has been upgraded to dual-polarization capabilities, providing operational and research meteorologists with a wealth of new information regarding the types and distributions of hydrometeors within precipitating storms, as well as a means for improved radar data quality. In addition to the conventional moments of reflectivity factor at horizontal polarization (ZH), Doppler velocity (Vr), and Doppler spectrum width (W), the new variables available from upgraded radars are the differential reflectivity (ZDR), differential propagation phase shift (ΦDP), specific differential phase (KDP), and the co-polar correlation coefficient (ρhv or CC). In the first part of this review series, a description of the polarimetric radar variables available from the newly polarimetric WSR-88D radars is provided. An emphasis is made on their physical meaning and interpretation in the context of operational meteorology.

XIPE: the X-ray imaging polarimetry explorer

Abstract: X-ray polarimetry, sometimes alone, and sometimes coupled to spectral and temporal variability measurements and to imaging, allows a wealth of physical phenomena in astrophysics to be studied. X-ray polarimetry investigates the acceleration process, for example, including those typical of magnetic reconnection in solar flares, but also emission in the strong magnetic fields of neutron stars and white dwarfs. It detects scattering in asymmetric structures such as accretion disks and columns, and in the so-called molecular torus and ionization cones. In addition, it allows fundamental physics in regimes of gravity and of magnetic field intensity not accessible to experiments on the Earth to be probed. Finally, models that describe fundamental interactions (e.g. quantum gravity and the extension of the Standard Model) can be tested. We describe in this paper the X-ray Imaging Polarimetry Explorer (XIPE), proposed in June 2012 to the first ESA call for a small mission with a launch in 2017. The proposal was, unfortunately, not selected. To be compliant with this schedule, we designed the payload mostly with existing items. The XIPE proposal takes advantage of the completed phase A of POLARIX for an ASI small mission program that was cancelled, but is different in many aspects: the detectors, the presence of a solar flare polarimeter and photometer and the use of a light platform derived by a mass production for a cluster of satellites. XIPE is composed of two out of the three existing JET-X telescopes with two Gas Pixel Detectors (GPD) filled with a He-DME mixture at their focus. Two additional GPDs filled with a 3-bar Ar-DME mixture always face the Sun to detect polarization from solar flares. The Minimum Detectable Polarization of a 1 mCrab source reaches 14 % in the 2–10 keV band in 105 s for pointed observations, and 0.6 % for an X10 class solar flare in the 15–35 keV energy band. The imaging capability is 24 arcsec Half Energy Width (HEW) in a Field of View of 14.7 arcmin × 14.7 arcmin. The spectral resolution is 20 % at 6 keV and the time resolution is 8 μs. The imaging capabilities of the JET-X optics and of the GPD have been demonstrated by a recent calibration campaign at PANTER X-ray test facility of the Max-Planck-Institut fur extraterrestrische Physik (MPE, Germany). XIPE takes advantage of a low-earth equatorial orbit with Malindi as down-link station and of a Mission Operation Center (MOC) at INPE (Brazil). The data policy is organized with a Core Program that comprises three months of Science Verification Phase and 25 % of net observing time in the following 2 years. A competitive Guest Observer program covers the remaining 75 % of the net observing time.

The Airborne Multiangle SpectroPolarimetric Imager (AirMSPI): a new tool for aerosol and cloud remote sensing

Abstract: . The Airborne Multiangle SpectroPolarimetric Imager (AirMSPI) is an eight-band (355, 380, 445, 470, 555, 660, 865, 935 nm) pushbroom camera, measuring polarization in the 470, 660, and 865 nm bands, mounted on a gimbal to acquire multiangular observations over a ±67° along-track range. The instrument has been flying aboard the NASA ER-2 high altitude aircraft since October 2010. AirMSPI employs a photoelastic modulator-based polarimetric imaging technique to enable accurate measurements of the degree and angle of linear polarization in addition to spectral intensity. A description of the AirMSPI instrument and ground data processing approach is presented. Example images of clear, hazy, and cloudy scenes over the Pacific Ocean and California land targets obtained during flights between 2010 and 2012 are shown, and quantitative interpretations of the data using vector radiative transfer theory and scene models are provided to highlight the instrument's capabilities for determining aerosol and cloud microphysical properties and cloud 3-D spatial distributions. Sensitivity to parameters such as aerosol particle size distribution, ocean surface wind speed and direction, cloud-top and cloud-base height, and cloud droplet size is discussed. AirMSPI represents a major step toward realization of the type of imaging polarimeter envisioned to fly on NASA's Aerosol-Cloud-Ecosystem (ACE) mission in the next decade.

