THE IMPACT OF IN-SITU PROBE ORIENTATION ON SMAP VALIDATION STATISTICS

Ongoing evaluation of the Soil Moisture Active Passive (SMAP) soil moisture products have utilized validation networks distributed in several regions around the world. The in-situ reference used for validation of the soil moisture retrieval algorithm is associated with measurements from soil moisture probes typically located at 5cm beneath the soil surface, however some networks also consider a vertically oriented probe that measures from 0-5cm. In this study we compare the correlation and ubRMSE (unbiased Root Mean Square Error) from the SMAP L2 radiometer soil moisture product when compared to in-situ measurements taken at 5cm (approximately 3.5-6.5cm) below the surface and measurements taken as an integrated measure from 0-5.7cm. The data was obtained from two SMAP validation networks in Canada the: Kenaston network in Saskatchewan and Carman network situated in Manitoba. At both sites, correlations between the in-situ and the SMAP L2 product were consistently higher with vertically oriented probes following rain events. With respect to the ubRMSE the vertically oriented probes at the Carman site had lower ubRMSE with the SMAP product than the horizontal probes that are currently used for validation activities. In some cases, vertical probe information should be considered in validation approaches when this data is available and could be considered in the design of in-situ calibration/validation networks. These results may be useful in design considerations of networks for upcoming soil moisture product validation.