The Experts below are selected from a list of 45555 Experts worldwide ranked by ideXlab platform
Takunori Taira - One of the best experts on this subject based on the ideXlab platform.
-
1 mw peak power single mode high brightness passively q switched nd 3 yag microchip laser
Optics Express, 2008Co-Authors: Hiroshi Sakai, Takunori TairaAbstract:A high-brightness diode end-pumped Nd:YAG microchip laser, passively Q-switched by a Cr4+:YAG saturable absorber (SA), has been developed. The dependences of pulse energy and Width were investigated based on theoretical verification to enhance the peak power. As a result, the peak power exceeded 1.2 MW with M2=1.04 and Spectrum Width Δλ<5.1 pm at a repetition rate of 100 Hz. Brightness of 98 TW/sr·cm2 was obtained with a supplied average electrical power of 2.3 W. The peak power increased up to 2.1 MW with M2=1.36. Peak power of 1.7 MW was obtained from a 2-cm-diameter×5-cm-long monolithic laser head.
-
1 mw peak power single mode high brightness passively q switched nd 3 yag microchip laser
Optics Express, 2008Co-Authors: Hiroshi Sakai, H Kan, Takunori TairaAbstract:A high-brightness diode end-pumped Nd:YAG microchip laser, passively Q-switched by a Cr(4+):YAG saturable absorber (SA), has been developed. The dependences of pulse energy and Width were investigated based on theoretical verification to enhance the peak power. As a result, the peak power exceeded 1.2 MW with M(2) = 1.04 and Spectrum Width Delta lambda < 5.1 pm at a repetition rate of 100 Hz. Brightness of 98 TW/sr x cm(2) was obtained with a supplied average electrical power of 2.3 W. The peak power increased up to 2.1 MW with M(2) = 1.36. Peak power of 1.7 MW was obtained from a 2-cm-diameter x 5-cm-long monolithic laser head.
Hiroshi Sakai - One of the best experts on this subject based on the ideXlab platform.
-
1 mw peak power single mode high brightness passively q switched nd 3 yag microchip laser
Optics Express, 2008Co-Authors: Hiroshi Sakai, Takunori TairaAbstract:A high-brightness diode end-pumped Nd:YAG microchip laser, passively Q-switched by a Cr4+:YAG saturable absorber (SA), has been developed. The dependences of pulse energy and Width were investigated based on theoretical verification to enhance the peak power. As a result, the peak power exceeded 1.2 MW with M2=1.04 and Spectrum Width Δλ<5.1 pm at a repetition rate of 100 Hz. Brightness of 98 TW/sr·cm2 was obtained with a supplied average electrical power of 2.3 W. The peak power increased up to 2.1 MW with M2=1.36. Peak power of 1.7 MW was obtained from a 2-cm-diameter×5-cm-long monolithic laser head.
-
1 mw peak power single mode high brightness passively q switched nd 3 yag microchip laser
Optics Express, 2008Co-Authors: Hiroshi Sakai, H Kan, Takunori TairaAbstract:A high-brightness diode end-pumped Nd:YAG microchip laser, passively Q-switched by a Cr(4+):YAG saturable absorber (SA), has been developed. The dependences of pulse energy and Width were investigated based on theoretical verification to enhance the peak power. As a result, the peak power exceeded 1.2 MW with M(2) = 1.04 and Spectrum Width Delta lambda < 5.1 pm at a repetition rate of 100 Hz. Brightness of 98 TW/sr x cm(2) was obtained with a supplied average electrical power of 2.3 W. The peak power increased up to 2.1 MW with M(2) = 1.36. Peak power of 1.7 MW was obtained from a 2-cm-diameter x 5-cm-long monolithic laser head.
Pavlos Kollias - One of the best experts on this subject based on the ideXlab platform.
-
on the forward modeling of radar doppler Spectrum Width from les implications for model evaluation
Journal of Geophysical Research, 2018Co-Authors: Yaosheng Chen, Johannes Verlinde, Eugene E Clothiaux, Andrew S Ackerman, Ann M Fridlind, Marcelo Chamecki, Pavlos Kollias, M P Kirkpatrick, Bicheng ChenAbstract:: Large-eddy simulations of an observed single-layer Arctic mixed-phase cloud are analyzed to study the value of forward modeling of profiling millimeter-wave cloud radar Doppler spectral Width for model evaluation. Individual broadening terms and their uncertainties are quantified for the observed spectral Width and compared to modeled broadening terms. Modeled turbulent broadening is narrower than the observed values when the turbulent kinetic energy dissipation rate from the subgrid-scale model is used in the forward model. The total dissipation rates, estimated with the subgrid-scale dissipation rates and the numerical dissipation rates, agree much better with both the retrieved dissipation rates and those inferred from the power spectra of the simulated vertical air velocity. The comparison of the microphysical broadening provides another evaluative measure of the ice properties in the simulation. To accurately retrieve dissipation rates as well as each broadening term from the observations, we suggest a few modifications to previously presented techniques. First, we show that the inertial subrange spectra filtered with the radar sampling volume is a better underlying model than the unfiltered -5/3 law for the retrieval of the dissipation rate from the power spectra of the mean Doppler velocity. Second, we demonstrate that it is important to filter out turbulence and remove the layer-mean reflectivity-weighted mean fall speed from the observed mean Doppler velocity to avoid overestimation of shear broadening. Finally, we provide a method to quantify the uncertainty in the retrieved dissipation rates, which eventually propagates to the uncertainty in the microphysical broadening.