Exploring underwater target detection by imaging polarimetry and correlation techniques

Abstract: Underwater target detection is investigated by combining active polarization imaging and optical correlation-based approaches. Experiments were conducted in a glass tank filled with tap water with diluted milk or seawater and containing targets of arbitrary polarimetric responses. We found that target estimation obtained by imaging with two orthogonal polarization states always improves detection performances when correlation is used as detection criterion. This experimentally study illustrates the potential of polarization imaging for underwater target detection and opens interesting perspectives for the development of underwater imaging systems.

Calibration methods for division-of-focal-plane polarimeters

Abstract: Division-of-focal plane (DoFP) imaging polarimeters are useful instruments for measuring polarization information for a variety of applications. Recent advances in nanofabrication have enabled the practical manufacture of DoFP sensors for the visible spectrum. These sensors are made by integrating nanowire polarization filters directly with an imaging array, and size variations of the nanowires due to fabrication can cause the optical properties of the filters to vary up to 20% across the imaging array. If left unchecked, these variations introduce significant errors when reconstructing the polarization image. Calibration methods offer a means to correct these errors. This work evaluates a scalar and matrix calibration derived from a mathematical model of the polarimeter behavior. The methods are evaluated quantitatively with an existing DoFP polarimeter under varying illumination intensity and angle of linear polarization.

XIPE: the X-ray Imaging Polarimetry Explorer

Abstract: X-ray polarimetry, sometimes alone, and sometimes coupled to spectral and temporal variability measurements and to imaging, allows a wealth of physical phenomena in astrophysics to be studied. X-ray polarimetry investigates the acceleration process, for example, including those typical of magnetic reconnection in solar flares, but also emission in the strong magnetic fields of neutron stars and white dwarfs. It detects scattering in asymmetric structures such as accretion disks and columns, and in the so-called molecular torus and ionization cones. In addition, it allows fundamental physics in regimes of gravity and of magnetic field intensity not accessible to experiments on the Earth to be probed. Finally, models that describe fundamental interactions (e.g. quantum gravity and the extension of the Standard Model) can be tested. We describe in this paper the X-ray Imaging Polarimetry Explorer (XIPE), proposed in June 2012 to the first ESA call for a small mission with a launch in 2017 but not selected. XIPE is composed of two out of the three existing JET-X telescopes with two Gas Pixel Detectors (GPD) filled with a He-DME mixture at their focus and two additional GPDs filled with pressurized Ar-DME facing the sun. The Minimum Detectable Polarization is 14 % at 1 mCrab in 10E5 s (2-10 keV) and 0.6 % for an X10 class flare. The Half Energy Width, measured at PANTER X-ray test facility (MPE, Germany) with JET-X optics is 24 arcsec. XIPE takes advantage of a low-earth equatorial orbit with Malindi as down-link station and of a Mission Operation Center (MOC) at INPE (Brazil).

Single-pixel polarimetric imaging spectrometer by compressive sensing

Abstract: We present an optical system that performs polarimetric spectral imaging with a detector with no spatial resolution. This fact is possible by applying the theory of compressive sampling to the data acquired by a sensor composed of an analyzer followed by a commercial fiber spectrometer. The key element in the measurement process is a digital micromirror device, which sequentially generates a set of intensity light patterns to sample the object image. For different configurations of the analyzer, we obtain polarimetric images that provide information about the spatial distribution of light polarization at several spectral channels. Experimental results for colorful objects are presented in a spectral range that covers the visible spectrum and a part of the NIR range. The performance of the proposed technique is discussed in detail, and further improvements are suggested.

