The measurement of the amplitude of the components of a complex waveform throughout the frequency range of the waveform. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed),The use of spectrographic techniques for deriving the physical constants of materials. (McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed),The study of electromagnetic spectra arising from either emission or absorption of radiant energy by various substances. (from McGraw-Hill Dictionary of Scientific and Technical Terms, 6th ed)