Abstract

A narrow absorption line of free gas can be distinguished from surrounding broad absorption and scattering features, i.e. due to solids and fluids, with tunable laser absorption spectroscopy. Studying free gas inside scattering media, for example clouds, fog, ice, wood, and human tissue, can provide useful information of environmental, biological, and medical processes. Lidar is a range-resolved method, which traditionally detects single scattering events in the atmosphere. This is because the small detection angle strongly reduces the probability of detecting multiple scattering events, which however, occur in a strongly scattering fog. In Differential Absorption Lidar (DIAL) laser pulses are sent out and the radiation is alternated between two wavelengths, one on the absorption line and one slightly off the absorption line, in order to provide gas concentration measurements.

© 2007 IEEE