A natural background consists of several thermal elements such as rocks, earth, soil, trees, etc. whose thermal diurnal behavior differs from each other. Individual properties such as the emissivity, thermal conductivity, heat capacity, etc. determine the influence of the surrounding environment on the surface temperature of these elements. However the surface properties are usually not known well enough to allow an analytical determination of the surface temperature. In this paper we present a simple thermal model which describes the surface temperature as a function of four meteorological parameters namely the solar irradiance, the long wave sky irradiance, the air temperature, and the wind velocity. Based on energy exchange processes that occur at the object-atmosphere interface a model is developed which gives a linear relation connecting the surface temperature to the above meteorological variables. Measured radiometric data along with simultaneous meteorological data is used to determine a set of five coefficients for each thermal element by means of a curve fit procedure. Examples of calculated and measured surface temperature curves are presented for two thermal elements namely a dirt path and a dry grass field.