scholarly journals Effect of the inhomogeneity of ice crystals on retrieving ice cloud optical thickness and effective particle size

2009 ◽  
Vol 114 (D11) ◽  
Author(s):  
Yu Xie ◽  
Ping Yang ◽  
George W. Kattawar ◽  
Patrick Minnis ◽  
Yong X. Hu
Keyword(s):  
Particle Size ◽  
Optical Thickness ◽  
Ice Crystals ◽  
Ice Cloud ◽  
Effective Particle Size ◽  
Effective Particle ◽  
Cloud Optical Thickness

scholarly journals Retrieval of Ice Cloud Optical Thickness and Effective Particle Size Using a Fast Infrared Radiative Transfer Model

2011 ◽  
Vol 50 (11) ◽  
pp. 2283-2297 ◽  
Author(s):  
Chenxi Wang ◽  
Ping Yang ◽  
Bryan A. Baum ◽  
Steven Platnick ◽  
Andrew K. Heidinger ◽  
...  
Keyword(s):  
Particle Size ◽  
Radiative Transfer ◽  
Optical Thickness ◽  
Radiative Transfer Model ◽  
Transfer Model ◽  
Distribution Method ◽  
Ice Cloud ◽  
Effective Particle Size ◽  
Effective Particle ◽  
Cloud Optical Thickness

AbstractA computationally efficient radiative transfer model (RTM) is developed for the inference of ice cloud optical thickness and effective particle size from satellite-based infrared (IR) measurements and is aimed at potential use in operational cloud-property retrievals from multispectral satellite imagery. The RTM employs precomputed lookup tables to simulate the top-of-the-atmosphere (TOA) radiances (or brightness temperatures) at 8.5-, 11-, and 12-μm bands. For the clear-sky atmosphere, the optical thickness of each atmospheric layer resulting from gaseous absorption is derived from the correlated-k-distribution method. The cloud reflectance, transmittance, emissivity, and effective temperature are precomputed using the Discrete Ordinate Radiative Transfer model (DISORT). For an atmosphere containing a semitransparent ice cloud layer with a visible optical thickness τ smaller than 5, the TOA brightness temperature differences (BTDs) between the fast model and the more rigorous DISORT results are less than 0.1 K, whereas the BTDs are less than 0.01 K if τ is larger than 10. With the proposed RTM, the cloud optical and microphysical properties are retrieved from collocated observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) in conjunction with the Modern Era Retrospective-Analysis for Research and Applications (MERRA) data. Comparisons between the retrieved ice cloud properties (optical thickness and effective particle size) based on the present IR fast model and those from the Aqua/MODIS operational collection-5 cloud products indicate that the IR retrievals are smaller. A comparison between the IR-retrieved ice water path (IWP) and CALIOP-retrieved IWP shows robust agreement over most of the IWP range.

scholarly journals Influence of Cloud-Top Height and Geometric Thickness on a MODIS Infrared-Based Ice Cloud Retrieval

2009 ◽  
Vol 48 (4) ◽  
pp. 818-832 ◽  
Author(s):  
Kevin J. Garrett ◽  
Ping Yang ◽  
Shaima L. Nasiri ◽  
Christopher R. Yost ◽  
Bryan A. Baum
Keyword(s):  
Particle Size ◽  
Optical Thickness ◽  
Lookup Table ◽  
Infrared Observation ◽  
Ice Cloud ◽  
Brightness Temperatures ◽  
Effective Particle Size ◽  
Effective Particle ◽  
Level 2 ◽  
Geometric Thickness

Abstract The retrieval of ice cloud microphysical and optical properties from satellite-based infrared observation remains a challenging research topic, partly because of the sensitivity of observed infrared radiances to many surface and atmospheric parameters that vary on fine spatial and temporal scales. In this study, the sensitivity of an infrared-based ice cloud retrieval to effective cloud temperature is investigated, with a focus on the effects of cloud-top height and geometric thickness. To illustrate the sensitivity, the authors first simulate brightness temperatures at 8.5 and 11.0 μm using the discrete ordinates radiative transfer (DISORT) model for five cloud-top heights ranging from 8 to 16 km and for varying cloud geometric thicknesses of 1, 2, 3, and 5 km. The simulations are performed across a range of visible optical thicknesses from 0.1 to 10 and ice cloud effective diameters from 30 to 100 μm. Furthermore, the effective particle size and optical thickness of ice clouds are retrieved from the Moderate Resolution Imaging Spectroradiometer (MODIS) measurements on the basis of a lookup-table approach. Specifically, the infrared brightness temperatures are simulated from the collocated Atmospheric Infrared Sounder (AIRS) level-2 product at 28 atmospheric levels and prescribed ice cloud parameters. Variations of the retrieved effective particle size and optical thickness versus cloud-top height and geometric thickness are investigated. Results show that retrievals based on the 8.5- and 11.0-μm bispectral approach are most valid for cloud-top temperatures of less than 224 K with visible optical thickness values between 2 and 5. The present retrievals are also compared with the collection-5 MODIS level-2 ice cloud product.

