Abstract
With the development and the improvement of meteorological satellites, different instruments have significantly enhanced the ability to observe clouds over large spatial regions. Recent geostationary satellite radiometers, e.g., Advanced Himawari Imager (AHI) and Advanced Geosynchronous Radiation Imager (AGRI) onboard the Himawari-8 and the Fengyun-4A satellite, respectively, provide observations over similar regions at higher spatial and temporal resolutions for cloud and atmosphere studies. To better understand the reliability of AHI and AGRI retrieval products, we compare their cloud products with collocated Moderate Resolution Imaging Spectroradiometer (MODIS) cloud products, especially in terms of the cloud optical thickness (COT) and cloud effective radius (CER). Our comparison indicates that cloud mask and cloud phase of these instruments are reasonably consistent, while clear differences are noticed for COT and CER results. The average relative differences (RDs) between AHI and AGRI ice COT and that of MODIS are both over 40%, and the RDs of ice CER are less than 20%. The consistency between AHI and MODIS water cloud results is much better, with the RDs of COT and CER being 29% and 9%, respectively, whereas the RDs of AGRI COT and CER are still larger than 30%. Many factors such as observation geometry, cloud horizontal homogeneity, and retrieval system (e.g., retrieval algorithm, forward model, and assumptions) may contribute to these differences. The RDs of COTs from different instruments for homogeneous clouds are about one-third smaller than the corresponding RDs for inhomogeneous clouds. By applying unified retrieval systems based on the forward radiative transfer models designed for each particular band, we find that 30% to 70% of the differences among the results from different instruments are caused by the retrieval system (e.g., different treatments or assumptions for the retrievals), and the rest may be due to sub-pixel inhomogeneity, parallax errors, and calibration.
Highlights
Clouds, covering approximately 65%–70% of the globe on average, are one of the most important components of the Earth’s atmosphere [1]
Similar to the Advanced Himawari Imager (AHI) Comprehensive Analysis Program for Cloud Optical Measurement (CAPCOM) algorithm, the Advanced Geosynchronous Radiation Imager (AGRI) cloud optical thickness (COT) and the cloud effective radius (CER) are obtained by using a Daytime Cloud Optical and Microphysical Property (DCOMP) algorithm based on the observed reflectances at 0.65 and 2.25 μm bands and a one-dimension variational (1DVAR) algorithm [38,55]
We look for all Moderate Resolution Imaging Spectroradiometer (MODIS) pixels within a primary sensor (AHI or AGRI) pixel circle that has a diameter of its spatial resolution
Summary
Clouds, covering approximately 65%–70% of the globe on average, are one of the most important components of the Earth’s atmosphere [1]. Compared with polar-orbiting satellite radiometers, geostationary satellite radiometers can observe a target area at a high temporal resolution to provide temporally continuous cloud product data Because of their high temporal resolution and large spatial coverage, those radiometers can continuously observe atmosphere in Asia and infer detailed cloud information, including cloud mask, types, microphysical and optical properties, and cloud life cycles. These products are widely used for weather analysis and forecasting, short-term climate prediction, and environmental and disaster monitoring in Asia [19,20,21]. The factors to which the differences in the three products may be attributed, especially their retrieval system, are discussed in Section 4, and Section 5 concludes this study
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