Spectral Polarimetry Research Articles

Study of Microphysical Signatures Based on Spectral Polarimetry during the RELAMPAGO Field Experiment in Argentina

Abstract Weather radars with dual-polarization capabilities enable the study of various characteristics of hydrometeors, including their size, shape, and orientation. Radar polarimetric measurements, coupled with Doppler information, allow for analysis in the spectral domain. This analysis can be leveraged to reveal valuable insight into the microphysics and kinematics of hydrometeors in precipitation systems. This paper uses spectral polarimetry to investigate precipitation microphysics and kinematics in storm environments observed during the Remote Sensing of Electrification, Lightning, and Mesoscale/Microscale Processes with Adaptive Ground Observations (RELAMPAGO) field experiment in Argentina. This study uses range–height indicator scan measurements from a C-band polarimetric Doppler weather radar deployed during the field campaign. In this work, the impact of storm dynamics on hydrometeors is studied, including the size sorting of hydrometeors due to vertical wind shear. In addition, particle microphysical processes because of aggregation and growth of ice crystals in anvil clouds, as well as graupel formation resulting from the riming of ice crystals and dendrites, are also analyzed here. The presence of different particle size distributions because of the mixing of hydrometeors in a sheared environment and resulting size sorting has been reported using spectral differential reflectivity (sZdr) slope. Spectral reflectivity sZh and sZdr have also been used to understand the signature of ice crystal aggregation in an anvil cloud. The regions of pristine ice crystals are identified from vertical profiles of spectral polarimetric variables in anvil cloud because of sZh < 0 dB and sZdr values around 2 dB. It is also found that the growth process of these ice crystals causes a skewed bimodal sZh spectrum due to the presence of both pristine ice crystals and dry snow. Next, graupel formation due to riming has been studied, and it is found that the riming process produces sZh values of about 10 dB and corresponding sZdr values of 1 dB. This positive sZdr indicates the presence of needle/columnar secondary ice particles formed by ice multiplication processes in the riming zones. Last, the temporal evolution of a storm is investigated by analyzing changes in hydrometeor types with time and their influence on the spectral polarimetric variables.

Harnessing disorder for photonic device applications

For photonic devices, structural disorder and light scattering have long been considered annoying and detrimental features that were best avoided or minimized. This review shows that disorder and complexity can be harnessed for photonic device applications. Compared to ordered systems, disordered systems provide much more possibilities and diverse optical responses. They have been used to create physical unclonable functions for secret key generation, and more recently for random projection, high-dimensional matrix multiplication, and reservoir computing. Incorporating structural disorder enables novel devices with unique functionalities as well as multi-functionality. A random system can function as an optical lens, a spectrometer, a polarimeter, and a radio frequency receiver. It is also employed for optical pulse measurement and full-field recovery. Multi-functional disordered photonic devices have been developed for hyperspectral imaging, spatial, and spectral polarimetry. In addition to passive devices, structural disorder has been incorporated to active devices. One prominent example is the random laser, which enables speckle-free imaging, super-resolution spectroscopy, broad tunability of high-power fiber laser, and suppression of lasing instabilities. Disordered devices have low fabrication costs, and their combination with advanced computational techniques may lead to a paradigm shift in photonics and optical engineering.

Validation of GRASP algorithm product from POLDER/PARASOL data and assessment of multi-angular polarimetry potential for aerosol monitoring

Validation of GRASP algorithm product from POLDER/PARASOL data and assessment of multi-angular polarimetry potential for aerosol monitoring

Application of Spectral Polarimetry to a Hailstorm at Low Elevation Angle

AbstractSpectral polarimetry has the potential to be used to study microphysical properties in relation to the dynamics within a radar resolution volume by combining Doppler and polarimetric measurements. The past studies of spectral polarimetry have focused on using radar measurements from higher elevation angles, where both the size sorting from the hydrometeors’ terminal velocities and polarimetric characteristics are maintained. In this work, spectral polarimetry is applied to data from the 0° elevation angle, where polarimetric properties are maximized. Radar data collected by the C-band University of Oklahoma Polarimetric Radar for Innovations in Meteorology and Engineering (OU-PRIME) during a hailstorm event on 24 April 2011 are used in the analysis. The slope of the spectral differential reflectivity exhibits interesting variations across the hail core, which suggests the presence of size sorting of hydrometeors caused by vertical shear in a turbulent environment. A nearby S-band polarimetric Weather Surveillance Radar-1988 Doppler (KOUN) is also used to provide insights into this hailstorm. Moreover, a flexible numerical simulation is developed for this study, in which different types of hydrometeors such as rain and melting hail can be considered individually or as a combination under different sheared and turbulent conditions. The impacts of particle size distribution, shear, turbulence, attenuation, and mixture of rain and melting hail on polarimetric spectral signatures are investigated with the simulated Doppler spectra and spectral differential reflectivity.

