In this thesis we investigate methods for measuring the vertical exchange of heat and momentum as well as key parameters that characterize turbulence in the stable atmospheric surface layer (SSL). The SSL is often confined to a shallow layer just above the surface that is often of an intermittent nature, i.e. quiescent periods with almost laminar flow are interchanged with turbulent “bursts”. These circumstances make that standard methods for measuring the vertical transport of heat momentum and gasses (H20, CO2 etc.) cannot be applied, because the required averaging time is long compared to the time that turbulence is present. Furthermore, standard equipment cannot be used close to the surface since the eddies responsible for the vertical transport are smaller than the eddies that can be detected.
The scintillometers used in this thesis are optical instruments that consist of a transmitter and receiver installed over a distance of ~0.1 to 10 km, depending on the type of scintillometer. The receiver registers the intensity fluctuations of the light beam emitted by the transmitter. These fluctuations are caused by refraction of the beam upon its passage through the turbulent atmosphere and are a measure of some key parameters that characterize turbulence, which in turn can be related to the vertical heat and momentum flux. Scintillometers have the great advantage that they combine both space- and time averaging of turbulence. This allows the application of very short flux averaging intervals (< 1 minute). In addition, a scintillometer can be installed just above the surface (< 1 m).