参考文献：
[1] Tobin, K. J., Torres, R., Crow, W. T. Multi-decadal analysis of root-zone soil moisture applying the exponential filter across CONUS [J]. Hydrology and Earth System Sciences, 2017, 21(9): 4403-4417.
[2] Zohaib, M., Kim, H., Choi, M. Evaluating the patterns of spatiotemporal trends of root zone soil moisture in major climate regions in East Asia: trend of root zone soil moisture [J]. Journal of Geophysical Research-Atmospheres, 2017, 122(15): 7705-7722.
[3] Xu, L., Chen, N., Zhang, X., et al. In-situ and triple-collocation based evaluations of eight global root zone soil moisture products [J]. Remote Sensing of Environment, 2023, 254: 112248.
[4] Tian, J., Zhang, Y. Q. Comprehensive validation of seven root zone soil moisture products at 1153 ground sites across China [J]. International Journal of Digital Earth, 2023, 16(2): 4008-4022.
[5] Bell, B., Hersbach, H., Simmons, A., et al. The ERA5 global reanalysis: preliminary extension to 1950 [J]. Quarterly Journal of the Royal Meteorological Society, 2021, 147(741): 4186-4227.
[6] Reichle, R. H., Draper, C. S., Liu, Q., et al. Assessment of MERRA-2 land surface hydrology estimates [J]. Journal of Climate, 2017, 30(8): 2937-2960.
[7] Saha, S., Moorthi, S., Wu, X. R., et al. The NCEP climate forecast system version 2 [J]. Journal of Climate, 2014, 27(6): 2185-2208.
[8] Rodell, M., Houser, P. R., Jambor, U., et al. The global land data assimilation system [J]. Bulletin of the American Meteorological Society, 2004, 85(3): 381-394.
[9] Reichle, R. H., Liu, Q., Koster, R. D., et al. Version 4 of the SMAP Level-4 soil moisture algorithm and data product [J]. Journal of Advances in Modeling Earth Systems, 2019, 11(10): 3106-3130.
[10] Tavella, P., Premoli, A. Estimating the instabilities of N-Clocks by measuring differences of their readings [J]. Metrologia, 1994, 30(5): 479-486.
[11] Galindo, F. J., Palacio, J. Estimating the instabilities of N correlated clocks [C]. Proceedings of the 31th Annual Precise Time and Time Interval Systems and Applications Meeting, 1999: 285-296.