Lidar Techniques for Environmental Monitoring
Abstract: Atoms and molecules absorb and emit light at certain, welldefined wavelengths, and this forms the basis of spectroscopy. The wavelengths are given by the discrete energy levels of the atoms/molecules. When illuminated by light of a suitable wavelength, the light will be absorbed, making it possible to deduce information on the presence and concentration of various elements and compounds. When atoms or molecules have been excited, they may spontaneously relax to their ground state, emitting species-specific light, defined by the energy levels. This concept can be used to induce fluorescence in the material, which again can be used to analyse the properties of the sample. Light detection and ranging techniques can be used to perform remote spectroscopic measurements. The sample is probed with a laser beam and the resulting light can be collected with a telescope of sufficient size. Useful results can be deduced at ranges as large as several kilometres, although, in this work the range was never more than a kilometre. In the work presented in this thesis, differential absorption lidar measurements have been performed to determine mercury fluxes from pollution sources. These measurements have been performed as field campaigns in different parts of Europe. Some measurements have been made at chlor-alkali factories, and one campaign at an abandoned mercury mine. Moreover, fluorescence lidar techniques have been used for remote investigation of façades of historical buildings and electrical insulators. These measurements have been performed both in a laboratory setting (albeit still remotely through an ordinary atmosphere) and as field campaigns. Biological contamination and surface treatment chemicals can be monitored, and types of stone in façades can be characterized. Finally, the remote laser-induced breakdown spectroscopy technique has been extended to make imaging possible. These measurements can be used to characterize materials in surface layers, which may be useful in cultural heritage monitoring.
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