Short-Wave Infrared Lidar on Atmospheric Aerosols and Insects
Abstract: This thesis focusses on the implementation of two elastic lidar (light detection and ranging) techniques for the monitoring of atmospheric aerosols and insects at short-wave infrared wavelengths. Data acquisition software was developed for a time-of-flight system, housed in the Lund University Mobile Biosphere Observatory (LUMBO), with consideration to the intended entomological application. Once up and running, the background signal and noise present in the system was characterised to facilitate future data filtering and background subtraction. The acquisition of a signal from a nearby building was achieved, but revealed that the signal-to-noise ratio of the system was too poor to be able to reliably distinguish any insect events. Attempts to improve the signal-to-noise ratio were made through the construction of a transimpedance amplifier for the receiving avalanche photodiode, but were unsuccessful. Proof-of-concept dual-band measurements on atmospheric aerosols and insects were performed with a Scheimpflug lidar system. The measurements demonstrated the high spatiotemporal resolution of the system, making possible the localisation and identification of, for example, vehicle emissions. Moreover, it was shown that the ratio between the backscattered signal in the two bands can be used to distinguish between different particle plumes, indicating the potential of the technique to identify aerosols. Furthermore, the dual-band measurements on insects demonstrated the ability of the apparatus to resolve the wing beat frequencies of the organisms in question, along with several associated higher harmonics in the Fourier transform of the time series data.
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