Measurement of turbulent water vapor fluxes using a lightweight unmanned aerial vehicle system

Abstract

Abstract. We present here the first application of a lightweight unmanned aerial vehicle (UAV) system designed to measure turbulent properties and vertical latent heat fluxes (λE). Such measurements are crucial to improve our understanding of linkages between surface moisture supply and boundary layer clouds and phenomena such as atmospheric rivers. The application of UAVs allows for measurements on spatial scales complimentary to satellite, aircraft, and tower derived fluxes. Key system components are: a turbulent gust probe; a fast response water vapor sensor; an inertial navigation system (INS) coupled to global positioning system (GPS); and a 100 Hz data logging system. We present measurements made in the continental boundary layer at the National Aeronautics and Space Administration (NASA) Dryden Research Flight Facility located in the Mojave Desert. Two flights consisting of several horizontal straight flux run legs up to ten kilometers in length and between 330 and 930 m above ground level (m a.g.l.) are compared to measurement from a surface tower. Surface measured λE ranged from −53 W m −2 to 41 W m −2 , and the application of a Butterworth High Pass Filter (HPF) to the datasets improved agreement to within +/−12 W m −2 for 86 % of flux runs, by removing improperly sampled low frequency flux contributions. This result, along with power and co-spectral comparisons and consideration of the differing spatial scales indicates the system is able to resolve vertical fluxes for the measurement conditions encountered. Challenges remain, and the outcome of these measurements will be used to inform future sampling strategies and further system development.

MASC – a small Remotely Piloted Aircraft (RPA) for wind energy research

“…Given these conditions, the agreement is a good basis for further investigations on the wind field at the site in Grevesmühlen and for the next experiments in complex terrain. The good accuracy of wind-vector measurements from RPA has also been shown in other studies (Martin et al, 2011;van den Kroonenberg et al, 2008).…”

“…In atmospheric boundary layer (ABL) research, systems like SUMO (Reuder et al, 2009) for vertical sounding of the atmosphere, or the M 2 AV (Spieß et al, 2007;Martin et al, 2011), which is additionally capable of measuring turbulent fluxes of sensible heat and individual turbulent outbursts like entrainment , have become valuable instruments for data collection. Also outside Europe similar systems are operated, as presented in Thomas et al (2012) and Bonin et al (2013). Boundary-layer research has become increasingly interesting for the wind-energy community, since efficiency of wind turbines is directly related to the effects in the boundary layer.…”

Eddy-covariance flux measurements with a weight-shift microlight aircraft

“…In order to further adjust results from tower and airborne EC measurements, the raw data could be high-pass filtered, which restricts low-frequency flux contribution to an identical threshold (e.g. Thomas et al, 2012).…”

“…Unmanned aerial vehicles on the other hand provide mobility, yet do not allow a comprehensive sensor package due to payload restrictions (e.g. Egger et al, 2002;Hobbs et al, 2002;Martin et al, 2011;Thomas et al, 2012). Here the weightshift microlight aircraft (WSMA) can provide an alternative at low cost-, transport-and infrastructural demand.…”

Towards higher accuracy and better frequency response with standard multi-hole probes in turbulence measurement with remotely piloted aircraft (RPA)

“…Within the last decade, RPASs (remotely piloted air systems) have become more and more affordable and suitable for atmospheric measurements and some have also been equipped with MHPs (Spieß et al, 2007;van den Kroonenberg et al, 2008;Thomas et al, 2012;Martin and Bange, 2014). The big advantage compared to manned aircraft is the decreased disturbance of the airflow by the aircraft, due to the smaller wingspan and wing load, which leads to smaller upwash (Crawford et al, 1996) and the reduced overall size, which decreases the disturbance of turbulence measurements according to Wyngaard et al (1985).…”