Broadband surface albedo over Arctic Ocean sea ice was measured using an unmanned aerial vehicle (UAV) system called Spectra during Leg 5 of the MOSAiC expedition in August–September 2020. A series of horizontal transects and vertical profiles were flown at altitudes of approximately 5 m, 10 m, and 30 m on seven separate days between August 29 and September 12. The primary goal of these measurements was to characterize the evolution of surface broadband albedo during the onset of autumn freezing and to investigate the spatial variability of albedo across the heterogeneous Arctic sea ice cover at multiple spatial scales.This dataset includes broadband downwelling and upwelling shortwave irradiance measurements recorded by upward- and downward-facing pyranometers at 5-second intervals. Both raw data and calibrated radiative flux values are provided. The pyranometers were mounted on three-axis stabilizing gimbals, which also recorded x, y, and z acceleration and inclination at 1-second intervals. Each pyranometer's temperature was logged every 5 seconds. Additionally, detailed UAV attitude and positional data were recorded by the autopilot system at 100–200 millisecond intervals. To supplement positional tracking, a secondary GPS unit mounted on the main body of the Spectra UAV offered redundant measurements of position and velocity.Data recording began when a custom measurement script was manually initiated and continued until the script was terminated or the system was powered off. Prior to each flight, instruments recorded for at least 30 minutes to allow sensor stabilization and thermal equilibration with the ambient temperature. UAV autopilot logs are available for periods when the UAV was armed.Metadata for all measurement activities, along with a description of the available data files, is provided in a dedicated Excel spreadsheet. In addition, a summary .txt file compiles information from the various data files. This summary includes indicative classifications of measurement subtypes - such as UAV hovering over approximately the same location, horizontal transect flights, stationary on ice, pre-flight preparations, or landing phases. Quality flags (/) have been added to indicate data values falling outside the physical measurement range. These flags are applied to both raw and calibrated pyranometer irradiance values, pyranometer temperatures, and broadband albedo measurements.The shortwave irradiance values in the original data files are based on sensitivity coefficients obtained during an outdoor calibration conducted prior to the expedition. In contrast, the accompanying .txt file uses updated sensitivity values derived from a more recent outdoor calibration performed after the expedition.