Coded aperture snapshot spectral polarization imaging.

Abstract: We describe a single-shot polarization spectral imager that combines two birefringent crystals with a binary coded aperture to encode the spatial, spectral and polarization data cube for compressive sampling on a two-dimensional (2D) detector array. We use a total variation prior to reconstruct the four-dimensional (4D) data cube from the single 2D measurement. The 4D data cube includes 1500×1240 pixels in the spatial domain, 19 wavelength channels between 400 and 680 nm and two Stokes parameters.

On the Reconstruction of Quad-Pol SAR Data From Compact Polarimetry Data For Ocean Target Detection

Abstract: Circular-transmit/linear-receive compact polarimetry synthetic aperture radar systems combine coherent dual polarization with wide-swath imaging. The polarization information in these data may be represented as a Stokes vector, or one can reconstruct several quadpolarized covariance elements. Two reconstruction algorithms have been published in the literature: one by Souyris and a refined algorithm by Nord We investigated the application of these two algorithms for reconstructing ocean clutter for the purpose of detecting targets. We tested the assumptions underlying these algorithms and found that they were not valid for ocean scenes. We present a simple empirical reconstruction model whose reconstruction and target detection performance is superior to the two published algorithms.

Image sensor pixel with on-chip high extinction ratio polarizer based on 65-nm standard CMOS technology

Abstract: In this study, we demonstrate a polarization sensitive pixel for a complementary metal-oxide-semiconductor (CMOS) image sensor based on 65-nm standard CMOS technology. Using such a deep-submicron CMOS technology, it is possible to design fine metal patterns smaller than the wavelengths of visible light by using a metal wire layer. We designed and fabricated a metal wire grid polarizer on a 20 × 20 μm(2) pixel for image sensor. An extinction ratio of 19.7 dB was observed at a wavelength 750 nm.

Polarization-sensitive THz-TDS and its Application to Anisotropy Sensing

Abstract: We review recent progress in polarization-sensitive time-domain spectroscopy at THz frequencies (THz-TDS). Developments in spectroscopic polarimetry and ellipsometry and various polarization components targeting THz frequencies are introduced. Polarization-sensitive measurements are suitable for studying the anisotropic responses of materials induced by factors such as structure, stress, and magnetic fields. Examples of observations of anisotropic characteristics of materials such as birefringence, optical activity, and magneto-optic effects are also presented.

Polarimetry in the hard x-ray domain with integral spi*

Abstract: We present recent improvements in polarization analysis with the INTEGRAL SPI data. The SPI detector plane consists of 19 independent Ge crystals and can operate as a polarimeter. The anisotropy characteristics of Compton diffusions can provide information on the polarization parameters of the incident flux. By including the physics of the polarized Compton process in the instrument simulation, we are able to determine the instrument response for a linearly polarized emission at any position angle. We compare the observed data with the simulation sets by a minimum χ2 technique to determine the polarization parameters of the source (angle and fraction). We have tested our analysis procedure with Crab Nebula observations and find a position angle similar to those previously reported in the literature, with a comfortable significance. Since the instrument response depends on the incident angle, each exposure in the SPI data requires its own set of simulations, calculated for 18 polarization angles (from 0° to 170° in steps of 10°) and unpolarized emission. The analysis of a large number of observations for a given source, required to obtain statistically significant results, represents a large amount of computing time, but it is the only way to access this complementary information in the hard X-ray regime. Indeed, major scientific advances are expected from such studies since the observational results will help to discriminate between the different models proposed for the high energy emission of compact objects like X-ray binaries and active galactic nuclei or gamma-ray bursts.

