Research at the ice-water interface below drifting sea-ice is crucial for the investigation of the fluxes of energy, momentum, and matter across the atmosphere-ice-ocean boundary. Transmission of solar energy through the ice and snow layers causes warming of the upper ocean and melting of the ice itself. It is also a key factor for in and under-ice primary production, supplying the ice associated food-chain, and causing carbon export to deeper water layers and the sea floor. The complex geometry of sea ice does not only cause a large spatial variability in optical properties of the ice cover, but also influences biomass accumulations and especially the hydrodynamic interaction between the ice cover and the uppermost ocean. Observations at the ice underside are however still sparse, as diving operations are risky and logistically challenging. In the last decade, robotic underwater technologies have evolved significantly and enabled the first targeted large-scale observations by remotely operated and autonomous underwater vehicles (ROVs and AUVs). A ROV was commissioned for under ice research at the Alfred Wegener Institute providing an extended interdisciplinary sensor platform supporting oceanographic, biological, biogeochemical, and physical sea-ice research. Here we present the first data obtained during the PS101 expedition of the German icebreaker RV Polarstern to the Central Arctic in September and October 2016. The ROV is designed for operations directly on the sea ice and is thus highly flexible for various sea ice applications on vessels, at stations, by helicopter, or in ice camps. Apart from measurements of spectral light transmittance of sea ice during the autumn freeze-up, we show vertical profiles of the bio-optical properties of the upper water column. This data is combined with under-ice topography obtained from upward-looking multibeam sonar, still imagery, and HD-video material.