Infrared detector array sensors for remote gas detection

This paper investigates the potential of infrared detector arrays for passive gas detection systems. At present, extractive methods are commonly used for the detection of gases and vapours. In case of large distances or in the open atmosphere remote measurement systems have to be employed. Remote detection can be used to monitor industrial and traffic emissions and to detect defects and leaks. Usually, the basic measurement principle is active and double ended: e.g. the sampling distance is probed by rays of light and the spectral transmission is measured. For example, using tunable laser sources in the mid-infrared roadside monitoring of the emissions of single moving cars can be achieved . However, establishing and alignment of the necessary closed optical path for such measurements (light source, retroreflector) is always time consuming, and may be rather difficult since it needs access to both ends of the path. LIDARs are single ended systems, but those systems are in most cases im practical due to size, weight, and cost. In such cases a single ended and in particular a passive sensor approach is more suitable than an active technique. A passive sensor approach has to prove sufficient sensitivity and selectivity but it is the only viable approach under weight and cost restrictions in particular for mobile applications. Infrared spectroscopy is an established technique to detect most molecular gases. The 8-12 mu m atmospheric window is part of the infrared fingerprint region where many organic substances can be identified. Using the ubiquitous thermal radiation as background results in a high versatility of passive sensing systems. Usually mid infrared spectroscopy is the domain of Fourier-transform-infrared (FTIR)-spectrometers. They have been successfully used for remote sensing of smoke stack and flare emissions. However, in case of remote gas detection they suffer from typical shortcomings like errors caused by fluctuations of the signal during scanning and ne ed of a high dynamic range. The infrared detector array sensor (IDAS) is an advantageous alternative for the spectrometer. IDAS systems are more robust than FTIR-spectrometers and do not suffer from the sensitivity restrictions of conventional (single detector) grating spectrographs. In addition, IDAS spectroscopy benefits from the rapid technological progress of detector arrays which are usually employed in thermal imaging systems.