PhD Defence by Joaquim Bernardino Dos Santos

Abstract

Plankton is arguably the most important class of organisms inhabiting the water column, playing a central role in the biological carbon pump and being essential to maintaining healthy aquatic ecosystems. These microorganisms are sensitive to their environment and are thus threatened by climate change. As a consequence, monitoring the variations in their distributions, abundance, and biodiversity is an urgent task to assess the health status of our oceans.

In this work, a novel optical sensing technology is developed named inelastic confocal light detection and ranging (LiDAR). This sensor system can generate high resolution volumetric images of the aquatic medium combined with spectroscopic information, while at the same time rejecting unwanted light by design. Multiple tests in lab are performed to demonstrate mapping of microplastics, free-floating microalgae, and four species of free-swimming zooplankton in a column of water. Furthermore, by training a machine-learning algorithm to discriminate optical fingerprints, accurate classification of multiple species is accomplished.

This instrument, when integrated in a water-tight housing with a dome window, to minimize optical distortions, and combined with artificial intelligence, to accomplish automated and objective analysis, unlocks non-intrusive large-volume surveying of the pelagic zone. Future studies will focus on shallow coastal waters in the Roskilde fjord, in Denmark, in which case the sensor might be mounted on a boat looking downwards into the water. Alternative deployment solutions include underwater unmanned vehicles, for deeper water research. These developments potentially enable the acquisition of statistically meaningful descriptions of phytoplankton profiles, microplastics proliferation, and zooplankton dynamics over time, and thus open up research that can connect intricate oceanic variables to crucial biological information at the taxonomic level.

Supervisors

• Principal supervisor: Professor Christian Pedersen, DTU Electro, Denmark.
• External co-supervisor: Professor Børge Hamre, University of Bergen, Norway
• Co-supervisor: Professor Paul Michael Pedersen, DTU Electro, Denmark.

Assessment committee

• Professor Peter Uhd Jepsen, DTU Electro, Denmark.
• Senior researcher Frederica Foglini, National Research Council, Institute of Marine Sciences, Italy
• Mikkel Brydegaard, Department of Physics, Lund University, Sweden

Master of the ceremony

• Associate Professor, Peter Tidemand-Lichtenberg, DTU Electro, Denmark.