Electromagnetic induction (EM) sounding provides a reliable and well-proven method of the remote estimation of sea-ice thickness. This technique has frequently been used in helicopter surveys and shows excellent correlation with sea-ice thickness measured by conventional drilling. However, the presence of ice shelves around 44% of the coastline of Antarctica causes the coastal sea ice in this region to be influenced by processes that take place at the base of ice shelves. In particular, it is known that ice crystals are formed at depth in the water column. These rise upwards to the sea-ice–water interface, causing a porous layer of loose crystals to accumulate at this boundary. In McMurdo Sound, close to the McMurdo Ice Shelf, the thickness of this layer may be several meters and its spatial distribution appears to be determined by the circulation of the Sound. Since the layer has a high liquid fraction, its presence may confound remote measurements of ice thickness. In 2009 a pilot survey of McMurdo Sound was conducted to test the performance of EM measurements over sea ice underlain with platelet ice, with the goal of accurately measuring ice thickness and detecting the occurrence and thickness of the loose layer of platelet ice. An airborne EM system (‘EM Bird’) was flown over regions of first-year and multi-year ice and over the adjacent ice shelf. Ground truth measurements were made on some lines, measuring snow thickness by radar and by ruler. Ice thickness and the thickness of the under-ice platelet layer were measured at 5 km intervals on selected lines by drilling. Results show that the real and imaginary components of the induced EM fields differ characteristically over regions with platelet ice, allowing its detection. Careful interpretation of the real and imaginary components may also allow the thickness of the under-ice platelet layer to be estimated. A preliminary map of the thickness of this loose layer in the McMurdo Sound compares well with the distribution of platelet ice incorporated into the structure of the solid ice cover.