Feng et al. (2025) A high-resolution (0.05°) global seamless continuity record (2002–2023) of near-surface soil freeze-thaw states via passive microwave and optical satellite data

Identification

• Journal: Earth system science data
• Year: 2025
• Date: 2025-11-20
• Authors: Defeng Feng, Tianjie Zhao, Jingyao Zheng, Yu Bai, Youhua Ran, Xiaokang Kou, Lingmei Jiang, Ziqian Zhang, Pei Yu, Jinbiao Zhu, Jie Pan, Jiancheng Shi, Yuei‐An Liou
• DOI: 10.5194/essd-17-6273-2025

Research Groups

• State Key Laboratory of Remote Sensing and Digital Earth, Aerospace Information Research Institute, Chinese Academy of Sciences
• University of Chinese Academy of Sciences
• State Key Laboratory of Cryospheric Science and Frozen Soil Engineering, Heihe Remote Sensing Experimental Research Station, Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences
• School of Civil Engineering, Shijiazhuang Tiedao University
• Key Laboratory of Roads and Railway Engineering Safety Control, Shijiazhuang Tiedao University, Ministry of Education
• State Key Laboratory of Remote Sensing and Digital Earth, Faculty of Geographical Science, Beijing Normal University
• School of Geospatial Engineering and Science, Sun Yat-sen University
• Aeronautical Remote Sensing Center, Chinese Academy of Sciences
• School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences
• National Space Science Center, Chinese Academy of Sciences
• Hydrology Remote Sensing Laboratory, Center for Space and Remote Sensing Research, National Central University

Short Summary

This study developed a novel downscaling method integrating passive microwave and optical satellite data to create a global, high-resolution (0.05°), daily seamless record of near-surface soil freeze-thaw states from 2002 to 2023, which achieved an overall accuracy of 83.78% comparable to coarse-resolution products but with enhanced spatial detail.

Objective

• To enhance the spatial resolution of global near-surface soil freeze-thaw (FT) state detection products to 0.05° without compromising accuracy, by integrating passive microwave and optical satellite data to create a daily seamless, long-term record.

Study Configuration

• Spatial Scale: Global, with a final resolution of 0.05° (approximately 5.5 km at the equator), downscaled from an original 0.25° resolution.
• Temporal Scale: Long-term record spanning 2002–2023, with daily seamless continuity.

Methodology and Data

• Models used:
  • Discriminant Function Algorithm (DFA) for initial coarse-resolution FT state discrimination from passive microwave data.
  • Linear regression model (FTI = a · LST + b · ATI + c) for spatial downscaling, establishing relationships between coarse-resolution FT Index (FTI) and high-resolution optical data (Land Surface Temperature and Apparent Thermal Inertia).
  • Sen’s Slope and Mann–Kendall (MK) test for trend analysis of frost days and freeze onset dates.
• Data sources:
  • Satellite:
    • Passive Microwave: AMSR-E and AMSR2 Level-3 Brightness Temperature (TB) standard products (18.7 GHz H-polarization and 36.5 GHz V-polarization).
    • Optical: MODIS/Terra LST Daily L3 Global 0.05° CMG (MOD11C1) and MODIS/Aqua LST Daily L3 Global 0.05° CMG (MYD11C1) for Land Surface Temperature (LST).
    • Optical: Global Land Surface Satellite (GLASS) GLASS02B06 dataset for surface albedo.
    • Ancillary: MODIS Land Cover Type CMG Yearly L3 Global 0.05° (MCD12C1) for land cover maps.
  • In-situ:
    • Soil temperature measurements (0–5 cm depth) from 41 dense observation networks and three sparse networks (SCAN, SNOTEL, USCRN) provided by the International Soil Moisture Network (ISMN).
    • Soil temperature measurements (0–5 cm depth) from two networks (Naqu and Pali) obtained from the Tibetan Plateau Observatory (Tibet-Obs).

Main Results

• A global, high-resolution (0.05°), daily seamless near-surface soil freeze-thaw (FT) state dataset (FT-HiDFA) was generated for the period 2002–2023.
• Validation against in situ soil temperature data showed overall accuracies of 87.63 % for ascending orbits and 83.78 % for descending orbits for the downscaled product, which are comparable to the original 0.25° products (87.72 % and 84.08 %, respectively).
• The downscaling approach successfully eliminated data gaps present in the original 0.25° microwave-derived FT product, providing a continuous record.
• Trend analysis of annual frost days (2003–2023) revealed:
  • An average of 187.8 ± 12.7 days of frost in regions north of 45° N.
  • A decreasing trend in frost days across 14.35 % of global land areas (2.67 % statistically significant), notably in Eurasia and Alaska.
  • An increasing trend in frost days across 11.17 % of global land areas (1.55 % statistically significant), including North America and West Asia.
  • High annual frost days showed spatial correspondence with permafrost distribution on the Qinghai-Tibet Plateau, with an average of 278.85 days in permafrost-classified pixels.
• Trend analysis of annual freeze onset dates (2003–2023) showed:
  • An average freeze onset date of 240.3 ± 7.2 days in high-latitude regions of the Northern Hemisphere, with earlier onset at higher latitudes and elevations.
  • A decreasing trend (earlier onset) in 9.10 % of global land areas (1.22 % statistically significant), most pronounced in eastern Russia.
  • An increasing trend (delayed onset) in 7.57 % of global land areas (0.91 % statistically significant), reflecting widespread global warming impacts.

Contributions

• Developed a novel and robust downscaling methodology that integrates passive microwave and optical satellite data to produce a high-resolution (0.05°) global near-surface soil freeze-thaw (FT) state dataset.
• Achieved daily seamless continuity and effectively addressed data gaps inherent in coarse-resolution microwave-only FT products, providing a more complete and reliable long-term record (2002–2023).
• Demonstrated that the enhanced spatial resolution of the FT product (0.05°) maintains accuracy comparable to the original coarse-resolution products while offering significantly more detailed information on FT dynamics.
• Provided a valuable dataset that meets the expanding spatial and temporal resolution requirements of the Global Climate Observation System (GCOS) for FT monitoring.
• Enabled more refined analyses of regional FT dynamics and trends, offering crucial insights for hydrological modeling, climate research, and ecosystem management, particularly in complex terrains.

Funding

• National Key Research and Development Program of China (no. 2021YFB3900104)
• Fengyun Application Pioneering Project (FY-APP-2022.0305)

Citation

@article{Feng2025highresolution,
  author = {Feng, Defeng and Zhao, Tianjie and Zheng, Jingyao and Bai, Yu and Ran, Youhua and Kou, Xiaokang and Jiang, Lingmei and Zhang, Ziqian and Yu, Pei and Zhu, Jinbiao and Pan, Jie and Shi, Jiancheng and Liou, Yuei‐An},
  title = {A high-resolution (0.05°) global seamless continuity record (2002–2023) of near-surface soil freeze-thaw states via passive microwave and optical satellite data},
  journal = {Earth system science data},
  year = {2025},
  doi = {10.5194/essd-17-6273-2025},
  url = {https://doi.org/10.5194/essd-17-6273-2025}
}