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Title:   Author  item
                                            QIU, J. - Chinese Academy Of Sciencesitem
                                            Crow, Wadeitem
                                            MO, X. - Chinese Academy Of Sciencesitem
                                            LIU, S. - Chinese Academy Of Sciences
  Submitted to: Geophysical Research Letters
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 6/1/2014
                                    Publication  Date: 7/15/2014
                                    Publication URL: https://handle.nal.usda.gov/10113/60023Citation: Qiu, J., Crow, W.T., Mo, X., Liu, S. 2014. The impact of vertical measurement depth on the information content of soil moisture times series data. Geophysical Research Letters. 41(14):4997-5004. DOI: 10.1002/2014GL060017.Interpretive Summary: The development of microwave remote sensing techniques to measure soil moisture from space represents a major advance in our ability to globally monitor agricultural drought. However, a potential limitation in these techniques is that they are generally only sensitive to moisture content within the top 5-cm of the soil column and therefore cannot characterize soil water availability within the entire crop root-zone (often assumed to extend down to the top 60-m of the soil column). Using a unique methodology, this paper explicitly measures the information content of both surface-zone (top 5-cm) and root-zone (top 60-m) soil moisture series times for agricultural drought applications. Results demonstrate that, while root-zone soil moisture is indeed more valuable than surface-zone observations, a simple filtering transformation of surface-zone soil moisture can be performed which allows (transformed) surface-zone moisture observations to effectively match the information content of (much deeper) root-zone soil moisture observations. This result suggests that the shallow vertical sampling of microwave-based surface soil moisture retrievals (within the soil column) is not as large a limitation as commonly assumed. As a consequence, the paper provides further motivation for the integration of satellite-derived surface soil moisture retrievals into operational drought monitoring systems. Improvements in the accuracy of these systems will, in turn, enable USDA to better anticipate - and even mitigate - the impact of drought on global agricultural markets.
                                Technical Abstract: Using a decade of high-quality ground-based soil moisture observations acquired from the United States Department of Agriculture’s Soil Climate Analysis Network (SCAN), we calculate the mutual information content between multiple soil moisture variables and near-future vegetation condition to examine the existence of emergent agricultural drought information in root-zone (integrated surface to 60-cm) soil moisture (RZSM) observations not present in either 5-cm surface soil moisture (SSM) observations or a simple low-pass transformation of SSM (F(SSM)). Results suggest that while RZSM is more valuable than SSM, the enhanced  information content in RZSM can be effectively duplicated by F(SSM). This implies that, for agricultural drought forecasting applications, the shallow vertical penetration depth of microwave-based SSM retrievals is not as large a practical limitation as commonly perceived.


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