Publication Abstracts

Bi et al. 2014

Bi, L., P. Yang, C. Liu, B. Yi, B.A. Baum, B. van Diedenhoven, and H. Iwabuchi, 2014: Assessment of the accuracy of the conventional ray-tracing technique: Implications in remote sensing and radiative transfer involving ice clouds. J. Quant. Spectrosc. Radiat. Transfer, 146, 158-174, doi:10.1016/j.jqsrt.2014.03.017.

A fundamental problem in remote sensing and radiative transfer simulations involving ice clouds is the ability to compute accurate optical properties for individual ice particles. While relatively simple and intuitively appealing, the conventional geometric-optics method (CGOM) is used frequently for the solution of light scattering by ice crystals. Due to the approximations in the ray-tracing technique, the CGOM accuracy is not well quantified. The result is that the uncertainties are introduced that can impact many applications. Improvements in the Invariant Imbedding T-matrix method (II-TM) and the Improved Geometric-Optics Method (IGOM) provide a mechanism to assess the aforementioned uncertainties. The results computed by the II-TM+IGOM are considered as a benchmark because the II-TM solves Maxwell's equations from first principles and is applicable to particle size parameters ranging into the domain at which the IGOM has reasonable accuracy. To assess the uncertainties with the CGOM in remote sensing and radiative transfer simulations, two independent optical property datasets of hexagonal columns are developed for sensitivity studies by using the CGOM and the II-TM+IGOM, respectively. Ice cloud bulk optical properties obtained from the two datasets are compared and subsequently applied to retrieve the optical thickness and effective diameter from Moderate Resolution Imaging Spectroradiometer (MODIS) measurements. Additionally, the bulk optical properties are tested in broadband radiative transfer (RT) simulations using the global circulation model (GCM) version of the Rapid Radiative Transfer Model (RRTMG) that is adopted in the National Center for Atmospheric Research (NCAR) Community Atmosphere Model (CAM, version 5.1). For MODIS retrievals, the mean bias of uncertainties of applying the CGOM in shortwave bands (0.86 and 2.13 μm) can be up to 5% in the optical thickness and as high as 20% in the effective diameter, depending on cloud optical thickness and effective diameter. In the MODIS infrared window bands centered at 8.5, 11, and 12 μm, biases in the optical thickness and effective diameter are up to 12% and 10%, respectively. The CGOM-based simulation errors in ice cloud radiative forcing calculations are on the order of 10 W/m2.

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BibTeX Citation

@article{bi09000n,
  author={Bi, L. and Yang, P. and Liu, C. and Yi, B. and Baum, B. A. and van Diedenhoven, B. and Iwabuchi, H.},
  title={Assessment of the accuracy of the conventional ray-tracing technique: Implications in remote sensing and radiative transfer involving ice clouds},
  year={2014},
  journal={J. Quant. Spectrosc. Radiat. Transfer},
  volume={146},
  pages={158--174},
  doi={10.1016/j.jqsrt.2014.03.017},
}

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RIS Citation

TY  - JOUR
ID  - bi09000n
AU  - Bi, L.
AU  - Yang, P.
AU  - Liu, C.
AU  - Yi, B.
AU  - Baum, B. A.
AU  - van Diedenhoven, B.
AU  - Iwabuchi, H.
PY  - 2014
TI  - Assessment of the accuracy of the conventional ray-tracing technique: Implications in remote sensing and radiative transfer involving ice clouds
JA  - J. Quant. Spectrosc. Radiat. Transfer
VL  - 146
SP  - 158
EP  - 174
DO  - 10.1016/j.jqsrt.2014.03.017
ER  -

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