MASINT measurement searches for differences from known norms, and characterizes the signatures of new phenomena. For example, the first time a new rocket fuel exhaust is measured, it would be a deviation from a norm. When the properties of that exhaust are measured, such as its thermal energy, spectral analysis of its light (i.e., spectrometry), etc., those properties become a new signature in the MASINT database. MASINT has been described as a "non-literal" discipline. It feeds on a target's unintended emissive byproducts, or "trails"—the spectral, chemical or RF emissions an object leaves behind. These trails form distinctive signatures, which can be exploited as reliable discriminators to characterize specific events or disclose hidden targets."