Submitted to: Chapman and Hall Medical Atlas Series
Publication Type: Book / Chapter
Publication Acceptance Date: 1/20/2014
Publication Date: 12/8/2014
Citation: Jackson, T.J., Cosh, M.H., Crow, W.T. 2014. Some issues in validating satellite-based soil moisture retrievals with in situ observations and their Impact on SMAP validation. In: Lakshmi, V. Remote Sensing of the Terrestrial Water Cycle. American Geophysical Union Geophysical Monograph 206. Washington, DC: John Wiley and Sons. p. 247-254.
Technical Abstract: The Soil Moisture Active Passive (SMAP) satellite is scheduled for launch in the fall of 2014. As the first of NASA’s Decadal Survey missions, efforts are being made to implement both best practices and innovations, which include calibration and validation of the remote sensing products (Cal/Val). This paper reviews best practices as related to soil moisture validation using in situ network observations. There are four primary reasons why calibration and validation are necessary for a successful satellite mission; mission requirements, quality assurance, data integration, and science. From the point of view of the satellite project and science team, validation is usually a requirement of the funding agency that is used to assess the mission success. These requirements define the mission goals and design. In the case of the Soil Moisture Active Passive (SMAP) mission, the requirement is an accuracy of 0.04 m3/m3 at a spatial resolution of at least 10 km. In addition to mission requirements criteria, validation provides the users with quality assurance-which in theory should lead to greater confidence and acceptance leading to use of the mission products. This in turn provides support for the mission and its successors. Validation also provides a common basis from which a single climate record can be compiled by integrating multiple satellite products of different origin. For soil moisture, this is a new problem that the community is beginning to address. It will be necessary to resolve the differences in soil moisture products from AMSR, ASCAT, SMOS, Aquarius, and SMAP. Finally, from the scientific perspective and considering microwave remote sensing in particular; there will always be some ambiguities in the products due to ambiguities of the defining contributing area and depth for the various satellite mission sensors and frequencies. Validation can help us resolve these issues and improve algorithms through a careful evaluation of algorithm performance and anomalies. Guidance on the design of a validation program is provided and how this translates to soil moisture. In situ observations play a major role in the validation of satellite-based soil moisture and several aspects of using these data resources are discussed. Finally, the implementation of these ideas into the SMAP Calibration/Validation (Cal/Val) plan is described.