On the Effective Surface Temperature of a Natural Landscape: Infrared or Not Infrared

Statistical methods are employed to assess the extent to which measurements of temperature using downward looking infrared thermometry (T0) are indicative of the effective boundary between the air and the subsurface environment. An effective interfacial surface temperature (Te) is determined from consideration of in-air (Ta) and subsurface (Ts) temperature data, being that which best satisfies the multi-media (air and soil) flux relationships. Using data obtained in studies conducted in Ohio in 2015, it is shown that during the daytime measured values of T0 exceeded Te by an amount reaching a near-noon maximum of about 2 °C when the crop (maize) was fully grown. Night-time observations indicated a near equality of T0 and Te, although often equality appears threatened by the presence of strongly stable layers in air near the surface. Ramifications of the observed differences are discussed, with particular attention to implications regarding determination of the thermal roughness length associated with the sensible heat flux.