Sea ice as a function of its thickness damps the heat exchange between the atmosphere and the ocean. The change of the heat flux with change in ice thickness is much stronger for thin than for thick sea ice, thus it is important to get an accurate estimate of the thin sea-ice thickness. Existing estimates of thin sea-ice thickness by measuring the radar cross-section (RCS) mostly are made at one microwave frequency and partly are inconsistent with each other, because of the not sufficiently known complex scattering mechanism of sea ice. The goal of our work is to investigate thin sea ice by measuring its RCS of sea ice at different incidence angles (20–65°) and at different frequencies and therefore to get a better identification and thickness estimation of thin sea ice. In August and September 2007 measurements of the sea-ice RCS with the Multi³Scat, together with in situ measurements, were carried out in the Arctic. The Multi³Scat is a helicopter-borne scatterometer of the University of Hamburg, which simultaneously measures the RCS at different frequencies at co- and cross-polarization at incidence angles of 20–65°. Video and infrared cameras simultaneously sense the surface in the scatterometer's footprint. After a short description of the Multi³Scat and the measurement campaign, we will show an overview of the gathered data and the results of the classification. The classification is based on a wishart classifier using together the co- and cross-polarization-RCS of C-, X- and Ku-band. With this classification we can distinguish between nilas, grey ice, old ice and open water. The verification with the video data shows a good agreement between the classification and the video data. Under the assumption that the above classification is the truth, the classification with only one band, for example C-band, yields to an overall difference of 28%.