RELATION BETWEEN VEGETATION CANOPY SURFACE-TEMPERATURE AND THE SUN-SURFACE GEOMETRY IN A MOUNTAINOUS REGION OF CENTRAL ITALY

Evapotranspiration is the dominant energy exchange process in dense ve getated environments with an adequate water supply. If water is availa ble vegetation canopy temperatures do not respond immediately upon int ercepting solar radiation because of the apportionment of absorbed sol ar radiation into sensible and latent heat. This lag in the thermal co nditions of vegetation canopy following the incident solar flux can be even more complex after sunrise because the presence of dew on the fo liage requires more available energy investment in evaporating water a nd less energy spent in warming the foliage. The aim of this Letter, w hich is based on remotely-sensed thermal data obtained from Landsat Th ematic Mapper in the daytime of a clear summer day, is to investigate the relationship between canopy surface temperatures and the incident solar radiation for a forested montainous landscape of central Italy. Results show that, under the conditions of our experiment, a time lag of one hour considerably increases the linear relation between vegetat ion canopy temperature and local solar illumination angle.