PX-1000: A Solid-State Polarimetric X-Band Weather Radar and Time–Frequency Multiplexed Waveform for Blind Range Mitigation

Abstract: In this paper, a compact, transportable, and dual-polarization X-band weather radar was developed at the Advanced Radar Research Center of the University of Oklahoma. The radar was designed using a software-defined radio (SDR) approach for waveform versatility. One of the key innovations in this paper is the combination of SDR design and the mitigation of blind range, which is inherent in pulse compression radars, using a time-frequency multiplexed waveform while compression is performed in pure software architecture. Internally, this radar has been referred to as the PX-1000. It is primarily used as a platform for waveform studies and various signal processing techniques, such as pulse compression, polarimetric signal processing, refractivity retrieval, and support of various field campaigns. The radar system has been completed and is operational. It has two identical and independent power amplifiers, one for each polarization. The system also features a 1.2-m parabolic reflector dish with dual-polarization feed, which provides a 1.8 ° beamwidth. A majority of the components are housed above the turntable of an azimuth-over-elevation pedestal. We also took this opportunity to design and develop a new software suite that includes signal processing, system control, and graphical user interface. The raw I/Q time series can be recorded and streamed out of the radar system in real time. In this paper, a detailed description of the radar and some experimental data will be presented.

Conical refraction as a tool for polarization metrology

Abstract: A method for polarization metrology based on the conical refraction (CR) phenomenon, occurring in biaxial crystals, is reported. CR transforms an input Gaussian beam into a light ring whose intensity distribution is linked to the incoming polarization. We present the design of a division-of-amplitude complete polarimeter composed of two biaxial crystals, whose measurement principle is based on the CR phenomenon. This design corresponds to a static polarimeter, that is, without mechanical movements or electrical signal addressing. Only one division-of-amplitude device is required, besides the two biaxial crystals, to completely characterize any state of polarization, including partially polarized and unpolarized states. In addition, a mathematical model describing the system is included. Experimental images of the intensity distribution related to different input polarization states are provided. These intensity patterns are compared with simulated values, proving the potential of polarimeters based on biaxial crystals.

Triple Wollaston-prism complete-Stokes imaging polarimeter

Abstract: Imaging polarimetry is emerging as a powerful tool for remote sensing in space science, Earth science, biology, defense, national security, and industry. Polarimetry provides complementary information about a scene in the visible and infrared wavelengths. For example, surface texture, material composition, and molecular structure will affect the polarization state of reflected, scattered, or emitted light. We demonstrate an imaging polarimeter design that uses three Wollaston prisms, addressing several technical challenges associated with moving remote-sensing platforms. This compact design has no moving polarization elements and separates the polarization components in the pupil (or Fourier) plane, analogous to the way a grating spectrometer works. In addition, this concept enables simultaneous characterization of unpolarized, linear, and circular components of optical polarization. The results from a visible-wavelength prototype of this imaging polarimeter are presented, demonstrating remote sensitivity to material properties. This work enables new remote sensing capabilities and provides a viable design concept for extensions into infrared wavelengths.

On the novel use of model-based decomposition in SAR polarimetry for target detection on the sea

Abstract: In this study, we show the novel applications of model-based scattering power decomposition analyses in synthetic aperture radar (SAR) polarimetry for man-made target detection on the sea surface. Model-based decomposition technique is primarily used for land-cover classification mainly because microwave scattering from land is composed of various scattering mechanisms. On the other hand, this technique has not been widely used for oceanic applications since the scattering from sea is mostly surface scattering, and obtaining a classification of different types of scattering is not as important as that on land. However, if an object is present on the sea surface, which gives rise to different scattering characteristics from the sea surface, the decomposition approach may be a useful technique for the detection and classification of the object. We suggest two approaches for target detection on the sea surface. One is to use the model-based decomposition as a polarimetric band-stop filter to block the domina...

Digital Correlation Microwave Polarimetry: Analysis and Demonstration

Abstract: The design, analysis, and demonstration of a digital-correlation microwave polarimeter for use in Earth remote sensing is presented. The authors begin with an analysis of a three-level digital correlator and develop the correlator transfer function and radiometric sensitivity. A fifth-order polynomial regression is derived for inverting the digital correlation coefficient into the analog statistic. In addition, the effects of quantizer threshold asymmetry and hysteresis are discussed. A two-look unpolarized calibration scheme is developed for identifying correlation offsets. The developed theory and calibration method are verified using a 10.7 GHz and a 37.0 GHz polarimeter. The polarimeters are based upon 1-GS/s three-level digital correlators and measure the first three Stokes parameters. Through experiment, the radiometric sensitivity is shown to approach the theoretical as derived earlier in the paper and the two-look unpolarized calibration method is successfully compared with results using a polarimetric scheme. Finally, sample data from an aircraft experiment demonstrates that the polarimeter is highly useful for ocean wind-vector measurement.

