Broadband Complex Refractive Indices of Ice and Water

Ray, Peter S.

doi:10.1364/ao.11.001836

Cited by 549 publications

(248 citation statements)

References 27 publications

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“…2, where the curves intercept the y axis). These values are computed using the water refractive index provided by Ellison (2007), and are similar to those listed in Table 2 in Lhermitte (1990) which were computed using the older water refractive index model from Ray (1972). In the Rayleigh approximation the attenuation coefficient per unit mass is dominated by the absorption component; it is linearly proportional to the imaginary part of the dielectric factor, K = (n 2 − 1)/(n 2 + 2) (where n the ice complex refractive index), and inversely proportional to the wavelength (Lhermitte, 1990).…”

Section: Hydrometeor Attenuationmentioning

confidence: 99%

“…For particles heavier than 0.1 mg, shape variability can account for almost an order of magnitude in variability of the attenuation coefficient both at 150 and 220 GHz, an important signature for distinguishing different habits. A proper validation of these attenuation coefficients is also of crucial importance for the ice/snow passive microwave remote sensing techniques that make use of frequency channels within the G band (Buehler et al, 2012;Grecu and Olson, 2008;Skofronick-Jackson et al, 2004).…”

Section: Hydrometeor Attenuationmentioning

confidence: 99%

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G band atmospheric radars: new frontiers in cloud physics

et al. 2014

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Abstract. Clouds and associated precipitation are the largest source of uncertainty in current weather and future climate simulations. Observations of the microphysical, dynamical and radiative processes that act at cloud scales are needed to improve our understanding of clouds. The rapid expansion of ground-based super-sites and the availability of continuous profiling and scanning multi-frequency radar observations at 35 and 94 GHz have significantly improved our ability to probe the internal structure of clouds in high temporal-spatial resolution, and to retrieve quantitative cloud and precipitation properties. However, there are still gaps in our ability to probe clouds due to large uncertainties in the retrievals.The present work discusses the potential of G band (frequency between 110 and 300 GHz) Doppler radars in combination with lower frequencies to further improve the retrievals of microphysical properties. Our results show that, thanks to a larger dynamic range in dual-wavelength reflectivity, dual-wavelength attenuation and dual-wavelength Doppler velocity (with respect to a Rayleigh reference), the inclusion of frequencies in the G band can significantly improve current profiling capabilities in three key areas: boundary layer clouds, cirrus and mid-level ice clouds, and precipitating snow.

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Section: Hydrometeor Attenuationmentioning

confidence: 99%

Section: Hydrometeor Attenuationmentioning

confidence: 99%

G band atmospheric radars: new frontiers in cloud physics

et al. 2014

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“…When the scattering properties of the melting particles are calculated with the T-matrix method, it is the DDA matching ice spheroid properties (radius, aspect ratio, and index of refraction) that are mixed with the water properties. The dielectric constant of the melting particle is calculated with the Maxwell Garnett formula mixing for ice/air inclusions in water, and the index of refraction of water is from Ray (1972). The particle temperature is at the melting point until the particle is fully melted, and then the ambient temperature is assumed.…”

Section: B4 Melting Modelmentioning

confidence: 99%

Ice hydrometeor profile retrieval algorithm for high-frequency microwave radiometers: application to the CoSSIR instrument during TC4

