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This paper experimentally and theoretically examines the scattering properties of simulated non-spherical hydrometeors including water oblates, ice oblates and ice sphere–cone-oblates, in terms of the backscattering cross-section and the differential reflectivity. The experimental measurements of the backscattering cross-sections of non-spherical hydrometeor samples were performed in the Electromagnetic Scattering Laboratory of China National Space Industrial Corporation. Meanwhile, the backscattering cross-sections have been computed with the transition (T) matrix method. The theoretical results are compared with the experimental data, showing that the calculations are consistent with the observations in general. Experimental and theoretical analyses indicate that the backscattering cross-section of non-spherical particles increases as the particle size parameter increases, and fluctuates when the sizes are larger under the effect of resonance scattering. Differential reflectivity Z DR of water oblates in natural rainfall is always greater than 0 dB whereas Z DR of hailstones may be negative. There is a good linear relationship between differential reflectivity and aspect ratio of a particle. These derivations agree with the literature and can be used to identify the presence of hail particles and distinguish between plate-type and columnar-type hydrometeors. In this study, the measuring experiment and the T-matrix method calculations for the scattering of simulated raindrop and ice particles are also briefly described.

This article presents an algorithm to correct the increase in reflectivity in the melting layer using weather radars. The correction starts with a fuzzy logic system (FLS) to classify rain, snow and melting snow using the reflectivity factor, the differential reflectivity, the linear depolarisation ratio and the height of the measurement from the ground surface. Using the output of the FLS, a correction is performed on the bright band contaminated reflectivity data assuming an idealised vertical reflectivity profile typical from stratiform precipitation and obtained from a considerable number of observations at S-band frequencies. Copyright © 2005 Royal Meteorological Society

Original article can be found at : http://www3.interscience.wiley.com/ Copyright Royal Meterological Society / John Wiley & Sons [Full text of this article is not available in the UHRA]

The paper presents a rainfall estimation technique based on algorithms that couple, along a radar ray, profiles of horizontal polarization reflectivity (ZH), differential reflectivity (ZDR), and differential propagation phase shift (ΦDP) from X-band polarimetric radar measurements. Based on in situ raindrop size distribution (DSD) data and using a three-parameter “normalized” gamma DSD model, relationships are derived that correct X-band reflectivity profiles for specific and differential attenuation, while simultaneously retrieving variations of the normalized intercept DSD parameter (Nw). The algorithm employs an iterative scheme to intrinsically account for raindrop oblateness variations from equilibrium condition. The study is facilitated from a field experiment conducted in the period October–November 2001 in Iowa City, Iowa, where observations from X-band dual-polarization mobile radar (XPOL) were collected simultaneously with high-resolution in situ disdrometer and rain-gauge rainfall meas...

Using Surface Differential Reflectivity (SDR) we have studied the optical properties of a PbSe(100) surface obtained by cleaving a PbSe sample in ultra-high-vacuum environment. SDR showed the existence of a gap of approximately 1.6 eV. The derived surface dielectric function showed, in the energy range of the present study (1.2–3.6 eV), three optical transitions observed at energies of 1.59, 2.01 and 2.39 eV. By putting together angle resolved photoemission data and theoretical calculations, these transitions have been, tentatively, assigned to different points in the surface Brillouin zone. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We have carried out an ultrafast time-resolved differential reflectivity study of a ferromagnetic semiconductor InGaMnAs and made a systematic comparison with low-temperature grown and high-temperature grown InGaAs reference films. Very short carrier lifetimes (∼2 ps) were observed in InGaMnAs and the low-temperature grown InGaAs film, but not in the high-temperature grown InGaAs film. We attribute the short lifetimes to carrier trapping by mid-gap states introduced during low-temperature MBE growth. Furthermore, at long times, we observed periodic oscillations in the differential reflectivity signal with period ∼20 ps, which we interpret as coherent acoustic phonons.

The intrastorm variability of raindrop size distributions as a source of uncertainty in single-parameter and dual-parameter radar rainfall estimates is studied using time series analyses of disdrometer observations. Two rain-rate (R) estimators are considered: the traditional single-parameter estimator using only the radar reflectivity factor (Z) and a dual-polarization estimator using a combination of radar reflectivity at horizontal polarization (Z(H)) and differential reflectivity (Z(DR)). A case study for a squall-line system passing over the Goodwin Creek experimental watershed in northern Mississippi is presented. Microphysically, the leading convective line is characterized by large raindrop concentrations (>500 drops per cubic meter), large mean raindrop sizes (>1 mm), and wide raindrop size distributions (standard deviations >0.5 mm), as compared to the transition region and the trailing stratiform rain. The transition and stratiform phases have similar raindrop concentrations and mean raindrop sizes. Their main difference is that the distributions are wider in the latter. A scaling-law analysis reveals that the shapes of the scaled spectra are bent downward for small raindrop sizes in the leading convective line, slightly bent upward in the transition zone, and strongly bent upward in the trailing stratiform rain. The exponents of the resulting Z-R relationships are roughly the same for the leading convective line and the trailing stratiform rain (approximate to1.4) and slightly larger for the transition region (approximate to1.5), with prefactors increasing in this order: transition (approximate to200), convective (approximate to300), stratiform (approximate to450). In terms of rainfall estimation bias, the best-fit mean R(Z(H), Z(DR)) relationship outperforms the best-fit mean R( Z) relationship, both for each storm phase separately and for the event as a whole.

