scholarly journals Microwave scattering from ice crystals: how much parameters can differ from equal volume spheres

2010 ◽  
Vol 25 ◽  
pp. 127-133 ◽  
Author(s):  
F. Teschl ◽  
W. L. Randeu ◽  
R. Teschl
Keyword(s):  
Cross Section ◽  
Single Scattering ◽  
Dipole Approximation ◽  
Ice Crystals ◽  
Spherical Particles ◽  
Scattering Parameters ◽  
Microwave Scattering ◽  
Millimeter Wavelengths ◽  
Ice Water ◽  
Huge Variety

Abstract. The scattering properties of ice crystals at centimeter and millimeter wavelengths are fundamental for their measurement with radars or radiometers as well as for many other applications in remote sensing. Only the scattering properties of homogeneous spheres can be computed in a mathematically exact way using the Mie theory. Therefore, for many approaches ice crystals and other frozen hydrometeors are approximated by ice spheres that have the same volume as the crystal or hydrometeor – so called equal volume spheres. However, many frozen hydrometeors are non-spherical. They exist in a huge variety of shapes and exhibit different mixtures of ice, water and air. Therefore it is desirable to accurately compute scattering from non-spherical particles in order to clearly understand the effect the shape of a hydrometeor has on its scattering pattern. In this study, single scattering parameters like scattering cross section (Csca) and absorption cross section (Cabs) were calculated for six pristine ice crystals by means of the Discrete Dipole Approximation (DDA). The calculations were carried out for frequencies from 1 GHz to 300 GHz – leading to size parameters of up to 4. The study calculates the scattering parameters for randomly oriented ice crystals and investigates to what extent the exact scattering parameters can differ from an approximation by equal volume spheres.

scholarly journals Bulk microphysical properties of semi transparent cirrus from AIRS: a six years global climatology and statistical analysis in synergy with CALIPSO and CloudSat

2011 ◽  
Vol 11 (9) ◽  
pp. 24671-24725
Author(s):  
A. Guignard ◽  
C. J. Stubenrauch ◽  
A. J. Baran ◽  
R. Armante
Keyword(s):  
Statistical Analysis ◽  
General Circulation ◽  
General Circulation Models ◽  
Single Scattering ◽  
Ice Crystals ◽  
Effective Diameter ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Microphysical Properties ◽  
Ice Water

Abstract. This article presents a retrieval method and a statistical analysis of the bulk micropysical properties of semi-transparent ice clouds using the Atmospheric Infrared Sounder (AIRS). Global and long-term coverage provides information on the effective diameter (De) and habits of ice crystals in relation with their environment, ice water path (IWP) and temperature. The method relies on spectral absorption differences between 8 and 12 μm that depend on ice crystal properties. Using single scattering properties for column-like or aggregate-like ice crystals, the method is sensitive to De of up to 85 μm and IWP of up to 120 g m−2. Uncertainties due to the hypotheses on atmospheric parameters and ice crystal single scattering properties as well as horizontal heterogeneities have been demonstrated to be small. The behaviour of bulk microphysical properties as a function of temperature demonstrates that pure ice clouds only occur when Tcld<230 K. On a global scale, these clouds represent practically 25 % of all high clouds and are mainly encountered in the mid-latitudes during winter and in the tropics. Colocated Radar-Lidar Geometrical Profiling (GEOPROF) data reveal an increase in the vertical extent of these cloud layers during mid-latitude winter but which does not significantly impact ice crystal characteristics. A comparative study with bulk microphysical properties from the TIROS-N Operational Vertical Sounder (TOVS) reveals improvements, especially for optically thin and thick semi-transparent ice clouds. Finally, we investigated parametrizations of De as a function of IWP or Ice Water Content (IWC), which could be useful for modelling cirrus in General Circulation Models.

scholarly journals Spectrally Consistent Scattering, Absorption, and Polarization Properties of Atmospheric Ice Crystals at Wavelengths from 0.2 to 100 μm

2013 ◽  
Vol 70 (1) ◽  
pp. 330-347 ◽  
Author(s):  
Ping Yang ◽  
Lei Bi ◽  
Bryan A. Baum ◽  
Kuo-Nan Liou ◽  
George W. Kattawar ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Single Scattering ◽  
Dipole Approximation ◽  
Ice Crystals ◽  
Crystal Habit ◽  
Ice Crystal ◽  
Particle Volume ◽  
Ice Clouds ◽  
Sensing Applications ◽  
Data Library

