## 2 Experiment Description
### Instrumentation
#### 2.1.2 UAV Platforms  
In order to obtain detailed information on the atmospheric state across the entire ABL and parts of the free atmosphere, a number of different UAV (Figure 2), both fixed and rotary-wing systems, were operated in the area around the main field site. A short description of the systems used during the campaign and their capabilities are given below. The Small Unmanned Meteorological Observer (SUMO) [83; 84] is a small fixed-wing UAV, equipped with the Paparazzi autopilot system and a set of basic meteorological sensors. The data acquisition system of the SUMO also records the aircraft's position and attitude, provided by an on-board Global Navigation Satellite System (GNSS) and an Inertial Measurement Unit (IMU). The SUMO is designed to take atmospheric profiles up to 5000 m and can be operated in wind speeds of more than 15 m s\({}^{-1}\). Under cold environmental conditions, the flight time is typically 45 min. The most important sensor specifications are summarized in Table 3. The meteorological sensors for \(T\) and \(RH\) are placed a fair distance from the battery and motor on top of the wings to assure good ventilation during flight. In addition to the directly-measured meteorological parameters, like temperature, relative humidity, and pressure, the horizontal wind speed and direction can be estimated by applying the \"no-flow-sensor\" wind estimation algorithm described in reference [68]. \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Parameter** & **Sensor** & **Acq. Frequency** & **Aircraft Type** \\ \hline Temperature, \(T\); relative & & & \\ Humidity, \(RH\) & & & \\ Temperature, \(T\) & Pt1000 Heraeus M222 & 8.5 Hz & SUMO, miniTalon \\ Pressure, \(p\) & MS 5611 & 4 Hz & SUMO, miniTalon \\ Infra-red temperature, \(T_{IR}\) & MLX90614 & 8.5 Hz & SUMO, miniTalon, \\ Wind components, \(u,v,w\) & Aeroprobe 5-hole probe & 100 Hz & miniTalon \\ Position, \(lat,lon,alt\) & GNSS & 4 Hz & SUMO, miniTalon, Bebop2 Met \\ Attitude angles, \(\theta,\phi,\psi\) & IMU & 4 Hz & SUMO, miniTalon, Bebop2 Met \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Specifications for the paparazzi-based UAVs: Small Unmanned Meteorological Observer (SUMO), miniTalon, and Bebop2 Met. Figure 2: UAV systems used during the Hailuoto-I campaign. The Multi-purpose Airborne Sensor Carrier (MASC-2) is an electrically-powered, single engine, pusher aircraft of 3.5 m wing span and a total weight of 6 kg, including a scientific payload of 1.0 kg [85]. This UAV is equipped with the ROCS (Research Onboard Computer System) autopilot system developed at the University of Stuttgart. Its endurance under polar conditions is up to 90 min at a cruise speed of 22 m s\({}^{-1}\). For the measurement of turbulence along horizontal straight flight legs and other atmospheric parameters, MASC-2 carries a scientific payload, as summarized in Table 4 and described in detail in [86; 87; 88]. The sensors are placed in a special sensor holding unit which is attached to the aircraft directly above the nose to face air that is as undisturbed as possible. The 3D-wind vector and the temperature measurements are capable of resolving turbulence up to frequencies of approximately 30 Hz, allowing turbulent fluctuations to be resolved in the sub-meter range. The data from these sensors is oversampled with an acquisition frequency of 100 Hz. Each component of the measurement system aboard MASC-2 was tested in the lab and during flight. The sensors were calibrated and airborne gathered data were validated by comparison to both other measurement systems and theoretical expectations [85; 86; 87]. A new UAV based on the the miniTalon produced by X-UAV with an EPP airframe of 120 cm wingspan and 83 cm length that was designed to carry a higher payload (up to 1000 g) was tested during the campaign. The system is a further development of the SUMO by Lindenberg und Muller GmbH & Co. KG and GFI, with increased dimensions.