The early histories of radar echo and polarization differential reflectivity (ZDR) from growing cumulus clouds observed in Florida with a 10-cm-wavelength radar are reported in detail. Raindrops 1 to several millimeters in diameter are present at about cloud-base level in most cases as soon as any identifiable precipitation echo is seen within cloud (distinct from Bragg scattering and echo from cloud droplets). This is in most cases by the time of the first 10-dBZ radar echo aloft. The very early occurrence of large drops is consistent with origination directly from coalescence on ultragiant aerosol. However, they appear to exist so early and so low in the clouds as to be unexpected if the cumulus were single, vigorous thermals. The explanation may lie in the presence of a more gradual, very early cloud stage that is generally not observed in any detail. Simultaneous Ze and ZDR measurements in the early stages of developing, warm cumulus will provide a powerful test of understanding the onset of ...

The rain attenuation was calculated by using the Marshall and Palmer, the gamma and the Weibull raindrop-size distributions. The microwave experimental measurement data from 8.4 GHz (3.75 mm) to 312.5 GHz (0.96 mm) were compared with our calculations. The Weibull distribution has the best agreement with the measurements, especially above 100 GHz. The differential reflectivity ZDR was also calculated using these three distributions. To this end, we used the horizontal and vertical radar cross sections which were computed from Waterman's T-matrix method. It is shown that ZDR greatly depends on raindrop-size distributions and has potential for determing drop-size distributions with high accuracy.

This report presents anterior segment optical coherence tomography (AS-OCT) images of Kayser-Fleischer ring (KFR) in a child. The AS-OCT images highlight differential reflectivity of the KFR depending on amount of copper deposited in cornea, thus supporting the role of AS-OCT as a follow-up tool. Utility of AS-OCT for diagnosing and documenting the KFR in children otherwise uncooperative for detailed slit lamp examination is discussed.

Computational electromagnetic analysis of scatting by oscillating rain drops with asymmetric shapes is presented. Mixed-mode oscillations of drops are attributed to sustained drop collisions in events having a highly organized line convection embedded within a larger rain system. The scattering matrix and differential reflectivity of drops are dependent on the particular oscillation modes and different time instants within the oscillation cycle. The results also demonstrate the superiority of the higher order method of moments over the conventional discrete dipole approximation method in oscillating rain drop analysis.

BACKGROUND AND OBJECTIVE: To assess the feasibility of intraoperative OCT (iOCT) during pars plana vitrectomy with subretinal tissue plasminogen activator (tPA) injection for subretinal hemorrhage. PATIENTS AND METHODS: Eyes that underwent vitrectomy and subretinal injection of tPA were identified from the PIONEER study, a prospective clinical study assessing the feasibility and utility of iOCT in ophthalmic surgery. A microscope-mounted spectral-domain OCT system was utilized for iOCT imaging. Standardized scan protocol and image acquisition were followed for intraoperative imaging. RESULTS: iOCT was successfully obtained in four of four eyes. In all cases, increased subretinal fluid was noted, with differential reflectivity visualized between the hemorrhage–tPA interface confirming appropriate localization of tPA injection. Image quality variability was significant. CONCLUSION: iOCT can successfully be performed during pars plana vitrectomy with subretinal tPA injection. Utilizing iOCT, appropriate placement of tPA solution and corresponding retinal architectural changes were visualized. [ Ophthalmic Surg Lasers Imaging Retina . 2015;46:327–332].

On June 5, 2013, Lubbock Texas is hit by a haboob at 10:30 pm. The storm is categorized as a wind event by television media and the dust component goes unreported. This event is used as a case study to evaluate the usefulness of the polarimetric variables differential reflectivity (ZDR) and correlation coefficient (CC) in identifying the storm as a haboob. Photographic evidence of the haboob is collected and correlated to NEXRAD signatures of base reflectivity and velocity from the Lubbock TX NEXRAD station (KLBB). NEXRAD level III products ZDR and CC are also obtained. The storm presents with gust front features to the north and east of the station. Low values returned from CC indicate nonmeteorological content. ZDR representations weakly indicate the presence of gust fronts to the east, with a stronger signal to the north. As no visual evidence of the northern gust front is available, the ZDR data are inconclusive. The correlation of low CC values to the visual representation of the haboob is an indicator that CC in combination with the NEXRAD base reflectivity and velocity products may be used to test wind events for the presence of sand, dust, and dirt and therefore exhibit predictive qualities.

