Fig. 10. (a) Reflectivities measured with the L-band radiometer at horizontal polarization (black thick line) compared with reflectivities Rt calculated by using the air-to-soil transition model considering a water content dependent transition zone of thickness h(
2,t) (thick gray line). The gray dotted line indicates reflectivities calculated during period 
1 if the transition zone dependence h(2,t) from period 2 is used, and reflectivities during period 2 calculated using h(2,t) from period 1. (b) Water content 2,t measured with the TDR 2 cm below the soil surface. The data section labeled as wet condition and dry condition refers to the discussion in the section Effect of the Extrapolation Approach within the Topsoil.