A novel airborne Doppler lidar system design for highresolution wind measurements

Wind is a core state variable of the atmosphere. Accurate weather predictions and a better understanding of atmospheric dynamics, transport and dispersion require improved wind information, especially inside the turbulent planetary boundary layer (PBL). The Doppler lidar technique provides advanced capabilities for remote sensing of wind using laser radiation. It has been widely deployed using ground-based and airborne platforms in the last decades. Extending the capabilities of ground-based measurement systems, airborne Doppler lidar (ADL) onboard research aircraft allows for targeted and spatially resolved wind measurements, which is crucial for localized severe weather events or in inaccessible regions such as over water and complex terrain. This contribution introduces a novel design for ADL systems, aiming to revolutionize the field of airborne wind measurements by providing higher measurement accuracy and spatial resolution, in combination with a simplified and more robust system design. Up to now, ADL systems use a single Doppler lidar attached to a scanner to provide multi-angle measurements. Due to cost and size reductions of Doppler lidar units over the recent years, it has now become possible to construct an ADL system that uses multiple lidars with fixeddirection beams, instead of a single lidar with a scanning beam. The new system design uses five eye-safe, compact and lightweight Doppler lidars pointing at fixed beam directions. LES-based simulation results have demonstrated that a fixed-beam system will have approximately one order of magnitude improved spatial wind measurement resolution as well as higher accuracy, compared to existing scanning systems. Further, these simulation results allow us to determine an optimal beam number and orientation. Due to the high resolution and accuracy, the retrieval of turbulence properties, such as vertical wind variance and turbulent kinetic energy becomes possible. Besides improved measurements, the greatly simplified ADL system design allows for more cost-effective manufacturing, certification, and application on a wider range of aircraft. For example, the more light-weight construction without scanner may enable measurements onboard smaller aircraft. Furthermore, routine measurements aboard larger commercial aircraft could be established. Overall, the higher measurement quality and order of magnitude higher spatial resolution present an important step forward to meet urgent needs to improve wind measurements. Atmospheric research and weather forecasting are expected to benefit through better process understanding and data assimilation. Additionally, through the availability of ADL measurements on a wider range of airborne platforms, a significant impact on weather forecast and aviation safety can be anticipated.