Disertacija skirta nepusiausvirųjų krūvininkų dinamikos tyrimams SiC, GaN bei deimantuose naudojant šviesa indukuotų dinaminių gardelių, diferencinio pralaidumo, diferencinio atspindžio bei fotoliuminescencijos metodikas. Taipogi pristatomos naujos sugerties koeficiento matavimo bei gyvavimo trukmės mikroskopijos metodikos. Tyrimai atlikti plačiame nepusiausvirųjų krūvininkų tankių ir temperatūrų intervale esant vienfotoniam bei dvifotoniam sužadinimui. Nustatytas stiprus krūvininkų difuzijos koeficiento priklausomumas nuo krūvininkų tankio ir temperatūros. Jis paaiškintas fononine sklaida, krūvininkų tarpusavio sąveikos procesais bei išsigimimu. Buvo nustatyta, kad netiesiatarpiuose SiC ir deimanto puslaidininkiuose prie mažų sužadinimų rekombinacija yra ribota taškiniais bei paviršiniais defektais, o GaN dominuoja rekombinacija ant tarpkristalitinių ribų. Taipogi pasireiškė netiesinis Ože rekombinacijos procesas, kuris prie žemų sužadinimų buvo sustiprintas kulonine sąveika bei susilpnintas prie didelių dėl elektron-fononinės sąveikos ekranavimo bei išsigimimo. Fotoliuminescencijos efektyvumas parodė, kad spindulinės rekombinacijos koeficientas GaN mažėja nuo sužadinimo, tuo tarpu SiC jis nuo žadinimo nepriklauso. Kompensuojančių defektų (aliuminio SiC ir boro deimante) koncentracijos ir aktyvacijos energijos nustatytos stebint jų sąlygotos sugerties įsisotinimą bei jų signalo relaksacijos spartos priklausomybę nuo temperatūros. The thesis is dedicated to investigation of carrier dynamics in SiC, GaN and diamond by using light-induced transient gratings, differential transmittivity, differential reflectivity and photoluminescence techniques. Also new absorption coefficient measurement and carrier lifetime microscopy techniques are presented. The experimental studies were performed in a wide range of excess carrier densities and temperatures under single- and two- photon excitation conditions. Strong diffusion coefficient temperature and injection dependences were determined. They were explained by phonon scattering, inter-carrier interaction processes and degeneracy. It was determined, that in indirect-gap SiC and diamond semiconductors at low injections lifetime is limited by point and surface defects, while in GaN recombination on grain boundaries prevails. Also nonlinear Auger recombination coefficient was observed. It was Coulombically enhanced at low injections and screened at high ones. Photoluminescence efficiency revealed radiative recombination coefficient reduction with injection in GaN. On the other hand, in SiC radiative coefficient was injection independent. Compensating defect (aluminum in SiC and boron in diamond) concentrations and activation energies were determined from their absorption saturation and recovery rate temperature dependences.

Hail is the most frequent damaging phenomena affecting northern Italy during severe weather. At the Servizio Meteorologico Regionale of the Emilia-Romagna region the analysis of the differential hail signal HDR (Aydin et al., 1986), which is a function of horizontal reflectivity and differential reflectivity, was carried out and checked against the ground truth coming from a dense hail pad network. That study, which used the data related to four hailstorms occurred in 1997, allowed the implementation of an operational technique since early summer of 1998. Since then, an automatic hail detection algorithm runs during the stormy season (March through October) with the issue of a hail warning for nowcasting purpose. The performance of such an automatic method is investigated in an operational and statistical perspective. First results highlight the difficult in correctly estimating the position of a hail shaft with respect to the coarse resolution of the pad network, e especially when hailstorms of small extension are involved.

Surface differential reflectivity and surface sensitive electron spectroscopies have been applied to study the optical properties of CdTe(110) surface. The comparison of the results acquired for the surfaces prepared by two different methods (cleavage and Ar + ion sputtering) enabled us to propose a model explaining the experimental results in a coherent way.

Multiparameter radar measurements of rainfall, namely, reflectivity factor Z/sub H/, differential reflectivity Z/sub DR/, and specific differential phase K/sub DP/ lie in a constrained three-dimensional (3D) space and therefore measurement of Z/sub H/, Z/sub DR/, or, K/sub DP/ should be consistent with the other two. This self-consistency relationship between Z/sub H/, Z/sub DR/, and K/sub DP/ is valid when the radar resolution volume is homogeneous. When there are reflectivity gradients within the radar resolution cell, the self-consistency relation is perturbed. This perturbation can be utilized to detect the presence of gradients in the radar resolution volume. This paper presents a technique to detect and estimate reflectivity gradients in the resolution cell. The technique is evaluated using theoretical analysis as well as experimental data collected by the NCAR CP-2 radar. It is demonstrated that the presence of reflectivity gradients larger than a few decibels can be detected using the algorithm developed in this paper.

