Potential of a mini-acoustic sounder in studying flow over forest canopy

Mini acoustic remote sensors are ideally suited for studies of turbulence in roughness layers and in internal boundary layers since they generally operate at higher frequencies. In the case of tall canopies, conventional instruments usually do not provide adequate canopy level information about turbulence. Whereas, mini-SODAR can measure turbulence at canopy top, thereby filling the gap in the conventional measurements. We used the BOKU mini-SODAR at a slash pine canopy to study the interaction between the ambient flow and the non local flow inside the canopy. This instrument measures three-dimensional wind speed profiles with a spatial resolution of 5 m, vertical range of 150 m at 1 Hz frequency. Spectral analysis is carried out for the layer immediately above the forest in the roughness sub layer and the region above it. The vertical variation of turbulent lengh scales and dissipation rates is derived from the mini-SODAR data. Various terms in the turbulent kinetic budget derived from mini-SODAR measurements are also presented.