Study of Accuracy Improvement on NIR Spectral Polarimetry and Application to Image Analysis by Backscattered Light for Measurement of Friction Coefficient of Icy Road Surface

Study of Accuracy Improvement on NIR Spectral Polarimetry and Application to Image Analysis by Backscattered Light for Measurement of Friction Coefficient of Icy Road Surface

近赤外偏光分光計測による凍結路面の表面粗さ解析(第3 報)

近赤外偏光分光計測による凍結路面の表面粗さ解析(第3 報)

近赤外偏光分光計測による凍結路面の表面粗さ解析(第2 報)

近赤外偏光分光計測による凍結路面の表面粗さ解析(第2 報)

Theoretical Study of NIR Spectral Polarimetry and Application to Image Analysis for Measurement of Friction Coefficient of Icy Road Surface

Theoretical Study of NIR Spectral Polarimetry and Application to Image Analysis for Measurement of Friction Coefficient of Icy Road Surface

Compact acousto-optic imaging spectro-polarimeter for mineralogical investigations in the near infrared.

Spectral imaging in the near infrared is a promising method for mineralogy analysis, in particular well-suited for airless celestial objects or those with faint atmospheres. Additional information about structure and composition of minerals can be obtained using spectral polarimetry with high spatial resolution. We report design and performance of laboratory prototype for a compact near infrared acousto-optic imaging spectro-polarimeter, which may be implemented for remote or close-up analysis of planetary surfaces. The prototype features telecentric optics, apochromatic design over the bandwidth of 0.8-1.75 µm, and simultaneous imaging of two orthogonal linear polarizations of the same scene with a single FPA detector. When validating the scheme, reflectance spectra of several minerals were measured with the spectral resolution of 100 cm-1 (10 nm passband at 1 µm). When imaging samples, the spatial resolution of 0.6 mm at the target distance of one meter was reached. It corresponds to 100 by 100 diffraction-limited elements resolved at the focal plane array (FPA) for each of the two light polarizations. A similar prototype is also being designed for the spectral range from 1.7 to 3.5 µm. This type of the spectro-polarimeter is considered as a potential reconnaissance and analysis tool for future planetary or moon landers and rovers.

Suprathermal electrons in a vacuum spark discharge

Results of experiments on the detection of suprathermal electron beams in the plasma of a highcurrent low-inductance vacuum spark by means of space-resolved spectral X-ray polarimetry are presented. It is shown that the observed polarization of bremsstrahlung may be caused by an ~100-keV electron beam propagating along the discharge axis from the pinching region toward the anode. The influence of the discharge initiation conditions on the parameters of the generated electron beams is analyzed.

Measurement of Surface Roughness of Icy Road Surface by Spectral Polarimetry

Measurement of Surface Roughness of Icy Road Surface by Spectral Polarimetry

ON THE COMBINATION OF IMAGING-POLARIMETRY WITH SPECTROPOLARIMETRY OF UPPER SOLAR ATMOSPHERES DURING SOLAR ECLIPSES

We present results from imaging polarimetry (IP) of upper solar atmospheres during a total solar eclipse on 2012 November 13 and spectropolarimetry of an annular solar eclipse on 2010 January 15. This combination of techniques provides both the synoptic spatial distribution of polarization above the solar limb and spectral information on the physical mechanism producing the polarization. Using these techniques together we demonstrate that even in the transition region, the linear polarization increases with height and can exceed 20%. IP shows a relatively smooth background distribution in terms of the amplitude and direction modified by solar structures above the limb. A map of a new quantity that reflects direction departure from the background polarization supplies an effective technique to improve the contrast of this fine structure. Spectral polarimetry shows that the relative contribution to the integrated polarization over the observed passband from the spectral lines decreases with height while the contribution from the continuum increases as a general trend. We conclude that both imaging and spectral polarimetry obtained simultaneously over matched spatial and spectral domains will be fruitful for future eclipse observations.

Polarization spectral characteristics of soil surface moisture in the mid-wave infrared range

The surfaces of soil with different moisture contents had been surveyed by the spectral polarimetry in the midw ave infrared range.The results indicate that the thermal radiation from the w ater-bearing soil surface is almost unpolarized,and the polarization characteristic of the soil surface is mainly caused by the reflection of solar light.Especially in the strong sunshine spectral range,the degree of polarization increases monotonically w ith the increase of soil moisture.This quantitative relationship provides basis for soil moisture monitoring by the remote sensing of the polarization of light in the mid-w ave infrared range.

Statistical Quality of Spectral Polarimetric Variables for Weather Radar

Abstract Spectral polarimetry for weather radar capitalizes on both Doppler and polarimetric measurements to reveal polarimetric variables as a function of radial velocity through spectral analysis. For example, spectral differential reflectivity at a velocity represents the differential reflectivity from all the scatterers that have the same radial velocity of interest within the radar resolution volume. Spectral polarimetry has been applied to suppress both ground and biological clutter, retrieve individual drop size distributions from a mixture of different types of hydrometeors, and estimate turbulence intensity, for example. Although spectral polarimetry has gained increasing attention, statistical quality of the estimation of spectral polarimetric variables has not been investigated. In this work, the bias and standard deviation (SD) of spectral differential reflectivity and spectral copolar correlation coefficient estimated from averaged spectra were derived using perturbation method. The results show that the bias and SD of the two estimators depend on the spectral signal-to-noise ratio, spectral copolar correlation coefficient, the number of spectrum average, and spectral differential reflectivity. A simulation to generate time series signals for spectral polarimetry was developed and used to verify the theoretical bias and SD of the two estimators.

