| 51. |
- Lian, Ming, et al.
(författare)
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Lidar mapping of atmospheric atomic mercury in the Wanshan area, China
- 2018
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Ingår i: Environmental Pollution. - : Elsevier BV. - 0269-7491. ; 240, s. 353-358
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Tidskriftsartikel (refereegranskat)abstract
- A novel mobile laser radar system was used for mapping gaseous atomic mercury (Hg0) atmospheric pollution in the Wanshan district, south of Tongren City, Guizhou Province, China. This area is heavily impacted by legacy mercury from now abandoned mining activities. Differential absorption lidar measurements were supplemented by localized point monitoring using a Lumex RA-915M Zeeman modulation mercury analyzer. Range-resolved concentration measurements in different directions were performed. Concentrations in the lower atmospheric layers often exceeded levels of 100 ng/m3 for March conditions with temperature ranging from 5 °C to 20 °C. A flux measurement of Hg0 over a vertical cross section of 0.12 km2 resulted in about 29 g/h. Vertical lidar sounding at night revealed quickly falling Hg0 concentrations with height. This is the first lidar mapping demonstration in a heavily mercury-polluted area in China, illustrating the lidar potential in complementing point monitors.
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| 52. |
- Lou, Xiutao, et al.
(författare)
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Detection of elemental mercury by multimode diode laser correlation spectroscopy
- 2012
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Ingår i: Optics Express. - 1094-4087. ; 20:5, s. 4927-4938
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Tidskriftsartikel (refereegranskat)abstract
- We demonstrate a method for elemental mercury detection based on correlation spectroscopy employing UV laser radiation generated by sum-frequency mixing of two visible multimode diode lasers. Resonance matching of the multimode UV laser is achieved in a wide wavelength range and with good tolerance for various operating conditions. Large mode-hops provide an off-resonance baseline, eliminating interferences from other gas species with broadband absorption. A sensitivity of 1 mu g/m(3) is obtained for a 1-m path length and 30-s integration time. The performance of the system shows promise for mercury monitoring in industrial applications.
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| 53. |
- Lou, Xiutao, et al.
(författare)
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Multimode diode laser correlation spectroscopy using gas-filled porous materials for pathlength enhancement
- 2012
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Ingår i: Applied Physics B. - : Springer Science and Business Media LLC. - 0946-2171 .- 1432-0649. ; 109:3, s. 453-460
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Tidskriftsartikel (refereegranskat)abstract
- A novel pathlength enhancement approach has been applied in multimode diode laser correlation spectroscopy measurements of gas concentrations. Reference and sample gas cells made of porous polystyrene foam and alumina ceramic, respectively, were employed in proof-of-principle measurements of molecular oxygen. Equivalent pathlengths of 164 and 52 cm were obtained for the reference and sample cells with physical pathlengths of 4 and 1 cm, respectively. With a measurement time of 60 s, a physical-pathlength-integrated sensitivity of 15 ppma <...m was achieved with an enhancement of more than one order of magnitude compared with an open-air setup. Practical application aspects were investigated including gas cell size and light alignment tolerance. This generic approach for pathlength enhancement provides advantages in terms of compactness and robustness.
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| 54. |
- Lu, Junchen, et al.
(författare)
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Monitoring of flying insects using a dual-wavelength CW lidar system
- 2019
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Ingår i: 2019 Asia Communications and Photonics Conference, ACP 2019 - Proceedings. - 2162-108X. - 9781943580705 ; 2019-November
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Konferensbidrag (refereegranskat)abstract
- A dual-wavelength continuous-wave lidar based on the Scheimpflug principle was employed to study the diurnal insect activity above a lake in South China. Insect numbers, wingbeat frequencies and reflectance sensitivity to different wavelengths were investigated.
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| 55. |
- Lundin, Patrik, et al.
(författare)
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Active feedback regulation of a Michelson interferometer to achieve zero-background absorption measurements
- 2011
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Ingår i: Applied Optics. - 2155-3165. ; 50:3, s. 373-378
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Tidskriftsartikel (refereegranskat)abstract
- An active phase-controlling scheme based on a proportional-integral-derivative-controlled piezoelectric transducer is presented with the purpose of stabilizing a quasi-zero-background absorption spectrometer. A fiber-based balanced Michelson interferometer is used, and absorption due to a gas sample in one of its arms results in an increased light signal to a detector, which otherwise, thanks to destructive interference, experiences a very low light level. With the presented approach, the sensitivity of already potent absorption measurement techniques, e.g., based on modulation, could be improved even further. (C) 2011 Optical Society of America
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| 56. |
- Lundin, Patrik, et al.