Effect of Cavities on the Optical Properties of Bullet Rosettes: Implications for Active and Passive Remote Sensing of Ice Cloud Properties

2008 ◽  
Vol 47 (9) ◽  
pp. 2311-2330 ◽  
Author(s):  
Ping Yang ◽  
Zhibo Zhang ◽  
George W. Kattawar ◽  
Stephen G. Warren ◽  
Bryan A. Baum ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Particle Size ◽  
Phase Function ◽  
Hollow Structure ◽  
Ice Clouds ◽  
Ice Cloud ◽  
Effective Particle Size ◽  
Effective Particle ◽  
Scattering Phase ◽  
Scattering Phase Function

Abstract Bullet rosette particles are common in ice clouds, and the bullets may often be hollow. Here the single-scattering properties of randomly oriented hollow bullet rosette ice particles are investigated. A bullet, which is an individual branch of a rosette, is defined as a hexagonal column attached to a hexagonal pyramidal tip. For this study, a hollow structure is included at the end of the columnar part of each bullet branch and the shape of the hollow structure is defined as a hexagonal pyramid. A hollow bullet rosette may have between 2 and 12 branches. An improved geometric optics method is used to solve for the scattering of light in the particle. The primary optical effect of incorporating a hollow end in each of the bullets is to decrease the magnitude of backscattering. In terms of the angular distribution of scattered energy, the hollow bullets increase the scattering phase function values within the forward scattering angle region from 1° to 20° but decrease the phase function values at side- and backscattering angles of 60°–180°. As a result, the presence of hollow bullets tends to increase the asymmetry factor. In addition to the scattering phase function, the other elements of the phase matrix are also discussed. The backscattering depolarization ratios for hollow and solid bullet rosettes are found to be very different. This may have an implication for active remote sensing of ice clouds, such as from polarimetric lidar measurements. In a comparison of solid and hollow bullet rosettes, the effect of the differences on the retrieval of both the ice cloud effective particle size and optical thickness is also discussed. It is found that the presence of hollow bullet rosettes acts to decrease the inferred effective particle size and to increase the optical thickness in comparison with the use of solid bullet rosettes.

scholarly journals Toward Cloud Tomography from Space Using MISR and MODIS: Locating the “Veiled Core” in Opaque Convective Clouds

2021 ◽  
Vol 78 (1) ◽  
pp. 155-166
Author(s):  
Linda Forster ◽  
Anthony B. Davis ◽  
David J. Diner ◽  
Bernhard Mayer
Keyword(s):  
Particle Size ◽  
Near Infrared ◽  
Tomographic Reconstruction ◽  
Significant Information ◽  
Single View ◽  
Convective Clouds ◽  
Effective Particle Size ◽  
Optical Distance ◽  
Effective Particle ◽  
Cloud Optical Thickness

AbstractFor passive satellite imagers, current retrievals of cloud optical thickness and effective particle size fail for convective clouds with 3D morphology. Indeed, being based on 1D radiative transfer (RT) theory, they work well only for horizontally homogeneous clouds. A promising approach for treating clouds as fully 3D objects is cloud tomography, which has been demonstrated for airborne observations. However, more efficient forward 3D RT solvers are required for cloud tomography from space. Here, we present a path forward by acknowledging that optically thick clouds have “veiled cores” (VCs). Sunlight scattered into and out of this deep region does not contribute significant information about the inner structure of the cloud to the spatially detailed imagery. We investigate the VC location for the MISR and MODIS imagers. While MISR provides multiangle imagery in the visible and near-infrared (IR), MODIS includes channels in the shortwave IR, albeit at a single view angle. This combination will enable future 3D retrievals to disentangle the cloud’s effective particle size and extinction fields. We find that, in practice, the VC is located at an optical distance of ~5, starting from the cloud boundary along the line of sight. For MODIS’s absorbing wavelengths the VC covers a larger volume, starting at smaller optical distances. This concept will not only lead to a reduction in the number of unknowns for the tomographic reconstruction but also significantly increase the speed and efficiency of the 3D RT solver at the heart of the algorithm by applying, say, the photon diffusion approximation inside the VC.

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