The joint distribution characteristics of size and shape of raindrops directly translate into features of polarization diversity measurements in rainfall. Theoretical calculations as well as radar observations indicate that the three polarization diversity measurements, namely, reflectivity, differential reflectivity, and specific differential propagation phase, lie in a constrained space that can be approximated by a three-dimensional (3D) surface. This feature as well as the vertical-looking observation of raindrops are used to determine biases in calibration of the radar system. A simple procedure is developed to obtain the bias in the absolute calibration from polarization diversity observation in rainfall. Simulation study as well as data analysis indicate that calibration errors can be estimated to an accuracy of 1 dB.

Carrier capture into quantum dots (QDs) grown on top of a 16 period quantum wire (QWR)-superlattice is studied as a function of temperature. Time-resolved differential reflectivity reveals an anomalous increase of the capture time between 40 and 100 K. Photoluminescence data indicate carrier re-emission out of the QWRs into the QDs, in this temperature range. The anomalous temperature dependence is interpreted as due to the temperature dependence of the effective carrier diffusion length in this structure.

An historical review of the development of optical spectroscopy of surface states in semiconductors is presented. The importance of symmetry considerations and of polarization properties is emphasized.

The kinetics of hydrogen adsorption on Si(111)7\ifmmode\times\else\texttimes\fi{}7 have been studied by means of real-time surface differential reflectivity. Experiments have been performed for a large exposure range and for temperature ranging from 170--370 K. Two different adsorption channels could be determined from the analysis of the spectra. The kinetics equations of the two elementary processes have been written, and their respective activation energies have been determined: a very low barrier for the H binding on the adatom dangling bonds and a barrier of about 20 meV for the H breaking of the adatom back bond. The kinetics of both processes can be understood by taking into account a large energy barrier that inhibits the adatom-back-bond breaking by H as long as the dangling bond of the adatom is not yet bound to H.

Optical transitions between surface state bands have been detected on the Si(111)-Pb(√3 × √3) mosaic phase by means of surface differential reflectivity (SDR) in the energy range between 1.3 and 3.8 eV. The SDR spectrum, obtained between the clean and the hydrogenated surface, presents a broad structure in this energy range with a maximum at 3.0 eV. The spectrum has been deconvolved into three Gaussian singlets at energies 1.8, 2.5 and 3.05 eV. These transitions have been, tentatively, assigned to different points in the surface Brillouin zone. No contribution from the hydrogenated surface is expected, as observed by angle resolved photoemission.

The Communications Research Laboratory (CRL) has developed a simultaneous reception Ku-band dual-polarization radar. Simultaneous reception can give high accuracy of the differential reflectivity (ZDR) measurement from fewer averaged samples because of a good correlation between simultaneously sampled horizontal and vertical reflectivity. This paper pursues the possibility of estimating the rainfall rate using ZDR alone by comparison with a conventional polarimetric radar algorithm using ZDR and ZH on the assumption of the data handling of a CRL's dual-polarization radar. A computer simulation based on a physical raindrop model is used to pursue this possibility. The results show that estimating the rainfall rate using ZDR alone is not a good method.

The electronic structure of Cu 3 Si is calculated with a self-consistent scalar relativistic linear muffin tin orbitals code in the atomic sphere approximation. The results are compared to UPS and differential reflectivity measurements on the reacted CuSi interface layer where Cu 3 Si formation is generally admitted. Both theoretical and experimental results show a shift of the d band towards lower energies with respect to pure Cu. The disappearance of a sharp absorption edge at 2.1 eV in differential reflectivity is related to the broadening of the Cu d band due to Si p-Cu d hydridization as shown by the calculation.

We report on the detection of a loss-inducing perturbation with variable localization accuracy along a test fiber based on the analysis of transmitted and reflected powers of an unmodulated continuous-wave light source. The required accuracy of localization is provided by suitable distribution of the differential reflectivity along the fiber. The localization accuracy for a strong disturbance has been estimated as /spl plusmn/ 1.0 m along the 3.939-km single-mode test fiber and as /spl plusmn/ 5.0 mm along a designated 10-cm fiber part for both strong and weak perturbations.

