Ground-penetrating radar (GPR) has been used to detect areas of present or potential structural weakness beneath a 3.2-km snow-covered ice runway on the Ross Ice Shelf, Antarctica. The bandwidths of the transmitted wavelets were centred near 500 MHz. The data show many horizons up to tens of metres long and occurring to about a 9-m depth, below which a brine intrusion limits penetration. The horizons are interpreted as discrete scatterers because of their diffraction nature and loss of higher frequencies with depth. The presence of porous ice or dispersed water is interpreted from wavelet phase. The water may be associated with apparent deepening and fading of the brine horizon. If the above interpretation is correct, water occurs at depths to 3.5m and extends as much as 40 m horizontally, which is greater and deeper than known previously. At 3.5 m depth, the water may be adsorbed on mineral particles rather than remain free. Migration of the diffractions with a single-layer migration scheme shows all horizons above the brine layer to be small dielectric perturbations within the ice. Stacking and Hilbert transformation of the data reveal slight folding along the length of the runway. Loss of high-frequency amplitude in the wavelets suggests that higher frequency radar might improve resolution only in the top few metres.