méthode du bilan énergétique

CONT: L'évapotranspiration instantanée peut être déterminée par la méthode du bilan énergétique, grâce à la mesure directe du rayonnement net, du flux de chaleur du sol, des gradients de température et de tension de vapeur à quelques décimètres au-dessus de la végétation.

CONT: Methods of measuring evapotranspiration generally are divided into two categories: water budgeting and energy budgeting. The former method relies on accurate accounting of water flow into and out of a control area. ... Energy budget methods rely on an accurate accounting of energy to and from the land surface and generally assume one-dimensional energy flow. Because the energy needed to evaporate water is relatively large (about 580 calories per gram), ET, or latent heat, can represent a significant component of the energy budget. Net radiation is the difference between incoming shortwave (solar) radiation and outgoing shortwave and longwave radiation, sensible heat is the energy transported from the land surface by air movement (convection), latent heat is the energy transported away from the surface by evaporating water, and soil/water heat is the heat that goes into changing the temperature of the soil or the water standing on the land surface. Any of these components may reverse in direction - for example, latent heat is added to the surface by condensation (dew formation), and net radiation is directed upward at night.