The combination of a near-infrared and a microwave scintillometer were used to estimate the line-averaged, latent heat flux density (A.Es) from a well-irrigated, vineyard valley during summer. The 2 km scintillometer beam passed over the valley floor at a height (z) of 30 m. Eddy covariance towers instrumented at 3 m above the valley surface provided an indepen dent check of vineyard evaporation. A formula for free convective A.Es compared favourably to the eddy covariance values, A.Ee at low wind speeds and under clear skies. As the convective boundary layer (CBL) developed and passed through the scintillometer beam it caused additional scintilla tions, in which case A.Es >> A.Ee. During unstable conditions the compari sons were in close agreement. However A.Es tended to overestimate A.Ee as the wind speed increased. For near-neutral conditions the scintillometer gave unrealistically large values of A.Es. The additional scintillations origi nated from the strong entrainment of advected dry and warm air into the newly formed surface boundary layer. During calm overcast days, cold days and during the early morning periods when the surface fluxes were small, the signal strength of the infra red scintillometer approached the system noise.
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