spectral signature

A spectral signature is a characteristic or set of characteristics of an emission's spectral energy distribution (SED) (i.e., a spectral feature) that reveal something specific about the material or conditions that produced the electromagnetic radiation (EMR). Typical would be characteristics suggesting the material and temperature such as particular spectral lines superimposed on a particular black-body spectrum. A specific spectral index over a specific band might be a signature for some type of emission, e.g., synchrotron radiation. There are spectral signatures associated with certain types of stars (spectral classes), as well as signatures for additional characteristics, such as metallicity. Similar can be said of galaxies, quasars, clouds, planets, etc. The term spectral signature is also used in planetary science (including Earth science), e.g., for sensing characteristics of a body's surface from an orbiting probe (satellite).