Methods of Processing Video Polarimetry Information Based on Least-Squares and Fourier Analysis

Abstract: 3 Abstract: The polarization state of light is a very significant source of information in biomedical imaging and diagnosis. Processing video polarimetry information can be quite difficult to measure. Effective calibration minimizes systematic errors in measuring intensity that appear due to movement of the optical components. In this article, we presented a comparison of two methods, namely, least square methods and Fourier analysis for the detection of Stokes parameters of a reflected by a biological tissue beam.

Polarimetry in the hard X-ray domain with INTEGRAL SPI

Abstract: We present recent improvements in polarization analysis with the INTEGRAL SPI data. The SPI detector plane consists of 19 independent Ge crystals and can operate as a polarimeter. The anisotropy characteristics of Compton diffusions can provide information on the polarization parameters of the incident flux. By including the physics of the polarized Compton process in the instrument simulation, we are able to determine the instrument response for a linearly polarized emission at any position angle. We compare the observed data with the simulation sets by a minimum \chi^2 technique to determine the polarization parameters of the source (angle and fraction). We have tested our analysis procedure with Crab nebula observations and find a position angle similar to those previously reported in the literature, with a comfortable significance. Since the instrument response depends on the incident angle, each exposure in the SPI data requires its own set of simulations, calculated for 18 polarization angles (from 0° to 170° in steps of 10°) and unpolarized emission. The analysis of a large amount of observations for a given source, required to obtain statistically significant results, represents a large amount of computing time, but it is the only way to access this complementary information in the hard X-ray regime. Indeed, major scientific advances are expected from such studies since the observational results will help to discriminate between the different models proposed for the high energy emission of compact objects like X-ray binaries and active galactic nuclei or gamma-ray bursts.

Photoelectric X-ray Polarimetry with Gas Pixel Detectors

Abstract: The Gas Pixel Detector, recently developed and continuously improved by Pisa-INFN in collaboration with IASF-Roma (INAF), can visualize the tracks produced within a low Z gas by photoelectrons of few keV. By reconstructing the impact point and the original direction of the photoelectrons, the GPD can measure the polarization plane of X-Ray photons, while preserving the information on the absorption point, the energy and the time of arrival of individual photons. Applied to X-ray Astrophysics, in the focus of grazing incidence telescopes, it can perform angular and energy resolved polarimetry with a large improvement of sensitivity, when compared with the conventional techniques of Bragg diffraction at 45° and Compton scattering around 90°. This configuration has been the basis of POLARIX and HXMT, two pathfinder missions, and was included in the baseline design of IXO, the very large X-ray telescope under study by NASA, ESA and JAXA. We have recently improved the design of this low energy polarimeter (2–10 keV) by modifying the geometry of the absorption cell to minimize any systematic effect that could leave a residual polarization signal for non-polarized source. We will report on the testing of this new concept.

Combined Stokes vector and Mueller matrix polarimetry for materials characterization.

Abstract: A robust way of measuring the optical properties of any material is to interrogate it with light of different polarizations. The 16-element Mueller matrix provides the most complete description of the optical properties of a sample based on its ability to alter the polarization state of transmitted or reflected light. This is valuable for ordered and isotropic materials alike. Similarly, the 4-element Stokes vector is the most complete description of the polarization of a light beam, including any depolarization effects. While the Mueller matrix offers the most chemical and physical insight, the Stokes vectors are easier to obtain, and there are more schemes for measuring them quickly in situations where time resolution is important. We describe a method where any Stokes polarimeter may be adapted to obtain Mueller matrices and discuss various approaches for achieving better time resolution.

