Applied hyperspectral LIDAR for monitoring fauna dispersal in aquatic environments

University essay from Lunds universitet/Förbränningsfysik; Lunds universitet/Fysiska institutionen

Abstract: This thesis work has been focused on evaluation and further development of a hyperspectral LIDAR (Light Detection And Ranging) system made by Ljungholm et. al. [1] for monitoring of aquatic fauna, and in particular zooplankton. The project, which was a ”proof-of-concept”, showed the possibility to create a relatively compact and low-cost LIDAR with both spectral, temporal and range resolution. Experiments were developed with the help of the Department of Limnology, Lund University and performed with the LIDAR system. The dispersal rate of the zooplankton genus Daphnia in a water tank was measured, and was found to be largely dependent on background light and laser duty cycle of the LIDAR. The intrusive degree of the laser was determined to be large, since the zooplankton genus Daphnia was attracted to the laser light source, but reduced by employing a low duty cycle. The laser intensity stabilisation was ensured by a ramp time before each duty cycle. Range resolution measurements showed that the modelled resolution was not achieved, and this was determined to be due to defocusing and misalignment of the LIDAR system. The defocusing problem also lead to a weakening of the signal by approximately a factor 102, and artifacts were introduced on the detector. Measurements on the interaction kinetics between the Daphnia and the midge larvae Chaoborus were performed, and species distinction was made by labelling the different species with different dyes and recording the wavelength spectrum. No interaction statistics could be deduced from the results, mainly due to the inactivity of Chaoborus. However, the dyeing of the aquatic fauna using marker pens were shown to be an easy way to label different species for spectral distinction. Lastly, 3D-scanning of a terrestrial plant was performed, with the aid of a simple robot acting as a whiskbroom LIDAR. The results were promising and the chlorophyll was readily distinguished from the branch, although the range resolution and uneven movement of the robot resulted in a relatively low image resolution.

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