Description: Raw data (horizontal and Vertical polarization voltages) of the mobile L-band radiometer, called ARIEL from BALAMIS Company. This raw data can be converted to Brightness Temperature, which can be used to measure ice thickness during the MOSAiC expedition legs PS122/4 and PS122/5. The files contains the horizontal and Vertical polarization voltages measured with the ARIEL radiometer during July and August 2020. The label of each columns are: 1 - On-board computer time stamp [hhmmss] 2 - Internal hot load [Volts] 3 - Antenna polarization 1 [Volts] (V-pol) 4 - Antenna polarization 2 [Volts] (H-pol) 5 - Internal cold load [Volts] 6 - Internal temperature [Celsius] 7 - Heater for temperature stabilization power [%] 8 - IR photodiode reading [Celsius] 9 - GPS time stamps [hhmmss] 10 - GPS latitude 11 - GPS longitude 12 - GPS altitude 13 - GPS connected flag 14 - Ethernet cable connected flag

Description: The data contains brightness temperature data measured by ARIEL at 1.4GHz, during the MOSAIC expedition, in particular from July to September 2022 (LEG4 and LEG5). The ARIEL radiometer is a dual polarization (H & V) total power radiometer with internal calibration. The central frequency is 1.41 GHz, with a bandwidth of 20 MHz. The system has a 2x1 patch antenna, with a beam width of 36 ◦ at 3 dB at the azimuth direction and 70 ◦ at 3 dB at the elevation angle. The radiometric accuracy of ARIEL is 1.06 K at 1 Hz sampling frequency, with the capability to measure at higher sampling rates (up to 10 Hz) at the expenses of the radiometric accuracy. A co-located thermal infrared photodiode to measure the surface temperature and a GPS receiver complete the sensor equipment. Calibration is performed with a hot load and a cold load. To adapt the ARIEL instrument to the harsh and cold conditions of the Arctic, two adaptions were required to increase the internal thermal resistance by adding isolating material and to apply conformal coating to protect the electronics against humidity. The ARIEL accuracy was 2.3 K (instead of 1 K, due to a software error on the sampling rate). This light (7 kg) and small radiometer (40 cm x 60 cm x 20 cm) is ideal for frequent manoeuvres. The radiometer was mounted on a wooden sledge to measure microwave emission at 40 ◦ incidence angle with respect to nadir. A calibration procedure for the radiometers is needed to convert the measured voltages to brightness temperatures. The calibration of the ARIEL was done pointing the radiometer to cold and hot targets. The cold target is the cold sky (approx. temperature of 6 K (from Le Vine and Skou (2006)), while the hot target was absorber material at the instrument frequency stored into a big box (which represent an emissivity of 1). The calibration routines were performed every few days (3-5 days). After filtering the outliers, the data was smoothed to further reduce the noise. A sliding window of 20 samples was applied, which has proven to work better with ARIEL data, reducing standard deviation and therefore the noise of the measurements (Fabregat (2021)). Moreover, since the radiometer was over a moving ice cap, the position with respect to the Polarstern is computed, in addition to the GPS position, to simplify the collocation with other instrument measurements. We used a Python code provided by Dr. Stefan Hendricks (AWI) to compute this relative position (Gitlab reference: https://gitlab.awi.de/floenavi-crs).