Determination of the effective emissivity and temperature under vertical observation of a citrus orchard. Application to frost nowcasting

In this work we use Becker's model for the determination of the effective temperature and emissivity under vertical observation of a citrus orchard. We apply this model to the particular case of a typically radiative night cooling (completely clear sky and calm wind) condition under which radiation frosts are normally produced which are damaging to the fruit and, consequently, to the Valencian economy. An attempt is made to establish a safety limit over which a frost cannot be produced. Ground and orange tree emissivity measurements were carried out by means of the box method. We were able to construct a hand-driven scanning system for the temperature measurement of the ground-orange tree system. We determined that a citrus orchard, under normal observation, can in practice be considered as a homogeneous system as far as the emissivity is concerned and that the orange tree's influence on the effective temperature is approximately three times that of the ground.