Abstract A data library is developed containing the scattering, absorption, and polarization properties of ice particles in the spectral range from 0.2 to 100 μm. The properties are computed based on a combination of the Amsterdam discrete dipole approximation (ADDA), the T-matrix method, and the improved geometric optics method (IGOM). The electromagnetic edge effect is incorporated into the extinction and absorption efficiencies computed from the IGOM. A full set of single-scattering properties is provided by considering three-dimensional random orientations for 11 ice crystal habits: droxtals, prolate spheroids, oblate spheroids, solid and hollow columns, compact aggregates composed of eight solid columns, hexagonal plates, small spatial aggregates composed of 5 plates, large spatial aggregates composed of 10 plates, and solid and hollow bullet rosettes. The maximum dimension of each habit ranges from 2 to 10 000 μm in 189 discrete sizes. For each ice crystal habit, three surface roughness conditions (i.e., smooth, moderately roughened, and severely roughened) are considered to account for the surface texture of large particles in the IGOM applicable domain. The data library contains the extinction efficiency, single-scattering albedo, asymmetry parameter, six independent nonzero elements of the phase matrix (P11, P12, P22, P33, P43, and P44), particle projected area, and particle volume to provide the basic single-scattering properties for remote sensing applications and radiative transfer simulations involving ice clouds. Furthermore, a comparison of satellite observations and theoretical simulations for the polarization characteristics of ice clouds demonstrates that ice cloud optical models assuming severely roughened ice crystals significantly outperform their counterparts assuming smooth ice crystals.

scholarly journals Bulk microphysical properties of semi-transparent cirrus from AIRS: a six year global climatology and statistical analysis in synergy with geometrical profiling data from CloudSat-CALIPSO

2012 ◽  
Vol 12 (1) ◽  
pp. 503-525 ◽  
Author(s):  
A. Guignard ◽  
C. J. Stubenrauch ◽  
A. J. Baran ◽  
R. Armante
Keyword(s):  
Statistical Analysis ◽  
Single Scattering ◽  
Ice Crystals ◽  
Crystal Habit ◽  
Ice Crystal ◽  
Ice Clouds ◽  
Mean Values ◽  
Temperature Range ◽  
Microphysical Properties ◽  
Ice Water

Abstract. This article presents a retrieval method and a statistical analysis of the bulk microphysical properties of semi-transparent ice clouds using the Atmospheric Infrared Sounder (AIRS). The method relies on spectral differences of cirrus emissivities in the 8–12 μm range and is sensitive to the effective ice crystal diameter (De) and ice water path (IWP) of up to 85 μm and 120 g m−2, respectively. An indication of the most frequent ice crystal habit in the cirrus has been obtained by using separately single scattering properties of column-like and aggregate-like ice crystals in the simulations. Uncertainties due to hypotheses on atmospheric parameters and ice crystal single scattering properties are discussed and the cirrus emissivity and temperature range for the applicability of the method are determined. To be sure that the cirrus only includes ice crystals, one has to restrict the cloud temperature range to Tcld<230 K. On a global scale, these semi-transparent ice clouds (cirrus) represent about 25% of all high clouds and are mainly encountered in the midlatitudes during winter and in the tropics, with an average De and IWP of 52 μm and 27 g m−2, respectively. A comparison with bulk microphysical properties from the TIROS-N Operational Vertical Sounder (TOVS) shows an agreement on global mean values. The addition of spectral information revealed improvements at the limits of the cirrus emissivity range. Collocated Radar-Lidar Geometrical Profiling (GEOPROF) data have been used to study the vertical structure of these clouds and to infer average ice water content (IWC) for cirrus with a small vertical extent. This allowed us to compare and contrast parameterizations of De as functions of IWC and IWP, respectively.

scholarly journals The Microwave Radiative Properties of Falling Snow Derived from Nonspherical Ice Particle Models. Part I: An Extensive Database of Simulated Pristine Crystals and Aggregate Particles, and Their Scattering Properties

2016 ◽  
Vol 55 (3) ◽  
pp. 691-708 ◽  
Author(s):  
Kwo-Sen Kuo ◽  
William S. Olson ◽  
Benjamin T. Johnson ◽  
Mircea Grecu ◽  
Lin Tian ◽  
...  
Keyword(s):  
Single Scattering ◽  
Dipole Approximation ◽  
Radiative Properties ◽  
Nonspherical Particles ◽  
Microwave Scattering ◽  
Microwave Frequencies ◽  
Scattering Coefficients ◽  
Sensing Applications ◽  
Snow Particle ◽  
The Asymmetry

