Radio-echo sounding (RES) is a technique used by glaciologists to measure the internal structure, ice thickness, and subice morphology of ice masses. It has been used extensively in Greenland and Antarctica to determine the volume of ice stored within large ice sheets, and in numerous locations to build an understanding of the sizes of smaller ice caps and glaciers. Such information has been central to quantifying the rise in global sea level that might occur through future climate warming and glacier melting.