Abstract
Accurate identification of soil freeze or thaw (FT) is important for road management, because it greatly affects a road’s load bearing capacity. Despite low-volume roads (LVR) being more susceptible to damage because of FT transitions compared with high-volume roadways, relatively few LVRs are monitored via temperature data probes (TDP). Frequent and global spaceborne retrievals of soil FT states may be valuable to fill this observational gap. NASA’s Soil Moisture Active Passive (SMAP) instrument provides FT retrievals up to twice a day, approximately corresponding to the top 0–10 cm of soils. This study compares SMAP FT data to TDP data at LVRs located in the contiguous United States (CONUS) and Alaska using hourly data obtained from the Meteorological Assimilation Data Ingest System for the 2016, 2017, and 2018 winters. Overall, SMAP FT retrievals show promise in distinguishing between cold and warm roads. For all cases, the median road temperatures corresponding to SMAP frozen and thawed retrievals were clearly below or above 0°C, respectively. SMAP 6:00 p.m. observations perform better than the 6:00 a.m. observations with overall accuracies of 76% in CONUS and 81% Alaska. However, SMAP’s accuracy for frozen conditions is below 50% in CONUS indicating that SMAP has a warm bias compared with the TDP sites. These preliminary results suggest that the SMAP FT states have potential value for road management.
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