This study has been made in connection with the investigation ‘Heat capacity mapping missions 050’ (Cassinis and Lechi 1981), in order to evaluate the potential of thermal remote sensors in discriminating lithological units on the earth's surface. Discrimination is based on different thermal inertia of rocks which, in turn, is evaluated from the measurement of the difference λT between the maximum and minimum value of the temperature of the ground surface during the day. The simulation model consists of an ‘island’ formed of blocks of three materials having different thermal inertia and surrounded by water (with very high apparent thermal inertia). The behaviour of surface temperature has been calculated in the hypothesis that only conduction governs the process and the thermal diurnal cycle is constant at a given latitude and season. The conclusion of the simulation study is that the difference λT = Tmax− Tmin, changes quite abruptly at the boundary between the blocks but remains fairly constant inside each material. The minimum contrast of thermal inertia needed to produce an observable λT has been determined.