Generally, surface temperature is calculated from easily measured parameters by theoretical methods. Surface emissivities for a black body and typical soils are 1 and 0.85, respectively. Subsurface temperature Subsurface soil temperature is easy to measure compared to the surface temperature. In other words, at 1 meter below the soil surface, it is hard to see any difference in daytime and nighttime temperature. Figure 1 shows a typical diurnal temperature wave.
Temperature changes at different depths.
Figure 2 shows the temperature change in winter at the Maricopa weather station. Note that the range of temperature variation in figure 1 at 2 in depth is approximately 20 o C, and the range of temperature variation in figure 2 at 2 in depth is approximately 12 o C. Figure 2. Temperature changes at different depths. The soil moisture content has a great effect to the diurnal range of soil temperature because with increased evaporation from the wet surface the increased heat capacity and thermal conductivity of the soil utilizes more energy instead of using the energy for increasing temperature. Thus, the soil temperature is moisture dependent.