Chemical Sensor Networks for Gas Detection and Environmental Monitoring

This paper reviews the principles and prospects for optical fibre based measurement techniques for determining gas concentrations. Most of these exploit the precision and versatility of tuneable diode laser spectroscopy in the near infrared. We demonstrate the potential offered by large area multipoint totally passive networks and establish the performance potential which these may offer in hostile environments. These benefits include more than adequate sensitivity for most applications, automatic recalibration of both zero point and scale factor and the ability to precisely determine line shape information and in some cases perform detailed line spectrum analysis to determine concentration, pressure and temperature simultaneously. We also briefly describe the principles and application of photo acoustic spectroscopy and outline the performance improvements which tuneable diode laser systems also offer in this context. These studies have illustrated that, in appropriate niche applications, fibre based gas measurement systems offer substantial long term engineering potential.