Parameterization of the freeze/thaw discriminant function algorithm using dense in-situ observation network data

ABSTRACT

The near-surface soil freeze–thaw (FT) transition is an important factor affecting land-atmosphere exchanges, hydrology and carbon cycles. Thus, effectively monitoring the temporal–spatial changes of soil FT processes is crucial to climate change and environment research. Several approaches have been developed to detect the soil FT state from satellite observations. The discriminant function algorithm (DFA) uses temperature and emissivity information from Advanced Microwave Scanning Radiometer Enhanced (AMSR-E) passive microwave satellite observations. Although it is well validated, it was shown to be insufficiently robust for all land conditions. In this study, we use in-situ observed soil temperature and AMSR-E brightness temperature to parameterize the DFA for soil FT state detection. We use the in-situ soil temperature records at 5 cm selected from available dense networks in the Northern Hemisphere as a reference. Considering the distinction between ascending and descending orbits, two different sets of parameters were acquired for each frequency pair. The validation results indicate that the overall discriminant accuracy of the new function can reach 90%. We further compared the Advanced Microwave Scanning Radiometer 2 discriminant results using the new function to the Soil Moisture Active Passive freeze/thaw product, and a reasonable consistency between them was found.

KEYWORDS:

• Soil freeze–thaw state
• discriminant function algorithm
• AMSR-E
• AMSR2
• SMAP

Acknowledgements

AMSRE, AMSR2 brightness temperature was provided by the GCOM-W Data Providing service, JAXA. The SMAP FTP data can be accessed at the National Snow and Ice Data Center. Pingkai Wang, Tianjie Zhao and Jiancheng Shi contributed to intellectual design and initial drafting. Pingkai Wang compiled and processed data. Pingkai Wang and Tianjie Zhao contributed to data analysis and interpretation. All the authors contributed to the writing of the final draft.

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Hui Lu http://orcid.org/0000-0003-1640-239X

Additional information

Funding

This study was jointly supported by the National Key Basic Research Program of China (2015CB953701), National Natural Science Foundation of China (41671355), Chinese Academy of Sciences Key Research Program of Frontier Sciences (QYZDY-SSW-DQC011), Strategic Pionner Program on Space Science (XDA15052300), ‘Light of West China’ Program and Youth Innovation Promotion Association (No. 2016061). Alexandre Roy was financed by the Canadian Space Agency and the Natural Science and Engineering Research Council of Canada.