Description: The Optical IP Camera was attached to the remote sensing hut during the MOSAiC expedition, saving 4K images in JPEG format in 5 minute intervals. It was installed during MOSAiC leg 2 and leg 3, 10 February to 17 April 2020. The camera is equipped with high brightness NIR LED spotlights, turning on automatically in low light situations. During its operation time, the camera had several remote sensing instruments in the field of view and can be used as a supportive dataset for events at the remote sensing site.

Description: 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.

Description: The Optical IP Camera was mostly observing the snow surface and aligned instruments at the remote sensing site during the MOSAiC expedition in the central Arctic, saving 4K images in JPEG format in 5 minute intervals. Between October to March it was mostly working continuously, while the data from April to September is more sparse. Occasional transects (remote sensing transects) and experiments were recorded in higher acquisition rates. The camera is equipped with high brightness NIR LED spotlights, turning on automatically in low light situations. Over the course of the expedition, the camera had several remote sensing instruments and the snow and ice surface in the field of view and can be used as a supportive dataset for events at the remote sensing site. It was operated always in conjunction with an infrared camera (doi:10.1594/PANGAEA.940717), pointing at the same targets but with a wider opening angle. The same camera model was also attached to the remote sensing hut (doi:10.1594/PANGAEA.939443) during parts of the campaign.

Description: The Hyperspectral camera Specim IQ measures relative reflectances for 512x512 pixels in 204 bands in a wavelength range from 400 nm to 1000 nm. Within the field of view, there was a white reference placed so that the reflectances can be compared to other datasets. During the MOSAiC expedition, the camera was installed at the remote sensing site on the ice. It was looking at the snow and ice, taking an image every 30 minutes for periods in April 2020 and July 2020. Each data record is a folder (compressed as one file) readable by the Specim IQ software, which is downloadable free of charge from the manufacturer (Specim) after registration. This dataset is from an experimental setup to explore the use of spatially resolved hyperspectral imaging of Arctic sea ice.

Description: The infrared camera (7.5–14 µm) was mostly observing the snow surface and aligned instruments at the remote sensing site during the MOSAiC expedition in the central Arctic, saving data in the proprietary IRB format in 10 minute intervals. The instrument used was the Infrared VarioCAM HDx head 625 S camera from InfraTec. Between October to March it was mostly working continuously while the data from April to September is more sparse. Occasional transects (remote sensing transects) and experiments were recorded in higher acquisition rates. Over the course of the expedition, the camera had several remote sensing instruments and the snow and ice surface in the field of view and can be used as a supportive dataset about the temperature and for events at the remote sensing site. It was operated always in conjunction with a visual camera (doi:10.1594/PANGAEA.939362), pointing at the same target. This raw data comes in the proprietary IRB format to open with the IRBIS 3.1 software from the InfraTec company.

Description: Warm air intrusions over Arctic sea ice can change the snow and ice surface conditions rapidly and can alter sea ice concentration (SIC) estimates derived from satellite-based microwave radiometry without altering the true SIC. Here we focus on two warm moist air intrusions during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition that reached the research vessel Polarstern in mid-April 2020. After the events, SIC deviations between different satellite products, including climate data records, were observed to increase. Especially, an underestimation of SIC for algorithms based on polarization difference was found. To examine the causes of this underestimation, we used the extensive MOSAiC snow and ice measurements to model computationally the brightness temperatures of the surface on a local scale. We further investigated the brightness temperatures observed by ground-based radiometers at frequencies 6.9 GHz, 19 GHz, and 89 GHz. We show that the drop in the retrieved SIC of some satellite products can be attributed to large-scale surface glazing, that is, the formation of a thin ice crust at the top of the snowpack, caused by the warming events. Another mechanism affecting satellite products, which are mainly based on gradient ratios of brightness temperatures, is the interplay of the changed temperature gradient in the snow with snow metamorphism. From the two analyzed climate data record products, we found that one was less affected by the warming events. The low frequency channels at 6.9 GHz were less sensitive to these snow surface changes, which could be exploited in future to obtain more accurate retrievals of sea ice concentration. Strong warm air intrusions are expected to become more frequent in future and thus their influence on SIC algorithms will increase. In order to provide consistent SIC datasets, their sensitivity to warm air intrusions needs to be addressed.

Description: Correction to: Scientific Data, published online 22 June 2023 The original version showed the wrong image for Figure 3, with the image for Figure 4 used for both. This has been corrected in the pdf and HTML versions of the article, with the correct version of Figure 3 replacing the duplicated figure. The dates in the figure captions were also incorrect and have been amended as follows: Figure 3 caption: “from 2019-10-25 - 2020-07-30” modified to “from 2019-10-25 - 2020-05-15” Figure 4 caption: “from 2020-02-25 - 2020-07-30” modified to “from 2020-06-13 - 2020-07-30”.

Description: Snow plays an essential role in the Arctic as the interface between the sea ice and the atmosphere. Optical properties, thermal conductivity and mass distribution are critical to understanding the complex Arctic sea ice system’s energy balance and mass distribution. By conducting measurements from October 2019 to September 2020 on the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition, we have produced a dataset capturing the year-long evolution of the physical properties of the snow and surface scattering layer, a highly porous surface layer on Arctic sea ice that evolves due to preferential melt at the ice grain boundaries. The dataset includes measurements of snow during MOSAiC. Measurements included profiles of depth, density, temperature, snow water equivalent, penetration resistance, stable water isotope, salinity and microcomputer tomography samples. Most snowpit sites were visited and measured weekly to capture the temporal evolution of the physical properties of snow. The compiled dataset includes 576 snowpits and describes snow conditions during the MOSAiC expedition.