Differential absorption lidar using an optical parametric oscillator source
Differential absorption lidar using an optical parametric oscillator source
This thesis describes the design, construction and performance of a differential absorption lidar system based upon a LiNbO3 optical parametric oscillator. This system has been used for both longpath absorption and range resolved DIAL measurements. The O.P.O. is suited to such measurements because of its continuous tunability over a broad spectral range from 1.4 to 4.0μm. The measurement of atmospheric methane by longpath absorption using a target at a distance of 1.1km is described. The performance of the system was such that pathlengths of up to 10km could be used. It is estimated that with certain modifications aimed at improving the reliability of the O.P.O., detection sensitivities of 1-5 ppb are possible for species with strong absorptions accessible to the system eg. HC1, CH_4, NO_2. Other species with weaker absorptions, eg. CO, SO_2, NO, should be detectable at concentrations of 10-100 ppb. The rather low transmitted energy, and consequently small return signals, together with the high receiver noise, restricted the system's performance in the range resolved DIAL mode of operation. In order to achieve reasonable S/N ratios the system bandwith was restricted to 0.25 MHz. Under these conditions measurements of atmospheric methane and water vapour have been made. A theoretical study showed that a bandwidth of at least 0.5 MHz is necessary if plumes of a reasonable width (200m) are to be monitored. To allow this a number of improvements aimed largely at increasing the O.P.O. output are proposed. These improvements should enable the system to detect a species with a strong absorption, eg. HCl, in a plume at a range of 1km at concentrations as low as 20 ppb. (D67822/86)
University of Southampton
1985
Collar, Andrew John
(1985)
Differential absorption lidar using an optical parametric oscillator source.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
This thesis describes the design, construction and performance of a differential absorption lidar system based upon a LiNbO3 optical parametric oscillator. This system has been used for both longpath absorption and range resolved DIAL measurements. The O.P.O. is suited to such measurements because of its continuous tunability over a broad spectral range from 1.4 to 4.0μm. The measurement of atmospheric methane by longpath absorption using a target at a distance of 1.1km is described. The performance of the system was such that pathlengths of up to 10km could be used. It is estimated that with certain modifications aimed at improving the reliability of the O.P.O., detection sensitivities of 1-5 ppb are possible for species with strong absorptions accessible to the system eg. HC1, CH_4, NO_2. Other species with weaker absorptions, eg. CO, SO_2, NO, should be detectable at concentrations of 10-100 ppb. The rather low transmitted energy, and consequently small return signals, together with the high receiver noise, restricted the system's performance in the range resolved DIAL mode of operation. In order to achieve reasonable S/N ratios the system bandwith was restricted to 0.25 MHz. Under these conditions measurements of atmospheric methane and water vapour have been made. A theoretical study showed that a bandwidth of at least 0.5 MHz is necessary if plumes of a reasonable width (200m) are to be monitored. To allow this a number of improvements aimed largely at increasing the O.P.O. output are proposed. These improvements should enable the system to detect a species with a strong absorption, eg. HCl, in a plume at a range of 1km at concentrations as low as 20 ppb. (D67822/86)
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Published date: 1985
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Local EPrints ID: 461505
URI: http://eprints.soton.ac.uk/id/eprint/461505
PURE UUID: 08649c42-b2eb-4dbe-82bb-708fb965e150
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Date deposited: 04 Jul 2022 18:48
Last modified: 04 Jul 2022 18:48
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Author:
Andrew John Collar
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