Radiative transfer in the cloudy atmosphere

Mayer, Bernhard

doi:10.1140/epjconf/e2009-00912-1

Cited by 274 publications

(243 citation statements)

References 15 publications

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“…The Monte Carlo code MYSTIC (Mayer, 2009) was used to solve the radiative transfer equation because it allows one to accurately calculate aureole even for strongly-peaked phase functions.…”

Section: Radiative Transfer Calculationsmentioning

confidence: 99%

Volcanic ash from Iceland over Munich: mass concentration retrieved from ground-based remote sensing measurements

et al. 2011

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Abstract. Volcanic ash plumes, emitted by the Eyjafjallajökull volcano (Iceland) in spring 2010, were observed by the lidar systems MULIS and POLIS in Maisach (near Munich, Germany), and by a CIMEL Sun photometer and a JenOptik ceilometer in Munich. We retrieve mass concentrations of volcanic ash from the lidar measurements; spectral optical properties, i.e. extinction coefficients, backscatter coefficients, and linear depolarization ratios, are used as input for an inversion. The inversion algorithm searches for model aerosol ensembles with optical properties that agree with the measured values within their uncertainty ranges. The non-sphericity of ash particles is considered by assuming spheroids. Optical particle properties are calculated using the T-matrix method supplemented by the geometric optics approach. The lidar inversion is applied to observations of the pure volcanic ash plume in the morning of 17 April 2010. We find 1.45 g m −2 for the ratio between the mass concentration and the extinction coefficient at λ = 532 nm, assuming an ash density of 2.6 g cm −3 . The uncertainty range for this ratio is from 0.87 g m −2 to 2.32 g m −2 . At the peak of the ash concentration over Maisach the extinction coefficient at λ = 532 nm was 0.75 km −1 (1-h-average), which corresponds to a maximum mass concentration of 1.1 mg m −3 (0.65 to 1.8 mg m −3 ). Model calculations show that particle backscatter at our lidar wavelengths (λ ≤ 1064 nm), and thus the lidar retrieval, is hardly sensitive to large particles (r 3 µm); large particles, however, may contain significant amounts of mass. Therefore, as an independent cross check of the lidar retrieval and to investigate the presence of large particles in more detail, we model ratios of sky radiances in the aureole of the Sun and compare them to measurements of the CIMEL. These ratios are sensitive to particles up to r ≈ 10 µm. This approach confirms the mass concentrations Correspondence to: J. Gasteiger (josef.gasteiger@lmu.de) from the lidar retrieval. We conclude that synergistic utilization of high quality lidar and Sun photometer data, in combination with realistic aerosol models, is recommended for improving ash mass concentration retrievals.

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“…The Monte Carlo code MYSTIC (Mayer, 2009) was used to solve the radiative transfer equation because it allows one to accurately calculate aureole even for strongly-peaked phase functions.…”

Section: Radiative Transfer Calculationsmentioning

confidence: 99%

Volcanic ash from Iceland over Munich: mass concentration retrieved from ground-based remote sensing measurements

et al. 2011

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“…The radiative transfer model MYSTIC (Monte Carlo code for the phYSically correct Tracing of photons In Cloudy atmospheres; Mayer, 2009) is used for this study. MYSTIC is operated as one of several radiative transfer solvers of the libRadtran radiative transfer package (Mayer and Kylling, 2005).…”

Section: Methodsmentioning

confidence: 99%

“…clouds, aerosols, and molecules. For general questions about the Monte Carlo technique and in particular about libRadtran and MYSTIC the reader is referred to the literature (Marchuk et al, 1980;Collins et al, 1972;Mayer, 2009;Marshak and Davis, 2005;.…”

Section: Methodsmentioning

confidence: 99%

The impact of aerosols on polarized sky radiance: model development, validation, and applications

et al. 2010

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Abstract. Although solar radiation initially is unpolarized when entering the Earth's atmosphere, it is polarized by scattering processes with molecules, water droplets, ice crystals, and aerosols. Hence, measurements of the polarization state of radiation can be used to improve remote sensing of aerosols and clouds. The analysis of polarized radiance measurements requires an accurate radiative transfer model. To this end, a new efficient and flexible threedimensional Monte Carlo code to compute polarized radiances has been developed and implemented into MYSTIC (Monte Carlo code for the phYSically correct Tracing of photons In Cloudy atmospheres). The code has been extensively validated against published benchmark results. The polarized downwelling radiation field is calculated for various aerosol types showing the high sensitivity of polarized ultraviolet radiances to the particle microphysics. Model simulations are compared to ground based measurements and found to be qualitatively in good agreement. Quantitative differences can be attributed to the assumed aerosol models based on the OPAC aerosol database, which does not include exactly the types of aerosols that have been observed. This comparison to the measurements shows that there is a high potential to retrieve information about the aerosol type from polarized radiance measurements.

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“…The heterogeneity of the surface albedo is considered by using the 3-D Monte Carlo model MYSTIC (Monte Carlo code for the physically correct tracing of photons in cloudy atmospheres), which is one of the solvers available within libRadtran (Mayer, 2009). With MYSTIC the radiation field is modeled by tracing individual photons on their paths through the 3-D atmosphere.…”

Section: Modelingmentioning

confidence: 99%

Influence of spatial heterogeneity of local surface albedo on the area-averaged surface albedo retrieved from airborne irradiance measurements

2013

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Spectral airborne upward and downward irradiance measurements are used to derive the area-averaged surface albedo. Real surfaces are not homogeneous in their reflectivity. Therefore, this work studies the effects of the heterogeneity of surface reflectivity on the area-averaged surface albedo to quantify how well aircraft measurements can resolve the small-scale variability of the local surface albedo. For that purpose spatially heterogeneous surface albedo maps were input into a 3-dimensional (3-D) Monte Carlo radiative transfer model to simulate 3-D irradiance fields. The calculated up- and downward irradiances in altitudes between 0.1 and 5 km are used to derive the area-averaged surface albedo using an iterative retrieval method that removes the effects due to atmospheric scattering and absorption within the layer beneath the considered level. For the case of adjacent land and sea surfaces, parametrizations are presented which quantify the horizontal distance from the coastline that is required to reduce surface heterogeneity effects on the area-averaged surface albedo to a given limit. The parametrization which is a function of altitude, aerosol optical depth, single scattering albedo, and the ratio of local land and sea albedo was applied for airborne spectral measurements. In addition, the deviation between area-averaged and local surface albedo is determined for more complex surface albedo maps. For moderate aerosol conditions (optical depth less than 0.4) and a wavelength range between 400 and 1000 nm, the altitude and the heterogeneity of the surface albedo are the dominant factors determining the mean deviation between local and area-averaged surface albedo. A parametrization of the mean deviation is applied to an albedo map that was derived from a Landsat image of an area in East Anglia (UK). Parametrization and direct comparison of local and area-averaged surface albedo show similar mean deviations (20% vs. 25%) over land

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Radiative transfer in the cloudy atmosphere

Cited by 274 publications

References 15 publications

Volcanic ash from Iceland over Munich: mass concentration retrieved from ground-based remote sensing measurements

Volcanic ash from Iceland over Munich: mass concentration retrieved from ground-based remote sensing measurements

The impact of aerosols on polarized sky radiance: model development, validation, and applications

Influence of spatial heterogeneity of local surface albedo on the area-averaged surface albedo retrieved from airborne irradiance measurements

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