Implementation of open-path measurement techniques
Résumé
For a long time INERIS has carried out metrological tests on automatic devices used in air quality monitoring networks. In France the standard text NF X 20-300 drives the evaluations in terms of the following metrological features : response time, linearity, limits, drift, ... In order to apply this text, the instruments have been fed with reference mixtures of gases in several reproducible concentrations. Compliance with this requirement is quite easy to obtain, in the case of conventional techniques, but the problems remain with optical remote sensing instruments. Indeed, it is impossible to manufacture a measurement cell as long as the optical path (greater than 100 meters). This difficulty can be solved by using the Beer-Lambert law indicating that the product of the concentration by the distance is a constant value.