EM Bird

The EM-Bird is a helicopter-towed electromagnetic induction sensor that measures total sea-ice plus snow thickness, developed by the Alfred Wegener Institute. It exploits the conductivity contrast between resistive ice and conductive seawater: the induced response locates the ice-water interface while a built-in laser altimeter measures the distance to the snow surface, the difference giving total thickness. The 3.5 m, roughly 105 kg pod operates near 4 kHz (with channels at 3.68 and 112 kHz), flown about 15 m above the ice. First used from Polarstern in the Arctic in 2001, it surveys long profiles that ground-truth CryoSat-2 and ICESat-2 freeboard retrievals.