## 2 Experiment Description
### Instrumentation  
#### 2.1.1 Basic Instrumentation  
Close to the selected field site, the Finnish Meteorological Institute (FMI) operates the World Meteorological Organization (WMO) automatic weather station (AWS) Hailuoto Marianiemi (ID 02873), henceforth referred to as AWS-FMI. The Western and Northern sectors of this station represent open water conditions during summer and typically, sea ice during winter, which was also the case during this campaign, as will be later seen in Section 4. East of the station (about 45\({}^{\circ}\) to 165\({}^{\circ}\)), the measurements are affected by the island and by some buildings at a distance of about 50 m to 100 m from the station, including a lighthouse and an ice radar tower. The measured parameters, installed instrumentation,  
Figure 1: Overview maps showing the Hailuoto-I campaign site, the location of the ground-based instrumentation and typical locations and paths of the Unmanned Aerial Vehicle (UAV) flights. and their heights are listed in Table 1. All measurements, except wind, are collected at the station; the wind speed and direction are observed at the top of the ice radar tower. The anemometer is supported by a 2 m high mast attached to the railing of the tower platform, the measurement height being about 29 m asl. The Finnish Transport Agency operates a network of coastal ice radars used for ice monitoring for navigation along the Finnish coast. One of the radars is located at Marjaniemi, at the top of a 30-m high tower next to the AWS-FMI and the light house. The ice radar is a 9.375 GHz (\(\lambda\approx 3\) cm), 25 kW magnetron radar manufactured by Terma A/S, Denmark. The range resolution (the pulse length) can be chosen operationally by Vessel Traffic Services depending on ice conditions and can vary from 50 ns to 1000 ns (pulse repetition frequency from about 0.7 kHz to 3.5 kHz). Rasterized images are provided with a temporal median filtering of 15 s to 20 s. However, due to the limited means of mobile data communication, preprocessed images can only be transmitted at 2-min intervals. More detailed information on the radar and image processing is provided in reference [82]. A 4 m mast, from here on referred to as AWS-ice, equipped with instrumentation for observations of wind speed, direction, temperature and relative humidity (all at 1 m agl, 2 m agl and 4 m agl, radiation balance, and ground heat flux (snow and ice), was installed on the sea ice (Figure 1). For observations of SL turbulence, the mast was additionally equipped with an EC system, consisting of a 3-dimensional sonic anemometer and an open-path gas-analyzer for H\({}_{2}\)O and CO\({}_{2}\), both mounted at 2.7 m agl. The EC system faced towards 238\({}^{\circ}\) (true direction) in order to have an undisturbed fetch over the sea ice sector. The sensor specifications are summarized in Table 2. \begin{table}
\begin{tabular}{l l l l} \hline \hline
**Parameters** & **Sensor** & **Acq. Period** & **Meas. Height** \\ \hline Cloud base height, \(h_{CB}\) & Vaisala CT25K Laser Ceilometer & 10 min & \\ \hline
50 SYNOP codes & Vaisala FD12P Weather Sensor & 10 min & \\ \hline Temperature, \(T\); & Vaisala HMP155 Humidity and & & \\ relative humidity \(RH\) & Temperature Probe & 10 min & 2.0 m agl \\ \hline Pressure, \(p\) & Vaisala PTB 201A Digital Barometer & 10 min & 7.3 m asl \\ \hline Temperature, \(T\) & \begin{tabular}{l} Pentronic AB Pt100 Platinum Resistance \\ Thermometer \\ \end{tabular} & 10 min & 2.0 m agl \\ \hline Wind speed, \(U\); direction, & \
\begin{tabular}{l} \end{tabular} &
\begin{tabular}{l} Adolf Thies GmbH \& Co. KG 2D Ultrasonic \\ Anemometer (UA2D) \\ \end{tabular} & 10 min, 3 s & 29 m agl \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Specifications of the operational automatic weather station (WMO station ID 02873) at Hailuoto.