The accurate measurement and control of temperature can be of great importance in most materials manufacturing and processing applications. With present-day technology such measurement almost always requires either physical contact with the subject or an extensive calibration procedure. In many cases contact is either not desirable, because such contact may significantly alter the temperature or other characteristics of the subject, or is not possible because the subject is moving, is too far away, is too hot or is in an otherwise hostile environment. Similarly calibration may not be possible if the characteristics change too much.