Analysis of 9 km quasi-global microwave land surface emissivity estimates derived from SMAP radiometer and CYGNSS reflectometer
Accurate estimation and high-resolution mapping of land surface emissivity are crucial for enhancing understanding of Earth system processes and facilitating informed decision-making across various fields. This study presents a method that combines Soil Moisture Active Passive (SMAP) radiometer and...
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Taylor & Francis Group
2025-04-01
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| Series: | Geo-spatial Information Science |
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| Online Access: | https://www.tandfonline.com/doi/10.1080/10095020.2025.2493713 |
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| author | Yifan Zhu Fei Guo Wentao Yang Zhiyu Zhang Zheng Li Ziheng Wu Xiaohong Zhang |
| author_facet | Yifan Zhu Fei Guo Wentao Yang Zhiyu Zhang Zheng Li Ziheng Wu Xiaohong Zhang |
| author_sort | Yifan Zhu |
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| description | Accurate estimation and high-resolution mapping of land surface emissivity are crucial for enhancing understanding of Earth system processes and facilitating informed decision-making across various fields. This study presents a method that combines Soil Moisture Active Passive (SMAP) radiometer and Cyclone Global Navigation Satellite System (CYGNSS) reflectometer data to derive 9 km quasi-global (within ±38° latitudes) microwave land surface emissivity estimates for the first time. In practice, the SMAP emissivity data serve as the base at 36 km scale, while CYGNSS reflectivity data are used to capture the spatial heterogeneity at 9 km scale. The combination is achieved through a spatially varying scaling factor that converts CYGNSS reflectivity to SMAP emissivity space. Global comparisons show a strong correspondence between the downscaled SMAP/CYGNSS 9 km emissivity and SMAP interpolated 9 km emissivity, yielding correlation coefficient (R) values ranging from 0.93 to 0.96 and Root-Mean-Square Error (RMSE) values from 0.018 to 0.020 for four 90-day periods. Moreover, the downscaled emissivity exhibits satisfactory spatial-temporal performance, with a median repeat period of 2.5 days for most mid-latitude regions and 4.7 days for all regions. When compared to SMAP native emissivity at 36 km scale, the upscaled SMAP/CYGNSS 36 km emissivity shows a significant increase of 66% in spatial coverage on the daily scale and a median increase of 64% in temporal coverage. These results indicate that the GNSS-R data are likely to be an effective supplement at small spatial scale with a sub-daily to daily scale for future remote sensing of microwave emissivity. |
| format | Article |
| id | doaj-art-b6036087bf9546f5a8e4df6537f54e00 |
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| issn | 1009-5020 1993-5153 |
| language | English |
| publishDate | 2025-04-01 |
| publisher | Taylor & Francis Group |
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| series | Geo-spatial Information Science |
| spelling | doaj-art-b6036087bf9546f5a8e4df6537f54e002025-08-20T02:19:15ZengTaylor & Francis GroupGeo-spatial Information Science1009-50201993-51532025-04-0111610.1080/10095020.2025.2493713Analysis of 9 km quasi-global microwave land surface emissivity estimates derived from SMAP radiometer and CYGNSS reflectometerYifan Zhu0Fei Guo1Wentao Yang2Zhiyu Zhang3Zheng Li4Ziheng Wu5Xiaohong Zhang6School of Geodesy and Geomatics, Hubei Luojia Laboratory, Wuhan University, Wuhan, ChinaSchool of Geodesy and Geomatics, Hubei Luojia Laboratory, Wuhan University, Wuhan, ChinaSchool of Geodesy and Geomatics, Hubei Luojia Laboratory, Wuhan University, Wuhan, ChinaSchool of Geodesy and Geomatics, Hubei Luojia Laboratory, Wuhan University, Wuhan, ChinaSchool of Geodesy and Geomatics, Hubei Luojia Laboratory, Wuhan University, Wuhan, ChinaSchool of Geodesy and Geomatics, Hubei Luojia Laboratory, Wuhan University, Wuhan, ChinaSchool of Geodesy and Geomatics, Hubei Luojia Laboratory, Wuhan University, Wuhan, ChinaAccurate estimation and high-resolution mapping of land surface emissivity are crucial for enhancing understanding of Earth system processes and facilitating informed decision-making across various fields. This study presents a method that combines Soil Moisture Active Passive (SMAP) radiometer and Cyclone Global Navigation Satellite System (CYGNSS) reflectometer data to derive 9 km quasi-global (within ±38° latitudes) microwave land surface emissivity estimates for the first time. In practice, the SMAP emissivity data serve as the base at 36 km scale, while CYGNSS reflectivity data are used to capture the spatial heterogeneity at 9 km scale. The combination is achieved through a spatially varying scaling factor that converts CYGNSS reflectivity to SMAP emissivity space. Global comparisons show a strong correspondence between the downscaled SMAP/CYGNSS 9 km emissivity and SMAP interpolated 9 km emissivity, yielding correlation coefficient (R) values ranging from 0.93 to 0.96 and Root-Mean-Square Error (RMSE) values from 0.018 to 0.020 for four 90-day periods. Moreover, the downscaled emissivity exhibits satisfactory spatial-temporal performance, with a median repeat period of 2.5 days for most mid-latitude regions and 4.7 days for all regions. When compared to SMAP native emissivity at 36 km scale, the upscaled SMAP/CYGNSS 36 km emissivity shows a significant increase of 66% in spatial coverage on the daily scale and a median increase of 64% in temporal coverage. These results indicate that the GNSS-R data are likely to be an effective supplement at small spatial scale with a sub-daily to daily scale for future remote sensing of microwave emissivity.https://www.tandfonline.com/doi/10.1080/10095020.2025.2493713Cyclone Global Navigation Satellite System (CYGNSS)Global Navigation Satellite System-Reflectometry (GNSS-R)microwave land surface emissivitySoil Moisture Active Passive (SMAP) |
| spellingShingle | Yifan Zhu Fei Guo Wentao Yang Zhiyu Zhang Zheng Li Ziheng Wu Xiaohong Zhang Analysis of 9 km quasi-global microwave land surface emissivity estimates derived from SMAP radiometer and CYGNSS reflectometer Geo-spatial Information Science Cyclone Global Navigation Satellite System (CYGNSS) Global Navigation Satellite System-Reflectometry (GNSS-R) microwave land surface emissivity Soil Moisture Active Passive (SMAP) |
| title | Analysis of 9 km quasi-global microwave land surface emissivity estimates derived from SMAP radiometer and CYGNSS reflectometer |
| title_full | Analysis of 9 km quasi-global microwave land surface emissivity estimates derived from SMAP radiometer and CYGNSS reflectometer |
| title_fullStr | Analysis of 9 km quasi-global microwave land surface emissivity estimates derived from SMAP radiometer and CYGNSS reflectometer |
| title_full_unstemmed | Analysis of 9 km quasi-global microwave land surface emissivity estimates derived from SMAP radiometer and CYGNSS reflectometer |
| title_short | Analysis of 9 km quasi-global microwave land surface emissivity estimates derived from SMAP radiometer and CYGNSS reflectometer |
| title_sort | analysis of 9 km quasi global microwave land surface emissivity estimates derived from smap radiometer and cygnss reflectometer |
| topic | Cyclone Global Navigation Satellite System (CYGNSS) Global Navigation Satellite System-Reflectometry (GNSS-R) microwave land surface emissivity Soil Moisture Active Passive (SMAP) |
| url | https://www.tandfonline.com/doi/10.1080/10095020.2025.2493713 |
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