1. A method for controlling operation of a substrate processing chamber, said method comprising: transferring a substrate into said substrate processing chamber; performing a first substrate operation on the substrate disposed within the substrate processing chamber; measuring a plurality of wavelengths of radiation reflected from an upper surface of said substrate during the first substrate processing operation; converting each of the plurality of measured wavelengths into digital data; and comparing the digital data in real time with the digital data collected from a previous substrate processing operation using a principal component analysis pattern recognition technique.