Evaluation of SMAP downscaled brightness temperature using SMAPEx-4/5 airborne observations

N. Ye*, J. P. Walker, R. Bindlish, J. Chaubell, N. N. Das, A. I. Gevaert, T. J. Jackson, C. Rüdiger

*Corresponding author for this work

Research output: Contribution to JournalArticleAcademicpeer-review


The Soil Moisture Active and Passive (SMAP) mission, launched by the National Aeronautics and Space Administration (NASA) on 31st January 2015, was designed to provide global soil moisture every 2 to 3 days at 9 km resolution by downscaling SMAP passive microwave observations obtained at 36 km resolution using active microwave observations at 3 km resolution, and then retrieving soil moisture from the resulting 9 km brightness temperature product. This study evaluated the SMAP Active/Passive (AP) downscaling algorithm together with other resolution enhancement techniques. Airborne passive microwave observations acquired at 1 km resolution over the Murrumbidgee River catchment in south-eastern Australia during the fourth and fifth Soil Moisture Active Passive Experiments (SMAPEx-4/5) were used as reference data. The SMAPEx-4/5 data were collected in May and September 2015, respectively, and aggregated to 9 km for direct comparison with a number of available resolution-enhanced brightness temperature estimates. The results show that the SMAP AP downscaled brightness temperature had a correlation coefficient (R) of 0.84 and Root-Mean-Squared Error (RMSE) of ~10 K, while SMAP Enhanced, Nearest Neighbour, Weighted Average, and the Smoothing Filter-based Modulation (SFIM) brightness temperature estimates had somewhat better performance (RMSEs of ~7 K and an R exceeding 0.9). Although the SFIM had the lowest unbiased RMSE of ~6 K, the effect of cloud cover on Ka-band observations limits data availability.

Original languageEnglish
Pages (from-to)363-372
Number of pages10
JournalRemote Sensing of Environment
Early online date28 Nov 2018
Publication statusPublished - Feb 2019


This work was supported within the framework of the MoistureMonitor project funded by the Australian Research Council ( DP140100572 ).

FundersFunder number
Australian Research CouncilDP140100572
Australian Research Council


    • Downscaled brightness temperature
    • Field experiment
    • SMAP
    • Validation


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