(författare)
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Laser spectroscopic gas concentration measurements in situations with unknown optical path length enabled by absorption line shape analysis
- 2013
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 103:3
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Tidskriftsartikel (refereegranskat)abstract
- The concentrations of molecular oxygen and nitrogen in a gas mixture were determined by their impact on the shape of a water vapor line in the near infrared region using diode laser absorption spectroscopy. The shape of the water vapor line depends on the composition of other gases in the mixture and can therefore be used to deduce the concentration of partner molecules, e. g., oxygen, in the buffer. The method enables gas concentration measurements in situations when the path length is unknown, measurements of many gases simultaneously, and measurements of gases lacking suitable absorption lines. (C) 2013 AIP Publishing LLC.
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| 57. |
- Lundin, Patrik, et al.
(författare)
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Non-intrusive headspace gas measurements by laser spectroscopy – Performance validation by a reference sensor
- 2012
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Ingår i: Journal of Food Engineering. - : Elsevier BV. - 0260-8774. ; 111:4, s. 612-617
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Tidskriftsartikel (refereegranskat)abstract
- Abstract in UndeterminedThe oxygen concentration in the headspace of a large number of liquid food containers is assessed with non-intrusive diode laser absorption spectroscopy. The results are compared to those given by a traditional intrusive measurement method. The upper portions of the containers are made of translucent but non-transparent plastic materials, through which the laser light is diffusively transmitted. Measurements are performed both on packages with modified atmosphere and with normal air conditions. It is concluded that the novel non-intrusive technique provides oxygen concentrations that generally differ by less than one percentage point from the reference sensor values.
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| 58. |
- Lundin, Patrik, et al.
(författare)
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Passive unmanned sky spectroscopy for remote bird classification
- 2011
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Ingår i: Remote Sensing For Agriculture, Ecosystems, And Hydrology XIII. - : SPIE. - 0277-786X .- 1996-756X. ; 8174
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Konferensbidrag (refereegranskat)abstract
- We present a method based on passive spectroscopy with aim to remotely study flying birds. A compact spectrometer is continuously recording spectra of a small section of the sky, waiting for birds to obscure part of the field-of-view when they pass the field in flight. In such situations the total light intensity received through the telescope, looking straight up, will change very rapidly as compared to the otherwise slowly varying sky light. On passage of a bird, both the total intensity and the spectral shape of the captured light changes notably. A camera aimed in the same direction as the telescope, although with a wider field-of-view, is triggered by the sudden intensity changes in the spectrometer to record additional information, which may be used for studies of migration and orientation. Example results from a trial are presented and discussed. The study is meant to explore the information that could be gathered and extracted with the help of a spectrometer connected to a telescope. Information regarding the color, size and height of flying birds is discussed. Specifically, an application for passive distance determination utilizing the atmospheric oxygen A-band absorption at around 760 nm is discussed.
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| 59. |
- Lundin, Patrik, et al.
(författare)
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Remote nocturnal bird classification by spectroscopy in extended wavelength ranges
- 2011
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Ingår i: Applied Optics. - 2155-3165. ; 50:20, s. 3396-3411
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Tidskriftsartikel (refereegranskat)abstract
- We present optical methods at a wide range of wavelengths for remote classification of birds. The proposed methods include eye-safe fluorescence and depolarization lidar techniques, passive scattering spectroscopy, and infrared (IR) spectroscopy. In this paper we refine our previously presented method of remotely classifying birds with the help of laser-induced beta-keratin fluorescence. Phenomena of excitation quenching are studied in the laboratory and are theoretically discussed in detail. It is shown how the ordered microstructures in bird feathers induce structural "colors" in the IR region with wavelengths of around 3-6 mu m. We show that transmittance in this region depends on the angle of incidence of the transmitted light in a species-specific way and that the transmittance exhibits a close correlation to the spatial periodicity in the arrangement of the feather barbules. We present a method by which the microstructure of feathers can be monitored in a remote fashion by utilization of thermal radiation and the wing beating of the bird. (C) 2011 Optical Society of America
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| 60. |
- Lundin, Patrik, et al.
(författare)
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Sensitivity enhancement and fringe reduction in tunable diode laser spectroscopy using hemispherical diffusers
- 2017
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Ingår i: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 88:5
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Tidskriftsartikel (refereegranskat)abstract
- The use of diffuse, highly reflective optical components, in particular, a hemispherical BaSO4 diffuser, at the point of light injection into non-transparent or turbid media was evaluated as a means to increase the measurement sensitivity of spectroscopic absorption measurements. By performing the light injection from, e.g., an optical fiber through a component designed to make the light diffuse and to reflect (and thereby re-inject) light scattered from the sample, the total amount of light delivered into the sample is increased. Further, the occurrence of possible interference fringes is strongly reduced.
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