The effects of the background hole density on the charge and magnitude of the magnetization dynamics in (Ga,Mn)As grown with independently fixed manganese and impurity densities. A pump and probe experiment monitored simultaneously the reflectivity and Kerr angle dynamics. Two relaxation steps are highlighted. First the cooling down of the charge clouds between 1ps and 100ps and second the carrier’s diffusion-recombination between 100ps and 1.500 ns. The latter depends on the ratio between the spatial extent of impurity states, which trap the photo electrons, and the Fermi velocity. To complete these experimental results, a numerical study of the ground state of the samples, using a density functional theory, relates the magnitude of the magnetization, the temperature of the carriers and the density of holes. Phase diagram are computed, and compared to already published results. We show that the magnitude of the magnetization dynamics can be fully determined from the reflectivity measurements. We conclude that it is possible to distinguish the dynamics of the magnetization magnitude and direction using the Kerr angle dynamical signal.; Ce travail étudie le rôle de la densité de trous à l’équilibre sur la dynamique des charges et de la norme de l’aimantation de (Ga,Mn)As pour des densités de manganèse et d’impuretés fixées indépendamment. Des expériences « pompe-sonde » mettent en relation les dynamiques de réflectivité et d’angle de rotation Kerr. Deux relaxations sont mises en évidence. La première traduit un échauffement variable du gaz de trous entre 1ps et 100ps. La seconde traduit une diffusion-recombinaison des charges entre 100ps et 1500ps et évolue en fonction du rapport entre extension spatiale d’états d’impuretés, piégeant les électrons photo générés, et vitesse de Fermi. Pour compléter l’approche, une étude numérique de l’état fondamental des échantillons par la théorie de la fonctionnelle de la densité relie aimantation, température et densité de trous. Elle interprète la dynamique de la norme de l’aimantation à partir d’un diagramme de phase statique correspondant aux données publiées pour (Ga,Mn)As, qui est fonction de la température et de la densité de trous. Cette dynamique se ramène à celle de la réflectivité. Ceci permet de préciser les contributions de la norme et de l’orientation de l’aimantation dans le signal dynamique de rotation Kerr.

Electron spectroscopies (photoemission (UPS) and Auger electron spectroscopy (AES)) together with the surface differential reflectivity (SDR) have been applied to observe and identify optical transitions between surface related states on CdTe(110) surfaces. The contributions to the band of optical transitions have been revealed at the photon energies of 2.9, 3.5, and 3.9 eV. Their correspondence to excitations from the occupied S1 band to the unoccupied U1 one at the Γ, X and, X′ points of the surface Brillouin zone is discussed. Dependence of the surface optical properties of CdTe(110) surfaces on cleavage quality and oxidation procedure are analysed, too.

Surface differential reflectivity together with photoemissioii and Auger electron spectroscopies have been applied to observe and identify optical transitions among surface related states on CdTe(110) surfaces. The strongest contributions to the band of optical transitions have been revealed at the photon energies of 2.8, 3.4, and 3.9 eV. Their correspondence to excitations from the occupied S1 band to the unoccupied U1 one at the Γ, Χ and Χ ' points of the surface Brillouin zone is discussed. PACS numbers: 73.20.-r, 78.66.Hf

Surface differential reflectivity experiments with polarised light have been carried out for cleaved and then oxidised CdTe(110) surfaces. It was shown that the optical anisotropy of the surface investigated is small and almost independent from photon energy. The interpretation of the spectra in terms of optical transitions between surface states is discussed.

While radars measure several quantities closely coupled to the rainfall rate, for frequencies less than 15 GHz, estimates of the rainwater content W are traditionally computed from the radar reflectivity factor Z or the rate of attenuation A--quantities only weakly related to W. Consequently, instantaneous point estimates of W using Z and A are often erroneous. A more natural, alternative parameter for estimating W at these frequencies is the specific polarization propagation differential phase shift phi(sub DP), which is a measure of the change in the difference between phases of vertically (V) and horizontally (H) polarized waves with increasing distance from a radar. It is now well known that W is nearly linearly related to phi(sub DP) divided by (1 - reversed R), where reversed R is the mass-weighted mean axis ratio of the raindrops. Unfortunately, such relations are not widely used in part because measurements of phi(sub DP) are scarce but also because one must determine reversed R. In this work it is shown that this parameter can be estimated using the differential reflectivity (Z(sub H)/Z(sub V) at 3 GHz. An alternative technique is suggested for higher frequencies when the differential reflectivity becomes degraded by attenuation. While theory indicates that it should be possible using phi(sub DP) to estimate W quite accurately, measurement errors increase the uncertainty to +/- 18%-35% depending on reversed R. While far from ideal, it appears that these estimates are likely to be considerably more accurate than those deduced using currently available methods.

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.

The estimates of rainfall rate derived from a multiparameter radar based on reflectivity factor (R sub ZH), differential reflectivity (R sub DR), and specific differential propagation phase (R sub DP) have widely varying accuracies over the dynamic range of the natural occurrence of rainfall. This paper presents a framework to optimally combine the three estimates, R sub zH, R sub DR, and R sub DP, to derive the best estimate of rainfall using coherent multiparameter radars. The optimization procedure is demonstrated for application to multiparameter radar measurements at C band.

