Development of Level 2 aerosol and surface products  from cross-track scanning polarimeter  POSP on board the GF-5(02) satellite

Chen, Cheng; Lei, Xuefeng; Liu, Zhenhai; Gu, Haorang; Dubovik, Oleg; Litvinov, Pavel; Fuertes, David; Cao, Yujia; Yu, Haixiao; Xiang, Guangfeng; Meng, Binghuan; Qiu, Zhenwei; Sun, Xiaobing; Hong, Jin; Li, Zhengqiang

doi:https://doi.org/10.5194/essd-17-3497-2025

Articles | Volume 17, issue 7

https://doi.org/10.5194/essd-17-3497-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/essd-17-3497-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 17, issue 7

Data description paper

|

22 Jul 2025

Data description paper |

| 22 Jul 2025

Development of Level 2 aerosol and surface products from cross-track scanning polarimeter POSP on board the GF-5(02) satellite

Cheng Chen, Xuefeng Lei, Zhenhai Liu, Haorang Gu, Oleg Dubovik, Pavel Litvinov, David Fuertes, Yujia Cao, Haixiao Yu, Guangfeng Xiang, Binghuan Meng, Zhenwei Qiu, Xiaobing Sun, Jin Hong, and Zhengqiang Li

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Final revised paper (published on 22 Jul 2025)
Preprint (discussion started on 18 Dec 2024)

Interactive discussion

Status: closed

RC1:
'Comment on essd-2024-483', Anonymous Referee #1, 09 Feb 2025
The study is well-organized, and the results demonstrate good agreement with other datasets. However, several concerns need to be addressed, and providing additional information will further strengthen the paper.
Are the images in Figures 4 and 5 averaged over the entire 18-month period? While it is clear that data was processed and made publicly available for 18 months, averaging all 18 months together may lead to an unbalanced seasonal representation, where certain seasons dominate the dataset. This results in an image that is neither an annual mean nor a seasonal mean, making it difficult to interpret. Additionally, the AERONET validation later in the paper appears to use only one year of data. This raises the question of whether it is necessary to average all 18 months in these figures. Also, I think it would be better to have more descriptions for Figure 4 and 5

In line 293, it is mentioned that SSA data was matched within ±180 minutes, which is different from the other validation datasets. It would be helpful to explain why this specific time window was chosen.

In lines 316–318 and 369–370, the paper states that the results are similar to previous studies. However, instead of just stating that they are similar, it would be more effective to include specific numerical comparisons in the form of figures or tables to support this claim.

In Figure 6, while it is true that the ocean validation results appear better than those for land and that most data points are well distributed around the 1:1 line, there seem to be several significant outliers. In other studies, ocean validation results have generally been more stable. Of course, as the number of validation points increases, some outliers are inevitable, but considering that Figure 6 shows only 219 ocean data points, the distribution appears somewhat scattered. Since the paper already mentions that the glint mask was applied too strictly and should be improved, this is likely not a glint-related issue. Instead, it would be helpful to provide additional explanations on whether the issue is due to bad pixel screening, a limitation in GRASP’s ocean retrieval algorithm, or some other factor.
Citation: https://doi.org/10.5194/essd-2024-483-RC1
- AC1: 'Reply on RC1', Cheng Chen, 25 Mar 2025
  
  We would like to thank the reviewer for your time reviewing the manuscript and appreciate the constructive comments on our paper. We provide a detailed response to the Reviewer’s comments in the Supplement.
  
  Citation: https://doi.org/10.5194/essd-2024-483-AC1
RC2:
'Comment on essd-2024-483', Anonymous Referee #2, 12 Feb 2025

Please see attached pdf file.

Citation: https://doi.org/10.5194/essd-2024-483-RC2
- AC2: 'Reply on RC2', Cheng Chen, 25 Mar 2025
  
  We would like to thank the reviewer for your time reviewing the manuscript and appreciate the constructive comments on our paper. We provide a detailed response to the Reviewer’s comments in the Supplement.
  
  Citation: https://doi.org/10.5194/essd-2024-483-AC2
RC3:
'Comment on essd-2024-483', Anonymous Referee #3, 13 Feb 2025

See attached PDF file.

Citation: https://doi.org/10.5194/essd-2024-483-RC3
- AC3: 'Reply on RC3', Cheng Chen, 25 Mar 2025
  
  We would like to thank the reviewer for your time reviewing the manuscript and appreciate the constructive comments on our paper. We provide a detailed response to the Reviewer’s comments in the Supplement.
  
