Dependent Scattering Effects in Aggregates with Touching or Overlapping Non-Absorbing Spherical Particles

Abstract. MonteCarlo simulations have been performed to evaluate the importance of multiple scattering effects in co- and cross-polar radar returns for 94GHz radars in Cloudsat and airborne configurations. Thousands of vertically structured profiles derived from some different cloud resolving models are used as a test-bed. Mie theory is used to derive the single scattering properties of the atmospheric hydrometeors. Multiple scattering effects in the cross polar channel (reflectivity enhancement) are particularly elusive, especially in airborne configuration. They can be quite consistent in satellite configurations, like Cloudsat, especially in regions of high attenuation and in the presence of highly forward scattering layers associated with snow and graupel particles. When the cross polar returns are analysed, high LDR values appear both in space and in airborne configurations. The LDR signatures are footprints of multiple scattering effects since they cannot be explained by single scattering computations, even including non-spherical particles. We see these signatures confirmed by some experimental data collected during the Wakasa Bay experiment. Multiple scattering effects can be important for Clousat applications like rainfall and snowfall retrievals since single scattering based algorithms will be otherwise burdened by positive biases.

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Evaluation of radar multiple scattering effects in Cloudsat configuration

Atmospheric Chemistry and Physics ◽

10.5194/acp-7-1719-2007 ◽

2007 ◽

Vol 7 (7) ◽

pp. 1719-1730 ◽

Cited By ~ 38

Author(s):

A. Battaglia ◽

M. O. Ajewole ◽

C. Simmer

Keyword(s):

Multiple Scattering ◽

Mie Theory ◽

Single Scattering ◽

Spherical Particles ◽

Test Bed ◽

High Attenuation ◽

Scattering Effects ◽

Wakasa Bay ◽

Linear Depolarization Ratio ◽

Multiple Scattering Effects

Abstract. MonteCarlo simulations have been performed to evaluate the importance of multiple scattering effects in co- and cross-polar radar returns for 94 GHz radars in Cloudsat and airborne configurations. Thousands of vertically structured profiles derived from some different cloud resolving models are used as a test-bed. Mie theory is used to derive the single scattering properties of the atmospheric hydrometeors. Multiple scattering effects in the co-polar channel (reflectivity enhancement) are particularly elusive, especially in airborne configuration. They can be quite consistent in satellite configurations, like CloudSat, especially in regions of high attenuation and in the presence of highly forward scattering layers associated with snow and graupel particles. When the cross polar returns are analysed [but note that CloudSat does not measure any linear depolarization ratio (LDR hereafter)], high LDR values appear both in space and in airborne configurations. The LDR signatures are footprints of multiple scattering effects; although depolarization values as high as −5 dB can be generated including non-spherical particles in single scattering modelling, multiple scattering computations can produce values close to complete depolarization (i.e. LDR=0 dB). Our simulated LDR profiles from an air-borne platform well reproduce, in a simple frame, some experimental observations collected during the Wakasa Bay experiment. Since LDR instrumental uncertainties were not positively accounted for during that experiment, more focused campaigns with air-borne polarimetric radar are recommended. Multiple scattering effects can be important for CloudSat applications like rainfall and snowfall retrievals since single scattering based algorithms will be otherwise burdened by positive biases.

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Electron crystallographic determination of the 3-D structure of staurolite at atomic resolution

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010008701x ◽

1991 ◽

Vol 49 ◽

pp. 540-541

Author(s):

Kenneth H. Downing ◽

Hu Meisheng ◽

Hans-Rudolf Went ◽

Michael A. O'Keefe

Keyword(s):

High Resolution ◽

Three Dimensional ◽

High Resolution Electron Microscopy ◽

Atomic Resolution ◽

Dimensional Structure ◽

Structure Information ◽

Resolution Electron ◽

Scattering Effects ◽

High Resolution Images ◽

Effects Of Radiation

With current advances in electron microscope design, high resolution electron microscopy has become routine, and point resolutions of better than 2Å have been obtained in images of many inorganic crystals. Although this resolution is sufficient to resolve interatomic spacings, interpretation generally requires comparison of experimental images with calculations. Since the images are two-dimensional representations of projections of the full three-dimensional structure, information is invariably lost in the overlapping images of atoms at various heights. The technique of electron crystallography, in which information from several views of a crystal is combined, has been developed to obtain three-dimensional information on proteins. The resolution in images of proteins is severely limited by effects of radiation damage. In principle, atomic-resolution, 3D reconstructions should be obtainable from specimens that are resistant to damage. The most serious problem would appear to be in obtaining high-resolution images from areas that are thin enough that dynamical scattering effects can be ignored.

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STEM Study of Surface Plasmon Excitation in Small Spherical Particles

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100133801 ◽

1990 ◽

Vol 48 (2) ◽

pp. 42-43

Author(s):

Daniel UGARTE

Keyword(s):

Energy Loss ◽

Spherical Particles ◽

Small Particles ◽

Bulk Materials ◽

Low Loss ◽

Plasmon Excitation ◽

Surface Modes ◽

Surface Plasmon Excitation ◽

Analytical Electron ◽

Analytical Electron Microscope

Small particles exhibit chemical and physical behaviors substantially different from bulk materials. This is due to the fact that boundary conditions can induce specific constraints on the observed properties. As an example, energy loss experiments carried out in an analytical electron microscope, constitute a powerful technique to investigate the excitation of collective surface modes (plasmons), which are modified in a limited size medium. In this work a STEM VG HB501 has been used to study the low energy loss spectrum (1-40 eV) of silicon spherical particles [1], and the spatial localization of the different modes has been analyzed through digitally acquired energy filtered images. This material and its oxides have been extensively studied and are very well characterized, because of their applications in microelectronics. These particles are thus ideal objects to test the validity of theories developed up to now.Typical EELS spectra in the low loss region are shown in fig. 2 and energy filtered images for the main spectral features in fig. 3.

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Dynamical Scattering in Electron Diffraction of wet Protein Crystals

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s1431927600000167 ◽

1980 ◽

Vol 38 ◽

pp. 42-43

Author(s):

B. B. Chang ◽

D. F. Parsons

Keyword(s):

Electron Diffraction ◽

Scattering Theory ◽

Protein Crystals ◽

Electron Diffraction Data ◽

Specimen Thickness ◽

Major Question ◽

X Ray ◽

Scattering Effects ◽

Diffraction Patterns ◽

Acceleration Voltage

The significance of dynamical scattering effects remains the major question in the structural analysis by electron diffraction of protein crystals preserved in the hydrated state. In the few cases (single layers of purple membrane and 400-600 Å thick catalase crystals examined at 100 kV acceleration voltage) where electron-diffraction patterns were used quantitatively, dynamical scattering effects were considered unimportant on the basis of a comparison with x-ray intensities. The kinematical treatment is usually justified by the thinness of the crystal. A theoretical investigation by Ho et al. using Cowley-Moodie multislice formulation of dynamical scattering theory and cytochrome b5as the test object2 suggests that kinematical analysis of electron diffraction data with 100-keV electrons would not likely be valid for specimen thickness of 300 Å or more. We have chosen to work with electron diffraction patterns obtained from actual wet protein crystals (rat hemoglobin crystals of thickness range 1000 to 2500 Å) at 200 and 1000 kV and to analyze these for dynamical effects.

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