et al. 2012

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Abstract.A Bayesian algorithm to retrieve profiles of cloud ice water content (IWC), ice particle size (D me ), and relative humidity from millimeter-wave/submillimeter-wave radiometers is presented. The first part of the algorithm prepares an a priori file with cumulative distribution functions (CDFs) and empirical orthogonal functions (EOFs) of profiles of temperature, relative humidity, three ice particle parameters (IWC, D me , distribution width), and two liquid cloud parameters. The a priori CDFs and EOFs are derived from CloudSat radar reflectivity profiles and associated ECMWF temperature and relative humidity profiles combined with three cloud microphysical probability distributions obtained from in situ cloud probes. The second part of the algorithm uses the CDF/EOF file to perform a Bayesian retrieval with a hybrid technique that uses Monte Carlo integration (MCI) or, when too few MCI cases match the observations, uses optimization to maximize the posterior probability function. The very computationally intensive Markov chain Monte Carlo (MCMC) method also may be chosen as a solution method. The radiative transfer model assumes mixtures of several shapes of randomly oriented ice particles, and here random aggregates of spheres, dendrites, and hexagonal plates are used for tropical convection. A new physical model of stochastic dendritic snowflake aggregation is developed. The retrieval algorithm is applied to data from the Compact Scanning Submillimeter-wave Imaging Radiometer (CoSSIR) flown on the ER-2 aircraft during the Tropical Composition, Cloud and Climate Coupling (TC4) experiment in 2007. Example retrievals with error bars are shown for nadir profiles of IWC, D me , and relative humidity, and nadir and conical scan swath retrievals of ice water path and average D me . The ice cloud retrievals are evaluated by retrieving integrated 94 GHz backscattering from CoSSIR for comparison with the Cloud Radar System (CRS) flown on the same aircraft. The rms difference in integrated backscattering is around 3 dB over a 30 dB range. A comparison of CoSSIR retrieved and CRS measured reflectivity shows that CoSSIR has the ability to retrieve low-resolution ice cloud profiles in the upper troposphere.

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“…The attenuation of the signals due to rain was evaluated using the Power law relationship between attenuation and rain rate, while an average water vapour density of 20 g/m 3 was assumed to calculate attenuation due to atmospheric gases using the parameters in [23]. Water temperature of 20 • C was also assumed to calculate the refractive index of water using the method of [24]. The 0 • C isotherm heights during rainy conditions, h F R , vary from 3.80-4.25 km in South Africa as obtained from the South African Weather Station (SAWS).…”

Section: Local Meteorological Parametersmentioning

confidence: 99%

Analysis of Bistatic Scattering Due to Hydrometeors on SHF and Ehf Links in a Subtropical Location: A Comparative Study Based on the Rain Cell Models

Owolawi¹,

Walingo²

2015

PIER M

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Abstract-The inevitable increase in radio interference within microwave systems continue to be of major concern as more of radio communication services compete with bandwidth assigned to the fixed service, fixed satellite service and broadcasting satellite service. Interference hampers coverage and capacity of these services often lead to the reduction in the signal to noise ratio at the receiving terminals. The existing global hydrometeor scatter model proposed by the International Telecommunication Union when applied to the tropical and subtropical location often leads to considerable inaccuracies due to the wide range of intense climatic and geographical nature of this region. In this study, the bistatic intersystem interference due to hydrometeors between satellite systems and terrestrial downlink receiver terminal systems in a subtropical station computation is based on the Awaka and Capsoni cell models. For the attenuation of both wanted and unwanted paths to the receiver, the existing model based on the specific attenuation has been modified to include the equivalent path length through rain in the estimation of the attenuation. Results obtained show that the Capsoni model exhibits the normal trend under a moist atmosphere with a gaseous attenuation more pronounced at frequencies greater than or equal to 30 GHz. Also at high rain rates greater than 70 mm/h and considering the rain with melting layer, up to about 70 dB difference was observed between transmission losses estimated using Awaka and Capsoni models at link probabilities ranging between 1-10 −3 % unavailability of the time.

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Broadband Complex Refractive Indices of Ice and Water

Cited by 549 publications

References 27 publications

G band atmospheric radars: new frontiers in cloud physics

G band atmospheric radars: new frontiers in cloud physics

Ice hydrometeor profile retrieval algorithm for high-frequency microwave radiometers: application to the CoSSIR instrument during TC4

Analysis of Bistatic Scattering Due to Hydrometeors on SHF and Ehf Links in a Subtropical Location: A Comparative Study Based on the Rain Cell Models

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