A land surface process/radiobrightness model with coupled heat and moisture transport in soil

Heat and moisture transport in soil are coupled processes that jointly determine temperature and moisture profiles. The authors present a physically based, one-dimensional (1D), coupled heat and moisture transport hydrology (1-DH) model for bare, unfrozen, moist soils subject to insolation, radiant heating and cooling, and sensible and latent heat exchanges with the atmosphere. A 60-day simulation is conducted to study the effect of dry-down on soil temperature and moisture distributions in summer for bare soil in the Midwest United States. Given a typical initial moisture content of 38% by volume, the authors find that temperature differences between the water transport and no water transport cases exhibit a diurnal oscillation with a slowly increasing amplitude, but never exceed 4.4 K for the 60-day period. However, moisture content of the surface decreases significantly with time for the water transport case and becomes only about 21% at the end of the same period. The 1-DH model is linked to a radiobrightness (1-DH/R) model as a potential means for soil moisture inversion. The model shows that radiobrightness thermal inertia (RTI) correlates with soil moisture if the two radiobrightnesses are taken from times near the thermal extremes, e.g., 2 a.m. and 2 p.m., and that RTI appears temperature-dependent at the ending stages of the drydown simulations where soils are dry and their moisture contents vary slowly. Near times of thermal crossover, the RTI technique is insensitive to soil moisture.