Comment on egusphere-2026-5631
Abstract
Abstract. This paper presents an intercomparison of liquid cloud droplet size retrievals from the three instruments onboard the Plankton, Aerosol, Cloud, and ocean Ecossystem (PACE) mission: SPEXone, HARP-2, and OCI. SPEXone and HARP-2 provide retrievals of cloud droplet effective radius (CER) and cloud effective variance (CEV) from respectively hyperspectral and hyper-angular polarization observations. OCI provides CER retrievals using radiometric measurements in the visible and shortwave infrared. In the one-year (June 2024 - May 2025) intercomparison, closest agreement is found between SPEXone and HARP-2 CER, while OCI generally retrieves larger CER than both polarimeters. The CER retrieval comparison between SPEXone and HARP-2 yields a mean difference (MD) of 1.45 µm (0.81 µm) over land (ocean) and a mean absolute difference (MAD) of 2.53 µm (2.58 µm). The MD between SPEXone and OCI is -2.06 µm (-2.67 µm) over land (ocean) and the MAD is 3.15 µm (3.60 µm). For the comparison between HARP-2 and OCI, the MD is -3.51 µm (-3.47 µm) over land (ocean) and the MAD is 3.89 µm (3.89 µm). Globally, annual CER statistic distribution peaks near 7 µm for SPEXone and HARP-2 and around 10 µm for OCI. CEV comparison between SPEXone and HARP-2 yield an MD of -0.003 both over land and ocean and an MAD of 0.039 (0.037) over land (ocean). The CEV global statistic distribution for both instruments peaks near 0.07. The results in this paper suggest that polarized retrievals consistently yield a substantially smaller CER than conventional bi-spectral retrievals, even for two polarized retrievals from different instruments, using different retrieval algorithms. These differences may be caused by differences in vertical sensitivity or biases caused by cloud inhomogeneity or 3D radiative transfer effects.
Authors 10
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Zihao Yuan corresponding Aachen Institute of Environmental Science SRON Netherlands Institute for Space Research
Leiden University · NWO-I · Space Research Organisation Netherlands
Affiliation as printed
Institute of Environmental Science (CML), Leiden University, Leiden, the Netherlands
SRON Netherlands Institute for Space Research (NWO-I/SRON), Leiden, the Netherlands
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NWO-I · Space Research Organisation Netherlands
Affiliation as printed
SRON Netherlands Institute for Space Research (NWO-I/SRON), Leiden, the Netherlands
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NWO-I · Space Research Organisation Netherlands
Affiliation as printed
SRON Netherlands Institute for Space Research (NWO-I/SRON), Leiden, the Netherlands
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Goddard Space Flight Center · University of Maryland, Baltimore County
Affiliation as printed
NASA Goddard Space Flight Center, Greenbelt, MD, USA
University of Maryland Baltimore County, Baltimore, MD, USA
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Goddard Space Flight Center · University of Maryland, Baltimore County
Affiliation as printed
NASA Goddard Space Flight Center, Greenbelt, MD, USA
University of Maryland Baltimore County, Baltimore, MD, USA
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Goddard Space Flight Center · Science Systems and Applications (United States)
Affiliation as printed
NASA Goddard Space Flight Center, Greenbelt, MD, USA
Science Systems and Applications, Inc., Lanham, Maryland, USA
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Affiliation as printed
NASA Goddard Space Flight Center, Greenbelt, MD, USA
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Leiden University · Shenzhen University of Advanced Technology
Affiliation as printed
Institute of Environmental Science (CML), Leiden University, Leiden, the Netherlands
School of Computer Science and Control Engineering, Shenzhen University of Advanced Technology, Shenzhen, China
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Affiliation as printed
Institute of Environmental Science (CML), Leiden University, Leiden, the Netherlands
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NWO-I · Space Research Organisation Netherlands
Affiliation as printed
SRON Netherlands Institute for Space Research (NWO-I/SRON), Leiden, the Netherlands
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