The horizontal variability of surface radiative fluxes at SHEBA (Surface HEat Budget of the Arctic) in spring is studied. Because of horizontal inhomogeneity in surface and cloud optical properties on scales of tens of meters, it is important to assess the representativeness of the surface radiation flux measurements for both modelling and remote sensing applications. Radiation fluxes were obtained with the NCAR C-130, four remote Flux-PAM (Portable Automated Mesonet) stations and a 20-m tower located near the ship. Additional radiometric measurements over newly formed leads and snow-covered ridges were obtained with mobile KT-19 and Licor radiometers. The NCAR C-130 flew a total of 16 missions over the SHEBA site during May and June, covering an area of (25 km)2 centered on the SHEBA site. We focus our analysis on days where the C-130 was able to sample the spatial variability of the surface radiation fluxes by flying below the clouds. Variations in the radiative fluxes on cloudy days are related to horizontal inhomogeneities in clouds observed with aircraft and ground-based instruments (cloud radar, lidar, microwave radiometer). Biases in the surface-based measurements relative to the areally-averaged fluxes determined by aircraft are calculated.