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Title: Validation of the ASAR Global Monitoring Mode Soil Moisture Product

Author
item Mladenova, Iliana
item LAKSHMI, V - University Of South Carolina
item WALKER, J - University Of Melbourne
item WAGNER, W - Vienna University Of Technology
item Doraiswamy, Paul

Submitted to: BARC Poster Day
Publication Type: Abstract Only
Publication Acceptance Date: 3/12/2010
Publication Date: 4/21/2010
Citation: Mladenova, I., Lakshmi, V., Walker, J.P., Wagner, W., Doraiswamy, P.C. 2010. Validation of the ASAR global monitoring mode soil moisture product [abstract]. Abs. 26. BARC Poster Day.

Interpretive Summary:

Technical Abstract: It is well established in literature that integration of land surface variables such as soil moisture into forecasting models will lead to improved hydrologic prediction. Furthermore, most hydrological processes are best monitored at spatial scales of 1 km or higher. However, current and future passive microwave systems are and will remain resolution limited; at this time the highest available resolution of the operational soil moisture products is 25 km. Utilizing active microwave remote sensing is particularly promising because of its high resolution (10 m to 1000 m). Direct retrieval of soil moisture using radar (active) observations requires a lot of ancillary data that are hard to acquire at a global scale. This makes the available active retrieval algorithms, none of which is currently operational, applicable only to very site specific conditions. An alternative is to use techniques that are based on temporal change detection. Here, we evaluate the sensitivity of an active surface soil moisture product derived using the Advanced Synthetic Aperture Radar (ASAR) on ENVISAT (1 km) and a temporal chance detection approach. Three independent soil moisture data sets (station, field, and aircraft) acquired over SE Australia, gave the opportunity to address the following issues: are point measurements of soil moisture adequate to achieve accurate validation of a satellite derived product, and what is the realistic fine spatial scale when disaggregating coarse resolution radiometer estimates. Spatial and temporal comparisons demonstrated that the change detection derived ASAR product has potential for monitoring soil moisture. However, its accuracy appeared to be largely controlled by the high system noise levels and to be strongly dependent on the spatial scale at which the analysis was performed and the resolution of the evaluation data set. Spatial averaging of the ASAR data to a coarser resolution allowed enhancing the soil moisture signal and indicated that ASAR should be up-scaled to at least 5 km before the data can be applied to any future studies. Thus, the results from this research support the SMAP (Soil Moisture Active Passive)-adopted approach for spatial averaging of the original 1-km radar estimates to a coarser resolution. Most importantly, ASAR availability enables soil moisture monitoring at a resolution suitable for local and watershed applications and gives the necessary means for development of combined passive-active down-scaling techniques.