-
on the unified estimation of turbulence eddy dissipation rate using doppler cloud radars and lidars
Journal of Geophysical Research, 2016Co-Authors: Paloma Borque, Edward P Luke, Pavlos KolliasAbstract:Coincident profiling observations from Doppler lidars and radars are used to estimate the turbulence energy dissipation rate (e) using three different data sources: (i) Doppler radar velocity (DRV), (ii) Doppler lidar velocity (DLV), and (iii) Doppler radar Spectrum Width (DRW) measurements. The agreement between the derived e estimates is examined at the cloud base height of stratiform warm clouds. Collocated e estimates based on power spectra analysis of DRV and DLV measurements show good agreement (correlation coefficient of 0.86 and 0.78 for both cases analyzed here) during both drizzling and nondrizzling conditions. This suggests that unified (below and above cloud base) time-height estimates of e in cloud-topped boundary layer conditions can be produced. This also suggests that eddy dissipation rate can be estimated throughout the cloud layer without the constraint that clouds need to be nonprecipitating. Eddy dissipation rate estimates based on DRW measurements compare well with the estimates based on Doppler velocity but their performance deteriorates as precipitation size particles are introduced in the radar volume and broaden the DRW values. Based on this finding, a methodology to estimate the Doppler spectra broadening due to the spread of the drop size distribution is presented. The uncertainties in e introduced by signal-to-noise conditions, the estimation of the horizontal wind, the selection of the averaging time window, and the presence of precipitation are discussed in detail.
A Khain - One of the best experts on this subject based on the ideXlab platform.
-
investigation of droplet size distributions and drizzle formation using a new trajectory ensemble model part ii lucky parcels
Journal of the Atmospheric Sciences, 2009Co-Authors: L Magaritz, Mark Pinsky, O A Krasnov, A KhainAbstract:Abstract A novel trajectory ensemble model of the cloud-topped boundary layer containing 1340 Lagrangian parcels moving with a turbulent-like flow with the observed statistical properties was applied to investigate the formation of the microphysical structure of stratocumulus clouds (Sc) in a nonmixing limit (when turbulent mixing between the parcels is not taken into account). The Sc observed in two research flights during the Second Dynamics and Chemistry of the Marine Stratocumulus field study (DYCOMS II)—RF01 (no drizzle) and RF07 (weak drizzle)—are simulated. The mechanisms leading to a high variability of droplet size distributions (DSDs) with different Spectrum Width and dispersion are discussed. Drizzle formation was investigated using the radar reflectivity–LWC and LWC–effective drop radius diagrams simulated by the model in the nondrizzle and drizzle cases. It is shown that in the RF07 case large cloud droplets that trigger drop collisions and drizzle formation form only in a small fraction (abo...
-
investigation of droplet size distributions and drizzle formation using a new trajectory ensemble model part i model description and first results in a nonmixing limit
Journal of the Atmospheric Sciences, 2008Co-Authors: Mark Pinsky, A Khain, L Magaritz, O A Krasnov, Alexander SterkinAbstract:Abstract A novel trajectory ensemble model of a stratocumulus cloud is described. In this model, the boundary layer (BL) is fully covered by a great number of Lagrangian air parcels that during their motion can contain either wet aerosols or aerosols and droplets. The diffusion growth of aerosols and droplets, as well as drop collisions, is accurately described in each parcel. Droplet sedimentation is taken into account, which allows simulation of precipitation formation. The Lagrangian parcels are advected by the velocity field generated by the turbulent-like flow model obeying turbulent correlation laws. The output of the numerical model includes droplet and aerosol size distributions and their moments, such as droplet concentration, droplet Spectrum Width, cloud water content, drizzle content, radar reflectivity, etc., calculated in each parcel. Horizontally averaged values are calculated as well. Stratocumulus clouds observed during two research flights (RF01 and RF07) in the Second Dynamics and Chemi...
