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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 24 Jul 2019

Submitted as: research article | 24 Jul 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

Retrieval of cloud properties from sky radiometer observed spectral zenith radiances

Pradeep Khatri1, Hironobu Iwabuchi1, Tadahiro Hayasaka1, Hitoshi Irie2, Tamio Takamura2, Akihiro Yamazaki3, Alessandro Damiani2, Husi Letu4, and Qin Kai5 Pradeep Khatri et al.
  • 1Center for Atmospheric and Oceanic Studies, Graduate School of Science, Tohoku University, Sendai, Japan
  • 2Center for Environmental Remote Sensing, Chiba University, Chiba, Japan
  • 3Meteorlogical Research Institute, Tsukuba, Japan
  • 4Institute of Remote Sensing and Digital Earth, Chinese Academy of Sciences, Beijing, China
  • 5School of Environment and Geoinformatics, China University of Mining and Technology, Xuzhou, China

Abstract. An optimal-estimation based algorithm to retrieve cloud optical thickness (COD) and cloud-particle effective radius (CER) from spectral zenith radiances observed by a narrow field of view (FOV) ground-based sky radiometer is developed. To further address the filter-degradation problem while analyzing data of long-term observation, an on-site calibration procedure is proposed, which is found to have a very good accuracy with respect to a standard procedure, i.e., a procedure of deriving calibration constants using a master instrument. An error evaluation study conducted by assuming errors in observation-based transmittances and ancillary data of water vapor concentration and surface albedo suggests that the errors in input data can influence retrieved CER more effectively than COD. Except for some narrow domains that fall within COD < 15, the retrieval errors are very small for both COD and CER. The retrieved cloud properties are found to reproduce the broadband radiances observed by a narrow FOV radiometer more precisely than broadband irradiances observed by a wide FOV pyranometer, justifying the quality of retrieved product (at least COD) and, at the same time, indicating the important influence of instrument FOV in cloud remote sensing. Further, CODs (CERs) between sky radiometer and satellite observations show fairly good (poor) agreement.

Pradeep Khatri et al.
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Pradeep Khatri et al.
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Publications Copernicus
Short summary
In an attempt of making the cloud retrieval from surface more common and convenient, we developed a cloud retrieval algorithm applicable for sun photometer and sky radiometer belonging to AERONET and SKYNET. It is based on an optimum method by fitting measured transmittances with modeled values. Further, a cost-effective and easy-to-use calibration procedure is proposed and validated using data obtained from standard method. A detail error analysis is performed and quality assessment is done.
In an attempt of making the cloud retrieval from surface more common and convenient, we...