Estimation of the Degree of Polarization for Hybrid/Compact and Linear Dual-Pol SAR Intensity Images: Principles and Applications

Abstract: Analysis and comparison of linear and hybrid/compact dual-polarization (dual-pol) synthetic aperture radar (SAR) imagery have gained a wholly new importance in the last few years, in particular, with the advent of new spaceborne SARs such as the Japanese ALOS PALSAR, the Canadian RADARSAT-2, and the German TerraSAR-X. Compact polarimetry, hybrid dual-pol, and quad-pol modes are newly promoted in the literature for future SAR missions. In this paper, we investigate and compare different hybrid/compact and linear dual-pol modes in terms of the estimation of the degree of polarization (DoP). The DoP has long been recognized as one of the most important parameters characterizing a partially polarized electromagnetic wave. It can be effectively used to characterize the information content of SAR data. We study and compare the information content of the intensity data provided by different hybrid/compact and linear dual-pol SAR modes. For this purpose, we derive the joint distribution of multilook SAR intensity images. We use this distribution to derive the maximum likelihood and moment-based estimators of the DoP in hybrid/compact and linear dual-pol modes. We evaluate and compare the performance of these estimators for different modes on both synthetic and real data, which are acquired by RADARSAT-2 spaceborne and NASA/JPL airborne SAR systems, over various terrain types such as urban, vegetation, and ocean.

Multichroic Bolometric Detector Architecture for Cosmic Microwave Background Polarimetry Experiments

Abstract: Characterization of the Cosmic Microwave Background (CMB) B-mode polarization signal will test models of inflationary cosmology, as well as constrain the sum of the neutrino masses and other cosmological parameters. The low intensity of the B-mode signal combined with the need to remove polarized galactic foregrounds requires a sensitive millimeter receiver and effective methods of foreground removal. Current bolometric detector technology is reaching the sensitivity limit set by the CMB photon noise. Thus, we need to increase the optical throughput to increase an experiment's sensitivity. To increase the throughput without increasing the focal plane size, we can increase the frequency coverage of each pixel. Increased frequency coverage per pixel has additional advantage that we can split the signal into frequency bands to obtain spectral information. The detection of multiple frequency bands allows for removal of the polarized foreground emission from synchrotron radiation and thermal dust emission, by utilizing its spectral dependence. Traditionally, spectral information has been captured with a multi-chroic focal plane consisting of a heterogeneous mix of single-color pixels. To maximize the efficiency of the focal plane area, we developed a multi-chroic pixel. This increases the number of pixels per frequency with same focal plane area.We developed multi-chroic antenna-coupled transition edge sensor (TES) detector array for the CMB polarimetry. In each pixel, a silicon lens-coupled dual polarized sinuous antenna collects light over a two-octave frequency band. The antenna couples the broadband millimeter wave signal into microstrip transmission lines, and on-chip filter banks split the broadband signal into several frequency bands. Separate TES bolometers detect the power in each frequency band and linear polarization. We will describe the design and performance of these devices and present optical data taken with prototype pixels and detector arrays. Our measurements show beams with percent level ellipticity, percent level cross-polarization leakage, and partitioned bands using banks of two and three filters. We will also describe the development of broadband anti-reflection coatings for the high dielectric constant lens. The broadband anti-reflection coating has approximately 100% bandwidth and no detectable loss at cryogenic temperature. We will describe a next generation CMB polarimetry experiment, the POLARBEAR-2, in detail. The POLARBEAR-2 would have focal planes with kilo-pixel of these detectors to achieve high sensitivity. We'll also introduce proposed experiments that would use multi-chroic detector array we developed in this work. We'll conclude by listing out suggestions for future multichroic detector development.

