Publication Abstracts

Sayer et al. 2025

Sayer, A.M., B. Cairns, K.D. Knobelspiesse, L. Lelli, C. Rajapakshe, S.E. Giangrande, G.E. Thomas, and Zhang Damao, 2025 : Evaluation of cloud height, optical thickness, and phase retrievals from the CHROMA algorithm applied to Sentinel-3 OLCI data. Atmos. Meas. Tech., 18, no. 22, 6681-6703, doi:10.5194/amt-18-6681-2025.

We previously developed the Cloud Height Retrieval from O2 Molecular Absorption (CHROMA) algorithm for the Ocean Color Instrument (OCI) on the new NASA Plankton, Aerosol, Cloud, ocean Ecosystem (PACE) mission. Here, we apply CHROMA to observations from the Ocean Land Colour Instrument (OLCI) to guide expectations for PACE, as it will take some time to obtain large-scale validation data for OCI. We use cloud top height (CTH), phase, and (for liquid clouds) cloud optical thickness (COT) data from the ground-based Atmospheric Radiation Measurement (ARM) network to evaluate the OLCI retrievals. We found that OLCI and Moderate Resolution Imaging Spectroradiometer (MODIS) CTH compare similarly well to the ARM reference. OLCI has a tendency to underestimate CTH as CTH increases, and algorithm assumptions about cloud geometric thickness may contribute to this. ARM COT from multifilter shadowband radiometers (MFRSR) and Sun photometers are well-correlated with one another, albeit with a roughly 30% offset on average; OLCI and MODIS COT agree more closely with the MFRSR data. OLCI retrieval uncertainty estimates show skill at telling low-uncertainty cases from high-uncertainty ones, although CTH uncertainties are underestimated. Additionally, we compare the OLCI data to satellite retrievals based on thermal infrared measurements from MODIS and Sea and Land Surface Temperature Radiometer (SLSTR) data. Differences are broadly consistent with physical expectations based on the A-band vs. thermal techniques, although one key challenge in such aggregated comparisons is different cloud masking sensitivities and algorithm failure rates meaning additional sampling differences are introduced. We conclude by discussing the transition to and possible enhancements for PACE OCI.

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BibTeX Citation

@article{sa05500d,
  author={Sayer, A. M. and Cairns, B. and Knobelspiesse, K. D. and Lelli, L. and Rajapakshe, C. and Giangrande, S. E. and Thomas, G. E. and Zhang Damao},
  title={Evaluation of cloud height, optical thickness, and phase retrievals from the CHROMA algorithm applied to Sentinel-3 OLCI data},
  year={2025 },
  journal={Atmospheric Measurement Techniques},
  volume={18},
  number={22},
  pages={6681--6703},
  doi={10.5194/amt-18-6681-2025},
}

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RIS Citation

TY  - JOUR
ID  - sa05500d
AU  - Sayer, A. M.
AU  - Cairns, B.
AU  - Knobelspiesse, K. D.
AU  - Lelli, L.
AU  - Rajapakshe, C.
AU  - Giangrande, S. E.
AU  - Thomas, G. E.
AU  - Zhang Damao
PY  - 2025 
TI  - Evaluation of cloud height, optical thickness, and phase retrievals from the CHROMA algorithm applied to Sentinel-3 OLCI data
JA  - Atmos. Meas. Tech.
JO  - Atmospheric Measurement Techniques
VL  - 18
IS  - 22
SP  - 6681
EP  - 6703
DO  - 10.5194/amt-18-6681-2025
ER  -

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