Changes in the Arctic sea ice result in a thinner and younger ice cover with changing physical properties and strong impacts on the energy budget. In addition to long-term trends, the physical properties of sea ice and its snow cover underlay a strong seasonal and spatial variability that impact observations and conclusions. Here, I present methods and results of recent studies to observe the sea ice energy budget on different time and length scales. Radiation measurements over and under sea ice reveal changes in the optical properties of sea ice and their implications for the energy and mass budget. The combination of different measurement platforms, incl. remotely operated vehicles (ROV) and autonomous stations, with large-scale observations and parameterizations allows discussing key processes over large regions and during different seasons.