Richard J. Doviak - One of the best experts on this subject based on the ideXlab platform.
-
A New Approach to Detect Ground Clutter Mixed With Weather Signals
IEEE Transactions on Geoscience and Remote Sensing, 2013Co-Authors: Yinguang Li, Guifu Zhang, Richard J. DoviakAbstract:Considering that the statistics of the phase and the power of weather signals in the spectral domain are different from those statistics for echoes from stationary objects, a Spectrum clutter identification (SCI) algorithm has been developed to detect ground clutter using single polarization radars, but SCI can be extended for dual-pol radars. SCI examines both the power and phase in the spectral domain and uses a simple Bayesian classifier to combine four discriminants: spectral power distribution, spectral phase fluctuations, spatial texture of echo power, and spatial texture of Spectrum Width to make decisions as to the presence of clutter that can corrupt meteorological measurements. This work is focused on detecting ground clutter mixed with weather signals, even if the clutter power to signal power ratio is low. The performance of the SCI algorithm is shown by applying it to radar data collected by University of Oklahoma-Polarimetric Radar for Innovation in Meteorology and Engineering.
-
significance of the coupled term in the doppler weather radar Spectrum Width equation
Journal of Atmospheric and Oceanic Technology, 2011Co-Authors: Ming Fang, Richard J. Doviak, Bruce A AlbrechtAbstract:AbstractThere is an additional zero mean random variable term that couples mean wind shear and turbulence in the Doppler radar Spectrum Width equation. This random variable, labeled the “coupled term,” has been neglected heretofore in the literature. Herein, the variance of the squared Spectrum Width ascribed to this coupled term is determined from data collected with a Weather Surveillance Radar-1988 Doppler (WSR-88D) in two snowstorms; it can exceed 1 m4 s−4. Thus, this coupled term can be a significant contributor to the variance of the Spectrum Width and must be considered when using Spectrum Width to deduce turbulence.
-
coupled contributions in the doppler radar Spectrum Width equation
Journal of Atmospheric and Oceanic Technology, 2008Co-Authors: Ming Fang, Richard J. DoviakAbstract:Abstract Contrary to accepted usage, the second central moment of the Doppler Spectrum is not the sum of the second central moments of individual spectral broadening mechanisms. A rigorous theoretical derivation of the Spectrum Width observed with short dwell times reveals that the sum cannot strictly be taken for the variances associated with various spectral broadening mechanisms and that an added-term coupling shear with turbulence is needed. Furthermore, shear and antenna rotation are coupled. The theoretical expressions derived herein apply to radars with fixed or scanning beams.
-
Spectrum Width measured by wsr 88d error sources and statistics of various weather phenomena
Journal of Atmospheric and Oceanic Technology, 2004Co-Authors: Ming Fang, Richard J. Doviak, Valery MelnikovAbstract:Abstract Spectrum Widths, one of the three moments measured and displayed by the Weather Surveillance Radar-1988 Doppler (WSR-88D), are categorized for various weather conditions showing both expected and unexpected results. Weather phenomena are classified into seven categories based on radar observations, and the statistics of the censored Spectrum Width fields for each of the categories are obtained. Daytime fair weather without birds, stratiform rain and snow, and isolated tornadic storms produce weather signals that have the smallest volumetric median values of Spectrum Widths (i.e., < 2 m s−1). Surprisingly, the median Spectrum Width values in the isolated tornadic storms are as low (i.e., <2 m s−1) as in the fair weather (without the presence of echoes from birds). The median Spectrum Width value from fair weather regions contaminated with bird echoes is larger (i.e., 3.0 m s−1). The largest median Spectrum Width values, ranging from 4.0 to 5.4 m s−1, are associated with embedded areal squall lines...
-
Spectrum Widths from echo power differences reveal meteorological features
Journal of Atmospheric and Oceanic Technology, 2002Co-Authors: Valery Melnikov, Richard J. DoviakAbstract:Abstract A new Doppler Spectrum Width estimator using the absolute power differences (APDs) at lag one is presented, and its performance is evaluated using simulated signals as well as those recorded from the National Severe Storms Laboratory's Research and Development WSR-88D. The APD estimate bias, its standard error of estimation, and the frequency of complex Widths are compared with that obtained with other single lag estimators [e.g., the pulse-pair logarithm (PPL) estimator]. For narrow spectra and signal-to-noise ratios more than 15 dB, the APD estimator has lower bias, lower standard deviation, and a lesser number of complex Width estimates than the PPL estimator. Spectrum Width fields, observed when this estimate technique is applied to the logarithms of echo power from an X-band radar, reveal meteorologically significant features that are not often seen in weather radar displays in regions of relatively small Spectrum Widths.
