A millimeter-wave radiometer technique for measuring ice thickness on the surface of the Space Shuttle's external fueltank

The presence of ice on the outside surface of the external tanks of a Space Shuttle can be detrimental to the launch and it is important to detect its presence and measure its thickness. A description is given of the design of a millimeter-wave radiometer system developed for this purpose. The design is based on model calculations and measurements of the emission properties of an external tank panel, performed at 35, 94 and 140 GHz.