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.

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.

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 Sensitivity of Thermal Infrared Radiation at the Top of the Atmosphere and the Surface to Ice Cloud Microphysics

2008 ◽  
Vol 47 (10) ◽  
pp. 2545-2560 ◽  
Author(s):  
Philippe Dubuisson ◽  
Vincent Giraud ◽  
Jacques Pelon ◽  
Bertrand Cadet ◽  
Ping Yang
Keyword(s):  
Optical Thickness ◽  
Particle Shape ◽  
Cloud Model ◽  
Cloud Microphysics ◽  
Ice Clouds ◽  
Ice Cloud ◽  
Brightness Temperatures ◽  
Microphysical Properties ◽  
Effective Particle ◽  
The Impact

Abstract This paper reports on the sensitivity of the brightness temperatures associated with radiances at the surface and the top of the atmosphere, simulated for the Imaging Infrared Radiometer (IIR) 8.7-, 10.6-, and 12-μm channels under ice cloudy conditions, to the optical and microphysical properties of ice clouds. The 10.6- and 12-μm channels allow simultaneous retrieval of ice cloud optical thickness and effective particle size (Deff) less than 100 μm. It is illustrated that the particle shape and size distributions of ice crystals have noticeable effects on the brightness temperatures. Using the split window technique based on the 10.6- and 12-μm channels in conjunction with cloud properties assumed a priori, the authors show that the influence of the cloud microphysical properties can lead to differences on the order of ±10% and ±25% in retrieved effective particle sizes for small (Deff < 20 μm) and large particles (Deff > 40 μm), respectively. The impact of cloud model on retrieved optical thickness is on the order of ±10%. Different particle habits may lead to ±25% differences in ice water path (IWP). Theoretically, the use of an additional channel (i.e., 8.7 μm) can give a stronger constraint on cloud model and improve the retrieval of Deff and IWP. The present simulations have confirmed that cloud microphysics has a significant impact on the 8.7-μm brightness temperatures mainly because of particle shape. This impact is larger than the errors of the IIR measurements for cloud optical thicknesses (at 12 μm) ranging from 0.3 to 8. Furthermore, it is shown that the characterization of optical and microphysical properties of ice clouds from ground-based measurements is quite challenging. Especially, water vapor in the atmosphere has an important impact on ground-based cloud retrievals. Observation stations at higher altitudes or airborne measurements would minimize the atmospheric effect.

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