Fisher Analysis on Wide-Band Polarimetry for Probing the Intergalactic Magnetic Field

Abstract: We investigate the capability of ongoing radio telescopes for probing Faraday rotation measure (RM) due to the intergalactic magnetic field (IGMF) in the large-scale structure of the universe which is expected to be of order $O(1) {\rm rad/m^2}$. We consider polarization observations of a compact radio source such as quasars behind a diffuse source such as the Galaxy, and calculate Stokes parameters $Q$ and $U$ assuming a simple model of the Faraday dispersion functions with Gaussian shape. Then, we perform the Fisher analysis to estimate the expected errors in the model parameters from QU-fitting of polarization intensity, accounting for sensitivities and frequency bands of Australian Square Kilometer Array Pathfinder, Low Frequency Array, and the Giant Meterwave Radio Telescope. Finally, we examine the condition on the source intensities which are required to detect the IGMF. Our analysis indicates that the QU-fitting is promising for forthcoming wideband polarimetry to explore RM due to the IGMF in filaments of galaxies.

Methods and apparatus for electromagnetic signal polarimetry sensing

Abstract: A system and method of identifying changes utilizing radio frequency polarization includes receiving a reflected and/or transmitted polarized radio frequency signal at a receiver, filtering, amplifying and conditioning the received signal, converting the received signal from an analog format to a digital format, processing the digital signal to elicit a polarization mode dispersion feature of the received signal, and comparing the polarization mode dispersion features to a known calibration to detect a change in a characteristic of the target object.

Uncertainty Estimates for Imager Reference Inter-Calibration With CLARREO Reflected Solar Spectrometer

Abstract: One of the Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission objectives is to provide a high accuracy calibration standard on orbit to enable inter-calibration of existing sensors. In order to perform an accurate inter-calibration of imaging radiometers, such as VIIRS, one must take into account instrument sensitivity to polarization of incoming light. Even if the sensitivity to polarization of an instrument is established or known on orbit, the knowledge of the polarization state of reflected light is required to make relevant radiometric corrections. In the case when coincident polarimetric measurements are not available, we propose to use a combination of empirical and theoretical models to predict the polarization of solar reflected light at the top-of-atmosphere. We used observations from on-orbit polarimeter PARASOL to derive a global set of empirical Polarization Distribution Models (PDM) as a function of scene type and viewing geometry. The PDM accuracy for the mean values is estimated to match the 3% PARASOL uncertainty in its polarization measurements. The instantaneous single sample uncertainty of the prototype PDMs for the linear degree of polarization is contained within 15%. We also present the formalism and numeric estimates for resulting uncertainty for inter-calibration of an imaging radiometer with the CLARREO reference observations, including uncertainty due to instrument sensitivity to polarization. The uncertainty estimates consider a range of scenarios with varying data sampling, uncertainty of polarization, and imaging radiometer sensitivity to polarization. These results are used to recommend CLARREO mission requirements relevant to reference inter-calibration and polarization effects.

Glacier Velocity Estimation by Means of a Polarimetric Similarity Measure

Abstract: The contribution of polarimetric synthetic aperture radar (PolSAR) images compared with that of single-channel SAR images in terms of temporal scene characterization has been found and described to add valuable information in the literature However, despite a number of recent studies focusing on single-polarized glacier monitoring, the potential of polarimetry to estimate the surface velocity of glaciers has not been explored due to the complex mechanism of polarization through glacier/snow In this paper, a new approach to the problem of monitoring glacier surface velocity is proposed by means of temporal PolSAR images, using a basic concept from information theory, ie, mutual information (MI) The proposed polarimetric tracking method applies the MI to measure the statistical dependence between temporal polarimetric images, which is assumed to be maximum if the images are geometrically aligned Since the proposed polarimetric tracking method is very powerful and general, it can be implemented into any kind of multivariate remote sensing data such as multichannel optical and single-channel SAR images The proposed polarimetric tracking is then used to retrieve the surface velocity of the Aletsch Glacier in Switzerland and the Inylchek Glacier in Kyrgyzstan with two different SAR sensors: the Experimental SAR airborne L-band (fully polarimetric) and Envisat C-band (single-polarized) systems, respectively The effect of the number of channels (polarimetry) into tracking investigations demonstrated that the presence of snow, as expected, affects the location of the phase center in different polarization and frequency channels, as for the glacier tracking with temporal HH compared to temporal VV channels In this paper, it is shown how it is possible to optimize these two different contributions, considering the multichannel SAR statistics