was published in August, 2016 [62], it is realistic that within two years after the end of IOC, Stages 1 through 3 will be complete, and work toward Stage 4 will be well underway. The SMAP Cal/Val plan [46] describes five types of resources that will be utilized as sources of calibration/validation data. These types of data are listed in Table 9, which describes their perceived role and issues that are currently being addressed by the SMAP team. The NSPIRES DCL entry in the table refers to a Dear Colleague Letter request for information that was released by NASA to the science community to solicit members of the SMAP cal/val team and core validation and other validation sites globally. A NASA panel in consultation with the SMAP team selected ~27 investigator sites or supported instrument networks in Summer, 2011. Since then several new sites have been added. Table 9. Overview of the SMAP Cal/Val Methodologies Methodology Role Issues Actions Core Validation Sites Accurate estimates of products at matching scales for a limited set of conditions Calibration Up-scaling Limited number In Situ Testbed Scaling methods NSPIRES DCL Sparse Networks One point in the grid cell for a wide range of conditions Calibration Up-scaling Limited number In Situ Testbed Scaling methods NSPIRES DCL Satellite Products Estimates over a very wide range of conditions at matching scales Validation Comparability Continuity Validation Studies CDF Matching Model Products Estimates over a very wide range of conditions at matching scales Validation Comparability Validation Studies Field Experiments Detailed estimates for a very limited set of conditions Resources Schedule Conflicts Simulators Partnerships The baseline validation for the L2_SM_P soil moisture will be a comparison of retrievals at 36 km with ground-based observations that have been verified as providing a spatial average of soil moisture at the same scale, referred to as core validation sites (CVS) in the SMAP Calibration / Validation Plan. This matches up closely with the Stage 1 validation described in Table 8. Data from core validation sites will be supplemented by field experiments. In order to achieve Stage 2 validation and include a wider range of conditions as well as a synoptic/global assessment, some combination of data from sparse networks, other satellite products, and model-based estimates must be utilized. Each of these data types has caveats associated with it that are described in Table 9. The following
sections provide some additional details on how each of the resources listed in Table 10 will be utilized specifically for the L2_SM_P soil moisture product validation. Table 10. SMAP Cal/Val Methodologies and Their Roles in the L2_SM_P Soil Moisture Product Validation Methodology Data Required Importance Metrics Core Validation Sites Grid Cell averages for each overpass Primary RMSE, ubRMSE, Bias, Correlation Sparse Networks Spatially scaled grid cell values for each overpass Secondary: Pending results of scaling analyses RMSE, ubRMSE, Bias, Correlation Satellite Products Orbit-based match-ups Key targets Primary: Pending assessments and continued operation RMSD, ubRMSD, Bias, Correlation Model Products Orbit-based match-ups Key targets Secondary RMSD, ubRMSD, Bias, Correlation Field Experiments Detailed estimates for a very limited set of conditions Primary RMSE, ubRMSE, Bias, Correlation 7.2.1 Core Validation Sites