SMAP Freeze–Thaw Subpixel Heterogeneity and Infrastructure Applications

The seasonal cycle of freeze/thaw (FT) has a significant impact on surface and subsurface water fluxes and pathways, heat fluxes, soil–atmosphere fluxes of trace gases and carbon budget. The onset of FT transition periods is emerging as a critical area of study in natural landscapes. In parallel, FT studies in the built environment are underway in order to characterize the cyclic redistribution of soil moisture and the soil thermal regime that affect geotechnical properties of soil layers. The motivation for the studies is that early spring thaw events lead to a weakened saturated layer under the pavement structure and elevated risks of damage to roads under heavy traffic loads. Previous studies have successfully characterized the FT status of roads using passive microwave observations from NASA’s Soil Moisture Active Passive (SMAP) FT products. Although roads are embedded in the natural landscape, the SMAP footprint is considerably larger than roads and is dominated by other elements of the footprint, natural environments. Nevertheless, SMAP products’ ability to estimate FT status of roads with reasonable accuracy raises questions about common FT features in heterogeneous natural landscapes in which roads are embedded. In this study, we will shed light on these commonalities by comparing seasonal freezing and thawing of roads with that of natural landscapes using paired in situ observations within a dozen mid-latitude SMAP footprints. The physical drivers that control temporal evolution of FT status in natural environments and roads with respect to fall freeze onset, mid-winter melt events, and spring thaw will also be presented.