Spectral polarimetry technique as a complementary tool to ellipsometry of dielectric films

Ellipsometry is a highly sensitive optical technique for coating characterization but usually presents multiple solutions in many cases. To prevent these, a method with addition of a spectral polarimetric technique is proposed. An initial film dispersion curve, independently of its physical thickness, is then provided using the same setup as spectral ellipsometry and at the same sample position, which later is used for thickness determination and dispersion refinement with increase of reliability of results. Characterization of thin TiO2 films with one and two ellipsometric solutions is shown to corroborate the validity of the proposed method.

Polarization mode dispersion spectrum measurement via high-speed wavelength-parallel polarimetry

We report experiments in which wavelength-parallel spectral polarimetry technology is used for measurement of the frequency-dependent polarization mode dispersion (PMD) vector. Experiments have been performed using either a grating spectral disperser, configured to provide 13.6 GHz spectral resolution over a 14 nm optical bandwidth, or a virtually imaged phased array spectral disperser, configured for 1.6 GHz spectral resolution over a 200 GHz band. Our results indicate that the spectral polarimetry data obtained via this approach are of sufficient quality to permit accurate extraction of the PMD spectrum. The wavelength-parallel spectral polarimetry approach allows data acquisition within a few milliseconds.

The polarization of scattered Lyα radiation around high-redshift galaxies

The high-redshift Universe contains luminous Lya emitting sources such as galaxies and quasars. The emitted Lyα radiation is often scattered by surrounding neutral hydrogen atoms. We show that the scattered Lyα radiation obtains a high level of polarization for a wide range of likely environments of high-redshift galaxies. For example, the backscattered Lya flux observed from galaxies surrounded by a superwind-driven outflow may reach a fractional polarization as high as ∼40 per cent. Equal levels of polarization may be observed from neutral collapsing protogalaxies. Resonant scattering in the diffuse intergalactic medium typically results in a lower polarization amplitude (<7 per cent), which depends on the flux of the ionizing background. Spectral polarimetry can differentiate between Lya scattering off infalling gas and outflowing gas; for an outflow, the polarization should increase towards longer wavelengths while for infall the opposite is true. Our numerical results suggest that Lya polarimetry is feasible with existing instruments, and may provide a new diagnostic of the distribution and kinematics of neutral hydrogen around high-redshift galaxies. Moreover, polarimetry may help suppress infrared lines originating in the Earth's atmosphere, and thus improve the sensitivity of ground-based observations to high-redshift Lya emitting galaxies outside the currently available redshift windows.

Fiber-based single-channel polarization-sensitive spectral interferometry

We present a novel, to our knowledge, fiber-based single-channel polarization-sensitive spectral interferometry system that provides depth-resolved measurement of polarization transformations of light reflected from a sample. Algebraic expressions for the Stokes parameters at the output of the interferometer are derived for light reflected from a birefringent sample by using the cross-spectral density function. By insertion of a fiber-optic spectral polarimetry instrument into the detection path of a common-path spectral interferometer, the full set of Stokes parameters of light reflected from a sample can be obtained with a single optical frequency scan. The methodology requires neither polarization-control components nor prior knowledge of the polarization state of light incident on the sample. The fiber-based single-channel polarization-sensitive spectral interferometer and analysis are demonstrated by measurement of phase retardation and fast-axis angle of a birefringent mica plate.

Fiber-optic spectral polarimeter using a broadband swept laser source

We present a novel fiber-optic spectral polarimetry instrument based on optical frequency domain interferometry to provide measurement of the Stokes spectra of collected light. Stokes spectra are encoded into discrete channels in the time delay domain. The instrument consists of a broadband swept laser source, calibrated wavemeter, two segments of polarization maintaining (PM) fiber, an analyzer and photo-receiver. Performance of the instrument is demonstrated by reconstruction of Stokes spectra for a variety of prepared incident polarization states.

Spectral polarimetry with a differential group delay bias

We show that the addition of a polarization controller and bias differential group delay to a spectral polarimeter increases the amount of polarization information that can be extracted from a Stokes spectrum measurement. We use this biased spectral polarimetry on 40-Gbit/s signals to measure the polarization mode dispersion of the optical fiber through which they propagate. Our measurements do not require any control of the polarization at the fiber input. Averaging measurements from several settings of the polarization controller yields improved accuracy, and, after data rejection is applied, both the accuracy and the number of valid data points is increased when using several measurements.