National Aeronautics and Space Administration Jet Propulsion Laboratory
National Aeronautics and Space Administration Jet Propulsion Laboratory California Institute of Technology Differences between Spatial Resolution and Grid Size in the SMAP Enhanced Soil Moisture Product (Andreas Colliander) Science Question: NASA SMAP (Soil Moisture Active Passive) mission provides a global radiometer-based soil moisture data product on a 9 -km grid. However, the spatial resolution of the product is about 33 -km. The product is spatially oversampled to facilitate more fidelity in the interpretation of spatial features. Many application users may, however, interpret the grid size as the resolution, because assuming 9 -km resolution would be a significant benefit for applications such as global weather forecast and climate modeling, drought monitoring and flood prediction. The question explored here is how significantly this assumption would add to the uncertainty of the product. Results: The grid size vs. spatial resolution issue was investigated over in situ core validation sites. The results show that assumption of 9 -km grid size equaling the resolution has a negligible statistical effect on the uncertainty (0. 003 m 3/m 3 difference in RMSE). This result stems from the generally large spatial structures in the soil moisture distribution and relative homogeneity of the sites; the result does not mean the resolution would equal the grid size. (Top) The locations of the core validation sites used in the study. (Bottom) Distribution of the differences between metrics obtained with 33 -km grid cells and 9 -km grid cells. Note the very low overall difference. Significance: The results indicate that for large scale applications an assumption that the 9 -km grid size of the SMAP radiometer-based soil moisture product equals the spatial resolution would not introduce large errors. However, for applications focusing on a single pixel or very localized conditions the impact of the small-scale soil moisture heterogeneity must be determined separately. Colliander, A. , T. J. Jackson, S. K. Chan, P. O’Neill, R. Bindlish, M. H. Cosh, T. Caldwell, J. P. Walker, A. Berg, H. Mc. Nairn, M. Thibeault, J. Martinez-Fernandez, K. H. Jensen, J. Asanuma, M. S. Seyfried, D. D. Bosch, P. J. Starks, C. Holifield Collins, J. H. Prueger, Z. Su, E. Lopez. Baeza, S. H. Yueh. An assessment of the differences between spatial resolution and grid size for the SMAP enhanced soil moisture product
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