Fiber optic sensors employ a high brightness light source such as a fiber optic supercontinuum source, multiplexed superluminescent light emitting diodes, or a broadband tunable laser diode. Light is delivered to the measurement location via fiber optics and sensor optics directs infrared radiation onto material the being monitored that is located in a hostile environment. A disperse element is positioned in the detection beam path in order to separate the wavelengths and to perform spectral analysis. A spectral analysis of the radiation that emerges from the sheet yields information on a plurality of parameters for the material. For papermaking applications, the moisture level, temperature and cellulose content in the paper can be obtained.