Several types of remote sensing data are applied synergistically to evaluate the chain of microphysical processes leading to precipitation in a high-resolution numerical weather prediction model. The data provides information relating to (i) cloud-top temperature and optical depth (SEVERI), (ii) ice cloud amount (AMSUB), (iii) type and amount of precipitation particles (polarimetric radar), and (iv) surface precipitation (raingauge-calibrated radar data). Forecasts are produced by the COSMO-DE model of the German weather service, with a horizontal resolution of 2.8 km. The comparison with data is done in a model-to-observation framework, that is, forward operators are applied to the model output to produce synthetic data sets that can be directly compared to the observations. Additional diagnostics based on diurnal cycle and system tracking are also considered. Two case studies over Germany from the summer of 2006 are examined. The first case is dominated by widespread stratiform precipitation. Together the various data sets show that the model overestimates the amount of high cloud, while underestimating the concentration of ice scatterers and overestimating reflectivity and differential reflectivity (ZDR). This indicates errors in both the amount and the size distributions of cloud and precipitation particles in the model’s microphysical parameterization. In the second case a narrow band of convective precipitation is embedded in a cold front, with significant modulation by the diurnal cycle. The model fails to show a significant diurnal cycle in cloud amount, and the timing and duration of convective cells is incorrect. In this case, both the microphysical parameterization, and errors in the interaction of the simulated front with the orography of the Alps appear to contribute. These results demonstrate the potential of combinations of remote sensing data for model evaluation, although a long-term trial will be required to determine whether the errors seen in the case studies are characteristic for COSMO-DE. Zusammenfassung Verschiedene Fernerkundungsdaten werden synergetisch zur Evaluierung der mikrophysikalischen Prozesskette der Niederschlagsgenerierung in einem hochaufgelosten numerischen Wettervorhersagemodell genutzt. Die Daten beinhalten Informationen uber (i) Wolkenobergrenzentemperatur und optische Dicke (SEVIRI), (ii) Vorkommen von Eis und Schnee (AMSU), (iii) Art und Gehalt an Niederschlagspartikeln (polarimetrisches Radar) und (iv) Bodenniederschlag (Radar mit Niederschlagssammler kalibriert). Die Vorhersagen stammen vom COSMO-DE des Deutschen Wetterdiensts mit einer horizontalen Auflosung von 2,8 km. Der Vergleich wird mittels eines “Modell zu Beobachtung”-Ansatzes durchgefuhrt, d. h. Vorwartsoperatoren werden auf den Modelloutput angewendet, um synthetische Beobachtungen zu generieren, die direkt mit den Beobachtungen verglichen werden konnen. Zusatzliche Diagnostiken basierend auf Tagesgang und Verfolgung einzelner Konvektionszellen werden ebenfalls angewendet. Zwei Fallstudien uber Deutschland aus dem Sommer 2006 werden untersucht. Die erste Fallstudie wird von ausgedehntem Niederschlag dominiert. Die verschiedenen Daten zeigen, dass das Modell den Anteil hoher, stratiformer Wolken uberschatzt, wahrend die Konzentration groserer streuender Eispartikel unter- und die bodennahe Reflektivitat und die differentielle Reflektivitat (ZDR) uberschatzt werden. Dies deutet auf Fehler in den mikrophysikalischen Parameterisierungen sowie in den Annahmen zur Grosenverteilung von Wolken- und Niederschlagspartikeln im Modell hin. In der zweiten Fallstudie ist ein enges Band konvektiven Niederschlages eingebettet in eine Kaltfront, mit signifikanter Modulation durch den Tagesgang. Dem Modell gelingt es nicht einen deutlichen Tagesgang in der Wolkenbedeckung zu reproduzieren und Einsetzen sowie Lebensdauer der konvektiven Zellen werden nicht getroffen. In diesem Fall scheinen sowohl die mikrophysikalischen Parametrisierungen als auch die Wechselwirkung der Front mit der Orographie der Alpen zum Fehler der Vorhersage beizutragen. Diese Resultate zeigen das Potential der Kombination verschiedener Fernerkundungsdaten fur die Modellevaluierung. Um zu uberprufen, dass diese Fehler charakteristisch fur das COSMO-DE sind, ist jedoch eine langfristige Vergleichsstudie notig.

Dual polarization radar measurements of rainfall parameters are based on the assumption of a mean shape-size relationship of raindrops. This paper focuses on retrieving and interpreting the mean raindrop shape-size relation from polarimetric radar observations. A procedure to retrieve the drop shape-size relation that governs the polarimetric radar observations of reflectivity (Z h ) differential reflectivity (Z dr ) and specific differential propagation phase (K dp ) is presented. The mean drop shape-size relations retrieved from measurements collected by the NCAR SPOL radar during three campaigns are analyzed to explore whether the natural raindrop shape-size relation can be described by a unique model.

