the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Dec 2024
Development of level 2 aerosol and surface products from cross-track scanning polarimeter POSP onboard GF-5(02) satellite
Abstract. Development of long-term continues, consistent and high-quality satellite remote sensing aerosol and surface products is crucial to constrain climate models and improve our understanding on climate change. Particulate Observing Scanning Polarization (POSP) is the first space-borne multi-spectral (UV-VIS-NIR-SWIR) cross-track scanning polarimeter dedicated to complement Directional Polarimetric Camera (DPC) multi-angular polarimetric measurements and perform synergetic observations namely the Polarization Cross-Fire suite (PCF) onboard Chinese Gaofen series GF-5(02) satellite. The POSP unique single-viewing spectral (UV-VIS-NIR-SWIR) high-precision polarimetric measurements provide rich information for atmospheric aerosol and surface characterization. Here we developed aerosol and surface products from POSP/GF-5(02) based on the Generalized Retrieval of Atmosphere and Surface Properties (GRASP)/Models approach. The detailed retrieval approach and processing scheme are provided. The baseline level 2 product was generated for the first 18 months POSP measurements from December 2021 to May 2023 and publicly available and registered at doi.org/10.57760/sciencedb.14748. The obtained POSP/GF-5(02) aerosol and surface products are validated and intercompared with ground-based AERONET reference aerosol dataset and other independent satellite products, such as NOAA-20 VIIRS/DB aerosol product and MODIS MCD43 surface product. The results show generally good consistency of POSP products with AERONET, VIIRS/NOAA-20 aerosol dataset and MODIS surface product. Moreover, it is possible to conclude the developed POSP product includes reliable estimates of not only total Aerosol Optical Depth (AOD), but also detailed properties of aerosol such as aerosol size, absorption, layer height, type, etc., as well as full surface Bidirectional Reflectance Distribution Function (BRDF), Bidirectional Polarization Distribution Function (BPDF), and black-sky, white-sky albedos and Normalized Difference Vegetation Index (NDVI). These parameters are of high importance to constrain the Earth-atmosphere radiation budget. The retrieval of these properties seems to be possible due to the polarimetric capabilities and wide UV-VIS-NIR-SWIR spectral range of from POSP observations and advances of used GRASP/Models retrieval approach. Finally, some potential improvements for POSP level 1 to level 2 processing chain are identified, and limitations and lessons learned are discussed.
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Status: open (until 24 Feb 2025)
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RC1: 'Comment on essd-2024-483', Anonymous Referee #1, 09 Feb 2025
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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 -
RC2: 'Comment on essd-2024-483', Anonymous Referee #2, 12 Feb 2025
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Please see attached pdf file.
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RC3: 'Comment on essd-2024-483', Anonymous Referee #3, 13 Feb 2025
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See attached PDF file.
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Aerosol and surface products from cross-track scanning polarimeter POSP onboard GF-5(02) satellite (December 2021 - May 2023) Cheng Chen, Xuefeng Lei, Zhenhai Liu, Haoran Gu, Jin Hong, and Zhengqiang Li https://doi.org/10.57760/sciencedb.14748
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