This datasets contains ground-based on sea-ice floe observations from the Helsinki University of Technology RADiometer (HUTRAD) at microwave frequencies 6.8 GHz 10.65 GHz and 18.7 GHz taken during Leg 3 (April - May, 2020), Leg 4 (July 2020) and Leg 5 (August - September 2020) of the MOSAiC campaign. Two types of data are provided. Raw observations of individual measurement periods (hutrad_.dat) for leg 3 to leg 5 and calibrated brightness temperatures (HUTRAD_.txt) for leg 3 and leg 5. The raw observations of HUTRAD (counts) are calibrated to brightness temperature using a standard two-point calibration approach by assuming a linear relation between the measurements of the cold sky and measurements at ambient temperature using a microwave absorber. Details about the data format, usage and the instrument can be found in the file Data_manual.pdf.