Spectrography is a form of sensor technology used to detect elements by means of comparing scans to the visual spectrum.
This form of technology was used by the geological lab aboard the USS Enterprise in 2254 to determine what elements would be encountered on the surface of Talos IV.
Spectrography scans determined in the preliminary lab survey that Talos had an oxygen-nitrogen atmosphere, with a surface heavy with inert elements. (TOS: "The Cage")