| 1. |
- Lindström, Torgny, et al.
(författare)
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Analysis of lidar measurements using nonparametric kernel regression methods
- 2002
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171. ; 74:2, s. 155-165
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Tidskriftsartikel (refereegranskat)abstract
- The lidar technique is an efficient tool for remote monitoring of the distribution of a number of atmospheric species. We study measurements of sulphur dioxide emitted from the Italian volcano Mt. Etna. This study is focused on the treatment of data and on the procedure to evaluate range-resolved concentrations. In order to make an in-depth analysis, the lidar system was prepared to store measurements of individual backscattered laser pulses. Utilizing these repeated measurements a comparison of three different methods to average the returned signals is made. In the evaluation process we use local polynomial regression to estimate the range-resolved concentrations. Here we calculate optimal bandwidths based on the empirical-bias bandwidth selector. We also compare two different variance estimators for the path-integrated curves: local polynomial variance estimation and variance estimation based on Taylor approximations. Results show that the method performs well. An advantage compared to previous methods for evaluation of lidar measurements is that an estimate of the mean squared error of the estimated concentration can be calculated.
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| 2. |
- Weibring, Petter
(författare)
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Environmental Monitoring by Multi-Spectral Lidar Techniques
- 2002
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Multi-spectral lidar (light detection and ranging) techniques have been developed and employed in various environmental studies, ranging from concentration mapping of volcanic emissions to fluorescence imaging of historical monuments. In both absorption measurements of gaseous species and fluorescence imaging of stones, multiple wavelength excitation and multiple wavelength detection have been applied. A mobile frequency agile lidar system, using all-solid-state technology, has been constructed for range resolved atmospheric gas concentration measurements in the ultraviolet, visible and mid-infrared wavelength regions. A measurement method based on multivariate statistical techniques has been developed to analyse the composition of complex gas mixtures from their combined absorption spectrum. Industrial emissions of mercury from chlor-alkali plants and hydrocarbons from a test site, have been studied to explore the capabilities of the new lidar system. Local polynomial regression with local data driven bandwidths has been developed and utilised as a flexible technique for evaluating DIfferential Absorption Lidar (DIAL) data. The method allows an optimally adapted range resolution and control of measurement accuracy. A new method for gas flux measurements using a combination of DIAL and wind videography has been developed. Validation of the method has been performed during measurements of sulphur dioxide at a paper and pulp mill. The emission of sulphur dioxide from the Italian volcanoes Mt Etna, Stromboli and Vulcano has been studied in several ship-borne measurements combining simultaneous passive and active optical spectroscopy techniques. The deviations between the instruments could be explained by modelling the light scattering through the plume, which allowed correction of data for most situations. Fluorescence imaging of the facades of the Lund Cathedral (Sweden) and the Parma Cathedral and Baptistery (Italy), employing a scanning fluorescence lidar system and multivariate analysis techniques, has been performed allowing classification of different stone types and algal colonisation. Range resolved fluorescence measurements of ocean, coastal and harbour water have been performed during a ship-borne cruise in the Mediterranean sea.
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| 3. |
- Weibring, Petter, et al.
(författare)
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Optical monitoring of volcanic sulphur dioxide emissions - comparison between four different remote-sensing spectroscopic techniques
- 2002
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Ingår i: Optics and Lasers in Engineering. - 0143-8166. ; 37:2-3, s. 267-284
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Tidskriftsartikel (refereegranskat)abstract
- The emissions of sulphur dioxide from the Italian volcanoes Mt. Etna and Stromboli were studied in ship-borne underpasses of their plumes. Four different optical spectroscopy techniques were used and inter-compared. All techniques utilise the absorption signature of the gas in the wavelength region of around 300 nm. A differential absorption lidar was employed in active gas concentration assessment. In parallel, a differential optical absorption spectroscopy system (DOAS) provided spectrally resolved absorption spectra, In one configuration the DOAS used a vertically looking telescope and the absorption of the skylight was studied, while a different DOAS implementation utilised the sun disc as the light source in slant-angle, long-path absorption measurements. Parallel measurements with the customary correlation spectroscopy method were also performed. Path length Monte Carlo simulations of the down-welling radiation through the volcanic plume at different sun altitude and azimuth angles have been performed taking into account also the effects of other geometric parameters as the plume height and extension. The results are discussed with special emphasis on systematic effects due to scattering.
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