Wind and turbulence measurements with different sonic sensor head geometries

Measurements of wind and turbulence variables have been performed for decades by means of ultrasonic anemometers (sonics), which have proven to be a reliable, cost-effective and accurate measurement technique for both operational and scientific applications. Sonics are using short ultrasonic pulses transmitted between transducers along different measuring paths to retrieve the 3D wind information. While the measurement principle of commercially available sonics follows comparable technical approaches a variety of sensor head geometries and path arrangements are used in order to minimize potential constraints in accuracy. Two main aspects have to be regarded here, a shadow effect appearing lee wards of each transducer element and a flow distortion caused by individual structures of sensor heads. Furthermore, the arrangement of the measuring paths determines the responsiveness of the sensor to specific wind components. For studies in the atmospheric boundary layer typically the vertical wind component is of highest interest. In order to address these various requirements with one system, trade-offs are unavoidable. The Multi-Path approach for sonics allows to establish redundant 3 x 3 measuring paths involving only six transducers. Depending on the inflow angle such overdetermined system of simultaneously measured radial winds allows to select measuring paths with minimized impact from shadowing and flow distortion for data retrieval. Three of these measuring paths are aligned vertically, providing three independent measurements of the vertical wind.

A six-month comparison of five sonic types was performed in northern Germany at an abandoned airfield with a homogenous surface. We will present derived time series of wind and comprehensive turbulences variables including vertical turbulent fluxes of heat and momentum also covering periods of different weather types, e.g. precipitation events. We focus on the sonic similarities and differences, which are also relevant if standardisation of techniques and data retrievals are considered, without discarding technical improvements such as the Multi-Path technology.