AbstractA 3D growth model is used to simulate pristine ice crystals, which are aggregated using a collection algorithm to create larger, multicrystal particles. The simulated crystals and aggregates have mass-versus-size and fractal properties that are consistent with field observations. The growth/collection model is used to generate a large database of snow particles, and the single-scattering properties of each particle are computed using the discrete dipole approximation to account for the nonspherical geometries of the particles. At 13.6 and 35.5 GHz, the bulk radar reflectivities of nonspherical snow particle polydispersions differ from those of more approximate spherical, homogeneous, ice–air particle polydispersions that have the same particle size distributions, although the reflectivities of the nonspherical particles are roughly approximated by polydispersions of spheres of 0.1–0.2 g cm−3 density. At higher microwave frequencies, such as 165.5 GHz, the bulk extinction (and scattering) coefficients of the nonspherical snow polydispersions are comparable to those of low-density spheres, but the asymmetry parameters of the nonspherical particles are substantially less than those of spheres for a broad range of assumed spherical particle densities. Because of differences in the asymmetry of scatter, simulated microwave-scattering depressions using nonspherical particles may well exceed those of spheres for snow layers with the same vertical water path. It may be concluded that, in precipitation remote sensing applications that draw upon input from radar and/or radiometer observations spanning a range of microwave frequencies, nonspherical snow particle models should be used to properly interpret the observations.

scholarly journals Aggregation affects optical properties and photothermal heating of gold nanospheres

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Yiru Wang ◽  
Zhe Gao ◽  
Zonghu Han ◽  
Yilin Liu ◽  
Huan Yang ◽  
...  
Keyword(s):  
Optical Properties ◽  
Cross Section ◽  
Laser Heating ◽  
Dipole Approximation ◽  
Gold Nanospheres ◽  
Extinction Cross Section ◽  
Heating Efficiency ◽  
Photothermal Heating ◽  
New Framework ◽  
Laser Calorimetry

AbstractLaser heating of gold nanospheres (GNS) is increasingly prevalent in biomedical applications due to tunable optical properties that determine heating efficiency. Although many geometric parameters (i.e. size, morphology) can affect optical properties of individual GNS and their heating, no specific studies of how GNS aggregation affects heating have been carried out. We posit here that aggregation, which can occur within some biological systems, will significantly impact the optical and therefore heating properties of GNS. To address this, we employed discrete dipole approximation (DDA) simulations, Ultraviolet–Visible spectroscopy (UV–Vis) and laser calorimetry on GNS primary particles with diameters (5, 16, 30 nm) and their aggregates that contain 2 to 30 GNS particles. DDA shows that aggregation can reduce the extinction cross-section on a per particle basis by 17–28%. Experimental measurement by UV–Vis and laser calorimetry on aggregates also show up to a 25% reduction in extinction coefficient and significantly lower heating (~ 10%) compared to dispersed GNS. In addition, comparison of select aggregates shows even larger extinction cross section drops in sparse vs. dense aggregates. This work shows that GNS aggregation can change optical properties and reduce heating and provides a new framework for exploring this effect during laser heating of nanomaterial solutions.

Numerical Simulation and Experimental Study on Light Scattering by Biological Cells with Discrete Dipole Approximation

2013 ◽  
Vol 760-762 ◽  
pp. 105-109 ◽  
Author(s):  
Jian Bin Liu ◽  
Hai Li ◽  
Ying Xin Zeng ◽  
Jia Wen Weng ◽  
Chu Ping Yang
Keyword(s):  
Cell Culture ◽  
Light Scattering ◽  
Culture Medium ◽  
Dipole Approximation ◽  
Spherical Particles ◽  
Biological Cells ◽  
Cell Culture Medium ◽  
Animal Cells ◽  
Experimental Apparatus ◽  
Liquid Suspensions

An experimental apparatus for the analysis of biological cells light scattering in liquid suspensions has been presented. Characterization is based on the scattering of a monochromatic laser beam by particles [which can be inorganic, organic, or biological (such as animal cells and bacteria)] and on the strong relation between the light-scattering pattern and the morphology and refractive index of the particles. In order to study light scattering in biological cells close to the actual situation, we focus on non-spherical particles in the cell-culture medium. Finally, we demonstrate the light scattering results of bovine kidney cells suspended in the cell-culture medium, and compares then with the simulated results.

scholarly journals Cramér-Rao Bound Study of Multiple Scattering Effects in Target Separation Estimation

2013 ◽  
Vol 2013 ◽  
pp. 1-10 ◽  
Author(s):  
Edwin A. Marengo ◽  
Paul Berestesky
Keyword(s):  
Multiple Scattering ◽  
Born Approximation ◽  
Single Scattering ◽  
Scattering Data ◽  
Approximation Model ◽  
Scattering Parameters ◽  
Helmholtz Operator ◽  
Scattering Effects ◽  
Cramer Rao Bound ◽  
Multiple Scattering Effects

The information about the distance of separation between two-point targets that is contained in scattering data is explored in the context of the scalar Helmholtz operator via the Fisher information and associated Cramér-Rao bound (CRB) relevant to unbiased target separation estimation. The CRB results are obtained for the exact multiple scattering model and, for reference, also for the single scattering or Born approximation model applicable to weak scatterers. The effects of the sensing configuration and the scattering parameters in target separation estimation are analyzed. Conditions under which the targets' separation cannot be estimated are discussed for both models. Conditions for multiple scattering to be useful or detrimental to target separation estimation are discussed and illustrated.

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