International collaborative study on atmospheric turbulence based on simultaneous observations with the MU radar, small unmanned aerial vehicles (UAV), and radiosonde and tethered balloons
|Hubert Luce (MIO, Toulon University, France)
|L. Kantha (University of Colorado)
R. Wilson (LATMOS, CNRS, France)
H. Hashiguchi (RISH, Kyoto University)
M. Yabuki (RISH, Kyoto University)
D. Lawrence (University of Colorado)
A. Doddi (University of Colorado)
A better knowledge of atmospheric turbulence characteristics is important, not only for understanding small-scale exchange processes in the lower atmosphere but also for applied aspects (propagation of electromagnetic and acoustic waves, aviation safety, and diffusion of atmospheric admixtures). For that objective, experimental in situ studies reported in the literature have been performed using balloon-borne radiosondes, tower-mounted instruments, tethered lifting systems, aircrafts, etc. In recent years, small unmanned aerial vehicles (UAV) have been employed for meteorological studies and atmospheric observations, owing to fast technological advances and the development of low-cost systems.
The controllable position of UAV, and thus the possibility of multiple measurements at the same location, their ease of operation and their possible re-use are major advantages over standard in situ instruments (that are mainly either limited in range or drifted by the wind). They can be equipped with any type of sensors, taking also benefit of recent technological improvements in sensor performances and radio communications. Lawrence and Balsley (2013) showed the potential of instrumented UAVs for measuring temperature structure constant and kinetic energy dissipation rate, which are key parameters for characterizing atmospheric turbulence. UAV measurements provide decisive information on small-scale atmospheric processes and contribute to help validate numerical models of atmosphere dynamics.
The UAVs can be operated near ground-based remote-sensing instruments such as atmospheric radars for simultaneous and collocated measurements. Combined observations thus offer unprecedented opportunities for validating the measurements and for interpreting the observations made by all the instruments. The primary objective of the proposed research is to better characterize turbulence in the planetary boundary layer and in the free lower troposphere from concurrent radars, meteorological and tethered balloons, and UAV measurements.
A collaboration between RISH and University of Colorado lead to three unprecedented field campaigns in 2015–2017 called ShUREX involving instrumented UAVs, MU radar, and radiosonde and tethered balloons. Simultaneous and nearly collocated data were collected for retrieving a large variety of turbulence and structure parameters. The wealth of the datasets collected during various atmospheric conditions is such that a large variety of aspects on measurement physics and small-scale atmospheric dynamics can be studied. The MU radar measurements clearly reveal the coexistence at the same scales of turbulent irregularities and coherent structures, such as thin horizontally stratified and laminar gradients of temperature and humidity at the edges of more or less neutral layers, Kelvin-Helmholtz or convective vortices in turbulent regions, nearly-monochromatic gravity wave oscillations in association with turbulent events. UAV measurement physics is still a subject area in its early stages. UAV provides either time series at constant altitude (at a much higher frequency than a standard airplane, 1 Hz or much less at a speed of ~15 m/s) or time-series along vertical helical flights at a vertical ascent of ~2 m/s with typical diameter of ~100 m. At present, our investigations have already yielded fruitful results in different aspects of the study and helped assessing some theoretical developments in the fields of stratified and convective turbulence and measurement physics.
The University of Colorado DataHawk UAV