Inelastic LIDAR for Monitoring Aquatic Fauna

Abstract: This thesis is oriented around designing the world first inelastic hyperspectral LiDAR(Light Detection and Ranging) system for aquatic use. The system was designed around the task of monitoring zooplankton and environmental indicators in water. Scheimpflug lidar was previously developed for monitoring flying insects, aerosols and gases. Here we extend the concept to inelastic hyperspectral ranging capabilities. During the project, a novel system was developed that uses relatively low cost off-the-shelf components to create a compact LiDAR with both spectral, temporal and ranging capabilities making it a very versatile system with many possible applications such as, plankton and chlorophyll detection and assessment of water quality. The system uses a high power GaN laser-diode to emit a laser beam that propagates through the water. The laser light is then scattered both elastically (Mie and Rayleigh scattering), and inelastically (Raman scattering) by the water or by particles and plankton crossing the laser beam. The light might also be absorbed and result in fluorescence. The scattered light is collected by the receiving lens, after which the light is analyzed in term of energy for all distances along the line of view. The system was simulated using a raytracing program (FRED Optics by Photon Engineering) to find a feasible design with the available components. The system was assembled in a lab environment and calibrated. Lastly, the setup was tested in a 5-meter-long test-tank containing leaves and zooplankton of the genus Daphnia.