OTTER – a new instrument for boundary layer turbulence profiling between drones and the ground

Direct measurement of the vertical profiles of turbulent fluxes in the atmospheric boundary layer is crucial for understanding of surface/atmosphere processes. Existing robust instrumentation such as eddy covariance provides only a single point measurement near the ground, with long averaging times. Profiles can be obtained by radiosonde, but with limited temporal resolution. Remote sensing is possible, for example by combining various types of LIDAR, however deployment is limited by high Size, Weight, Power and Cost (SWaP-C) requirements.

Here we present a new instrument, OTTER (Optical Turbulence for Tracing Energy in the atmospheRe) which aims to provide profiles of turbulent quantities in the boundary layer with high vertical (10 m) and temporal (<30 minute) resolution at the price point of an eddy covariance setup. OTTER observes the scintillation (twinkling) of laser light as it passes through the atmosphere and applies a mature profiling method from astronomy (SCIDAR – Scintillation Detection and Ranging) to obtain profiles of the optical turbulence strength, from which we can compute the profile of sensible heat flux, although we aim to expand this to other fluxes and turbulence parameters.

The lasers are mounted on small commercial drones which fly up to several kilometres away from a ground-based receiver station, allowing profiles along horizontal, slant or vertical paths along the line of sight. OTTER is designed to be robust and low SWaP, capable of deployment to harsh and remote environments such as ice sheets.

We will present the instrument concept and design, including development of the drone-mounted laser systems and ground station. We will conclude with results from a testing campaign in the UK.