Publication Abstracts

Zhang et al. 2017

Zhang, Z., F. Werner, H.-M. Cho, G. Wind, S.E. Platnick, A.S. Ackerman, L. Di Girolamo, A. Marshak, and K. Meyer, 2017: A framework for quantifying the impacts of sub-pixel reflectance variance and covariance on cloud optical thickness and effective radius retrievals based on the bi-spectral method. In Radiation Processes in the Atmosphere and Ocean (IRS2016): Proceedings of the International Radiation Symposium (IRC/IAMAS), 16-22 April 2016, Auckland, New Zealand, AIP Conference Proceedings, vol. 1810, p. 030002, doi:10.1063/1.4975502.

The so-called bi-spectral method retrieves cloud optical thickness (τ) and cloud droplet effective radius (re) simultaneously from a pair of cloud reflectance observations, one in a visible or near infrared (VIS/NIR) band and the other in a shortwave-infrared (SWIR) band. A cloudy pixel is usually assumed to be horizontally homogeneous in the retrieval. Ignoring sub-pixel variations of cloud reflectances can lead to a significant bias in the retrieved τ and re. In this study, we use the Taylor expansion of a two-variable function to understand and quantify the impacts of sub-pixel variances of VIS/NIR and SWIR cloud reflectances and their covariance on the τ and re retrievals. This framework takes into account the fact that the retrievals are determined by both VIS/NIR and SWIR band observations in a mutually dependent way. In comparison with previous studies, it provides a more comprehensive understanding of how sub-pixel cloud reflectance variations impact the τ and re retrievals based on the bi-spectral method. In particular, our framework provides a mathematical explanation of how the sub-pixel variation in VIS/NIR band influences the re retrieval and why it can sometimes outweigh the influence of variations in the SWIR band and dominate the error in re retrievals, leading to a potential contribution of positive bias to the re retrieval.

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BibTeX Citation

@inproceedings{zh04200y,
  author={Zhang, Z. and Werner, F. and Cho, H.-M. and Wind, G. and Platnick, S. E. and Ackerman, A. S. and Di Girolamo, L. and Marshak, A. and Meyer, K.},
  title={A framework for quantifying the impacts of sub-pixel reflectance variance and covariance on cloud optical thickness and effective radius retrievals based on the bi-spectral method},
  booktitle={Radiation Processes in the Atmosphere and Ocean (IRS2016): Proceedings of the International Radiation Symposium (IRC/IAMAS), 16-22 April 2016, Auckland, New Zealand},
  year={2017},
  volume={1810},
  pages={030002},
  series={AIP Conference Proceedings},
  doi={10.1063/1.4975502},
}

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RIS Citation

TY  - CPAPER
ID  - zh04200y
AU  - Zhang, Z.
AU  - Werner, F.
AU  - Cho, H.-M.
AU  - Wind, G.
AU  - Platnick, S. E.
AU  - Ackerman, A. S.
AU  - Di Girolamo, L.
AU  - Marshak, A.
AU  - Meyer, K.
PY  - 2017
TI  - A framework for quantifying the impacts of sub-pixel reflectance variance and covariance on cloud optical thickness and effective radius retrievals based on the bi-spectral method
BT  - Radiation Processes in the Atmosphere and Ocean (IRS2016): Proceedings of the International Radiation Symposium (IRC/IAMAS), 16-22 April 2016, Auckland, New Zealand
T3  - AIP Conference Proceedings
VL  - 1810
SP  - 030002
DO  - 10.1063/1.4975502
ER  -

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