ARCADE radiometer. Computer illustration of an ARCADE (Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission) radiometer attached to a high-altitude balloon (not shown) by a cable (top). A radiometer, or roentgenometer, is a device for measuring the radiant flux (power) of electromagnetic radiation. ARCADE uses high-altitude balloon instruments to measure the heating of the universe by the first stars and galaxies after the big bang and to search for the signal of relic decay or annihilation. In July 2006 a very strong radio source was found, known as the space roar.