Dual-polarization radar measurements of precipitation are primarily influenced by the size, shape, orientation, and phase of scattering hydrometeors. As a result, these measurements can serve as a tool for remote identification of hydrometeor characteristics. This paper presents an overview of the definitions, observed values, and applications of differential reflectivity (ZDR) and linear depolarization ratio (LDR) measurements. Brief examples of these measurements are given for widespread stratiform precipitation, a rapidly developing convective cell, and a severe hailstorm. The results outline the role that ZDR can play in the differentiation of rain and solid precipitation, identification of supercooled raindrops above the 0°C level, and identification of hail at the surface. LDR measurements are seen to reveal contrasts in ice-particle shape, orientation, and particle phase. These contrasts are of particular benefit toward delineation of hail regions aloft and identification of mixed-phase particle gr...

Recent advances in the radar system design allow to perform Doppler and polarimetric measurements simultaneously. This paper considers behavior of a Doppler-polarimetric parameter - spectral differential reflectivity and its characteristics. Slope of differential reflectivity which is connected with turbulence intensity in rain zone is considered using real data processing.

Small time (1 to 15 min) and space (0.5 to 1. 5 km) measurements of the mean rainfall rate have been made within 10 km from a dual-polarization radar, during several widespread or convective precipitation events. At first, the time and space characteristic scales of the gage and of the radar data are evaluated in order to find the minimum time interval Δt and spatial resolution Δx for which the mean rainfall rate values have a large enough statistical significance. Then the quantitative comparisons am made between the mean rainfall rate RG deduced from the gage data and that deduced from the radar measurements either without (RZ) or With (RD) using the differential reflectivity ZDR values

We examine the utility of the correlation coefficient between linear orthogonally polarized echoes for determining precipitation type and gauging hail size. Models and measurements from pure rain coincide in predicting very high correlations (0.98); similar results are obtained with pure hail. Several mechanisms could cause the lowering of correlation but the behavior of the examined data is definitely attributed to a mixture of hydrometeor types. This decrease is an indicator of hail size; it is shown theoretically that in at least two other realistic situations the correlation would decrease with hail size. For the examined case a model of hail shape and orientation during fall is able to reproduce the essential features of polarimetric measurements. It suggests, together with our data and data from other investigators, that substantial negative differential reflectivity (about −1 dB) in a region of high reflectivity factor values is caused by hailstones larger than about 2 cm in diameter.

Precipitation comprising rain and hail is studied. Specifically, techniques to identify and quantify such precipitation in terms of rain and hail fall rates using dual polarized radar data, are presented. Included for consideration are ZH, the reflectivity factor for horizontal polarization, ZDR, the differential reflectivity, and KDP, the differential propagation constant. A variety of simple models of mixed-phase precipitation are first examined. Electromagnetic scattering computations are performed to simulate and study the behavior of ZH, ZDR, and KDP. It is shown that it is possible to distinguish the mixed-phase precipitation from either rain or hail by using ZH, KDP pair and also to infer the thermodynamic phase and orientation from ZH, ZDR pair. On the basis of physical principles, it is shown that KDP senses primarily liquid water in the form of raindrops even when these are mixed with hailstones. The self-consistency Of ZH, ZDR, and KDP is then exploited to estimate both the rain and ha...

A differential reflectivity radar technique for observing hailstorms is demonstrated using measurements obtained during the 13 June 1984 Denver hailstorm. The hail regions of the storm are identified with the differential reflectivity hail signal. Histograms of ZH and ZDR are generated for different heights in the hail regions and the relative variation of these parameters is also determined. It is observed that due to melting, the mean values of ZH and ZDR increase with decreasing height below the 0°C level (which is around 2.6 km above ground level). Furthermore, at the lower levels ZDR varies between −1 and +2 dB and ZH is generally greater than 50 dBZ. The value of ZH peaks at around 60 dBZ or more when ZDR is in the range −0.5 to 0 dB and 1.5 to 2 dB at 1.5 km and 2 km below the 0°C level, respectively. These and other features of ZH and ZDR are interpreted in terms of the size, shape and fall behavior of the hailstones using the dual wavelength ratio and the linear depolarization ratio rada...

The optoelectronic compounds of GaAs and ZnSe are difficult to analyze by PIXE (particle-induced X-ray emission) due to the strong absorption of the As and Se K α X-rays. As part of a program to investigate optoelectronic materials using ion beam techniques, we have explored the possibility of using the high sensitivity of PIXE to check these materials for stoichiometry and dopant concentrations. The K α X-ray intensity ratios of Ga to As and Zn to Se have been investigated using H beams of 0.5 to 2.5 MeV and He beams of 1.0 to 2.5 MeV. The variation in the X-ray intensity ratio with beam energy and target thickness is modelled in terms of the cross section for X-ray production and the absorption coefficients of the X-rays in the target. The results of this model show the experimental conditions that must be satisfied in order that the X-ray intensity ratios are not strongly affected by X-ray absorption; and therefore, the conditions necessary for accurate analysis. To demonstrate this, four 1 μm Al x Ga 1− x As-on-GaAs samples were analyzed and gave results in agreement with those obtained by differential reflectivity.