  Citation: https://doi.org/10.5194/essd-2024-483-AC3

Peer review completion

AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload

AR by Cheng Chen on behalf of the Authors (25 Mar 2025) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (26 Mar 2025) by Jing Wei

RR by Anonymous Referee #1 (31 Mar 2025)

RR by Anonymous Referee #2 (31 Mar 2025)

Suggestions for revision or reasons for rejection

I was a reviewer of the previous version of the manuscript. In this revision, the authors have addressed most of my previous issues. I appreciate these efforts. This includes improvements to the data file format – global processing attribute metadata have been added (some other dataset-level metadata are still missing such as variable long_names, although these are documented in the paper itself, so while not ideal I think it’s acceptable if it is difficult for the authors to add these without a larger-scale processing effort).

As a result, I feel the paper is acceptable for publication in ESSD pending a few minor corrections, unless other reviewers identify problems I missed. As ESSD is primarily a data set description journal I see the requirements as being a little different from e.g. AMT/ACP and think the overall level of detail is appropriate here.

I think the below could probably be handled without further peer-review but would be happy to review again if the Editor would like.

1. Line 17: “continues” should be “continuous”

2. Line 30: This sentence is too strong, it’s not right to conclude that these products are all reliable. Only AOD, Angstrom, and fine/coarse split are validated against AERONET. The other things are compared against other satellites (not a validation!) or not at all (e.g. BPDF). I would just start this sentence as “Moreover, the data set provides not just total aerosol optical depth (AOD), but …” That is a more honest representation of what is shown in the paper.

3. Line 61: “China has traditionally prioritized the development of Earth observation technologies and it has recently launched… ” This statement veers into propaganda, not science (and is unsupported in any case). I suggest just starting “China has recently launched …”

4. Line 64: “past” is written twice, one can be removed.

5. Table 1: is “spectral resolution” the full width at half maximum or something else? This should be defined more clearly as there are several possible interpretations. is it correct that the bandwidth for the 1380 nm channel is 40 nm? That seems quite wide compared to historical instruments, given the water vapor absorption here is quite narrow and the usual goal for this wavelength is to get a narrow band to increase sensitivity to only high-altitude features (e.g. cirrus).

6. Line 160: from reading the response to reviewer comments, it’s not clear to me if (for the Dubovik AERONET inversion product) only the almucantar scans are used or also the hybrid scans. The hybrid scans were implemented to increase retrieval quality and availability during the day and are in the same file format (but a different data stream) from the almucantar scans. I initially assumed both were used but from reading the response to reviewers, this is no longer clear to me.

7. Line 168: please add the Deep Blue data version used.

8. Line 241: I would delete the word “new” as this technique has been used for 15+ years now by GRASP. So this is not a novel aspect to this specific application of GRASP.

9. Figure 16 and discussion: I’m not sure if the difference in the 2 micron band albedo is really from aerosols. At this wavelength, the aerosol contribution is small unless the coarse optical depth is high. I think that the spectral difference between 2130 (MODIS) and 2250 (POSP) nm band centers is probably the biggest factor (of course as the authors point out radiometric calibration can be important as well). This spectral difference can be quite significant because the absorption of different surfaces (and water) can vary a lot over this range. This can be seen in e.g. hyperspectral libraries (for example this soil spectrum from the ECOSTRESS library): https://speclib.jpl.nasa.gov/ecospeclibdata/soil.aridisol.haplargid.none.all.89p1793.jhu.becknic.spectrum.txt and also in things like PACE OCI surface reflectance data which has SWIR bands at both these wavelengths (for example Figure 1 here): https://www.tandfonline.com/doi/full/10.1080/2150704X.2025.2470905#d1e924

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ED: Publish subject to minor revisions (review by editor) (13 Apr 2025) by Jing Wei

AR by Cheng Chen on behalf of the Authors (15 Apr 2025) Author's response Author's tracked changes Manuscript

ED: Publish subject to technical corrections (18 Apr 2025) by Jing Wei

AR by Cheng Chen on behalf of the Authors (20 Apr 2025) Manuscript

Short summary

Particulate Observing Scanning Polarization (POSP) on board the second GaoFen-5 (GF-5(02)) satellite is the first space-borne ultraviolet–visible–near-infrared–shortwave-infrared (UV–VIS–NIR–SWIR) multi-spectral cross-track scanning polarimeter. Due to its wide spectral range and polarimetric capabilities, POSP measurements provide rich information for aerosol and surface characterization. We present the detailed aerosol/surface products generated from POSP's first 18 months of operation, including spectral aerosol optical depth, aerosol-size-/absorption-related properties, surface black-sky and white-sky albedos, etc.