A mobile system for active otpical pollution monitoring

The remote monitoring of atmospheric pollutants can now be performed in several ways. Laser radar techniques have proven their ability to reveal the spatial distribution of different species or particles. Classical optical techniques can also be used, but yield the average concentration over a given path and hence no range resolution. One such technique is Differential Optical Absorption Spectroscopy, DOAS. Such schemes can be used to monitor paths that a preliminary lidar investigation has shown to be of interest. Having previously had access to a mobile lidar system, a new system has been completed. The construction builds on experience from using the other system and it is meant to be more of a mobile optical laboratory than just a lidar system. A complete system description is given along with some preliminary usage. Future uses are contemplated

Gas-correlation lidar

Basic principles for the extension of gas-correlation techniques to the lidar situation are discussed. Favorable signal-to-noise ratios and relaxed laser requirements characterize the technique. Preliminary experiments on atomic mercury are reported

Differential Optical-absorption Spectroscopy (doas) System For Urban Atmospheric-pollution Monitoring

We describe a fully computer-controlled differential optical absorption spectroscopy system for atmospheric air pollution monitoring. A receiving optical telescope can sequentially tune in to light beams from a number of distant high-pressure Xe lamp light sources to cover the area of a medium-sized city. A beam-finding servosystem and automatic gain control permit unattended long-time monitoring. Using an astronomical code, we can also search and track celestial sources. Selected wavelength regions are rapidly and repetitively swept by a monochromator to sensitively record the atmospheric absorption spectrum while avoiding the detrimental effects of atmospheric turbulence. By computer fitting to stored laboratory spectra, we can evaluate the path-averaged concentration of a number of important pollutants such as NO2, SO2, and O3. A measurement of NH3 and NO close to the UV limit is also demonstrated

Fluorescence Lidar Multicolor Imaging of Vegetation

Multicolor imaging of vegetation fluorescence following laser excitation is reported for distances of 50 m. A mobile laser-radar system equipped with a Nd:YAG laser transmitter and a 40-cm-diameter telescope was utilized. The laser light was Raman shifted to 397 nm with pulse energies of approximately 30 mJ. An image-intensified CCD camera with a specially designed split-mirror Cassegrainian telescope was utilized for the simultaneous recording of fluorescence images of leaves and branches in four different spectral bands. Additionally, fluorescence spectra at selected points within the detection area were measured with an image-intensified diode array system. Image processing permits extraction of information related to the physiological status of the vegetation and might prove useful in forest decline research

Differential Optical Absorption Spectroscopy (DOAS) Measurements of Ozone in the 280--290 nm Wavelength Region

The differential absorption structure of the ozone spectrum between 250 and 330 nm has been investigated in order to determine the optimal wavelength region to be utilized for active differential optical absorption spectroscopy (DOAS) measurements. Considering aspects of atmospheric attenuation and interference from other species as well as the magnitude of the differential absorption cross section, an interval around 283 nm was found to be a good candidate for this application. This result was also verified during 12 months of continuous ozone monitoring in an urban environment

Measurement of Aromatic-hydrocarbons With the DOAS Technique

Long-path DOAS (differential optical absorption spectroscopy) in the ultraviolet spectral region has been shown to be applicable for low-concentration measurements of light aromatic hydrocarbons. However, because of spectral interferences among different aromatics as well as with oxygen, ozone, and sulfur dioxide, the application of the DOAS technique for this group of components is not without problems. This project includes a study of the differential absorption characteristics, between 250 and 280 nm, of twelve light aromatic hydrocarbons representing major constituents in technical solvents used in the automobile industry. Spectral overlapping between the different species, including oxygen, ozone, and sulfur dioxide, has been investigated and related to the chemical structure of the different aromatics. Interference effects in the DOAS application due to spectral overlapping have been investigated both in quantitative and in qualitative terms, with data from a field campaign at a major automobile manufacturing plant