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<front>
<journal-meta>
<journal-id journal-id-type="publisher">EGUsphere</journal-id>
<journal-title-group>
<journal-title>EGUsphere</journal-title>
<abbrev-journal-title abbrev-type="publisher">EGUsphere</abbrev-journal-title>
<abbrev-journal-title abbrev-type="nlm-ta">EGUsphere</abbrev-journal-title>
</journal-title-group>
<issn pub-type="epub"></issn>
<publisher><publisher-name>Copernicus Publications</publisher-name>
<publisher-loc>Göttingen, Germany</publisher-loc>
</publisher>
</journal-meta>
<article-meta>
<article-id pub-id-type="doi">10.5194/egusphere-2026-5631</article-id>
<title-group>
<article-title>Intercomparison of Liquid Cloud Droplet Size Retrievals from Different PACE Instruments</article-title>
</title-group>
<contrib-group><contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Yuan</surname>
<given-names>Zihao</given-names>
<ext-link>https://orcid.org/0000-0002-0177-9998</ext-link>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>van Diedenhoven</surname>
<given-names>Bastiaan</given-names>
<ext-link>https://orcid.org/0000-0001-5622-8619</ext-link>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Fu</surname>
<given-names>Guangliang</given-names>
<ext-link>https://orcid.org/0000-0001-8916-0243</ext-link>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Martins</surname>
<given-names>J. Vanderlei</given-names>
</name>
<xref ref-type="aff" rid="aff4">
<sup>4</sup>
</xref>
<xref ref-type="aff" rid="aff5">
<sup>5</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Sayer</surname>
<given-names>Andrew M.</given-names>
<ext-link>https://orcid.org/0000-0001-9149-1789</ext-link>
</name>
<xref ref-type="aff" rid="aff4">
<sup>4</sup>
</xref>
<xref ref-type="aff" rid="aff5">
<sup>5</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Rajapakshe</surname>
<given-names>Chamara</given-names>
<ext-link>https://orcid.org/0000-0002-7264-9867</ext-link>
</name>
<xref ref-type="aff" rid="aff5">
<sup>5</sup>
</xref>
<xref ref-type="aff" rid="aff6">
<sup>6</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Cairns</surname>
<given-names>Brian</given-names>
</name>
<xref ref-type="aff" rid="aff5">
<sup>5</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Lin</surname>
<given-names>Hai Xiang</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
<xref ref-type="aff" rid="aff3">
<sup>3</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Erisman</surname>
<given-names>Jan Willem</given-names>
</name>
<xref ref-type="aff" rid="aff2">
<sup>2</sup>
</xref>
</contrib>
<contrib contrib-type="author" xlink:type="simple"><name name-style="western"><surname>Hasekamp</surname>
<given-names>Otto P.</given-names>
<ext-link>https://orcid.org/0000-0002-1494-2539</ext-link>
</name>
<xref ref-type="aff" rid="aff1">
<sup>1</sup>
</xref>
</contrib>
</contrib-group><aff id="aff1">
<label>1</label>
<addr-line>SRON Netherlands Institute for Space Research (NWO-I/SRON), Leiden, the Netherlands</addr-line>
</aff>
<aff id="aff2">
<label>2</label>
<addr-line>Institute of Environmental Science (CML), Leiden University, Leiden, the Netherlands</addr-line>
</aff>
<aff id="aff3">
<label>3</label>
<addr-line>School of Computer Science and Control Engineering, Shenzhen University of Advanced Technology, Shenzhen, China</addr-line>
</aff>
<aff id="aff4">
<label>4</label>
<addr-line>University of Maryland Baltimore County, Baltimore, MD, USA</addr-line>
</aff>
<aff id="aff5">
<label>5</label>
<addr-line>NASA Goddard Space Flight Center, Greenbelt, MD, USA</addr-line>
</aff>
<aff id="aff6">
<label>6</label>
<addr-line>Science Systems and Applications, Inc., Lanham, Maryland, USA</addr-line>
</aff>
<pub-date pub-type="epub">
<day>23</day>
<month>09</month>
<year>2026</year>
</pub-date>
<volume>2026</volume>
<fpage>1</fpage>
<lpage>17</lpage>
<permissions>
<copyright-statement>Copyright: &#x000a9; 2026 Zihao Yuan et al.</copyright-statement>
<copyright-year>2026</copyright-year>
<license license-type="open-access">
<license-p>This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this licence, visit <ext-link ext-link-type="uri"  xlink:href="https://creativecommons.org/licenses/by/4.0/">https://creativecommons.org/licenses/by/4.0/</ext-link></license-p>
</license>
</permissions>
<self-uri xlink:href="https://egusphere.copernicus.org/preprints/2026/egusphere-2026-5631/">This article is available from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-5631/</self-uri>
<self-uri xlink:href="https://egusphere.copernicus.org/preprints/2026/egusphere-2026-5631/egusphere-2026-5631.pdf">The full text article is available as a PDF file from https://egusphere.copernicus.org/preprints/2026/egusphere-2026-5631/egusphere-2026-5631.pdf</self-uri>
<abstract>
<p>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 &amp;micro;m (0.81 &amp;micro;m) over land (ocean) and a mean absolute difference (MAD) of 2.53 &amp;micro;m (2.58 &amp;micro;m). The MD between SPEXone and OCI is -2.06 &amp;micro;m (-2.67 &amp;micro;m) over land (ocean) and the MAD is 3.15 &amp;micro;m (3.60 &amp;micro;m). For the comparison between HARP-2 and OCI, the MD is -3.51 &amp;micro;m (-3.47 &amp;micro;m) over land (ocean) and the MAD is 3.89 &amp;micro;m (3.89 &amp;micro;m). Globally, annual CER statistic distribution peaks near 7 &amp;micro;m for SPEXone and HARP-2 and around 10 &amp;micro;m 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.</p>
</abstract>
<counts><page-count count="17"/></counts>
<funding-group>
<award-group id="gs1">
<funding-source>China Scholarship Council</funding-source>
<award-id>202106220072</award-id>
</award-group>
<award-group id="gs2">
<funding-source>Netherlands Space Office</funding-source>
<award-id>ALWGO.2019.006</award-id>
</award-group>
</funding-group>
</article-meta>
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