The roughness of Si(111) surfaces induced by heating at temperatures between 900 and 1000°C is studied by differential reflectivity measurements. For the lowest temperatures, the stepped-roughness of the surface is smoothed out by annealing the surface, leading to an increase of reflectivity for light energies below 3 eV. For the highest temperatures, a larger scale roughness (of the order of several tens of nm) is formed at the surface. This roughness increases with temperature and induces essentially a scattering of light leading to a decrease of reflectivity in the UV range.

The site preference of the bromine (Br) atom adsorption process on $\mathrm{Si}(111)\text{\ensuremath{-}}7\ifmmode\times\else\texttimes\fi{}7$ at room temperature was investigated. The density of the reacted adatom bonds of dimer-adatom-stacking fault structure and the total coverage were determined by means of surface differential reflectivity and thermal desorption spectroscopy, respectively. Partial coverage on the rest atoms was then obtained. At the initial stage below 0.1 ML, Br atoms are adsorbed selectively on dangling bonds at the Si adatoms, but not on those at the rest atoms. Above 0.1 ML, dibromide species are formed at the adatoms even when half of the adatom dangling bonds remain intact. The observed site preference of Br atoms is quite different from that of Cl atoms, which are adsorbed randomly on the dangling bonds at both the adatoms and the rest atoms, and form dichloride only after about 80% of the adatoms and the rest atoms are covered. This study provides direct evidence of the adsorption site preference and suggests pattern formations of Br adsorbates on Si(111).

Multilayer laserscanner sensors measure a precise range profile of road traffic situations. Moreover, they are able to detect different reflectivities of object surfaces. In addition to object detection and object tracking, these sensory features enable a roadway and lane detection function without requiring additional sensors. A special multilayer laserscanner prototype has been developed for this purpose. The roadway detection is based on an identification of changes in the distance profiles pattern at the borders of roadways. A classification and tracking of reflection posts extends the effective range of the roadway detection and enhances its robustness. The lane detection makes use of the differential reflectivity of lane markings and road surface. The lane detection operates within a distance range of 4m up to 30m and has been tested on highway scenarios.

[1] Several authors have reported the correlation between the shape (μ) and slope (Λ) of the gamma distribution of raindrops to reduce the number of parameters required to measure rainfall by remote sensing methods. However, we find that there are no well-defined μ-Λ, or associated relations between reflectivity (Z) and rain rate (R) or differential reflectivity for all storms or portions thereof. Rather, there is a general behavior such that A and b (in the Z = ARb relation) and median volume drop diameter Do all decrease from convective (C) to stratiform (S) to transition (T) rains. The μ-Λ correlation of the investigators in question appears to be limited to rainfall events which do not include convective rain; it is biased toward S and T rains. They miss the narrow (large μ), large Do DSDs of convective rain that are often found to have equilibrium spectra. The dependence of Do on the strength of the updraft and the findings of others concerning the association with the physics, dynamics, and climate regime strongly suggests that it is necessary to characterize the physical and dynamic nature of the storms in order to select the appropriate remote sensing algorithms.

Strong radar echoes from targets a few kilometres across have been found in the absence of rain, and were attributable to burnt straw particles rising from large field fires. The echoes showed a marked difference of reflectivity between horizontally and vertically polarised radar transmissions. This paper describes the way the reflectivity and differential reflectivity with polarisation are distributed in space, gives a theoretical model to explain these effects, and analyses the basic propagation characteristics.

We have measured the time-resolved differential reflectivity (TRDR) signal of ZnO epilayers and nanorods as a function of temperature and excitation wavelength. Non-exponential decays are observed, and relaxation times depend strongly on excitation wavelength.

The polarimetric technique consists of simultaneous transmission and reception of Horizontally and Vertically polarized waves. Thus, transmitted polarization will be elliptical with equal horizontal and vertical components and arbitrary phase between the two. This scheme has been tested at NSSL on the NOAA research and development WSR-88D radar. Here reports on backscatter differential phase measurements with this radar. The radar also has a mode of transmitting horizontal polarization and receiving both the strong H and the weak V component (for short we refer to this mode as Linear Depolarization Ratio mode, LDR). Backscatter differential phase is considered a secondary polarimetric variable of lesser value for precipitation measurements than (the forward) specific differential phase or differential reflectivity. This is because backscatter differential phase is seldom significant. At 10 cm wavelength the only precipitation that can cause appreciable backscatter differential phase is hail. But it turns out that backscatter differential phase from other scatters provides two benefits. (1) it is suitable for discrimination between nonmeteorological scatters and precipitation and (2) it offers a way to calibrate (measure) the system differential phase. Of relevant and special importance is that, for some scatters, the measured total differential phase in the SHV scheme can differ from the value obtained in the sequential H, V scheme. The radar system contributes two distinct phases to the total differential phase. One is the differential phase in the transmission channel, the other is the differential phase in the receiver channel