Ionization disturbances were disturbances related to ionization, the process of turning an atom or molecule into an ion. Cloaking devices produced such disturbances. In 2366, a Federation class-1 probe detected ionization disturbances in orbit of Nelvana III. Data considered it possible those were produced by cloaked Romulan ships. It later turned out that they were created by a cloaked orbital probe, which the Romulans claimed to use for archaeological research. (TNG: "The Defector" )